White Christmas? 10% chance.

The attached “sound effect” will become more or less intense on the White Christmas possibility in coming posts if it looks more or less likely. Yes, I act like a kid sometimes. But, to me, even the possibility of this once in 100 years event happening in Birmingham is enough to be exciting! And, as a researcher, I have the luxury of being speculative in a forecast, moreso than the people on TV or at the NWS.

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00 UTC models are in. And, they seem to be painting a little more consistent picture for the potential Christmas storm.

Overall summary is that models are showing very active pattern, with numerous upper-level disturbances (waves) coming through the southern U.S. for several days. One wave comes through Alabama Christmas Eve into Christmas Day, maybe with some type of surface trough development along the Gulf Coast and precipitation in Alabama. There is debate in models on amount of precip and how far south cold air will be.

GFS model has weakened system somewhat from 12 UTC run, but also now keeps any weak surface development farther south, along with colder air. If this model were correct, parts of north Alabama (Huntsville) could see 2″+ of snow by Christmas morning. (The 0 C temp line at 850 mb is a good indicator of the rain/snow line.)

Canadian GEM is now coming in line with other models in showing a system with enough moisture to produce 0.10″ water equivalent precip over central Alabama. It shows the cold air being further south, with the rain/snow line in Alabama typically near the 542 thickness line (just south of the gray shaded area), running from Aliceville to Clanton to Anniston.

The European has weakened somewhat, like the GFS. We only get to see small pieces of this model, but it looks like its general solution hasn’t changed much since 12 UTC, with a broad trough of low pressure near the Gulf coast, and the rain/snow line (542 thickness) also near BHM on Christmas morning.

The CMC model shows a weak trough of low pressure along the Gulf Coast by Christmas morning (left, msl pressure), but the more telling feature in this model is the area of colder 850 mb temps surging into south Alabama. This indicates to me that this model is producing precip and associated evaporative cooling. Also, the 0 C 850 mb temp (rain/snow line, right) on this model is near BHM.

The US Navy NOGAPS model shows the strong upper-level disturbance, and plenty of cold air for snow, but shows no precipitation Christmas morning. This model may be the outlier at this point.

So, in summary, I would say this, at least, looks like the best chance for a White Christmas in Alabama in the computer models in several years. But, it’s still 5 days away…a lot can change. The weakening trend could continue and we could wind up with no precip. The cold air could stay in Tennessee, giving us some light rain. The timing could be off and whatever happens is on Wednesday. But, I see enough going on here to bump the chance for a White Christmas – measurable snow in BHM on Dec 25, to 10%.

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