Glossary

Bow Echo
A “bow echo” is a name for a pattern of a storm seen on rainfall radar as shown in the example image above. Its shape resembles a bow and therefore it’s name is bow echo. The echo shows a line of storms which bends in the direction of propagation. Bow echos are usually accompanied by severe wind gusts, these being usually the strongest at the apex of the bow.
Bears Cage

A Bears Cage is a region of a supercell thunderstorm that is located under a low-level mesocyclone and often close to a tornado. It is a term often used by stormchasers who generally try to avoid this region. This is because very strong winds and sometimes heavy rain are encountered in a Bears Cage. It is difficult to drive fast in such conditions and since a tornado can be located in the Bears Cage it is dangerous to be in such conditions close to a tornado. From outside the Bears Cage often looks like a cage formed of a ring of precipitation around the center of the rotating mesocyclone with the tornado (the bear) inside. In some cases a wedge tornado can fill the entire Bears Cage.

CAPE
CAPE is the acronym for “Convective Available Potential Energy” which is the energy available in the atmosphere to convection. This energy can’t be directly measured at the surface, but needs to be calculated from an atmospheric profile of dry bulb temperature and dew-point temperature that is obtained by the use of a radiosonde (a meteorological balloon).
Here is a bit more technical explanation of CAPE and how it can be represented. A radiosonde (meteorological balloon) obtains dense readings of temperature approximately throughout the troposphere, approximately one every 10 meters in height. An example radiosonde sounding is shown in the image above (this is called a skew-t chart). Here, the red line represents ambient temperature and the light blue line represents dew-point temperature. The black line which borders the yellow area on the right side shows the temperature and dew-point temperature (which differ below the cloud base) an air parcel would have if it started rising from the surface. The air parcel begins on the ground, having the same temperature as the ambient temperature. The parcel first rises dry adiabatically as no condensation occurs below the cloud base (temperature in the air parcel decreases by approximately 9 degrees per 1 km). This is shown by the black line that begins at the surface (the line starting at equal temperature as the ambient temperature (red line) and being parallel to the green lines (dry adiabats)). The cloud forms at a height where condensation in the parcel occurs. This is visible as a cloud base. This height can be estimated by obtaining the dew point temperature at the surface and following a constant mixing ratio line on the skew-t chart (being parallel to the pink lines which show constant mixing ratio). Where this line meets the parcel temperature condensation occurs. Above condensation and cloud base the parcel rises moist-adiabatically since latent heat is being released and its temperature trace follows one of the moist adiabats (moist adiabats shown every 5 degrees on this skew-t).  Whenever the trace of the air parcel is to the right of the red temperature trace it means the parcel is warmer than its environment and is positively buoyant. The greater the difference the greater the buoyancy. CAPE is equal to the area between the parcel and ambient temperature traces where the parcel temperature is greater than the ambient temperature (here represented by the yellow area). The units of CAPE are J/Kg (Joules per kilogram of air lifted). As an example, if the value of CAPE is 1000 J/Kg it means that an energy of 1000 Joules, or 1 kJ, is released to every kilogram of air that rises throughout this atmospheric profile.
Meteorological models can forecast values of CAPE up to two weeks ahead. The higher the value of CAPE the more energy there is for convection and the greater the strength of potential thunderstorms. However, CAPE is not the only parameter that determines the potential strength of eventual thunderstorms, but it can be used as a useful guide. As a rule of thumb:

-If CAPE is less than 100 J/Kg thunderstorms are very unlikely (unless they are supported by fast-moving cold fronts mainly in the winter half of the year)
-If CAPE reaches 100 – 300 J/Kg then there is a good chance of at least some lightning if convective showers develop, but the electric activity is generally short lived and sporadic
If CAPE reaches 300 – 1000 J/Kg then there is a high chance that thunderstorms will form somewhere in the area. If they form there will likely be decent lightning activity and these thunderstorms can usually manage to persist for several hours (if multi-cellular)
If CAPE reaches 1000 – 2500 J/Kg then unless there is a strong convective inhibition thunderstorms are very likely. These thunderstorms can be long-lived and can organize into Mesoscale Convective Systems. Thunderstorms can be accompanied by hail larger than 1 cm in diameter and by frequent lightning. Values of 2000 J/Kg or more are rare in the UK but when such values are present they are nearly always accompanied by strong thunderstorms or large Mesoscale Convective Systems.
-Values of CAPE over 2500 J/Kg are very rare in the UK and do not occur every year. However, such values occur much more often in other countries in central and western Europe (e.g. France, Germany). If thunderstorms form in such a strong CAPE environment they will nearly always be accompanied by frequent lightning and very often by at least some hail. The strength of the thunderstorms then very strongly depends on the wind shear.
-Values over 3000 J/Kg are rare even in central Europe, but occur several times per year over the great plains of the US. Such values do not need much wind shear for thunderstorms to organize and if supercell thunderstorms form in such a high CAPE environment they can produce hail greater than 5 cm in diameter.
-Values over 4000 J/Kg are very rare anywhere in Europe, but occur at least once a year in the US. Thunderstorms are always very strong in such extreme CAPE conditions and can produce hail over 5 cm in diameter if mesocyclones/supercells occur.
-Values over 5000 J/Kg are rare even in the US and there is only a handful of cases of such a strong CAPE recorded in Europe. In the US, the highest values of CAPE ever recorded were approaching 10.000 J/Kg and it’s likely that such extreme values also occur over northern India south of the Andes.
As already mentioned the intensity and degree of organization of storms also strongly depends on values of wind shear (how wind speed and direction changes with height). If there was a profile with 4000 J/Kg CAPE but zero wind shear (no wind between the ground and 6 km above the ground) then thunderstorms can be very strong but they will likely not persist for long or they will be disorganized and will weaken with time. During the initiation stage such storms may produce hail of 3-4 cm in diameter, but if there is no wind shear the hail and precipitation would fall into the updraft of the storm, cutting it off eventually.
Hook Echo
A Hook echo is a name given to a pattern on rainfall radar which resembles a hook. An example is shown on my iPad case in the image above. A hook echo is one of many signs of a potential supercell thunderstorm and is normally located on the southwest side of the thunderstorm. A supercell contains a mesocyclone which is a region of rotation in the storm. This rotation also usually occurs at the southern end of the storm and usually rotates in the anticlockwise direction in the northern hemisphere. Hook echoes are dangerous parts of the storm as they can be accompanied by tornadoes (usually in the southern end of the hook) and very large hail (usually in the north or northwest part of the hook/rotation). There is also a “clear notch”, which is an area of very weak or zero rainfall echo to the right of the hook (area with no rainfall). This is because the strong updraft that rotates in the anticlockwise direction brings all the rain and hail away from this area whereas it brings the heavy rain and largest hailstones back south on the left side of the rotation. This very large hail and rain then forms the hook echo.
Lapse Rate

A lapse rate is a rate of change of temperature with height. For a rising air parcel in the atmosphere there are two types of lapse rates, a dry adiabatic lapse rate and a moist adiabatic lapse rate. If an air parcel rises through the atmosphere (such as in an updraft of a thunderstorm) its temperature reduces purely due to decreasing pressure acting on that parcel with height. If the parcel rises dry adiabatically which means that no condensation occurs within the parcel (a parcel of hot air rises, but no cloud forms) the rate of change of its temperature is approximately 0.9 degrees per 100 meters (or 9 degrees per kilometer). However, if condensation of water vapor does occur in this air parcel, latent heat due to condensation is released and heats up that air parcel which causes the decrease in its temperature to be slower, approximately 0.6 degrees per 100 meter (or 6 degrees to kilometer).

