People are constantly asking me where and when I’m going for storm chasing. The answer is “where the storms are,” but that’s not very satisfying. Therefore, I do the best I can to answer in detail without taking up too much time, but, really, I could spend a lot of time explaining where and when we chase. This post is a short description of where chasers chase, when they chase, and how they decide where and when to chase. It is the third of a series of six posts on storm chasing that began with a post on the joys of storm chasing. The intended audience for this series is non-chasers who are interested in chasing or how chasing works. Right after this series of posts, I will launch into a day-to-day blog on my storm chase next week.
The short answer, to where and when chasers SHOULD chase, is primarily Tornado Alley during tornado season. Tornado Alley is the U.S. and Canada Great Plains bordered on the west by the Rocky Mountains, the east by the Mississipi River, the south by Mexico and the Gulf of Mexico, and the north approximately 200 miles north of the Canadian-U.S. border. Everyone’s definition of the borders of Tornado Alley will be different, but mine would be good enough for most people. Tornado season begins in April in Texas and Oklahoma, finishing in July in the extreme northern U.S. and Canada. But you can't be more specific than that about where you will chase more than a few days out.
Of course, tornadoes occur all over the world, and one could argue that nowadays there are more tornadoes in the southeastern U.S. than in Tornado Alley. While that all might be true, and while some people do chase tornadoes outside of Tornado Alley, Tornado Alley’s flat plains, with few trees or buildings, make it especially inviting to chasers due to improved visibility. In fact, I do not recommend that anyone chase outside of Tornado Alley due to safety issues: trees, buildings and hills obscure your vision of the tornado, and visual cues are key to staying a safe distance away from a tornado; and road networks can be sparse and/or not laid out in a grid, and so escape routes from a tornado may be difficult to find or not even exist altogether.
As hinted in the previous paragraph, the peak time for tornado activity travels from south to north as the season wears on. April chases are primarily in Texas, Oklahoma and Arkansas. May chases are primarily in Oklahoma, Kansas and Missouri. June chases are primarily in Colorado, Nebraska and Iowa. July chases are primarily in the Dakotas, Minnesota, and Manitoba. The tornadoes are the most severe in April, but the tornadoes are the most numerous in late May and early June. Most chasers like to chase in May or June, but I know one veteran chaser who hates to chase in May (but still does). There are chasers who will chase year-round, on the rare occasions of tornadoes outside the April through July time-frame, though you’d be hard pressed to find any severe storms in Tornado Alley in November, December, or January. Chasing before April or after August is less rewarding because of earlier sunsets.
Storm chasers are, among other things, weather forecasters. They combine long-range and short-range forecasts to know where to be when to optimize for catching severe storms. The most simple and widely-used long-range forecast tool is the Storm Prediction Center’s Convective Outlook, which predicts where the severe storms will be from 3 to 8 days out. This forecast, combined with others, guides the chaser to where the storms will be on a specific day. Thus, chasers can “position” themselves at the end of one day to be near where the storms will be the next day.
The picture at the top of this post is the SPC Convective Outlook for tornadoes today, June 1, 2011 (this is the early morning one, it might be updated significantly later today, but I like this one because it is a good example). Note that there are two “5%” chance locations for tornadoes (shaded in brown). This means that in these areas there is a 5% chance of a tornado occurring within 25 miles (a 2,000 square mile area) of any given point. Based on this map, a chaser might target Ogallala, Nebraska, though other forecasting models might lead the chaser to a slightly different location. Almost no one is going to chase the northeastern US portion. This is because of the safety issues I referred to previously, and also because chasers are almost never positioned to reach the east coast of the US within several hours of driving time.
Based on this SPC forecast, either it's almost certain there will be at least one tornado in the northeastern US today, or there is a small chance for several tornadoes. The SPC gives more detailed guidance about the nature of the exact threat. And looking at the guidance and other models, I'd say it's the former. The air is amazingly unstable over the northeastern US, with little warmth in the upper layers to prevent storm formation. (For those of you who know what it means, 5000 CAPE and very little cap. Yikes!). According to SPC, these storms should start forming as early as 11am EDT.
Once the chase day begins, SPC plus other shorter range forecasts help the chaser pick a “target area” for the day. Since storms almost always form late in the afternoon, the chaser has the opportunity to travel for several hours to hit the “target area.” Once the “target area” is reached, even shorter range forecasts aide the chaser to get to the area where the storms are expected to form.
For example, on day 1, a chaser may have chased in Limon, CO, but seen that the next day’s storms would be in Kansas City, MO. That night, the chaser might drive to Colby, KS, driving to Kansas City the next day, driving from 10am to 4pm, catching the storms forming at that time.
Finally, I should address the issue of night chasing. Chasing at night can be a LOT of fun. You get your visual cues by watching the storms, including tornadoes, lit up by lightning. It can be very surreal. I’ll address this more when I describe the dangers of storm chasing, but suffice to say you should not start night chasing on your own until you have been on several night chases with someone who is experienced in night chasing.
Next post: The dangers of storm chasing
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