Things still appear to be shaping up for a severe weather event in Alabama on Thursday. In its new day 1 convective outlook, SPC has placed us in slight risk, but mentions that an upgrade to moderate risk may be required.
A cold front will approach Alabama from the west during the day, as a low pressure area strengthens and moves into the Midwest. The rapidly falling pressures to our north will tighten the pressure gradient and allow strong low-level winds to come in out of the SW, bringing Gulf moisture northward rapidly. Dewpoints as of midnight were in the low to mid 60s near the Gulf coast, and these high dewpoints will move into Alabama today, creating an unstable air mass for this time of year. Area balloon data show a cap of warm in place near 3000 ft., so thunderstorms may be suppressed early today, but once temperatures and dewpoints reach the 60s, air parcels should be able to break this cap and thunderstorms will develop.
Wind shear for storm rotation will be high, increasing from 200 in the morning to 400 in the afternoon (about 150 is needed for storm rotation). The possible limiting factor is the lack of instability. Either way, this system is strong enough to bring a line of severe storms, with damagaing winds and hail, through here by late afternoon or evening. But, if we get a little sunshine this morning, and temperatures warm into the lower 70s, the air will be unstable enough that tornadoes become a larger threat, even ahead of the main line of storms. Low clouds and fog are present over south and central Alabama now, but they are shallow and may burn off by 9 or 10 am, allowing some sunshine.
If the sun comes out for a while as far north as I-59, the largest threat for tornadoes will probably be in the area from Birmingham and Montgomery westward to Columbus and Meridian, Mississippi.
Keep a source of weather information nearby today!