The ambient atmospheric temperature (temperature surrounding the parcel) also normally drops with height (determined by the environmental lapse rate), but the decrease varies across different atmospheric environments. If the decrease in ambient temperature is lower than 6 degrees per kilometer then the rising air parcel in a cloud which rises moist-adiabatically and is cooled by 6 degrees per kilometer will begin to be cooler than its surroundings at some point. As long as a parcel is warmer than its surroundings it has a positive buoyancy and tends to rise upwards. As soon as it becomes cooler than its surrounding it acquires a negative buoyancy and tends to sink. If however the ambient atmospheric temperature decrease is greater than 6 degrees per kilometer the air parcel would continue to rise since a moist-adiabatically rising air parcel cools at 6 degrees per kilometer and hence will remain warmer than its surroundings. Eventually, in an unstable atmosphere the air parcel will reach a point where its surroundings become warmer again, normally at the tropopause. 

We can therefore conclude that if the environmental lapse rate is greater than the moist adiabatic lapse rate (rising air parcel in a cloud cools slower than its ambient temperature), parcels of air in clouds tend to rise until they reach some point where they become colder again which is either at some inversion (a temporary rise in temperature with height) or at the tropopause where temperature naturally again rises with height. Since the moist adiabatic lapse rate is 6 degrees per kilometer, environmental lapse rates greater than 6 degrees per kilometer tend to create an unstable atmosphere – an atmosphere susceptible to the formation of deep moist convection (deep moist convection are convective clouds that form showers and thunderstorms).

Now we can describe what environments are typical for different environmental lapse rates. Environmental lapse rates of less than 6 degrees often occur in areas of high pressure or some form of warm advection (where warmer air is advected (transported from elsewhere) at higher levels). Such environmental lapse rate makes the atmosphere stable and the formation of convective showers or thunderstorms is unlikely. Typically, the environmental lapse rate over the UK varies between 5 and 7 degrees per kilometer on average throughout the whole troposphere. Environmental lapse rates approaching 9 degrees per kilometer (dry adiabatic lapse rates) are rare. Under such conditions air parcels would rise even if condensation (formation of clouds) does not occur. This is called dry convection. Such steep envirnmental lapse rates can form over dry and hot regions such as deserts or dry plateaus such as in Iberia. In these regions the air is very dry so formation of clouds in not possible until the air cools substantially (down to its dew-point which is very low in deserts). However, very strong solar radiation makes the ground very hot which heats up the near-ground layer of air. This very hot air begins to rise and cool at the dry adiabatic lapse rate (since condensation does not occur in this very dry air). Because the solar radiation lasts long and heats the surface layer to very high temperatures these air parcels rise to substantial heights (up to several kilometers). Because they rise dry adiabatically at 9 degrees per kilometer they eventually mix the lowest approximately two kilometers of the atmosphere in such a way that the environmental lapse rate in this several kilometer thick layer is 9 degrees per kilometer (e.g. 40 degrees near the surface, 31 degrees at 1 km height, 22 degrees at 2 km height, etc.). If this environment of such steep lapse rates is advected elsewhere at higher levels it is called an “Elevated Mixed Layer”. In Europe we often see this “Elevated Mixed Layer” being advected either from the Sahara Dessert or from Iberia (called a “Spanish Plume). If such “Elevated Mixed Layer” is transported over a very moist and warm airmass near the ground it can cause a very unstable atmosphere since the warm and moist air would then form clouds where the updrafts would rise at a moist adiabatic lapse (6 degrees per kilometer) rate in an environment characterized by 9 degrees per kilometer dry lapse rates. However, Elevated Mixed Layers can form in other areas as well, often over high mountain ranges which are also strongly heated in the summer but where the supply of moisture is restricted (blocked) by the mountains. An example are the Alps or the Pyrenees (although its often difficult to distinguish an EML (Elevated Mixed Layer) originating from Iberia from that originating from the Pyrenees). A lapse rate greater than 9 degrees per kilometer is extremely rare. This is because if such an environment develops the air becomes very unstable in the layer of such a lapse rate and convection (either dry or moist) immediately begins, trying to mix out such a lapse rate. An example of how this occurs is on hot summer days when the solar radiation is very strong. If there is a dark surface which strongly absorbs solar radiation it can heat up the surrounding near surface air at a faster rate than what the lower atmosphere manages to transport upwards. Under such conditions dry convection often develops resulting in dust devils which again try to equalize the very steep lapse rate. Another example is if a very cold air is advected over much warmer air, such as if an arctic air is brought over a relatively warm sea. In such conditions steam devils can form over the warm water surface.

 

Supercell Parameter

A “Supercell Parameter” is a severe thunderstorm index (like e.g. CAPE) that is determined by a combination of several convective parameters including CAPE, Storm Relative Helicity, etc. It is calculated by several equations which I will not describe here in detail. If anyone is interested in the deep maths and more details you can Google it or email me at keblecollege@gmail.com

