This map, with the colors showing dewpoint, shows a sharp warm front moving NE through central Alabama tonight. Dewpoints are already in the low 60s in central AL, with upper 60s in south MS moving this way. The flow is very strong out of the SW, and will get even stronger as the big low to our NW strengthens and moves east over the next few hours. The RUC model expects 850 mb (4,000 feet) winds to increase to 60 to 80 knots (around 80 mph) late this evening, meaning fast-moving storms.
As you can see in the chart of dewpoints above, the most humid air is still over southern MS, but is rapidly approaching west Alabama. This event will not have much unstable air, but with so much wind shear it may not matter. One thing that concerns me is the presence of the warm front over central Alabama…sometimes these fronts can produce additional rotation in storms near them.
With tornado warnings arleady in eastern MS, we could see tornado warnings in west Alabama in the next hour. It looks like the main threat here in BHM will be from 10 pm to 2 am. Take a look at RUC model instability (CAPE) and helicity (shear for storm rotation) at midnight CST.
The CAPE is only 500-1,000 J/kg, modest at best but enough to produce strong storms in a high-shear environment. The helicity is 500-1,000 m2/s2 over most of north and central Alabama, meaning any storms that manage to survive the wind shear will rotate, so a few tornadoes are likely.
As the storms form into a squall line late tonight, and even before, storm downdrafts may bring down some of that air just above the surface moving at 80 mph, so expect wind damage, including trees and power lines down.
With the speed the storms are moving, if a tornado warning is issued, don’t wait around. Go to shelter immediately. Make sure your family is prepared with a tornado plan now. Put helmets on the kids, go to the lowest floor or basement (if available), get near the center, away from outside walls or windows or doors, and get under something sturdy (pool table, desk, etc.) if you have one. Keep your NOAA Weather Radio turned on when you go to bed.
