Updated 800am CT – Wednesday / 17 September 2014
…. An Unsettled Weather Pattern ….
…. Abundant Moisture and Passing Upper Air Low Pressure Disturbances ….
…. The Latest Guidance Trends Wetter with Much Better Rain Chances over Next Few Days ….
On this Wednesday morning…. a weakening stationary front extends from central Mississippi westward into northern Louisiana then northwestward into Oklahoma into a surface low pressure area over central Kansas. As a result of this surface weather pattern, our local surface winds are southeasterly.
In the upper levels of the atmosphere… a broad trough.. or line.. of upper level low pressure is moving eastward through the eastern half of the USA with another trough of low pressure is situated off the west coast. The upper air reflection of tropical cyclone Odile.. with abundant high and mid level Pacific moisture.. is located over northwest Mexico just across the USA border from Tucson, AZ. Weakened upper level high pressure.. acting like a lid on the atmosphere.. extends eastward from southeastern New Mexico and southern Texas southward into northern Mexico. 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 west northwesterly less than 20 mph.
With the upper level trough to our northeast and the advancement eastward of the remnants of Odile, the upper level high pressure area, or the “lid” on the atmosphere, has continued to weaken a little, shrink in size and shift southward as upper level winds increase a bit from the west northwest and the system itself settles southward a bit.
More clouds and abundant low level moisture continues, along with an increasingly unstable air mass, over the area. At the same time, upper air disturbances and mid and upper level moisture.. from the west.. traverses the area and creates atmospheric lift. This will result in much better rain and thunderstorm chances over the next couple of days. The latest computer and NWS manual guidance suggests higher rainfall probabilities and amounts over the next few days with rainfall totals, in general, in the 1 to 3 inch range with isolated heavier amounts. While the rainfall will certainly be beneficial in nature overall, localized urban and small stream/low water crossing flooding is possible. In addition, with cloud cover and precipitation chances over the next few days, afternoon high temperatures remaining slightly below seasonal averages.
By late Friday into the weekend, the upper level high pressure ridge (the “lid” on the atmosphere) will strengthen a bit with rain chances coming down and clouds thinning out a bit.
Guidance suggests that another cold front will move southeastward across the area by late Sunday into early Monday with a renewed chance of rain showers and thunderstorms.
Regarding my forecast, my local forecast confidence: My forecast confidence over the next two to three days is high to very high (still concerned with the exact rain timing and amounts). My confidence is very high Friday night through much of the upcoming weekend. My forecast confidence falls back to medium to high for late Sunday night into Monday in reference to precipitation and cold frontal timing.
Have a good Wednesday….
Meteorologist Troy Kimmel
Contact me:
tkimmel@austin.utexas.edu
http://www.facebook.com/troykimmel