Here, I will give a simplified explanation. A Supercell Parameter depends strongly on CAPE since for supercells to form there needs to be instability in the atmosphere for thunderstorms to develop. Another very important variable is 0-3 km Storm Relative Helicity. This depends on the wind speed and direction between the ground and the height of 3 km above the ground. An example of strong Storm Relative Helicity is if the near surface wind direction is from the southeast, 500 meters above the ground from the south, at 1km above ground from the south-southwest, at 1.5km from the southwest, at 2km from the west-southwest, at 2.5km from the west and at 3km from the northwest. The greater the wind speed the higher the values of Storm Relative Helicity and the higher the values of the Supercell Parameter. The higher the Supercell Parameter is the higher the chance of the formation of supercell thunderstorms and the greater the chance of strong and long-lived supercells. However, a Supercell Parameter is only one of many parameters that need to be studied when producing a forecast and including the probability of supercell thunderstorms. Based on my experience, Supercell Parameter is a very useful variable when forecasting supercells over the Great Plains of the US. In Europe, however, I have seen situations with very high values of the Supercell Parameter, but no supercells developed in the end. The problem in Europe is often related to weak values of convective inhibition and topography, which lead to a high number of thunderstorms. These interact with each other, disrupting the general environment that is favourable for supercells. Normally, supercells like to stay isolated if they are to be long-lived. On the other hand, I have also been surprised by a few nice supercells in Europe where the Supercell Parameter was not forecasting storms to be as good as the situation verified. As a rule of thumb, values of the Supercell Parameter less than 1 mean that the chance of supercell formation is very low. Values between 1-4 means that there is a higher chance of a supercell, but conditions are not yet good enough to produce a strong or long-lived supercell so these are usually just transitioning supercellular structures. If the value is 4-8 then probability of supercells is quite high. If it goes above 8 then conditions are normally very good for supercell formation and if any storm manages to remain isolated for some time it will very likely become a supercell. Values of Supercell Parameter rise quadratically with improving conditions (hence 2,4,8,16, etc.). I have not seen values greater than 16 in Europe, but have seen such values in the US and such situations were ​​often associated with strong supercells accompanied by giant hail and tornadoes.

How to stay safe when a storm approaches?

Are you afraid of thunder and lightning? Do you want to reduce the chance of being struck or do you want to protect your house and belongings from irreparable damage? This article provides important information about what measures can be taken to reduce the risk of being struck as much as possible and to increase the safety of electrical appliances inside your house should lightning strike the power line. I do not take any responsibility for the information given here. It should be taken as an advice on how to reduce the risk, but not how to eliminate it completely.

Once a thunderstorm is present, there is a risk of lightning and the lightning is very unpredictable. To predict exactly when lightning will strike, or even the exact place that will be hit is (and probably will for a very long time be) impossible. There are certain detectors of electric field which can warn against imminent lightning, but they are not accurate enough to determine when and where will lightning strike next. However, there are measures that can effectively reduce the risk of damage to people and property

Regarding protection of property against lightning it is essential to have a lightning rod, or several rods, installed in the correct places. Installation of lightning rods should be carried out by a specialized company who should be able to service all the lightning rods and earth conductors after a certain period of time (once every few years I believe, but check with the company).  The reason for the service and check is that if the lightning rod is not properly grounded it’s effectiveness diminishes. In addition, if there are any changes done to the outlay of the building such as an addition of an antenna the existing lightning rods need to be checked since they may not provide a complete protection any longer and additional lightning rods may need to be installed in that case. While lightning rods are the best protection available against lightning they are not a 100% guarantee that lightning won’t do any damage to your house. An example of where lightning rods would likely fail is when ball lightning occurs. However, it is a very rare phenomenon which is observed somewhere in the UK no more than ~10 times per year and it is not yet fully understood. Because lightning is unpredictable it has the potential to hit any object, not necessarily the highest one. Lightning is triggered by the connection of stepped-leaders with upward streamers (ionized channels of air that form under high electric potential). There are normally many such leaders and streamers, but usually only one or two connect. Whichever connects first is where the lightning then strikes. These often originate from tall pointy and conducting objects.
In order to protect yourself and other people from the risk of being struck by lightning there are no universal rules. The most obvious and common sense action to take is that if you can hear thunder you should go inside or at least avoid the areas outside that are most dangerous during a thunderstorm (being on a hill or near isolated tall objects) or avoid wearing some items that could attract lightning more easily (e.g. carrying golf clubs on your back and even carrying an umbrella is speculated to play some role in attracting lightning). The most important thing is to be aware of the fact that if you hear thunder you might be struck! Lightning has been known to strike as far away as 10 miles away from a thunderstorm (known as “strike from the blue”) and thunder is normally heard up to a distance of approximately 10 miles. Therefore, if you hear thunder, seek shelter and stay there until it’s been at least 15 minutes since the last clap of thunder that you’ve heard. It may seem unnecessarily long, but when a thunderstorm dissipates lightning intensity can drop off slowly, first being several strikes per minute, then 1 strike per minute and towards the end of the thunderstorm life-cycle lightning can strike only once every 5 minutes or more. These last strikes are normally from the strongly positively charged anvil and are very powerful even that there are not many of them. You can estimate the distance of a lightning strike from your location by counting the number of seconds between the strike and thunder. Every 5 seconds between the seeing the strike and hearing thunder is 1 mile and every 3 seconds is 1 kilometer (this is because sound travels at much slower speed than light). Therefore, if you see a flash and hear thunder 10 second later it means that the strike was 2 miles away.

A useful device to warn people when lightning is in the vicinity is a so-called personal lightning detector. It is a 15x8x3cm box that detects electromagnetic waves that are produced by lightning and if it detects any it makes a beep and shows the approximate distance of the strike in miles from the detector. There are several types of personal lightning detector ranging in price from approximately £20 to £150. The detector however needs to be switched on for it to detect lightning so the weather forecast still needs to be monitored for the possibility of thunderstorms and if thunderstorms are possible, switch the detector on (a daily thunderstorm forecast is produced www.estofex.org which includes a map of lightning probability. I’d recommend to switch on your lightning detector anytime that you are within the 15% line). Such a personal lightning detector can either be plugged in to the wall or it is possible to insert a classic AA battery (or other battery depending on the model) and take it out with you. If there is a strike in the vicinity of up to approximately 50 miles the detector will alert you and show the range in distance at which the lightning was detected. Sometimes it can, however, suffer strong interference which can make it beep even if there is no lightning. This most often occurs if you switch on a TV, if you are in a car with an engine running and sometimes even if you switch on your lights at home. It is therefore best to keep it in a place away from other appliances and not use it in a car. If the detector shows lightning detected 12 miles away or closer I would recommend not to be outdoors or seek shelter and wait at least 15 minutes after the detector stops detecting lightning less than 12 miles away.

