Extended Abstract (28K)JP2.3
Late November 2001 Winter Precipitation Event Over South Central Texas
Robert A. Blaha, NOAA/NWS, New Braunfels, TX
On November 28 to 29, 2001, an early season snow and winter precipitation event evolved over South Central Texas. Snow was the predominant precipitation type, mixed with some sleet, from Val Verde County east to parts of Edwards, Real, Bandera, Kerr, Gillespie, Llano, and Burnet Counties. Maximum snowfall near 50 to near 152 mm was reported over parts of Val Verde County on November 28. In Western Kerr County near Hunt near 13 mm of snow was reported the morning of Wednesday, November 28th. Further east, the depth of sub freezing cold air became shallower and warmed from the effects of down sloping subsidence winds; greater distance from the initial sub freezing regions to the northwest; and latent heat feedback from precipitation processes. This created conditions more favorable for freezing rain, sleet and isolated snow flurries from 00 UTC to 12 UTC November 29, across parts of Kinney, Maverick, Uvalde, Medina, Bexar, Comal, Hays, Travis, Williamson, Caldwell, Bastrop, Lee, and Fayette Counties.
Synoptically speaking, from 00 UTC to 12 UTC November 28, an increasing amplitude 700 to 300 MB trough evolved from the Southwest U.S. to North Central Mexico, west of South Central Texas. From the surface to 850 MB, a sub freezing layer of cold air was advected over Val Verde, Edwards, Real, Bandera, Kerr, Gillespie, Llano, Burnet, Blanco and Kendall Counties, from the Texas Panhandle and Southern Plains, where a snow event occurred. Sub freezing conditions surged across Val Verde County in the early morning, helped at low levels by the funneling affects of the Pecos River Valley, running north to south. The combination of favorable upper level dynamics and a sub freezing surface to 850 MB layer favored snow formation. By 00 UTC November 29, the strong dynamics of the 700 to 300 MB trough began to create widespread precipitation from Del Rio to Eagle Pass to west of Laredo. As the area of precipitation developed eastward from around 02 UTC to 06 UTC November 29, strong dynamics caused just enough latent heat release to help transform the event to more of a freezing rain, mixed with sleet and isolated snow flurry event. The mixed winter precipitation event occurred in sub freezing areas north and west of an Eagle Pass to San Antonio to New Braunfels to Austin Line. The rapid movement of the weather system from 06 UTC to 12 UTC November 29th allowed drying and subsidence from the west to decrease the precipitation area. A brief round of winter precipitation, associated with strong lift aloft, occurred from the Austin Area to eastern parts of South Central Texas between 09 UTC and shortly after 12 UTC November 29. The event ended after 12 UTC November 29, as dry air was advected across the area from the west at low levels, and subsidence increased at Mid and Upper Levels in wake of the 700 to 300 MB Trough.
Supplementary URL: http://www.srh.noaa.gov/ewx/wx/nov282001/nov28.htm
Joint Poster Session 2, Severe Local Storms Forecasting (Joint with 21SLS and 19WAF/15NWP) new
Tuesday, 13 August 2002, 3:00 PM-4:30 PM
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