85th AMS Annual Meeting

Wednesday, 12 January 2005: 4:30 PM
Extreme rainfall in Texas: patterns and predictability
John W. Nielsen-Gammon, Texas A&M University, College Station, TX; and F. Zhang, A. M. Odins, and B. Myoung
Extreme rainfall, with storm total precipitation exceeding 500 nm, occurs several times per decade in Texas. Through a compositing analysis, the large-scale weather patterns associated with extreme rainfall events involve a northward deflection of the tropical trade winds into Texas, with deep southerly winds extending into the middle troposphere. One such event, the July 2002 South-Central Texas flood, is examined in detail. This particular event was associated with a stationary upper-level trough over central Texas and northern Mexico, which established a steady influx of tropical moisture from the south. While the onset of the event was triggered by destabilization caused by an upper-level vortex moving over the northeast Mexican coast, a succession of upper-level processes allowed the event to become stationary over south-central Texas and produced heavy rain for several days. While the large-scale signatures of such extreme rain events evolve slowly, the many interacting processes at smaller scales make numerical forecasts highly sensitive to details of the simulations.

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