Extended Abstract (1.3M)P9.6
Applying a Mixed Tornado/Flooding Event to the New National Weather Service Training Environment
Nezette N. Rydell, NOAA/NWS, New Braunfels, TX; and J. D. Ward
A long-lived heavy rain and severe weather event occurred November 14-16, 2001 in Central Texas. During the afternoon hours of the 15th, flash flooding, main stem river flooding, and tornadoes developed across central counties of the county warning area. Rainfall rates of 75 mm per hour, rainfall totals over 250 mm, and 16 confirmed tornadoes occurred in a span of 8 hours. Data from this event were captured locally and used to develop several simulations on the National Weather Service's (NWS) Weather Event Simulator (WES). The WES is an important research and training tool in NWS forecast offices that allows archived weather data to be replayed in displaced real time or interrogated in detail. An analysis of the event is presented, as well as a methodology for developing simulations from both a meteorological and a hydrological perspective.
A nearly stationary strong upper-level trough to the west of the surface weather system helped provide areas of upward vertical motion and destabilization in the storm region. Satellite imagery revealed a slot of middle tropospheric dry air moving into the area from the west. Low-level satellite imagery and surface analysis revealed three air masses, with their boundaries concentrating over areas which experienced multiple tornadoes and heavy rains. Data in the WES included an isolated supercell thunderstorm which developed two tornadoes upon crossing a weak surface temperature/moisture boundary, a bogus radar tornado vortex signature, and a series of tornadoes along a line of strong thunderstorms. Instructions with the simulation assists the forecaster in analyzing the various data fields and the radar displays. Guidance in recommended warnings also are included. The official NWS warning computer software program is available for practice warnings.
The data encompass the evolution of focused rains over a number of watersheds and portray the development of flash flooding, on-going and developing main stem river flooding, and the development of headwater flooding in five disparate headwater basins. Instructions with the simulation guide the forecaster in assessing both continuing and developing flash flood threats and recognizing developing headwater flood threats. The instructions also guide the forecaster in the development of a methodology for addressing headwater and main stem flood threats and composing appropriate warnings.
Supplementary URL: http://www.srh.noaa.gov/ewx/wx/nov152001/nov15.htm
Poster Session 9, Warning, Dissemination and Verification
Wednesday, 14 August 2002, 3:00 PM-4:30 PM
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