Updated 845am CT Friday / 20 December 2013
…. Upper Air Storm System and Cold Front Headed Our Way ….
…. Beneficial Rainfall and Possibility of Stronger Thunderstorms Over Next 24 Hours ….
…. Sunshine and Cooler Temperatures Late Saturday Afternoon into Next Week ….
On this Friday 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 central Missouri and Oklahoma into west Texas /around Lubbock/ then northwestward into a developing low pressure storm system over Colorado and 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 the northern part of the Baja Peninsula and northwestern Mexico. As a result, the upper level winds over south central Texas and the Austin metro area about 18,000 feet above the ground have increased and are southwesterly at 45 to 55 mph.
Southerly surface winds continue to return abundant low level moisture. By later today into tonight, the upper level trough over the western USA.. and the associated intense upper air low pressure disturbance over northern Baja/Mexico.. will move eastward toward Texas. As it approaches, atmospheric instability and lift are already increasing with an increasing likelihood of rain showers and thunderstorms by tonight into the morning hours Saturday. Current guidance continues to suggest upward of 1/2 to 1 inch of rain over our area with the NWS Storm Prediction Center including the local area in a “slight” risk of severe thunderstorms for the 3am to 12 noon time period tonight into Saturday morning with larger hail and damaging straight line thunderstorm wind being the main threats.
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 mid to late afternoon hours tomorrow. In the wake of the cold front, clouds will break with sunshine returning to the area by as early as late tomorrow afternoon and then continuing Sunday into early and middle parts of next week with below average temperatures returning to the area.
Another storm system and associated cold front will increase clouds and give us a slim chance of rain by late next Wednesday /Christmas Day/ into Thursday. Temperatures will once again cool down following this front next Thursday.
Regarding my forecast, my local forecast confidence: My confidence in my forecast is high today. For tonight through Saturday, my forecast confidence falls to medium to high (exact timing of rain and the timing of the cold front still a question). My forecast confidence returns to very high for Sunday into early and mid parts of next week.
Have a good Friday…
Meteorologist Troy Kimmel
Contact me:
tkimmel@austin.utexas.edu
http://www.facebook.com/troykimmel