A line of strong thunderstorms is moving through Mississippi right now, and will move into west Alabama by 4 pm, and into the Birmingham area between 5 pm and 7 pm. These storms will produce very heavy rain, gusty winds up to 50 mph, and dangerous lightning.
It will be interesting to see how the storms change as they move into Alabama. The air over northeast Alabama is very dry (dewpoints in the 40s), while it is humid here in Birmingham (dewpoints in the 60s). You can see the large difference in instability associated with this moisture gradient.
CAPE values (instability for thunderstorms) are 1000-2000 J/kg here in BHM, but drop quickly to near zero up around Cullman. Sometimes when a line of storms interacts with a boundary like this, the storms near the boundary could intensify a bit, and a small tornado is even possible north and central Alabama. However, movement into a drier air mass overall could weaken them a little bit too, so it's hard to say for sure! The thunderstorms will be the most intense here in Birmingham and Tuscaloosa, with some weakening likely occurring up near Huntsville, Gadsden, and Anniston. VORTEX-Southeast field operations are going on today to take detailed measurements of the storms as they move across north Alabama.
There is very little wind shear, so we do not expect widespread or intense tornadoes, but gusty straight line winds could knock down some trees, and the lightning may be intense. If you have outdoor activities planned this evening, watch the weather very closely this afternoon.
With a big upper low over the western US, and warm moist air over central and south Alabama, we could see thunderstorms just about anytime this weekend. However, it is almost impossible to pin down when they will form. The weekend will not be a rain out, and I still plan on going to the Warrior River tomorrow!
Dr. Tim Coleman