Secret to Suppressing Severe Storms

For the sake of V.O.R.T.EX.-2 and assorted independent storm observers now strewn far and wide across the Great Plains, in a state of resigned convective despair, I hope May 21 finally represented the very rock bottom of severe weather for this lame season. Sure, the mass hunger for atmospheric violence is unlikely to be satiated anytime soon; the short- to medium-range numerical models indicate only marginal hopes (at best) for the next week and a half, at least.

As Greg Carbin notes on his “official” BLOG, the 7 day period bracketed by the dates May 17-23 never has lacked tornado and severe thunderstorm watches…’til so far this year. Quiescent conditions, indeed…disturbingly so!

Still, we hit the ultimate severe storms nadir with a strikingly rare occurrence: no severe reports for an entire convective day in mid-late May (as of this writing). Unfortunately, I had the dubious honor of issuing the strikingly rare mid-late May national convective outlook that contained no severe probabilities, valid for that whole day-1 period. [Russ Schneider made the general thunder lines.]

The categorical outlook…

The (preliminary) verifying map…

No severe events forecast, and no severe events reported. This was in an era of the most saturated weather radar coverage ever known to mankind, ever-rising severe storm report inflation and very liberal warning practices, no less! How bizarre is that?

I’ve often said that some of the most difficult forecast decisions to make are those for the non-event. Staring into the razor-toothed jaws of the climatological sharks-mouth, with the possibility that any given thunderstorm could yield a cheesy “severe” report nowadays, I still have trouble believing such a forecast could be made. Do you have any idea how hard it is to forecast no severe thunderstorms for a whole day in mid-late May? But the evidence was compelling and powerful that the probability of severe storms wasn’t even worth drawing a single marginal line for, anywhere, despite the likelihood of a general thunder threat in a couple of fairly broad swaths.

I don’t believe in hexes, curses or voodoo, despite my frequent facetious remarks to the contrary when it comes to my extraordinary powers of tornado repulsion while roaming afield, so I shall speak only to known facts and findings. There is something more to May 21 than meets the eye, besides its utter absence of severe storms this year.

Consider the following histogram, created by Chuck Doswell for his formal research paper in EJSSM, Small Sample Size and Data Quality Issues Illustrated Using Tornado Occurrence Data.

It represents “The number of days with 7 or more reported tornadoes during the period from 1970-2002, as a function of the calendar date” (Doswell 2007). Chuck made it a specific point to highlight May 21 (green, which also is the color of the emerald, the birthstone for May) as a pronounced, historic, meteorologically inexplicable, nationwide minimum in days with at least 7 tornadoes, total, over the whole CONUS.

I’ve heard a few storm enthusiasts utter lamentations to the effect of, “It figures that such a rotten, watchless pattern and a totally non-severe day would happen during V2.” But that’s just more hocus pocus talk, isn’t it?

I’ve got another insightful fact: May 21 is my birthday.

And before anyone asks…no, while preparing the outlook, I didn’t even think about the fact that the forecast day was my birthday. [I have been known to forget my own birthday, anniversary, etc.] The scientific integrity of the product is too important to let such ridiculous non-meteorological thinking intrude.

Nor have I ever seen a tornado on my birthday. I have witnessed and photographed them (with example links) on May 20 and May 22.

Surely there’s no connection in all this. 🙂



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