Updated 845am CT Tuesday / 3 December 2013
…. Unseasonable Warmth Continues ….
…. Massive Arctic High to Move into Central USA by End of Week ….
…. Chance of 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 developing over the southern plains states. 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… an intense upper level low moving slowly southeastward over eastern Idaho and western Montana as a trough deepens over the western USA. As a result, the upper level winds over south central Texas and the Austin metro area about 18,000 feet above the ground are westerly 40 to 50 mph.
A southwesterly surface wind and a mostly dry and stable weather pattern continues with plenty of sunshine and well above average temperatures expected today and tomorrow. With increased low level moisture, we’ve seen and may see patchy morning low clouds and fog through tomorrow.
By tomorrow into Thursday, we’ll transition to a more northerly wind aloft as the 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 -31 F.. is already breaking loose and will ultimately surge southward into the western and central USA as the upper level low pressure moves to the east. 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 and primarily north of the Austin area, 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 unseasonably cold weather pattern will likely persist for a few days before a warm up kicks in once again as sunshine returns late Sunday into Monday and Tuesday.
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 Tuesday…
Meteorologist Troy Kimmel
Contact me:
tkimmel@austin.utexas.edu
http://www.facebook.com/troykimmel