Figure 1: NEXRAD Base Reflectivity image over Huntsville, Alabama on February 17th, 2022 4:15 PM CST. As the dBZ values increase, in the upper right-hand corner of the image, the more intense the rain is. The first tornado occurred in the red box indicating a tornado warning over a supercell west of Birmingham, Alabama. (Source: Iowa Environmental Mesonet)
With a squall line advancing eastward across the central United States, Alabama was in the crosshairs yet again for possible tornadic activity on February 17th, 2022 after just experiencing a tornado outbreak two weeks prior. There were 3 recorded tornadoes that occurred in central Alabama, with the first touching down at 4:14 PM CST in north Tuscaloosa County between Wallace Branch and Old Cheatam Road, lasting only 5 minutes. Overall, these tornadoes were relatively weak on the Fujita scale, with maximum estimated sustained winds peaking at 100 mph. No injuries or fatalities were reported with this system, but the winds were strong enough to uproot trees and overturn semi-trucks.
Figure 2: Tornado report summary on February 17th, 2022. (Source: weather.gov)
A surface analysis map at 3 CST February 17th, 2022 shows different surface parameters just an hour before the first tornado touched down in central Alabama. As the cold front continues to push across the central United States, there is a clear boundary layer between temperatures. Northwest of the cold front in Arkansas, the weather station plots, indicated by circles, show a northwest wind barb bringing in dry, cold air with temperatures getting into the lower 40s. To the east of the cold front, Alabama is experiencing temperatures in the 70s with dewpoints in the lower 60s. There is a south wind bringing in moisture from the Gulf of Mexico. This is a key ingredient for severe weather. The low-pressure strength is depicted by the 1006 mb underlined value over northern Louisiana. Over the next hour, this system will intensify as it moves over Alabama.
Figure 4: Surface Analysis at 6 PM CST over Alabama. (Source: weather.gov)
A special recorded sounding over the KBMX weather station shows a vertical temperature profile of the atmosphere at 5 PM CST. It is important to note the vertical effective shear being 74 kts pointing towards dynamic instability. Wind shear is necessary for vertical rotation within a column of air. When this parameter is within the range of 25-40 kts or greater, the formation of supercells becomes more probable. Regarding the thermodynamics, there is a recorded CIN value of -8 J/kg at the surface with a CAPE value of 191 J/kg. CIN represents convective inhibition which is an area on a sounding it must be overcome for a storm to initiate. When CIN is less than 50, there is a high chance for thunderstorms to develop. CAPE represents the convective available potential energy in the atmosphere where parcels can be lifted to its level of free convection. CAPE does not need to be high (>1000 J/kg) to fire off supercell like structures if the CIN is low. Therefore, we can consider this atmosphere to be thermodynamically instable. Additionally, the atmosphere is saturated due to the positioning of the temperature and dew points lines (red & green) being so close to each other. The warm, moist Gulf of Mexico air is the reason for this. It is depicted by the south surface wind barb at 1000mb.
Figure 5: Sounding image of KBMX at 5 PM CST. (Source: weather.gov)