I did not follow the weather very closely yesterday, so I did not see how the storms developed. I do see that no tornadoes were reported, and that there was a large line of hail and wind reports across Oklahoma and a few over northwestern Missouri. I would be willing to bet that storms quickly became linear, reaching severe limits and then using up the available energy. Here it the storm reports graphic, as generated by the Storm Prediction Center (SPC):
The SPC has issued a Slight Risk today for parts of the Dixie Alley.
Associated with the Slight Risk is a 5% Tornado Threat Ring.
The SPC is basing this threat on some of the same players as yesterday. We have the same surface low, though it has moved into Illinois, we have the same surface cold front, and we have the same trough. However, the severe threat will be tempered by the limited instability in the warm sector.
Synoptically speaking, the 300 mb NAM chart (from Unisys) shows trough is quite broad today. There is an embedded shortwave in this trough that is adding some energy to the severe threat today.
The 500 mb NAM chart shows some Negative Voriticty Advection (NVA) followed by some weak Positive Vorticity Advection (PVA). This is often a good combinations, especially on days with low instability due to cloud cover. The NVA will cause some sinking air and may clear out some of the clouds, but then follow up with the PVA which will generate new, stronger convection.
The 700 mb NAM chart shows a pocket of rapidly-rising air over the Slight Risk area by this evening. This is a good sign for thunderstorm development.
The 850 mb NAM chart shows that the Warm Air Advection (WAA) is much weaker today; the warm front today is not as pronounced as it was yesterday. The Cold Air Advection (CAA) is still quite strong.
The 12Z upper air sounding from Jackson, MS, shows that there is some threat of severe weather today. So far this morning, there was only 287 J/kg of Convective Available Potential Energy (CAPE), though there is plenty of shear. The deep layer shear was 34 kts and the low-level shear was 41 kts. There was some directional shear at the low levels and mostly speed shear aloft. The lowest 500 mb of the column are quite humid, and the 0-3 km average lapse rate was 6.3 C/km.
TwisterData.com shows CAPE building near the Alabama and Mississippi border by 21Z.
Currently, the surface observations (from the SPC Mesoscale Analysis Map) show humid conditions throughout the threat area. Temperatures are in the low 60’s and dewpoints in the 50’s as the cold front approaches.
The Supercell Parameter is expected to reach 8 in the next six hours over a few areas in Alabama. I expect this to spread beyond six hours, but that is as far as the RAP graphic shows into the future.
Overall, I expect a linear mess with a few embedded supercells today. The shear is great again, and the cold front will provide some lift to initiate storm formation. I wouldn’t call this system a very chase-able one, based on the linear nature and the terrain, however, severe storms are possible.
Thank you for reading my forecast.
The upper air soundings and mesoscale analysis plots are from the Storm Prediction Center website.
The forecasted upper air soundings are from TwisterData.com.
The surface observation and upper level charts are from Unisys Weather.
The satellite data is from NASA – MSFC