I am watching the radar around Poplar Bluff, MO, where there is a tornado warning in progress. I have spent a busted chase day in Poplar Bluff, and passed through there this summer as well. It is a beautiful part of Missouri, and I wish them the best. On this radar image, you will also see the towns of Marmaduke, AR and Caruthersville, MO, both of which were heavily damaged by a tornado in 2006. When I chased with Virginia Tech that year (six weeks after the tornado), our route took us through this damage path. I will be thinking of those folks as well.
Today is going to be a busy day in the south. The Storm Prediction Center (SPC) has issued a Moderate Risk for the Mississippi River Valley.
Associated with the Moderate Risk is a 15% Tornado Threat ring.
The 12Z upper air sounding from LZK is showing ample Convective Available Potential Energy (CAPE) and little capping inversion. The surface dewpoint was 71F, and the temperature 72F. There is also 47 kts of deep-layer shear to support rotating storms. The supercell parameter was calculated to be 8.2.
The 16:45 Z surface observations and analysis (by Unisys) show the ongoing storms ahead of a cold front in the warm sector of a strong mid-latitude cyclone. The warm sector of this storm features 70 degree dewpoints, temperatures in the 80s and wind blowing parallel to the cold front. Behind the cold front, temperatures drop into the 60s.
The 850 mb NAM chart shows some weak Warm Air Advection (WAA) in the Moderate Risk area. The temperature gradient (from cold to warm) is not very sharp, which is the limiting factor for the WAA. On the backside of the mid-latitude cyclone, the Cold Air Advection (CAA) is much stronger, explaining the 20 degree temperature drop behind the cold front.
The 700 mb NAM chart shows the potential for rapidly rising air in northwestern Mississippi and southwestern Tennessee. This rapidly rising air will contribute to strong updrafts.
The 500 mb NAM chart shows an unbelievably tight vorticity gradient, and winds blowing almost directly across it. This is an example of very strong Positive Vorticity Advection (PVA), which is contributing to the severe storms in this region.
Zooming in on the strongest PVA shows this tight gradient in more detail.
The 300 mb NAM shows the deep, narrow trough that is supplying the upper level support for these storms. There is some divergence over the same area.
This is a very dangerous situation. Those of you who are out chasing today, be very careful. This is a long squall line, and so there is no escape routes. Chasing storms like this mean finding a weak spot in the line to wait out the storm sometimes. The terrain is unforgiving as well; hilly, lots of trees, and limited visibility for chasing.
Aside: Yesterday, there was a number of wind damage reports across the country. There were two in my county (Sandoval, NM)- it was exceptionally windy at my house yesterday afternoon. Also, a line of storms formed in the eastern Texas Panhandle, one county up from Childress, TX. I consider my prediction for yesterday sound.
The Severe Weather Outlook is from the
Storm Prediction Center website. The satellite imagery is from the NOAA Satellite and Information Service.
The surface observation and upper level charts are from Unisys Weather.