Friday, December 18, 2009

Strong Storm Could Hit Just Before Christmas

The week of Christmas looks very interesting around East Texas to say the least. A very strong Lee Side low pressure system looks to develop Tuesday afternoon in the Colorado High Plains and move east northeast into the Midwest Christmas Eve. Out ahead of this storm system warm moist air from the Gulf of Mexico will surge northwest into the circulation of this strong low pressure. Because of this surface dewpoints in East Texas could easily reach the low 60s setting the stage for a possible severe weather event early Wednesday.
Surface Dewpoints

Right now it appears there will be plenty of instability in the lowest level of the atmosphere to produce scattered thunderstorms. The Lifted Index, or the difference between the lifted parcel temperature and the parcel’s surrounding temperatures, is negative across most of East Texas Wednesday morning.

Lifted Index

Also, the amount of bulk shear needed for supercell development will be more than enough, on the order of 50 to 70 knots.

Finally, the amount of surface based CAPE is enough to get the air rising from the surface leading to thunderstorm development. Now the amount of CAPE is nothing compared to what we might find during the spring severe weather months. However, when you take the normalized CAPE, or the amount of CAPE and divide it by the distance between the level of free convection and equilibrium level, you get a level conducive for strong updraft strength.


Bottom Line, it looks as though the atmosphere is setting up for a round of low topped supercells Wednesday from East Texas through much of the lower Mississippi Valley with the potential for gusty winds, large hail, and even a few tornadoes.

Now for what everyone wants to know, will it snow for Christmas? Well, if I were a betting man I would bet against it however, the chances of snow are not at zero. That means there is hope for all you snow lovers of a few flurries flying on Christmas morning but no accumulation would occur. So what could lead to the possibility for snow flurries? The answer is a mid level disturbance, or shortwave, that sometimes produces surprise snow events in winter, especially across the south. (December 2004 Texas Gulf Coast)

On Christmas Eve a fast moving disturbance will drop out of Canada and race towards the southeast. Behind this disturbance will be a reinforcing shot of colder air for Christmas day. As this system drops south, clouds and flurries will form in the Northern Plains.

This disturbance will continue to move overnight Christmas Eve into Christmas Morning. As it moves into the Southern Plains, moisture will be very limited but it still appears there could be a few flurries as this system moves in.

By 6AM Christmas morning this system is forecast to be moving through the Metroplex. The big question will be moisture. Right now it appears there will not be enough moisture to produce snow flurries across East Texas. However, we will also be located in the left exit region of a strong jet streak that will aid in lift. If there is a little more moisture available than forecast, we could see a few flurries on Christmas day. I do want to stress that the odds of this occurring are very slim. Right now my official forecast for Christmas is partly cloudy and cold with highs around 40 and lows in the 20s. Snow lovers, keep believing……maybe Santa will bring a surprise.

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