Wednesday, May 08, 2013

Weather Channel: "May's 10 Worst Tornado Outbreaks"



Nick Wittgen has a “short film” on the “May’s 10 Worst Tornado Outbreaks” in the US, some of it quite graphic, with a lot of explanation, here.
   
It starts with tornadoes in California and then Italy.


The film comprises many little videos, each preceded by a commercial.
  
There is a video that asks “Has Tornado Alley Moved?”  There is some sense that it has tended to shift east, and that the southeast, east of the Appalachians as far north  as the Virginia Tidewater, has tended to become riskier.

The fourth and fifth deadliest tornadoes in history were spawned in Tupelo, MS in 1936, and in the 1930s two tornadoes actually collided in Gainesville, GA.

There’s a video that analyzes the 2012 tornado outbreak.  Another shows damage from the two largest in 2011, Tuscaloosa and Joplin.

May is typically the most “dangerous” month, because warm humid air from the Gulf can get hot, whereas there is still some very cold air in the Rockies that can collide with it, causing explosively unstable air. 
Tornadoes do occur near Washington DC, but the most severe storms tend to occur on the lower Potomac and move northeast over the Dalmarva, or northwest of the City in Frederick county , MD, possibly because of the Bernoulli effect of the Harpers Ferry Gap to the southwest.  The Blue Ridge has a mixed effect on the severity of storms, making them more severe in some locations (like Culpeper)  relative to the mountain gaps, and less in others.  But there was an F4 tornado in Frostburg, MD, in the Allegehenies, in 1998 (very rare for the area), and another in La Plata, in southern MD, in 2002, in an area that is flat, near water, and more exposed.   
  
  
The Weather Channel link is here.  It seems that it is getting updated.

Note that Accuweather weighs in on the cool April and May for 2013, actually reducing tornadoes so far. The link is here. When I was a boy, we typically hit 80 degrees in Arlington in early May, and 90 by late May, but often had strong cold fronts that would drop the highs for following days to 60.  Heavy spring thunderstorms were frequent in the 1950s, but less destructive, because the tree canopy was not as high and there wasn't as much development.  

Wikipedia attribution link for global distribution map, double vortices. 

Update: May 20, 2013

This has been a terrible period for the southern plains, especially around Granbury, TX (where I almost got an IT contract with Texas Energy in 1988), and today south of Oklahoma City, in Moore, which I have driven through on I35 many times.  The area where I35 runs was hit by an F5 in 1999, with 300 mph winds, the strong surface winds ever measured on Earth.  (On Neptune, they are 900 mph.)  

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