...SEVERE THUNDERSTORM WATCH MISSISSIPPI...
....WIND ADVISORY FOR ALABAMA THURSDAY...
A strong cold front is located in Arkansas early this morning, and is moving southeast rather quickly. Southerly flow ahead of the front has started to bring warm, moist air at the lower levels into Mississippi and west Alabama (see Wes's post below), and as the front gets closer, winds will increase this morning, possibly gusting to 30 mph in valleys and 40 mph or more on ridgetops.
As is often the case with winter time systems, there is a lot of wind shear with this one. Winds at the surface are blowing out of the SE at 20 mph or so, but at 3,000 feet, winds are blowing out of the SW at 60 mph, producing spin in the atmosphere. Helicity values, that represent the spin in the atmosphere necessary for storm rotation, are between 200 and 400 m2/s2 in MS this morning, and these values will spread over Alabama by 6 am. This means that storms can survive in a more stable environment than normal, and also that storms that do form may rotate.
However, the air is not that unstable for thunderstorms, and is not expected to become very unstable today in areas north of I-20. Even with some warm air at the ground, temperatures aloft are not too cold, therefore storms do not have much energy. However, we will have to watch closely, as there have been some reports of wind damage with the storms in Arkansas and Texas last evening, and with winds of 60 mph just above the surface, it will not take much of a downdraft in a storm to bring some of those winds down, producing scattered wind gusts of 50 mph around central Alabama and maybe some power outages. This should not be a major storm for Birmingham, Tuscaloosa, or Anniston. Farther south, where the air will be more unstable, a few more storms may be severe, and there is a small chance of tornadoes. You can never rule anything out as we learned last week in the storms that came through and produced a tornado on Finley Avenue that lasted 2 minutes, but most of us will see wind and rain.
It will get much colder after the front goes by Alabama, with temperatures dropping into the 40s by this afternoon, and wind chill near 30 by 5 pm. Friday morning will be very cold with temperatures near 30 and wind chills near 20.
More later, as we will be watching this situation carefully at WBRC.
On the northern end of this winter storm, snow is falling tonight, and thundersnow, much like we had in the Blizzard of 1993, is occurring over parts of Iowa. Check out this video.
Dr. Tim Coleman
Fox 6 Severe Weather Expert and Blogger
Twitter at timbhm