…SEVERE WEATHER OUTBREAK…INCLUDING TORNADOES AND HIGH WINDS…ON WEDNESDAY…
I already went over most of the atmospheric mechanics behind this likely tornado outbreak in a blog early yesterday morning…for that see https://ckweather.com/2021/03/16/tornado-analysis-for-wednesday/
Not a whole lot has changed in 24 hours, but we do have a little better handle on the timing and locations. Right now, the cold air wedge has come into parts of Alabama from around the Appalachians to the east. Current temperatures show this cold air region. It is 56 at my house in Trussville, but 64 at the lake cabin on The Warrior River, only 35 miles west of here.
As the large upper-level system slowly moves toward Alabama this morning, SW winds will bring in warm, moist air from the Gulf. It will take some time to push the denser, cooler air out of the way over northeast AL…but the warm and unstable air will make into BHM by noon.
Even with the center of the upper-level storm in Oklahoma at mid-afternoon, there will be strong wind fields in place over Alabama…between 50 and 60 mph at 5,000 feet. With the humid, unstable air in place over much of the area during the afternoon hours, despite the lack of forcing from the distant upper system and associated cold front, scattered thunderstorms will likely develop over Mississippi and parts of west Alabama between 1 and 6 pm, and any of these may become severe and produce large hail, damaging winds, and even tornadoes. The computer model estimate of the atmospheric temperature and wind profile is from Tuscaloosa at 2100 GMT (4 pm CDT). The CAPE of 2,700 indicates instability more typical of a May or June afternoon, while the storm relative helicity (SRH) that causes storm rotation is significant, but not extreme, at 170. These combined together produce an energy-helicity index (EHI), a great meaaure of tornado potential, at 3.0. Tornadoes are generally considered possible for EHI > 1.0, so at 3.0 there will probably be a few tornadoes, mainly west of a line from Decatur to Talladega to Auburn, including TCL, BHM, and Jasper.
The main event for the entire state will come after sunset, as the upper-level system and cold front move through. Winds at 5,000 feet will increase to 75 mph. The air will not be quite as unstable as it was in the afternoon with the lack of sunshine (this is why Mississippi has the highest risk for tornadoes). However, with the forcing, high wind shear (SRH 350-400), and sufficient instability, an intense line of storms will move through the state during the evening hours, probably arriving in BHM between 11 pm and 2 am. Tornadoes and straight-line wind gusts up to 75 mph are all likely with this line of storms.
You will hear a lot of hype on TV, and a lot more hype on Facebook, often from people who are NOT meteorologists. I don’t understand why people take weather advice from a pipe fitter, architect, or salesperson, but they wouldn’t allow a lawyer to take out a gall bladder, or a dentist to build a bridge. Don’t be scared. Even during the worst outbreak in 70 years, April 27, 2011, only 1% of the land area of Alabama was affected by a tornado. The graphic below shows the percent chance of a tornado passing within 25 miles of any point in that area. In Birmingham, according to NOAA, that chance is about 20%. This means that in the ~2,000 square mile area around your house, there is a 20% chance that a tornado, typically one that covers only a few square miles of area, will occur at all.
Still, you and your co-workers and family should discuss your tornado plans for work, school, home, and anywhere else you might go, and do so this morning. The best location is inside a sturdy building, in an interior room near the center of the building, away from outside walls. Stay away from doors and windows. Get down low. Protect your head with a helmet, or pillow if nothing else is available. A basement is best in a regular home, but even in the basement you need to get inside the car or under a sturdy table, etc. Falling bricks, concrete blocks, and lumber can hurt you.
Have your NOAA Weather Radio programmed and ready with battery backup, and also have a good app on your phone to receive Tornado Warnings (I recommend the app “tornado” or the Fox 6 weather app). Make sure your phones and mobile devices are charged, and that you have batteries for flashlights, etc. We will be OK. This will not be April 27, 2011. We just need to use common sense and protect ourselves.
Dr. Timothy A. Coleman
Coleman and Knupp, LLC