It's hard to believe that on Sunday, the high was a balmy 79 degrees. The cold front that moved in Monday morning brought us back to reality -- Tuesday is December 1st. The front brought a chilly rain to Houston and there's more on the way Tuesday through Wednesday morning. Earlier Monday, snow fell in the far West Texas town of El Paso due to an upper-level low-pressure system sitting and spinning out there. That low represents a pool of cold air cut-off from the jet stream. Eventually, it will drift east and move across the rest of the state. The only impact we'll see from that low is the rain we're expecting through Wednesday.
So what is the origin of our snow chance? An arctic blast developing in Western Canada will pour down through the Rockies and then into Texas starting Wednesday. By Friday, we'll be shivering in the 30s. Cold air is one ingredient you need for snow. The other is moisture, and the long-range models I look at show moisture building up from the Gulf of Mexico beginning Thursday night and meeting up with the Canadian cold air Friday. Remember that even if the ground temperature isn't 32 degrees, we still could have snow if the air above the ground is freezing, and it should be. Temperatures at the ground might not be cold enough to allow the snow to stick to anything other than elevated surfaces or grassy areas.
Forecasting snow in Houston is tricky, especially several days out. The scenario I outlined above depends on quite a few essential factors coming together in precisely a certain way. If the air isn't cold enough, we might just see more cold rain. If the Gulf moisture shifts to the east, we'll miss a snow chance altogether. The timing of what time during the day on Friday the snow will fall is still another big question mark, but it looks like this would be an afternoon event. A computer model that I depend on has consistently painted this picture for several consecutive runs, which builds my confidence that it will happen. As we get closer to Friday, I will have a better sense of how far south that Canadian cold air is getting and how and where the Gulf moisture is setting up.
If it all works out, it might be a pretty scene for the City of Houston's Tree Lightning in front of City Hall. I'll shamelessly promote the fact that Channel 11 will cover that event and show it as part of a program Saturday night at 7 p.m. Stay tuned, but don't make plans to buy a snow shovel on eBay just quite yet.