While it’s much more dangerous to be outdoors than inside during a thunderstorm it’s not totally safe even indoors, especially if the building has no lightning rods installed. If the storm is less than 10 miles away and you are at home I would recommend to manually disconnect the electricity (switch off the mains switch, normally located at or inside the fuse box). This protects your home appliances should lightning strike the mains power cables and get into your house along the electrical wiring. If you go on a holiday, especially during the summer months when thunderstorms occur most often, I would recommend disconnecting all the devices that can be disconnected (TV, computers, routers, radios, etc.). If you do not have a device that you can not disconnect (fridge, freezer, etc.), I recommend buying special “lightning protection”, which is a device that is plugged in between the socket and the appliance and in case lightning strikes the electrical mains outside the protection would act like a fuse and would not let the high voltage current damage your appliance. In this case the lightning protection gets damaged and hence your fridge would stop working, but I would say it’s much better to return home and find bad smelly food in your fridge and buy a new lightning protection for less than £10 than to find bad food inside a broken fridge that needs to be replaced. Another way how lightning can get inside a house is along water pipes. Therefore, I would not recommend using the sink, washbasin, the bathtub, or even avoid being at the toilet as much as possible during a thunderstorm. The safest place to be inside a house during a thunderstorm is away from doors and windows, any electrical appliances and away from any pipes that lead outside. Best place would be to stay in an inside room with no outer doors or windows. Chimneys have also been known, on occasions, to be a way how lightning can get inside a house. Therefore, avoid sitting next to a fireplace. To maximize your protection you could wrap inside a blanket which would act as an insulator and should, to some degree, prevent lightning to hit you if it indeed entered your house. If you want to be in a place that is as safe as possible during a thunderstorm (regarding the risk of lightning strike) you need to find a place that would act like a “Faradays Cage” and would have a metal frame that would guide the lightning current around you away into the ground. An example of such a Faradays Cage is a car (not a convertible! The soft roof of convertibles is not conductive and hence doesn’t act like a Faradays Cage!). Other means of transport often act like a Faradays Cage since they have a metal frame or a frame made from some conductive material (e.g. buses, trains, airplanes, etc.).

If you find yourself far from any shelters, for example in rural areas or outside in nature you can still do something to reduce the chance of being struck. Places to avoid if caught outside are tall solitary trees or stones, tops of hills and any largely open spaces. Swimming in a sea, lake or river is very dangerous if a thunderstorm is nearby. Even if lightning does not strike you directly, if it strikes the water where you are swimming up to a mile away you would feel the electric shock which may cause temporary loss of consciousness leading to drowning. So if you do get caught in a rural location find the lowest place in the vicinity away from any tall trees, buildings (unless you can go inside them) or other objects. It may be tempting to go and hide from the rain or hail under a tree, but if you do so you are in much greater danger of being struck. The best thing to do would be to find a ditch and crouch in it, but watch out for any flash floods as ditches can fill quickly with water if the rain is very heavy. If you are caught in a park or a forest you are actually in a safer place then if you were in an open field, as long as you avoid the tallest trees. If the storm is strong and accompanied by wind gusts there is of course a danger of falling trees or branches in a forest. If you get caught in the mountains, definitely leave the highest ridge (if there is time and it’s not a dangerous route) and try to get into a valley or at least away from the highest stones and ridges. Being just below the ridge is not safe as well since if lightning hits the top a very large electric potential forms which can cause electric shock solely due to different locations of your feet (it’s called step charge).

To conclude, there is no place that would be 100% safe from being hit by lightning, but if you follow the above advice you will greatly reduce the risk of injuries or damage to property. While the chance of being hit by lightning is still very small in comparison to other risks that threaten us in our everyday life there is no excuse not to follow these safety procedures. The people who are struck by lightning often did not take appropriate action when near a thunderstorm. It’s questionable how high the proportion of people that was struck knew about the presence of a thunderstorm nearby, but if everyone was aware of thunderstorms in their vicinity and always took precautionary action the number of injuries and fatalities related to lightning could still be greatly reduced. And if you are terrified of lightning (astrapophobia) you can always do the opposite of stormchasing. By learning about thunderstorms and weather in general you can learn what conditions are favorable for thunderstorms and if storms do develop or are forecast just drive into a location where the chance of storm development is zero or the lowest. I did this a few times when observing eclipses of the Sun and while finding a place to be cloud free is difficult (but easier than stormchasing), simply avoiding storms is really easy and I can be confident that by driving to a different location I could avoid all lightning (unless there is a large squall-line that would cross the whole of the UK, but such a case would be extremely rare).

How to chase a storm

People usually imagine that chasing a storm must be very simple. Just wait for a storm to be nearby and then drive to a good vantage point to observe lightning or drive in the direction where it appears that most of the lightning activity is. Many people who like to observe storms do this and only driving to a given location with a good view and only when there is a storm within a visible distance of their home location. This can be described as “storm spotting”, but not as true “stormchasing”.  If we want to increase the chance to see some interesting phenomena we need to be at the right place at the right time. This can be very difficult and challenging as the space and time where very interesting phenomena can be seen is usually restricted. Therefore, no stormchase can guarantee us to see anything interesting but we can considerably increase the chance of seeing something interesting by having at least basic knowledge of meteorology and the current meteorological situation. If we can correctly analyze the current meteorological situation we can then decide with reasonable confidence where the situation would be best for good storms. When I prepare for a stormchase I always study the meteorological situation several days, sometimes even a week, in advance.  In fact, I analyze the weather almost every day of the year, watching the values ​​of various indexes which suggest what the environment is like at a given location and if/how storms may develop and where they may develop. These indexes include CAPE, CIN, Lifted Index, Wind Shear, Storm Relative Helicity, Equilibrium Level and several other parameters, such as where different weather models develop precipitation and potential thunderstorms. I will not describe these indexes in great detail since such description can be found elsewhere. Instead I will give a general idea of what values I think are “not good”, “good enough” or “perfect”. If we want to see a storm, we need instability in the atmosphere. CAPE (Convective Available Potential Energy) is the best measure of this energy. Based on my experience, lightning can occur with values of CAPE as low as 100, even lower if there is strong synoptic forcing (such as a very strong fast moving cold front in winter-half of the year). But the minimum I normally have to see to go stormchasing is about 300 J/Kg in the UK, but 500+J/Kg is  preferred. With such a CAPE it is possible to get thunderstorms with a decent amount of lightning and the storms usually tend to persist for at least a few hours. In such a situation it is crucial to be in the region where storms develop as if we wait in a wrong region too far away from the storms we may not have enough time to reach the storms before they dissipate. If CAPE goes above 1000 J/Kg we could expect much better storms. If there is good wind-shear on top we could get Mesoscale Convective Systems forming and persisting overnight. In situations where CAPE goes over 1000 J/Kg we can generally expect to see at least some lightning and if we are at the wrong place at the wrong time we should normally have enough time to get to the right place, unless the developed storms propagate away from us. Care always needs to be taken since some days can have high 1000+ J/Kg values of CAPE, but no storms develop at all. This is because there may be too much convective inhibition (CIN) and even that there is a lot of energy, storms don’t manage to develop. This often happens in anticyclonic situations. If values of CAPE reach 2000 J/Kg or more (this is rare in the UK, but more frequent in Central Europe, the Mediterranean or the USA) then we can expect very strong storms. In such situations the organization of thunderstorms largely depends on the wind-shear profile, but if CAPE trespasses about 2000 J/Kg it is not advisable to chase close to storm cores as the likelihood of large hail increases. Another index which is related to instability is Lifted Index. I personally prefer CAPE since it tends to be more accurate than Lifted Index. If I decide that conditions and indexes are favorable for a good storm situation I start to plan a stormchasing trip. Even if conditions look very favorable I re-check them at least once a day since only a minor change can mean the difference between a very good day with nice storms and a “bust” which means a chase when no storms where observed. A useful resource is Estofex, which is a website that issues thunderstorm forecasts for Europe every day, usually a day in advance. This is published on the European Storm Forecast Experiment website at www.estofex.org.

