SUMMARY…Several supercells have developed within tornado watch 25. The highest tornado threat will be over north central Alabama for the next several hours.
DISCUSSION…A line of supercells has continued into northern Alabama. These storms have exhibited good mid-level rotation, but low-level rotation has been limited. The 18Z Birmingham sounding showed a small inversion between 850mb and 700mb which has likely limited more robust updraft development up to this point. Farther north, the 18Z Huntsville Vortex-SE sounding showed limited instability. Given extensive cloud cover which has now overspread this area and northward moisture transport which is becoming increasingly cut off with northward extent, expect the severe threat has decreased significantly in the northern half of tornado watch 25. This is further supported by the 18Z HRRR which shows convection intensity decreasing across far northern Alabama and central Tennessee. The best region for a continued severe and tornado threat will likely be from areas south and east of Columbus, MS to areas near Tuscaloosa and north of Birmingham over the next 2 hours. In this area, instability has increased with MLCAPE in excess of 1000 J/kg and low-level shear remains moderate to strong (>250 m2/s2 0-1 SRH according to 18Z BMX sounding and 19Z BMX VWP). In addition, the storms in Kemper County, MS and Lamar County, AL have shown considerable updraft strengthening in the last 30 minutes suggesting that this region is starting to feel the effects of better buoyancy.
