BMX AFD
The upper low currently over southern California will round the base of an amplifying trough over the Plains Sunday and Sundayn night taking on a negative tilt at upper levels and a slight negative tilt at mid-levels by Sunday night. Very strong wind fields will be in place with this system, e.g. jet maxes of 155 kts at 250mb, 115 kts at 500mb, 75 kts at 700mb, 65 kts at 850mb, and 50 kts at 925mb. In response to strong upper-level forcing a surface low will lift northeastward from the Southern Plainsto the Great Lakes by Monday morning, rapidly deepening from992 mb to 978mb during this time frame and resulting in backed surface winds across Central Alabama. A weak shortwave moves across the area Sunday morning as the surface warm front lifts northward. Most activity during the morning will probably be elevated but will have to watch for any surface-based development along the warm front. Current thinking is the morning activity will not inhibit afternoon destabilization, as warmer drier air will move in at 700mb associated with an EML by midday allowing for daytime heating.
A very volatile environment will be in place across Mississippi and Alabama during the afternoon and evening hours, as rich Gulf moisture lifting northward results in CAPE values around 1500-2500 Jkg. Dew points/instability have trended upward in our northern counties from previous forecasts. 80-90 kts of 0-6km bulk shear willbe present, with 400-600 m2/s2 of 0-1km SRH and 200-400 m2/s2 of0-500m SRH and large curved low- level hodographs. Southwesterly shear vectors in the warm sector becoming more southerly close to the front and will be supportive of both an intense QLCS and supercells developing ahead of the line. The strong 0-6km and 0-8km shear will help these supercells stay ahead ofthe line, supporting the threat of strong (possibly violent) long-track fast-moving tornadoes. The QLCS will also be capable of producing widespread damaging winds and embedded tornadoes with embedded supercells, which could be strong as well, not just brief spin-ups.
As always, the severe threat will come down to mesoscale details asthe event gets closer and difficult to forecast complex storm interactions which ultimately will determine how significant the threat ends up being. But the parameter space is certainly supportive of a moderate risk. The threat appears slightly higher westof I-65 than east of I-65, however want to emphasize that all of Central Alabama needs to take this seriously no matter the
color of the risk area.
Besides the threat of severe storms, the strong LLJ and deepening surface low will be supportive of strong gradient winds reaching wind advisory criteria. PWATs around 2 inches will also be supportive of localized flooding, however this potential will be limited by fast storm motions, relatively dry conditions over the past couple weeks, and springtime vegetation.
