Tuesday, September 09, 2014

Active Fall Severe Weather Season?!



A lot of people are focused on what kind of winter we will have, but we shouldn't forget the change of seasons can bring violent weather.  Our secondary severe weather season will ramp up soon and we really need to pay attention this year.

I have quoted Weatherbell.com meteorologist Joe Bastardi's winter forecast several times here on the blog.  He continues to say this winter will be similar to, but not exactly like 2002/2003 and 2009/2010.  Let's go back and look at the fall severe weather season in 2002 and 2009.  Both had very significant events.

In late October of 2009, a very strong area of low pressure aloft pulled out of the western United States.  The top picture is at a level called "500 mb".  That strong storm helped wrap up a strong area of low pressure at the surface and you can clearly see that in the bottom panel located over Kansas.  This map was valid at 7AM that morning.  Arkansas is very firmly entrenched in an area of surface stability.  HOWEVER, later that day, the warm front you see over TX and LA surged northward and produced severe thunderstorms over western and southern Arkansas.
Look at all the tornado tracks that day.  especially over south Arkansas.  One hit East Camden and the Fire Training Academy.  There were a total of 15 tornadoes that day.
On December 18, 2002, a massive storm system ejected out of the Rocky mountains.  In the top panel, you can see the area of low pressure and the trough over the Dakotas.  What makes this 500mb map ominous looking is the negative tilt of the trough.  You see how it is oriented from the NW to the SE?  This can spawn a strong storm system with extreme shear as winds change rapidly with height.  The bottom panel shows the surface low over Iowa and the trailing cold front over eastern OK.  Very moist and unstable air is flooding the mid-south ahead of it.
There were 28 tornadoes that mid December day in 2002.  Most of them over the SE half of the state.   The large majority of them were EF0 and EF1 twisters.  However, there was an EF3 over Faulkner county.  The map above shows ALL tornadoes that year with the ones from that December day circled in red.  Notice how quiet that year was until December.  It's sort of like this year.  Outside of April 27th (Mayflower/Vilonia), it has been quiet.
In summary... Every year we need to watch our secondary severe weather season.  Some more than others and I worry about this year.  I hope we can escape it and get overwhelmed with colder weather.  One thing for sure, we'll be watching it for you!

1 comment:

Shane Lee said...

Very interesting, Todd. The winter severe weather season is always worth watching here in Arkansas. As we have seen with the April 27th storm, it only takes one tornado to make a whole year a traumatic one. How often do we experience strong tornadoes in the fall season? (EF3-EF5) Is there any difference in the behavior of these tornadoes versus the spring storms (i.e. more rapid formation, long track, slower/faster movement, discrete supercell vs embedded, etc)?