Jim Tang’s analysis is impressive but I’m having a little trouble following the conclusion. Admittedly I didn’t take the time to really study the “tornado cluster” concept, but how do these two statements from the article reconcile:
“...if you took a two-week chasecation ending on June 12 every year between 1996 and 2017, and you nailed the biggest tornado cluster every time (good luck!), you would’ve experienced a little over 80 clusters. Or around four per year.”
“...a two-week chasecation that ends on May 31 has resulted in about 30 big tornado days in the past 22 years. In other words, we should expect 1-2 such events if we chase two weeks in late May, and that’s not counting the smaller events that can also yield an incredible chase.”
From these two statements, it would seem like June is preferred over May if the criteria is number of events. What is it that makes late May better, is it the quality of the events?
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It seems that late May has less "big" events than early June, but has a fairly steady stream of medium to big events, while there is a bit more variability in early June. It seems to be more boom or bust in early June, even though there is still fairly steady activity as well in most years. One might have to consider playing the Midwest a bit more (east of I-29) for an early June chasecation, as tornado probabilities increase across Iowa and southern Minnesota, for example.
My takeaway (might not be exactly what he's saying) is that if you chase in the last two weeks of May, you'll have more tornado chase opportunities and at least a good probability of one or two higher-end events. On the flip side, if you chase for the first two weeks of June (his period overlaps late May a bit for some reason), you'll probably have a couple/few higher-end events, but there will almost certainly be a few down days as well.
If one chases in late May, unless it's a horrific year, one would expect to probably only have a small handful of down days with little to no tornado activity. Likewise, chasing in early June, there will probably be more down days in comparison to late May, but the big days will have the potential to be as big, if not bigger than late May.
Some of my biggest days since 2014 have been in mid-June (My best 3-day stretch was June 16-18, 2014 and last year's June 12th was the highlight of the year), but activity becomes much more hit and miss from mid-June on. Not to mention that bigger events become much less common as one heads into late June and beyond. They do happen, but they don't occur every year.
Early May is an odd period as well. His data suggests there is a secondary (really third) peak over the first 7-10 days of May. There are higher-end events mixed in with some dull periods (most notably 2011). I've had mixed success in early May, but if you look at tornado counts over the past 10-15 years, you'll notice that it's fairly common to see a 3-5 day stretch (or longer) with little to no tornado activity.
In a perfect world, if one wanted to play the odds and had a full month to take off for storm chasing, I guess you could argue for the first week in May, then the last two weeks in May, spilling over into the first two weeks of June. If one took off the entire month of May, there would probably be a lot of variability and one would almost certainly miss out on some big events in early June.
My favorite part of June is that tornado activity shifts northward, so you're not always chasing in the same parts of Kansas/Oklahoma/Texas that May commonly features. If one chases regularly in June, expect to see a broader target area, expanding from parts of Wyoming and Montana, eastward into Illinois. While some May activity can and often does spill over into parts of the Midwest, there is a fairly obvious bulls-eye over Oklahoma and adjacent states.
There's even another little peak in the last week of April, but that involves being willing to chase in parts of Dixie, as well as considerable downtime between events, unless it's 2011...
