Updated 800am CT – Friday / 12 September 2014
…. Big Weather Changes ….
…. Stronger Cold Front Late Today into Tonight with Rain Chances into Tomorrow ….
On this Friday morning…. a cold front is moving slowly southeastward from central Mississippi into northern Louisiana and south central Texas (just north of the Austin area) into southwest Texas then northwestward into New Mexico. As a result of this surface weather pattern, our local surface winds are variable south southeasterly.
In the upper levels of the atmosphere… a deepening trough.. or line.. of upper level low pressure is moving east southeastward from Minnesota and the eastern Dakotas southwestward into eastern Colorado. Upper level high pressure.. acting like a lid on the atmosphere.. is weakening a bit in response to the trough to the north and covers the southern USA from the southeastern USA westward into Texas. As a result of this pattern, the upper level winds over south central Texas and the Austin metro area, about 18,000 feet above the ground, are variable generally less than 20 mph.
As the upper level trough.. moving east southeastward.. over the central and northern USA moves eastward, the upper level high pressure area (think “the lid on the atmosphere”) is weakening a little and shrinking in size as upper level winds increase a bit from the west northwest.
As this occurs, it sets the stage for the cold front overhead just to our.. the strongest so far of the late summer/early fall season.. to move south southeastward through our area in a couple of surges and off the Texas coast into far south Texas by later today into tonight. Increased cloud cover and scattered rain showers and thunderstorms will occur ahead of.. along and even behind the front as it moves across our area. Current guidance suggests that we could see up to 1 to 2 inches of rainfall mainly between now and tomorrow afternoon with the greatest chance of precipitation in the time frame from midday and early afternoon today through daybreak tomorrow (Saturday).
Drier and slightly cooler high pressure.. behind the front.. will settle into Texas for late Friday night and the weekend and into Monday as the front becomes stationary over the northern Gulf of Mexico and far south Texas. The latest guidance is keeping more clouds and even some slim rain chances back behind the front into early next week as upper air disturbances.. from the west and northwest.. traverse the area with temperatures slightly below average for this time of year.
Afternoon high temperatures are expected to warm back to seasonal averages by the middle part of next week with slim daily rain chances continuing.
Regarding my forecast, my local forecast confidence: My forecast confidence over the next 36 hours is high to very high (still concerned with exact rain chances as well as exact timing of the passage of the cold frontal boundary). My confidence remains at high to very high late tomorrow and tomorrow night through Sunday and into next week (concerned with the precipitation timing and rain chances as well as increased cloud cover).
Have a good Friday….
Meteorologist Troy Kimmel
Contact me:
tkimmel@austin.utexas.edu
http://www.facebook.com/troykimmel