The loud storms that have been moving through the BHM area over the past 3 hours are elevated storms, with unstable air aloft but still cool, stable air at the surface. But the line of storms over west Alabama is in a confluence zone out ahead of the main low pressure area, that is ahead of schedule and according to my non-atristic analysis, is sitting in Southeast AR now. A couple of the storms are near the warm front (circled) and are starting to acquire rotation over TCL and Walker Counties…we will have to watch those. Note the wind blowing toward the orange confluence line I drew in on both sides. I expected this zone today, but not until afternoon. But it’s ahead of schedule too.
With strong 850 mb winds (50-60 kt) blowing from the now very moist and unstable airmass over southern Mississippi, the warm front will continue to slowly move north as the surface low moves north along the Mississippi River. The storms north of the front help to slow it down due to the cooling effect of the rain (and it is a warm front after all)., but it will likely move on north slowly into the afternoon. The system moving a bit faster has helped us somewhat, and the longer we keep getting elevated storms north of the warm front, the more it will slow it down and give us less time to destabilize. But, it does look like the warm, unstable air will make its way into north and central AL just through advection by 1 or 2 pm.
You can see the shadows cast by the big storms in central Alabama on visible satellite…but there are breaks in the clouds over Mississippi, and temperatures are rising quickly over there. 70s as far north as Tupelo. Hard to say if we get sunshine here in Alabama today, but it is most likely in the high risk zone over northwest AL.
The SPC doesn’t often issue a HIGH risk at all. And they don’t often say things like they did in the above paragraph.
Despite the morning storms possibly delaying things and maybe even keeping a few areas a little less volatile, this is still a dangerous situation. The wind shear will still be very high (although not quite as high as we thought after the morning storms), but even 75% of the forecast numbers from last night still support tornadic supercells over western AL this afternoon…then a line of tornadic storms moving into central AL this evening. Don’t let your guard down…it still looks like a dangerous day. We will get a better handle on the effects of the earlier confluence zone and morning storms over the next 2 hours. That zone may stay in place from eastern MS into west AL through the afternoon…providing a focus for tornadic storms as the more unstable air moves in.
SPC is planning to issue Tornado Watches for much of AL and MS soon.
Dr. Tim Coleman
Coleman Knupp and Dice Weather Blog 