Monday, August 12, 2013

2013 Has Been A Relatively Quiet Severe Year Nationally

Save for the Oklahoma tornado outbreaks in the latter parts of May, 2013 has been a rather quiet year for severe weather across the country, even compared to 2012 (which was also a quiet year for the US). Nationally, this year has seen just 490 severe weather watches issued through the US, about 80 fewer than last year through August 10th.

The US last year had 197 tornado watches, with the vast majority of them centered across Alabama, Mississippi, and a secondary spot in Oklahoma.  The tornado watches across the Deep South were due to the combination of early season outbreaks in January, February, plus the impact of Hurricane Isaac in early September near the Mississippi Delta adding additional watches to their high water mark total in the Deep South.

This year, the amount of severe weather outbreaks and watches in the Deep South are lower in comparison, while the main axis of severe weather this year has shifted to the Plains from Oklahoma northeast to Missouri.   The biggest events this year have been in Oklahoma during the month of May.

The one thing you'll notice about both graphics is how tornado watches and more significant widespread severe weather outbreaks occur east of the Rocky Mountains due to the combination of storm system interaction with humid Gulf moisture and the dry air pushing downwind from the Rockies (or from the northwest from Canada) in the wake of cool fronts. Tornado watches are much more uncommon out across the West as a result of the lack of those factors.

Locally, in terms of tornado watches this year we've seen two issued for Philadelphia and anywhere from one to three issued in the Delaware Valley, depending on location, similar to what we've seen last year around here.

Nationally, that's not the case...nor are the number of tornado reports.

Through last Saturday, we're about 200 tornado reports behind 2012's total (712 v. 911) and this year is running at about half of 2011's near record-setting pace. In fact, 2013 is the quietest year for tornado reports since at least 2005.

All it takes is one or two big tornadoes (Moore and El Reno) to set a perception and be the standard for severe weather in a year, much like 1992's hurricane season is remembered for Hurricane Andrew despite the inactivity '92's hurricane season produced. It also shows once again that despite a quiet year, one or two storms can definitely bring notoriety and significant damage.