Monday, November 30, 2009

Snow for Parts of Texas This Week.

An area of low pressure in the upper atmosphere associated with very cold air aloft will move across the state of Texas early this week. Out ahead of this low pressure copious amounts of Gulf Moisture will spread across East Texas. Rain will begin to develop late Tuesday and could be heavy at times Tuesday night.

While heavy rain breaks out across our area Tuesday night, under the actual upper low across west Texas, heavy snow could develop. There are winter storm warnings out for much of west Texas and southern New Mexico where up to 6 to 8 inches of snow could fall. As this area of low pressure moves east, the core of upper level cold air will move with it bringing a threat of snow mixing in with rain across much of west Texas Tuesday night and Wednesday morning.

Will this threat of snow move into East Texas? Although I can’t rule it out completely, there are a few things going against us getting any snow. The main obstacle preventing snow is the fact that our elevation is much lower in East Texas.

Below is an image of the forecast 850mb temperatures. We usually need these temperatures to be below freezing for snow to fall, which they are, running -2 to -4 degrees Celsius.

850mp Temps

Below is an image of the forecast surface temperatures Wednesday Evening. Temperatures are forecast to be between 35 and 40 degrees. In this range snow could reach the surface.

Surface Temps

The final image is the accumulated 6 hour precipitation. This image shows the heaviest wrap around precipitation north of I-30, some of which could be snow. If you look at the surface temperature map again you will see areas north of Mt. Pleasant where temperatures are below 35. This could allow for a light dusting if this verifies on elevated surfaces.

6 Hour Precip

The mid and upper levels of the atmosphere will be plenty cold enough for snow to develop but the depth of above freezing temperatures near the surface is just too great to allow the snow to reach the surface. There are a few areas in East Texas where the elevation is over 700’ and in these locations, it is possible a few wet flakes could reach the surface. If this area of low pressure is slightly stronger than forecast then there could be heavier precipitation under the core and this would drag the colder temperatures aloft to the surface which could lead to a better chance of snow. Many surprise snow events have happened with these upper lows including the snow on Easter of 2007 here in East Texas and the heavy snow event on Christmas Eve of 2004 along the Gulf Coast. So this will need to be watched closely.

One thing is certain. Behind this low, the coldest air of the season will move into East Texas. Temperatures by Thursday morning could be in the upper 20s to lower 30s area wide bringing the first widespread freeze to East Texas.

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