A fairly significant cold front will move through Alabama tonight, bringing more seasonal temperatures for late December. After high temperatures in the 60s and 70s the past few days, we will drop into the 50s tomorrow, and possibly stay in the 40s during the day Friday and Saturday.
As it moves through and upper-level winds strengthen, we will have some wind shear over the area, with helicity values above 300 m2/s2. Instability will be the limiting factor (as it usually is with wintertime severe weather), as temperatures at the surface will not be that warm, and there will be a small cap in place tonight. You can see that temperatures decrease very little with height at low-levels in the computer model sounding for BHM for 9 pm tonight, but then decrease more at upper-levels. This likely means most storms will stay elevated, or their updraft base will be above the surface.
We will still likely have a line of thunderstorms move through after midnight, and with the wind shear, some of the storms may rotate and produce damaging winds. If the air cools off a little bit at 1,000 feet, or it gets a little warmer than expected at the surface, allowing the storms to become surface-based, an isolated tornado is possible. But, this should not be a significant outbreak of severe weather. Mainly just some rain and wind coming through our area between midnight and 6 am. But, in case things change, have a source of weather information tonight, check the weather before going to bed, and have a NOAA weather radio on hand to alert you if a warning is issued while you are asleep.
Dr. Tim Coleman