If there are hints on an interesting situation where good thunderstorms are possible I begin planning a stormchasing trip and roughly plan the location where storms may develop, where the storms may propagate, what routes I may have to take and what time I would have to leave home to be there on time. The precise planning stage is usually done no more than 2 days in advance so being flexible is crucial when stormchasing if we want to make sure to be able to chase the best situations of the year. Forecasts of storm indexes (as described above) ​​are normally issued up to approx. 14 days ahead, but their accuracy starts to improve about a week ahead and there are often considerable changes in these forecasts up to a day or two before the storm situation. Often, especially with potentially very good situations, variables can change last-minute either for better or for worse. This is because very good storm situations are often finely balanced. The precision of the forecast also improves with time. An example of how a forecast could evolve with time is that one week before the situation I can see that there is a potential for 1000 J/Kg CAPE somewhere in England and there is a good chance for storms to develop in that situation. Three days ahead, more details begin to be converge and it appears that a good area to be targeted would be Central Southern England where storms may develop around noon on the chase day and propagate northeast, reaching somewhere near the Wash around 9pm and propagating away into the North Sea thereafter. CAPE shows as being about 1500 J/Kg now and there is a decent wind shear for an MCS to form, but not enough Storm Relative Helicity for supercells. Two days before the situation changes a bit. Models tend to delay a cold front and therefore storms appear to form further west, maybe as far west as Devon, then tracking north-northeast passing Wales and the bordering regions of England, possibly propagating all night all the way to southern Scotland as an MCS. On the evening before the chase CAPE goes down a bit to around 1200 J/Kg, but there now appears to be good storm-relative helicty as models develop a wave on the approaching front so there is a chance of a supercell. Storms are now not expected to develop over SE Wales around 2pm and propagate northeast,  reaching the coast of Lincolnshire before midnight and then propagating off to the sea. On the chase day I may decide to go somewhere near the M4 corridor (for the possibility of quick re-positioning west or east), planning to arrive there by noon and waiting how the situation unfolds. The real situation unfolds in a way that some thunderstorms develop over NW France and Brittany already before noon and their anvils propagate over SW England, largely reducing insolation, temperature and hence CAPE. CAPE would still be around 1000 J/Kg, but the reduced insolation prevents local initiation in England. Instead, the storms over France merge into an MCS which arrives at the south coast of England around 4pm. These are good storms since they have a warm and moist inflow from the east-southeast, but because there are too many storms interacting with each other, no supercell forms, but the storms instead merge into a squall-line. The chase doesn’t take me neither to Lincolnshire or the Wash, but I just drive east near the coast since the best storm cells develop on the outflow on the southern end of the squall-line. The chase is finished at 1am near Dover when the system has moved too far away over the North Sea. This is just one example how a storm chase planning and the actual chase may end up. Sometimes models tend to forecast storms really well and the forecast changes little and the actual storm evolution is very similar to what was forecast, but more often than not, the actual storm evolution tends to differ, although the models are now very good in estimating the approximate storm parameters so the differences mainly arise due to the fine balance of various variables where little changes can make large differences.

Every stormchase is different. Someone may think a thunderstorm is just a thunderstorm, but in reality, even very similar situations can fold out differently and every single storm, even if similar to a previous event, is characterized by something unique. Some chases are more successful than others. Usually, the further I decide to travel the better the storms are, but I have seen very good storms within 30 miles of my home and I’ve had disappointing trips where I traveled e.g. to France for a good situation and it didn’t realize. On most chases I see at least one thunderstorm. In the UK it’s usually a weak one, but that doesn’t have to mean it’s boring. Normally I see nice cloud structures at first which eventually develop into a thunderstorms. Then I see some lightning, if I’m lucky I capture it on my high speed camera and sometimes I drive through small hail which sometimes accumulates to create a white scenery and sometimes I see flooded roads. To see something more extreme such as hail with a diameter of 3cm or more, a funnel cloud, lightning strike less than 100 meters away, thundersnow or some more serious flooding is quite rare. Every year there are chases where I don’t see a single lightning strike. This is either because storms don’t develop or because convective showers do develop but they are not strong enough to produce lightning. In such a case I can still see many interesting aspects like rainbows, nice cloud structures, some hail, etc. Or I could be in the wrong location too far away from where thunderstorms occur. In such a case I can either try to re-position to get to the storms or if it doesn’t look realistic to reach the storms on time I just abandon the chase. A chase when no lightning or nice cloud structure is observed is called a “bust”. In the US, many stormchasers call every chase where they don’t see a tornado a “bust”. In the UK we are not so lucky to have such an expectation from each stormchase, but to call a “bust” a chase when no lightning is observed makes us having only a few busts each year, whereas most chases in the US by a regular stormchasers would end up being busts as tornadoes are seen on less than about 20% of chases there (based on talking to several friends who live and chase most good situations in the US). This shows how the “satisfaction” with each chase is affected by the “expectation”. I would not be happy if I there was a rare 2000+ J/Kg CAPE situation with strong wind shear and I positioned myself in the wrong location which would then result in only 1 hour of seing a thunderstorm with maybe 50 lightning strikes seen and none of them on my high speed camera. On the other hand, I would be very happy if I saw 5 close lightning strikes in a blizzard after driving 300 miles to western Scotland at the end of December in one of the winter situations.                    

