Updated 845am CT Monday / 2 December 2013
…. Unseasonably Warm Over the Day or So ….
…. Massive Arctic High to Move into Central USA by End of Week ….
…. Chance of Freezing Precipitation Again by Late Friday into Next Weekend ….
On this Monday morning…. an eastward moving surface high pressure is over the southeastern USA with a low pressure area over southeastern Colorado. Another high pressure area is over the four corners region. As a result of this surface weather pattern, surface winds are south southwesterly across our area.
In the upper levels of the atmosphere… a trough, or line, of low pressure trough is over the eastern third of the USA while another intense upper level low moving slowly southeastward over British Columbia and the Pacific northwest. As a result, the upper level winds over south central Texas and the Austin metro area about 18,000 feet above the ground are west northwesterly 30 to 40 mph.
As we start the new week, a south southwesterly surface wind and a mostly dry and stable weather pattern continues with plenty of sunshine and well above average temperatures expected over the next couple of days. With increased low level moisture, we’ve seen and may see over the next few days a little patchy morning low clouds and fog.
By mid into late week, we’ll transition to a more northerly wind aloft as an area of low pressure moves from the Rockies into the plains states. A massive area of arctic high pressure.. now located over northwest Canada and eastern Alaska with surface temperatures underneath the high as cold as -40 F.. will break loose and will surge southward into the western and central USA. By Friday into the weekend, the leading edge cold front will move well into the Gulf of Mexico and the arctic air mass will overtake much of the lower 48 states.
As the colder surface air moves in, the subtropical jet stream (higher in the atmosphere) off the tropical Pacific, will send disturbances overhead and will create an overrunning pattern where moisture comes back on top of the colder air. As the upper air disturbances move overhead, they will cause atmospheric lift with periods of precipitation possible back in the colder air. With temperatures expected to be near or even slightly below freezing, especially in the overnight hours, we could see periods of freezing drizzle and freezing rain given the very shallow layer of surface based arctic air. I’ll continue to watch these precipitation prospects closely.
The cloudy and unseasonably cold weather pattern will likely persist into early next week before a warm up kicks in once again.
Regarding my forecast, my local forecast confidence: Very high forecast confidence into Wednesday.. then dropping to medium to high later Wednesday into Thursday (exact frontal passage time and rain chances along front being the question). For Friday through the weekend, my forecast confidence drops to low to medium with the main questions being the intensity of the cold air along with liquid/freezing precipitation chances.
Have a good Monday…
Meteorologist Troy Kimmel
Contact me:
tkimmel@austin.utexas.edu
http://www.facebook.com/troykimmel