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.