A big shield of rain and elevated thunderstorms is moving into Alabama this morning. Dewpoint temperatures are still in the upper 40s and lower 50s so the atmosphere is pretty stable. We're looking at mainly a cloudy, rainy, and cool start to Christmas Day. Our primary concern still remains after sunset.
Models can only do some much with this type of forecast. We're going to really have to monitor the weather in real-time (NOWCASTing) to get a handle on the timing of this severe weather. I'm still thinking we'll be under the gun for tornadoes this evening. The question is - just how far northward that severe weather threat will exist.
I will say with pretty good confidence the highest tornado potential will be south of I-20/59 and west of I-65. For folks living in Pickens, Sumter, Hale, Greene, Perry, Tuscaloosa, Bibb, and Chilton counties - the weather will be of particular concern. It is this region where the highest instability and wind shear will come together. Again - we have no problem with the wind shear, but the models and observations both are having a tougher time with the amount of instability that will move into the area.
Take at look at the map for 1 p.m. today. This is instability based off the NAM model. The "juicy" air is still staying confined to the Gulf Coast. For things to really kick off - we need to have more green up our way. I will tell you the more it rains today, the tougher the warm front will have lifting northward.
Let's take a look at the instability later tonight based off the same model. This is the CAPE values projected around 9-10 p.m.
You can now see that narrow "tongue" of higher instability tracking northward into the southwestern portion of Alabama. Instability will continue to increase tonight. That's why I'm sticking to this mainly being a nightime weather event.
What can we expect?
I think we'll see something that is two-fold. We will have the tornado threat. The tornadoes that do develop could be signifcant and long-track south of the warm front. In addition, we will have a more widespread damaging wind threat. Even if you're not in the bullseye for tornadoes - it's likely you'll experience winds over 50mph across much of the state. With the high wind shear - just about every thunderstorm will show rotation on radar.
Is severe weather guaranteed with this system?
No. This is still not a clear-cut system. I think what has everyone so stirred up regarding this system is the incredible wind shear. It would not take much instability to result in tornadoes. There is still some question on how far north the instability reaches. If the warm front hangs down to the south - we'd likely just get some gusty winds and rain. But - it's much too early for me to make that kind of call so we must remain on-guard with this system. We'll have a better idea as the system progresses through the day.
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