…Tornado Watch in effect for much of north and west Alabama…includes Huntsville, Birmingham, and Tuscaloosa…
Right now, we have an area of showers with some claps of thunder moving through central Alabama. One of the storms in this band earlier prompted a tornado warning for counties in extreme north Alabama, but that warning is gone and I have not heard of any reports of damage.
We have an environment today that has limited instability for updraft growth (surface temperatures are only in the low 70s in most areas, with dewpoints in the low to mid 60s). An area of dry air is parked over central Alabama, and as it gets mixed down to the ground, it limits our instability. The largest instability (CAPE values) are currently in northeast MS and extreme NW AL, where the dry air has not made it (and may not).
This storm system is mainly scary at all because it has very large wind shear for storm rotation (and the dynamics created by the wind shear can help updrafts grow also). 850 mb pressure level winds (about 5,000 feet) are about 60 mph over the Birmingham area, and increase to 80 mph over NE MS in the mid-level jet max. This is producing the large wind shear. 0-1 km storm-relative helicity values, a really good measure of wind shear for storm rotation, is extremely high, with areas in NW AL near 400 m2/s2. It is near 250 m2/s2 here in BHM.
The storms that are currently moving through central Alabama should move on out in the next hour or so without incident. It is that next line of storms in northern MS that is somewhat concerning. However, the sun sets in one hour, so as it gets dark it will be difficult for the atmosphere to destabilize any further. However, the strongest wind shear will move into NW Alabama around 6:00 pm with those storms, and the most unstable air is also up there (areas like Florence, Moulton, Russellville, Hamilton, Double Springs, and Vernon). So, the largest risk for tornadoes in Alabama will be in those areas between 5 pm and 8 pm.
As the storms move farther southeast toward Birmingham and Tuscaloosa, the instability will be weaker. However, given the strong wind shear in the environment, we will likely see some damaging winds and we can’t rule out a tornado here in central Alabama this evening. The storms will move through the BHM metro between 10 am and 2 pm.
This does not look like it will be a tornado outbreak, especially not here in central Alabama. We will have to watch the storms coming out of north Mississippi into NW Alabama very carefully over the next 2 hours. We are under a tornado watch, so have a safety plan in mind for wherever you are. Remember, lowest floor, middle of the building, away from windows and doors, protect your head.
Dr. Tim Coleman
Twitter @timbhm
Coleman Knupp and Dice Weather Blog 