I’ll describe a typical spring/summer stormchase. As already described in this and other posts I usually try to target an area where I expect thunderstorms to develop. An exception would be if fast and organized storms were expected, in which case it would often be better to wait for them near the east coast in a location where they may encounter sea-breezes that could intensify them or even cause a spin-up or a funnel when sea-breeze vorticity gets entrained into their updrafts. But here I want to describe a typical single or multi cell thunderstorm situation where I expect storms of medium intensify that do not propagate faster than what can be chased on the road network. Late spring and summer is the season with most thunderstorms in the UK. In this season, thunderstorms normally begin to form in the afternoon, but I always try to arrive one hour before the expected initiation at the latest. When I arrive I try to find an area with a good view of developing cumulus clouds, which later develop into thunderstorms. Then I just wait, watch the clouds, switch on my lightning detector and check the radar, satellite and lightning detection regularly. While I have to keep an eye on the location where I wait, I also have to study real time weather data (such as surface observations or radiosonde ascents) to see if there is anything that weather models didn’t capture or predicted incorrectly. If it is the case, I have to monitor latest model outputs and try to nowcast what may happen based on storm climatology and I have to monitor other areas for possible storm initiation as well. If I see rapidly growing clouds, such as cumulus mediocris or cumulus congestus, I drive to their proximity as these are the clouds that have the best potential to develop into thunderstorms. Sometimes I drive directly below them if its possible so I know what’s happening in them in real time. If there is just a little rain with no large drops, it’s not a good sign and it means the cloud is falling apart. If there are large drops or even hail that is a good sign and often means that the first lightning strike is imminent. Usually, but not always, the first strike is a weak one inside the cloud so I just hear thunder. Once storms initiate it’s important to have a good view of them, but also to be able to keep up with them. Therefore I need to predict or have an approximate idea in which direction they will propagate and what the road network is like in that direction. I normally try to be ahead of the storm in a rain-free location, but close enough to have a good chance of capturing lightning at close range with my high-speed camera. More often than not, the storm catches up with me so I end up either in its core or sometimes the storm moves too fast so I can’t keep up with it. This is, however, preceded by some time where I have a good view of the storm and where I see nice cloud structure and lightning. Best roads to use when stormchasing are motorways and dual carriageways since they offer fast options for re-positioning. Storms however don’t always follow these and therefore I need to use my SatNav to find the quickest route to keep up with them. I always try to avoid big towns and if it’s rush hour I avoid some sections of the busiest motorways such as the M1 or M6. If I can’t keep up with the storm there are always two options. One is to finish the chase and go home (or for dinner or to have a look somewhere interesting where I am) and the other is to find another area where storms may develop or are already ongoing and it’s realistic to get to them in time. This decision is much more difficult than deciding on the first storms of the day as the subsequent storms form in an environment already affected by the first storms and this environment can be very different from what I’ve been studying during the days before the storm. Also, if forecasting models get the first storms wrong, they have little chance of getting subsequent evolution of other storms correct. In addition, there is usually little time to study models if I decide to go to another area with storms and hence it’s mainly guess based on experience that needs to be made. If I manage to keep up with storms until their decay and they don’t propagate out into the sea, their decay can be beautiful. When a storm falls apart it leaves behind an area with heavy precipitation or anvil clouds where very nice and long cloud-to-cloud lightning strikes (anvil crawlers) occur.

Now I’ll describe the equipment needed for a stormchase. Obviously, one needs to have a car (although I’ve chased storms by train, it’s much more difficult and more expensive to do it that way). Regarding the equipment in the car, I’d say a source of power is necessary. This can be provided by a power inverter. It’s a little box that plugs in the cigarette lighter socket and outputs 220 volts in a normal electric socket. Every power inverter can produce a specified maximum output of power (specified as how many Watts it can produce) and I’d think 500W should be enough for a typical stormchaser. A divider/splitter is then plugged to the power inverter so that we have more live sockets available in the car. These provide power to a laptop and a camcorder which I deem necessary to have on any chase. A laptop with a dongle and a working internet connection is needed for the purpose of meteorological data downloading (such as live radar and lightning detection) and a camcorder is a must on such a chase even if the chaser only wants to photograph lightning. There are many interesting things to be seen on a chase and before I had my camcorder that I could run from departure till arrival back home I often regretted not having my camcorder on. A dash cam wouldn’t be a substitute for a camcorder since the video quality is often not good enough (I’d recommend an HD camcorder which should run during the whole chase and should resolve a cloud to ground lightning strike during daytime as a minimum). A Go Pro mounted on the wind screed may be an option or a normal HD camcorder could be mounted to the dashboard by using sticky mounts where the camcorder could be screwed onto. A SatNav is also a must. Even if planning to chase in a well-familiar area nobody knows all the roads in any 100×100 km square (perhaps except some taxi drivers) and a SatNav can always guide you where you want. I’d recommend a SatNav with live traffic information especially if chasing near large towns at rush hour. I also carry a high-speed camera that captures lightning strikes at up to 20.000 fps, although the highest I’ve managed so far is 5.000 fps. This camera is the main part of my project where I try to capture a close lightning strike at high frame-rate. Additionally, I carry things like a flashlight which is very useful especially at night either if I want to analyze hail, depth of water on the road or if there is any problem I need to solve. I also carry a lightning detector. It is a little box smaller than a normal mobile phone and it beeps if it detects a lightning strike within a radius of around 60 miles. It detects electromagnetic waves produced by lightning, but is often subject to interference from the engine so I need to switch off the engine in the car to use it. It’s most useful when waiting for storms to develop as it beeps when the first lightning strike occurs. Also, I leave it on at night if I sleep between chases in my car or if there is a situation which begins at night (not often). If I’m asleep and lightning occurs within 60 miles of me, it wakes me up. However, I use it mainly for this purpose or when I wait for storms somewhere with poor 3G signal coverage as lightning data available on the internet nowadays is very up to date and precise. The best website to track lightning in real time is LightningMaps.org, which shows dots where lightning stroke in real time (but there needs to be a good signal strength). Another necessary tool for stormchasing is rainfall radar which shows the intensity and location of rainfall. Based on my experience the best radar for the UK is provided by Netweather. They have several free and paid options. The paid option provides data every 5 minutes with a delay of only 6 minutes, which I believe is the most up to date publicly available rainfall radar in the UK. There is also a map where it’s possible to zoom-in nearly to street-level to see where exactly rain and storm cores are, but one needs to bear in mind the delay between the data and real time especially for fast moving storms.

