11:30 AM CDT | December 5, 2017
As another piece of energy swings into the Southern Plains, moisture will be lifted over the cold airmass that has moved through the state. Precipitation chances increase this evening and continue through Thursday before shifting east. What is getting ready to happen is very interesting. It is something that I have noted numerous times since the start of our weather pattern in October. That is the trend of overrunning events. An overrunning setup is when moisture is lifted over a cold airmass. The temperatures with this airmass are not expected to be supportive of wintry precip, initially. Due to a process called evaporative cooling, as moisture begins to fall through this very dry air, the dew points will rise and the temperatures will lower. The temperatures will cool until they reach their wet-bulb temperature. The wet-bulb temperature is the lowest temperature that can be reached by evaporating water into air.
Temperatures will become supportive of wintry precipitation, primarily snow, in West Texas later tonight and tomorrow. A Winter Storm Watch has been issued for far West Texas, including Fort Stockton, Pecos, and a few other cities. This is effective from Wednesday morning to Thursday morning. Snowfall up to 3-5 inches appears possible across parts of the Winter Storm Watch area.
What about areas farther east? Well, the situation becomes a lot more complicated across West Central Texas. Temperatures will be warmer than areas farther west. This means that confidence in the temperatures dropping enough for snow is much lower. You have probably seen a bunch of snowfall graphics being shared on social media over the last day or so. Take these with a grain of salt, unless they have come from a reputable source like the National Weather Service or your trusted local news station. While snow is possible in West Central Texas, just a cold rain is on the table as well. Even if temperatures support rain mixing with or switching to snow, most areas are expected to be above freezing with warm ground temperatures. This means that accumulations may be difficult to achieve, even on grassy surfaces. It would still be a nice early winter treat for parts of Central Texas, though.
It is a good sign that we are seeing these types of setups early in the season. We did not see much of these overrunning events during the past two winter seasons. This is one reason I still believe most Texans will see an actual "winter", unlike the last two years. If some snowflakes mix with the rain in Central Texas on Wednesday, it could shatter what some saw all of last winter. :)
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