***Watch WISN 12 News for LIVE coverage of the tornado aftermath in Alabama!***
A devastating once in a generation tornado outbreak hit the deep South on Wednesday. This tornado outbreak will rival the ‘Super Outbreak’ that hit some of the same areas back on April 3-4, 1974.
Meteorologist Mark Baden will be live in the areas hardest hit bringing the pictures and stories of the event to everyone here in southeast Wisconsin. Make sure to watch WISN 12 News at 5, 6, & 10pm for the LIVE reports.
So how did this tornado outbreak occur? In this blog we’ll discuss look at how this tornado outbreak occurred.
Let’s start with this incredible video from the Tuscaloosa News via You Tube showing one of the violent tornadoes from April 27, 2011.
The ‘Super Outbreak’ from April 3-4, 1974 produced 148 tornadoes. In Wednesday’s tornado outbreak there were 179 reported tornadoes. We’ll have to see how many are documented, but this will certainly either top or be very close to what many consider the worst tornado outbreak in U.S. history.
Below are the storm reports from the SPC from Wednesday.
Now why did severe weather form? In order for severe weather to occur, you need three ingredients – moisture, lift, and instability. Those ingredients came together to produce strong and violent tornadoes in the south. The surface map below shows low pressure over Arkansas with a trailing front. This low helped to pump in warm, moist air over the South on Wednesday. Dew points(a measure of moisture) were already in the 60s to 70s at 7 a.m. Wednesday. Also, the surface winds ahead of the low pressure area were south-southeast.
While surface winds over the South were out of a south-southeast direction the jet stream was screaming into the region around 100mph out of the west-southwest. Below is a 300mb map at 1 p.m. Wednesday. The blue area is called a ‘jet streak’ or where the winds were the strongest.
The change in wind speeds and direction with height is called shear. Shear helps thunderstorms to rotate, and in turn produce tornadoes under ideal conditions. Shear is probably the #1 ingredient needed for tornado formation once the thunderstorm has developed. Here is a simulated thunderstorm showing how all of this works. The model below is from the NSSL.
We will continue to update the situation in the South here in the blog and on WISN 12 News. The tornado outbreak on Wednesday was a topic we discussed along with other severe weather aspects at Farmington Elementary in Kewaskum. I had a chance to visit the 3rd grade students at the school Thursday morning, they were a great group and had many fantastic questions. Thank you for inviting me to your school! Below is a picture of the students.
Have a great day and make sure to let us know your thoughts and comments on this very busy month of severe weather across the U.S.! Just drop a note in the comments section of the blog.