A squall line brought severe thunderstorms and tornadoes to Alabama and Mississippi Wednesday night and early this morning. Storms will continue to move east through Georgia, the Carolinas, and parts of West Virginia later today, producing more severe weather later this evening. The Storm Prediction Center’s Day 1 Convective Outlook (Figure 1) shows the current tornado risk for today associated with this storm system.
Figure 1: SPC Day 1 Convective Outlook
Tornado watches are currently in effect across southern Georgia and the Florida panhandle as a well-defined squall line moves through the area, as spotted on radar shown by Figure 2. This squall line formed along the cold frontal boundary of an extratropical cyclone (as seen in Figure 3) developing across the US. The red colors on radar correlate to the most severe aspects of the storm such as tornadoes. Radar can be used to identify the debris ball of a tornado and the classic hook shape of a supercell. Supercells usually develop ahead of a cold front, so now that the squall line has formed, less supercells are moving through Georgia.
Figure 2: NEXRAD Radar Reflectivity
Figure 3: GeoColor Satellite Imagery, currently showing multispectral infrared imagery
However, this storm system is well supported by an upper-level trough and strong jet stream as shown in Figure 4. As this trough moves east across the US, winds are expected to pick up, increasing shear, giving these storms the potential to develop back into supercells in the Carolinas. After the trough moves through continental US, a zonal flow pattern appears regionally in the Southeast, bringing clear weather and the conclusion of this area’s severe weather.
Infrared satellite imagery in Figure 5 shows bright green clouds along the squall line and over Indiana, Illinois, Ohio, Michigan, and Kentucky. These green colors correlate to the coldest temperatures of clouds, indicating where the thickest clouds are and relating to areas of strong convection. Indiana, Illinois, Ohio, and Kentucky are expected to receive thunderstorms as the warm front of the northern side of this extra-tropical cyclone develops throughout the day and moves through the area.
Figure 1 https://www.spc.noaa.gov/products/outlook/day1otlk.html
Figure 2 https://tempest.aos.wisc.edu/radar/se3comphtml5.html
Figure 3 https://www.star.nesdis.noaa.gov/GOES/conus_band.php?sat=G16&band=GEOCOLOR&length=48
Figure 4 https://www.tropicaltidbits.com/analysis/models/?model=gfs®ion=us&pkg=uv250&runtime=2021031712&fh=0
Figure 5 https://www.star.nesdis.noaa.gov/GOES/conus_band.php?sat=G16&band=11&length=60