Severe weather threat Thursday?

SPC severe wx outlook for Thursday

The next upper-level storm system in this active Spring is currently moving through Oklahoma, producing thunderstorms, with a few of them severe, and even some Tornado Warnings in Texas this afternoon.

Current upper-level flow. Note wave in flow in north TX/west OK

A lead line of storms associated with this system will move through Alabama early tomorrow morning, likely reaching BHM by 7 am. However, these storms will not be surface-based nor produce any tornadoes, as the air mass will still be very stable. Currently, dewpoints are in the 40s, and they will not recover by tomorrow morning.

Current dewpoints

Even with elevated storms, as we saw on Sunday morning, we can get a lot of lightning and heavy rain, and even sometimes high winds and hail. A very unique event occurred from Clanton through Rockford, Dadeville, and Alex City Sunday morning, where the downdrafts from elevated storms produced large hail and an atmospheric wave that produced very high winds. But that is for another blog post! Either way, the storms tomorrow morning are unlikely to do that again, but expect heavy rain, possibly some hail, and local wind gusts up to 60 mph. Tornadoes should not be a threat in the morning.

The question comes during the day tomorrow. After the initial line of storms moves through, the main storm system will still be to our NW, and the air mass will start to recover (warm and humidify). By tomorrow afternoon, especially if we get any sunshine, the air will be unstable over central AL. Take a look at this NAM model sounding at Bluff Creek, AL, for tomorrow at 4 pm.

It has CAPE of 2,700 J/kg, so plenty of fuel for thunderstorm re-development. However, the wind shear by then will have decreased as surface winds veer to the SW, and 0-1 km helicity is only projected here to be around 100 m2/s2. Not really enough for any significant storm rotation. The instability will be moving in as the shear leaves. Now, if the system slows down and wind shear hangs around longer, we could see a few tornadic storms in central AL tomorrow afternoon. That is unlikely. The best chance for tornadoes tomorrow will be over SE Alabama and south Georgia, where the instability and shear will phase better.

We have been having difficulties with our computer models due to the lack of aircraft observations going into them, since most commercial airplanes are sitting idle right now and not flying. So there is higher than usual uncertainty in the forecast.

Dr. Tim Coleman

Consulting Meteorologist

Coleman and Knupp, LLC

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