Updated 845am CT Thursday / 19 December 2013
…. Clouds and Humidity Picks Up Tonight and Tomorrow Through Late Week ….
…. Upper Air Storm System and Cold Front Due Late Tomorrow into Saturday ….
…. Beneficial Rainfall and Possibility of Stronger Thunderstorms Saturday ….
On this Thursday morning…. a surface high pressure area is over the western Atlantic Ocean and westward into the Carolinas and Georgia. A trough.. or line.. of low pressure extends southward from a low pressure area in southwestern Kansas into west Texas and then into far southwest Texas. Another high pressure area is over western Colorado. A strong cold front extends southwestward from the northern Great Lakes into central Kansas the northwestward into a developing low pressure storm system over Wyoming. As a result of this surface weather pattern, surface winds are southerly across our area.
In the upper levels of the atmosphere… a deepening/strengthening upper level low pressure trough is moving southeastward through the western USA with an intense upper level disturbance embedded within the trough over central California southeast of the San Francisco Bay Area. As a result, the upper level winds over south central Texas and the Austin metro area about 18,000 feet above the ground have become more southwesterly at 35 to 45 mph.
The dry and stable weather pattern over the area is coming to an end as southerly surface winds are returning abundant low level moisture with clouds becoming more common. As this moisture continues to increase, we’ll continue to see clouds thicken and lower. In addition, late night and early morning low cloudiness.. patchy fog and light drizzle is possible late tonight into early tomorrow morning.
The upper level trough over the western USA.. and the associated intense upper air low pressure disturbance over central California.. will move eastward Rockies and plains over the next 24 to 48 hours. As it approaches, atmospheric instability and lift will increase with an increasing likelihood of rain showers and thunderstorms especially by tomorrow night into Saturday and Saturday night. Current guidance suggests upward of 1/2 to 1 inch of rain over our area with the NWS Storm Prediction Center putting the local area in a “slight” risk of severe thunderstorms for Saturday into Saturday night with larger hail and damaging straight line thunderstorm wind being the main risks.
As the upper air low pressure disturbance moves by late Saturday, the upper level wind pattern will shift allowing a strong cold front to surge southeastward through the area by the morning hours on Sunday. In the wake of the cold front, clouds will break with sunshine returning to the area by midday Sunday into early and middle parts of next week with below average temperatures returning to the area.
Regarding my forecast, my local forecast confidence: My confidence in my forecast is very high today. For tomorrow through Saturday, my forecast confidence falls to medium to high (exact timing of rain, exact rain chances and the timing of the cold front still a question). My forecast confidence returns to very high for Sunday into early next week.
Have a good Thursday…
Meteorologist Troy Kimmel
Contact me:
tkimmel@austin.utexas.edu
http://www.facebook.com/troykimmel