…Significant outbreak of severe weather including tornadoes next 12 hours…
The Storm Prediction Center has gone all in with this one…we are in the seldom-used “high risk” for severe weather, and we are under a PDS (Particularly Dangerous Situation) Tornado Watch here in much of Alabama. The warm front between the cool wedge from the NE and the extremely warm and humid air from the Gulf is sitting across central Alabama now. It shows up well in the following map of CAPE (best measure of instability). The front extends from roughly MSL to BHM to AUB.
Storm-relative helicity is generally 100-200 m2/s2 right now, but with a weak surface trough, there is a maximum in SW Alabama centered around Grove Hill and Monroeville. The entire area from there and SE Mississippi near Meridian…up to TCL…must be watched closely for tornado development over the next 2 hours. Dewpoints at several stations in eastern MS and SW AL are in the lower 70s, so any storms there will grow quickly and potentially rotate.
Visible satellite shows breaks in the clouds over MS and parts of AL…so we will get some sunshine in some areas today…especially western AL. Temps may reach 75-80 over parts of west and south AL, creating a volatile environment for storms.
With thunderstorms and heavy rain developing along and north of the warm front over central AL…the front may be slow to move further north over the next few hours due to rain reinforcing the cool air to its north.
Computer model consensus would take it to a line from DCU to ANB by 5 pm CDT…with the best chance for severe weather SW of that line over places like Hackleburg, Hamilton, Jasper, Tuscaloosa, Birmingham, Selma, Montgomery, and Grove Hill (see below).
The primary 850 mb jet and highest SRH (over 400 m2/s2 in many locations) will move through between 04Z and 08Z. Even though CAPE will be reduced by darkness, there will be enough along with the wind shear to produce a line of intense storms, some of them with tornadoes.
Dr. Tim Coleman
Coleman Knupp and Dice Weather Blog 