Winter weather – the current water cooler topic

I hope that everyone had a very enjoyable, if cold, Christmas! After nearly two weeks of discussion on the possibility of winter weather for Christmas this year (see previous blog posts from this month on the subject), the net result was a couple of hours of flurries/light snow over the metro area. Most of it ended up in the joints of roof lines thanks to a very gusty wind and an official “trace” of snow was recorded for Christmas Day. Not a “White Christmas” by any stretch, but we can say it snowed on Christmas Day!

As cold air continues to hang over the region, we now turn our attention to the next weather system taking shape to our west. An upper-level low over Baja California will move east-northeast over the next 24 hours, encountering cold air over southern and western TX and form into low pressure that will again move by to our south. As with all of these scenarios, the timing of moisture and the amount/depth of cold air will be crucial for the formation of any wintry weather.

It appears that the moisture side of the equation arrives just before dawn on Wednesday, while the cold air side indicates temperatures in the lower to mid 30s at the surface at that time. Temperatures just above the surface will be warm enough for rain, but also very dry, so as the initial precipitation falls it will evaporate, moistening the air it is falling through, and cooling it (a process called evaporative cooling). How much cooling takes place will determine the initial precipitation type Wednesday morning. One thing is fairly certain, and that is that as the low pressure system gets closer, the atmosphere will get warmer and precip will become all rain by late in the morning, continuing Wednesday and Wednesday night. On the backside of the system, cold air will once again filter in, leaving us in the predicament of timing the cold air’s arrival and sufficient moisture departing. Recent computer model runs have been trending warmer with the whole system, which is not good for winter weather lovers.

So, given that, my forecast this afternoon will call for a slight chance of wintry precipitation, perhaps a rain/sleet/snow mix, for a few hours Wednesday morning before changing over to rain that will last through at least Thursday morning. There could be some flurries Thursday afternoon as that next round of cold air moves in. Overall, no big deal though. I don’t think there is any threat for poor road conditions Thursday afternoon if you are headed to the sold-out FedExForum to see the Memphis Tigers take on the UT Vols. Take a coat though; temps will be dropping (outside) even as the building inside heats up!

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