Saturday, December 8, 2012

First of Several December Winter Blasts on the Way...

Cold air is gathering across the northcentral U.S. this morning, and is destined to make a major move to the South on Sunday and Monday, spreading the coldest air so far this season into much of the southcentral U.S.

The cold front is forecast to stretch from southwest Texas into the Midwest by tomorrow afternoon at 3pm.  You can pick out the front nicely on the NAM computer model forecast temperature image below, valid at 3pm CST on Sunday:

At least a broken line of thunderstorm activity likely to form along and ahead of the front, and some of the storms may become strong to severe across the South.  The forecast radar image below is from the high resolution NAM model, valid at 9pm CST on Sunday evening:

As I always caution when examining a model depiction of the radar at a future date/time, use caution.  While it is not likely that thunderstorms will exist exactly where shown, you at least have a good idea as to where the best chance of storms will be.

There is a chance for some of the stronger storms to produce hail and/or wind gusts to severe limits, and the Storm Prediction center is forecasting that risk within the brown and especially the yellow shaded areas on the image below for tomorrow afternoon and evening:

For folks across the South, the major news with this system will  be the sharply colder temperatures.  For example, the Austin/San Antonio area in Texas will plummet from readings in the lower 80s on Sunday afternoon: readings in the 40s on much of the day Monday:

Strong Northerly winds of 20-30 mph with gusts to 40 mph are likely behind the front on Sunday night and Monday morning, which will drive wind chill values into the 20s and 30s across a large part of the southcentral U.S.  The image below depicts forecast wind speeds near the surface at 6am CST on Monday morning.  Gusts of 30-40 mph are likely within the green shaded areas:

At this time it appears that wintry precipitation will be relatively scarce in association with this first major system of December, as far as the central and southern U.S. is concerned.  The high resolution NAM computer model suggests that some accumulating sleet and/or snow may take place in a relatively narrow corridor from the Texas panhandle into southwestern Oklahoma on Sunday night and early Monday.  The image below is valid 6am CST on Monday:

We'll need to watch this general area closely for any significant changes in how the system comes out with respect to precipitation potential behind the cold front Sunday night and early Monday.

A widespread, hard (killing) freeze can be expected across much of southcentral and southeastern Texas (areas that have not had one yet this season) on Monday night and Tuesday morning.  In the Austin/San Antonio area for example, the potential exists for sub-freezing temperatures for a period of 8-10 hours - including a 5-6 hour period with readings in the middle to upper 20s.  This is very unusual for so early in the season in this area.

As I've been talking about for a week to 10 days now, this cold blast will be just the first installment in what looks to be a much more active December weather pattern with respect to cold weather, as well as wintry precipitation in some stay tuned!

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