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.