Because I mentioned I’ve chased storms by train, I will quickly describe that here as well. Between 2004 and 2008, when I was at University, I had no access to any car and I was very keen to chase some of the good situations that were occurring in those years. Since I come from the Czech Republic and in 2004 I came to England for the first time I wasn’t familiar with driving on the left side of the road with the steering wheel on the right-hand side of the car. Therefore I thought I couldn’t chase storms in the UK, at least until I could buy a car once and become confident on UK roads. While I studied at Oxford University one weekend in early spring of 2005 I took a train to Stevenage to visit a couple of friends. We experienced a thunderstorm there with hail and lightning and the hail covered the ground like snow for a while. When I returned back to Oxford I realized the there wasn’t any storm or lightning observed from Oxford and I just had the idea “Would it be possible to go somewhere by train in order to experience a thunderstorm there?” I knew the UK had a very dense railway network with quite frequent services on most of it so the very next day I downloaded and printed out maps of both main and local railway lines, wrote down approximate frequencies of trains on every line and wrote down what time is the latest train I had to take from every main town in order to make it back to Oxford that day. At first I did about 10 “virtual chases” by train, where I studied thunderstorm situations from the previous summer and used current train timetables to see where I could get at what time. I imagined I left Oxford by train in the morning, traveled around by trains based on my storm forecast and the real storm development (I didn’t play the radars to see how storms will develop, but like in reality, I used archived model runs and archived data and pretended they were happening in real time) and I used train timetables to “virtually travel” around the train network. This was much easier than reality as I didn’t take into account any delays and I was at my computer the whole day which wouldn’t be possible on real chases since network coverage was much worse in those years than it is now. This type of “virtual chasing” could also be done by car. Just use a SatNav or a route planner to calculate how long it would take by car to travel somewhere. Then watch storms on radar in real time and change your position based on the real time information that is available. You can then see how well you would have done if you chased in reality, although care must again be taken since such technique doesn’t take into account traffic, flooded streets, branches blocking the road, etc. Based on my “dry run” of chasing storms by train, I would have gotten to less than 10 miles of lightning activity on 7 out of 10 chases and hence I decided to do a real chase. As far as I believe, nobody had chased storms by train like that before. The actual chasing was quite similar to chasing storms by car with the added challenge of being limited by available trains and their destinations and with the fact that it’s quite difficult to find a good viewing point near most stations (although not always). My first ever chase by train was taking a train to Birmingham in late April of 2005 where I expected storms to develop in Wales and then track northeast via Birmingham. This was a bust since lightning occurred only in Wales and the system went over Birmingham only as an area of weak showers. So my first ever chase was sitting approximately 5 hours in an internet cafe in Birmingham and then going back to Oxford. After this chase I was quite reluctant to chase by train in the future as I wasted a train journey, whole afternoon and didn’t even get anywhere close to a storm. Furthermore, several of my stormchasing friends in the Czech Republic told me that I could never be any successful if I chase storms by train and that it was a waste of time. However, their reasons were based on the Czech railway network which is by far not as dense as UK network with only a few trains per day to most towns. In a few days I analyzed the chase again and thought what I would have done if I chased by car. If I had a car, I would have gone to Wales and waited there where the storms first developed and did produce lightning and I thought if I drove to Wales I would have seen at least lightning. Then I realized that if I had left Oxford earlier in the day by train I would have had a chance of getting to Wales where the lightning occurred in time, experience the storm and get back. I actually realized that I could have left Oxford at 7am, arrived in Worcester before 9am to go to a local internet cafe (or plug in my laptop at one of the local pubs) and I could have had time to properly analyze the situation there and have the options to go to several places in Wales.  Most of the lightning occurred west of Hereford and I thought if I waited until about noon in Worcester, I would have had enough information to decide to go to Hereford where I would have arrived on time to see the storms. So I decided I needed to have much more information about the railway network and I have saved detailed maps with railway lines and timetables to my laptop and I thought the key here is to travel as close as trains allow to the storms and not wait at a bigger hub and assume storms will make it there. So I did my next chase in May 2005. A convergence line lay across most of England between approximately Bristol and Hull, there was nearly 1000 J/Kg CAPE forecast and the wind shear was sufficient for organized storms. I don’t remember the exact date now, but it was a weekend and I took an early morning train to Birmingham. I waited in my usual Birmingham internet cafe for about 1 hour when it started to look like first storms will develop over the Peak District.I took a train to Derby, waiting at Derby train station for another hour before cumulus clouds started to grow over the Peak District. Than I decided to get even closer so I took a train towards Matlock. In the meantime, thunderstorms developed and I saw the first flash of lightning near Cromford, where I got off the train since the terrain became not very good for a nice view towards the storm. I had to walk a bit to find a nice place to watch the storm and then I saw a nice structure, storm base, rain shaft and frequent lightning. I only had about 10 minutes before I had to go back without being caught in heavy rain and close to dangerous lightning so I ran back to catch a train to Ambergate, where I had to wait for a train northward. The storms were propagating from the Peak District towards the northeast so I planned to catch a train north and get ahead of them either in Chesterfield or Sheffield. It was a long wait before there was a train and I saw that I wouldn’t get to Sheffield in time for the initial storm. However, a new storm cell began to develop further south so I could get off in Chesterfield and be right in the path of that cell. When I arrived the clouds were darkening and I could see flashes and hear distant thunder. I just had approximately 5-10 minutes to find a parking lot, where I could walk to the top floor and get a view towards the storm. After a few minutes the core approached and heavy rain began so I had to observe from inside. The storm lasted approximately 20 minutes and pea sized hail occurred for approximately 2 minutes. After this storm there was no time to go anywhere else (since it was approximately 5pm), although there were much better storms further north. I had to catch a train back to Oxford via Birmingham. While I only had a few minutes with each storm, I considered this to be a large success, which demonstrates that chasing storms by train was indeed possible. I was able to use the train network to get close to a developing storm and then follow it to intercept a new cell on the southern side of the storm system. While this type of chase was not ideal, it could be done and from that chase I started to regularly chase the best situations. I didn’t get very close to the storms often, but more often than not, I could see at least some lightning and a nice storm structure. Nearly all my chasing trips by train were one day only, except one overnight chase in November 2005 where I took a train from Oxford to Eastbourne in the evening and then sat on the coast all night watching lightning in showers over the English Channel. Crazily enough, it involved being outside with no place to go to from approximately 10pm until about 8:30am, but I was so eager to see some lightning during the quite winter period that I was ready to undertake that. In fact, it was one of my most successful chases by train as I’ve had 9-10 hours with intermittent lightning activity and because of the nighttime and the coast I could see many cloud-to-sea strikes very clearly. It was cold and some of the gaps between lightning activity were up to 1 hour long, but I just walked around the town and beaches when there was no lightning visible. I also chose to chase this situation because the wind was flowing offshore so I knew that the showers would not reach the shore and soak me outside in case there was no place to hide inside. This worked until about 6am when an occluded front arrived from the west and brought the last few lightning strikes, but then brought heavy rain even to my location on the coast and I got a little wet from the rain before the first cafe opened at 7am. After that I took a train back to Oxford and was very happy to see such a display of lightning in November, since before this chase I was never sure how much lightning these showery situations over the sea could produce. This chase also showed me a new potential of winter time chasing and that lightning could be chased in the winter half of year as well, even by train!
I will probably describe some of the other good chases by train in separate posts, but I just want to mention a few techniques I used to travel around as cheap as possible (I’m not sure if they were all legal or would be now, so don’t want to encourage anyone to do them unless checking with the railway company first, but I have never been caught). I avoided buying Advance tickets because I needed the flexibility. I only bought advance tickets for a single journey in the morning where I was sure that I would go e.g. Oxford to Birmingham. Everything else had to be fully flexible. I always avoided the expensive peak trains, rather leaving very early than during the rush hour if chasing mid-week. Using a detailed searching of fares I realized that tickets between some towns are cheaper than between other towns, so I always bought return tickets to the farthest cheap town on the route and then I had the flexibility to get off the train on the way earlier. Sometimes I even noticed that when I needed to travel somewhere it would be much cheaper to buy tickets to a town that is further on the way. I don’t remember exact examples, but e.g. train ticket from Oxford to Wolverhampton might be cheaper than ticket to Birmingha, so I bought a ticket to Wolverhampton, but got off the train in Birmingham. I also did another “trick” which I’m sure is not legal, but worked for me several times (but please don’t do this as I’m sure you could get a penalty fare if caught!). Buying a return ticket is normally only slightly more expensive than a single ticket (when buying off-peak), e.g. a single may be £30, but a return only £31. Therefore I always bought return tickets even in cases where I was sure I wouldn’t use them as they were normally valid for a month. I kept them for a later date so I didn’t have to pay an expensive single next time. Many of the long journeys were done either very early or very late when only a few ticket inspectors were present. Therefore, nobody would often “cross out” my ticket and the ticket would remain intact at the end of the journey. The only problem were ticket machines in Oxford, which would “swallow up” my ticket upon exiting the station so I did this little trick. Every morning I bought a return ticket from Oxford to Bradley, which used to cost less than £2. I went through the barrier on that ticket and when I got back in the evening I let the barrier swallow my return ticket from Bradley so I could keep my unchecked e.g. Derby to Oxford ticket safe and valid for the next month. Sometimes I got my return ticked crossed off, but this was not very often and the extra ticket to Bradley certainly paid off in the long term by saving large on a few longer journeys. These little tricks are described here only out of interest and there is definitely no intention to encourage anyone to do them and I strongly discourage anyone, either when trying to chase storms by train or when taking a train for any other purpose, from doing these.

