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wxman57 wrote:TeamPlayersBlue wrote:The wet bulb temp is below 32F for SE Tx for friday morning. Unfortunately, the models are showing the precip staying further south or off the coast. Key will be where the divergence and the most lift from overrunning occurs.
So in my opinion, whatever falls out of the sky in SE Tx will be wintery, not just a flat rain.
I'm still a bit of a novice on where gulf lows form under certain situations and also have trouble finding data in the models for divergence. These two things are key with the ULL rolling through big bend area. The setup is pretty nice for SE Tx, as long as the cold air is in place. Very similar to 2004 snowstorm, but it was much colder in 2004.
I've been observing/studying West Gulf Lows (WGL) since the late 1970s. A prerequisite for a WGL is a stalled cold front offshore. Typically, cold air accelerates southward down the TX coast all the way to the Bay of Campeche, trapped by the higher terrain along the coast of Mexico. The same push does not exist off the Louisiana coast. This leads to an east-west oriented front across the northern Gulf and a north-south oriented front from the lower TX coast southward. The bend in this front is the focus for a WGL. As I was taught at A&M, once the 500mb vorticity max reaches west Texas, the WGL forms along the natural bend in the front. As the upper trof progresses east, the WGL strengthens and moves east off the northern Gulf Coast. Steady, moderate precipitation can be expected northwest and north of the low due to isentropic lifting (overrunning). Once the low axis passes, the precip ends. I would add that the models are forecasting this WGL to track a little farther south, which is why precip will be limited across the upper Texas coast. You want the WGL to be close enough to the coast to provide the moisture, but not too close to the coast to cause a significant warm layer aloft. It's a very delicate balance between cold rain and snow, depending on the track of the WGL.
A WGL typically precedes most winter weather events along the Gulf Coast. The strongest WGL I've ever seen occurred on March 12-13 of 1993. This was the "Storm of the Century" (https://en.wikipedia.org/wiki/1993_Storm_of_the_Century). It produced heavy snow along the Gulf Coast all the way to the Florida Panhandle and wind gusts over 100 kts offshore and in a squall line out ahead of it that hit the Florida Peninsula. See the link for more details. As is often the case across south TX and the Gulf Coast in general, we occasionally have cold enough air for snow aloft, but there is no moisture available. If a strong cold front moves offshore but then stalls, a developing WGL can provide the moisture necessary for snow.
We've seen a number of WGLs so far this winter, more than normal. That's why I've said if the air ever gets cold enough this winter then we would have a good chance of a Gulf Coast snow event. So far, the cold air has been too shallow this far south. I can't say whether that will be the case in February, which is a month of most frequent heavy snow events in SE TX. So far, the pattern hasn't been right to push deep enough cold air this far south. It's getting close this week, though.
Awesome explanation, thank you! Makes more sense to me now.
