Friday, August 11, 2023

Severe Thunderstorm Warnings

This summer the National Weather Service in Fairbanks has issued a lot of severe thunderstorm warnings, including three in the last couple of days, and another one just now.  Remarkably, yesterday evening's warning was for a storm near Eagle - a very long way from Fairbanks.

The total of 28 severe thunderstorm warnings this summer is far and away the most issued by the Fairbanks office, based on an archive back to 2004.

What's going on?  Has this summer actually produced far more severe thunderstorms across the central interior than any other summer in the last 20 years, or has there been a change of procedure?

It would be very interesting to work with the radar data to create an objective measure of the number of intense storms each summer, but it would be a lot of work - a good project for a Masters degree student, perhaps.  Lacking such an analysis, we can look at the lightning data, and it turns out that this summer is still on the low side of normal, although activity has been extremely high in the last two and a half weeks.  (But note that this pertains to the entire ALDN region west of 129°W, i.e. including a good portion of NW Canada.)

Have all the severe warnings been issued since late July?  Not at all: 18 of 28 were issued on or before July 17, when lightning activity was unusually low.  Here's a look at the date distribution of all severe thunderstorm warnings issued by Fairbanks; note that sometimes several are issued on the same day.

This summer has seen warnings issued periodically since mid June.

There has in fact been no change to the criteria for issuing these warnings, and so the most likely explanation is that the NWS meteorologists are much less hesitant to issue them this year.  It's probably not a good thing to see such a drastic change in practice; but there may be a few people receiving benefit from the warnings.

One other note, and this is a comment on the lightning chart, reproduced below.  It's quite interesting to see a bifurcation between active and inactive years from mid-July onward: the slopes of the cumulative lightning counts through the end of July are quite distinct.  And this highlights how unusual summer 2023 has been: it started out very inactive indeed for lightning, but now at the eleventh hour the lightning activity has ramped up at a rate worthy of a very active year, but a full month later on the calendar.

Notice too that none of the last 11 years has seen any really significant lightning activity after mid-August; so it would be extraordinary indeed if anything like the current pace continues for more than another few days.

1 comment:

  1. Great day f8/16 for thunderstorms and lightning strikes. Late in the season for this stuff. Soon Fall starts this weekend with SW flow, cooler temps, and moisture. Summer 2023 was fun, some.