What is stormchasing and how to chase storms with safety in mind

This post describes what the words “stormchasing” and “storm chaser” mean and what stormchasing involves, including my personal experience I gained stormchasing since the summer of 2003.

While not everyone knows what “stormchasing” really involves, most people certainly saw the American film Twister where Bill Harding (starred by Bill Paxton) chases tornadoes with his colleagues to obtain certain data in order to study tornadoes and improve warning systems. What these scientists do in the movie can be described as “stormchasing” or rather “tornado chasing”. The activity itself can be described as driving a car (or traveling by any other means of transport) into a proximity of a storm. This can be done for various reasons ranging from professionals who try to obtain scientific data to both amateur and professional photographers who want to take videos and pictures of storm structure and lightning. In the USA there is also a network of “storm spotters” who monitor storm activity and visually observe storms in order to provide warnings of developing tornadoes to the general public.

I have been a stormchaser since the summer of 2003. While I have been interested in storms, lightning and severe weathe, since being a child I did my first proper stormchase in that year. At the beginning I did it only for my personal interest, rarely even shooting any video. A few years later I started to take videos during all of my chases and since 2021 I have been involved in several scientific projects which required me to obtain data in a close proximity of thunderstorms. I have chased storms in many countries and the list still grows. My first stormchase in 2003 was in Cuba, but since then I chased storms in: USA, UK, France, Germany, Spain, Italy, Switzerland, Austria, Belgium, Netherlands, Luxembourg, Poland, Czech Republic, Slovakia, Hungary, Croatia, Slovenia, Greece, Romania, Malta, Argentina, Panama and Australia.

I have had a website in the Czech language for approximately 10 years (see www.stormchaser.webgarden.cz).  Why in Czech? Because I come from the Czech Republic originally and most of  my stormchasing in my early stormchasing years was done in the Czech Republic. However, I have permanently lived in the UK since 2012 and because many of my stormchases have since been done in the UK, visits to my original Czech website started to originate in the UK and earlier in 2017 more than 25% of people visited my original website from the UK. Furthermore, the ratio of traffic generated from general public sources to visits from professional meteorologists and amateur stormchasers has increased showing that general public is increasingly more interested in stormchasing with time. This led me to develop a new UK website where I will focus on my UK stormchases and will, as time permits, translate and update this website based on my original Czech website.

So let’s get to the description of how to chase storms and stay safe. First of all, before I encourage anyone to chase storms I need to stress that chasing storms is a dangerous hobby if not done in a safe and responsible way. Any thunderstorm can be life-threatening because it is always associated with dangerous phenomena such as lightning, large, severe wind gusts or some rarer and more dangerous phenomena like tornadoes and flash floods. Everyone who chases storms needs to be aware of these and take appropriate measures to avoid injuries or getting into a life threatening situation. The number one killer in a thunderstorm is lightning. It strikes fast and the exact point where it strikes can’t be predicted. The danger of lightning can, however, be easily avoided when chasing in a car, because its metal construction works like a “Faraday Cage” and any strike that may hit the car would be guided along the metal chassis around the people inside. This does not apply to convertibles! Furthermore, a car is not, unless it has tall antennas installed, an object that would be “preferred” as a target for a lightning strike as its shape is elongated and there are no pointy objects from its roof. A tree, chimney or a person standing outside is much more likely to be hit. However, while cars are very safe they still do not offer 100% protection. A car is not a perfect Faraday Cage, but for the purpose of relative safety, it is much safer than many other locations (including houses and other buildings!) where we may be during a thunderstorm. I have personally been several times in a car within 10 meters of a lightning strike and have never felt any electric shock or any other effects except very loud bang of thunder. While a car could be a very safe refugee from a weak thunderstorm or in a safe distance from a storm, it may not be a wise option to hide in a car in a core of a strong thunderstorm. Strong thunderstorm cores often bring severe wind gusts which can cause trees, branches or other objects to hit the car and injure people inside and the near zero probability of being hit by lightning in a car may then be offset by the danger of wind-driven objects hitting or falling onto the car. In addition, thunderstorms can be accompanied by large hail which can in extreme cases break the windows of the car. These phenomena are always located near and inside a core of a thunderstorm and therefore such core should be avoided whenever possible. Most stormchasing actually involves watching a storm from ~10 miles away as that offers much better view of the storm structure and lightning. In addition, if the core of the storm approaches, there is enough time to retreat or find shelter (such as a petrol station). While I often chase in a core of a thunderstorm, I do this for scientific purposes where I have to follow certain guidelines to lower any danger. For this reason, any videos that I publish and where I chase a core of a storm (called “core punching”) should definitely not encourage anyone to do it. A core of a thunderstorm can be identified on a radar and the use of radar is always recommended when stormchasing. The core of a storm can also be identified with some experience without a radar. It is a location with locally intense rainfall where visibility suddenly drops. There is often intense lightning activity in or near a core and the lightning is usually not visible well as the rain and hailstones hide it. It normally appears as a dark area of heavy rain with frequent flashes of lightning. Generally, the more frequent the lightning is the stronger the core. While heavy rain, hail and strong gusts of wind are usually located in a core of a storm, tornadoes, on the contrary, always form under an updraft where warm and humid air flows into the storm. An updraft normally appears as a dark cloud base with no or little rain falling from it.