Extended Abstract (1.5M)1.1
The dramatic effect of tornadic severe weather on a rapidly growing urban interface
Ivory J. Small, NOAA/NWS, San Diego, CA; and T. Mackechnie and S. Vanderburg
Much attention has been given to blocked flow and the associated helicity generation along the southern California coast, or island effect phenomena as key producers of supercells and tornadoes over the coastal plain. Much less attention has been given to the patterns and processes that affect the valley areas in regard to the production of supercells and/or tornadoes. Recently there has been rapid urbanization of the inland areas of extreme southwestern California, and there has also been an upswing in the number of tornadoes being reported in the inland areas as well.
A particular upper air pattern seems to be emerging as a key feature for the production of long lived supercells and tornadic activity in extreme southwestern California. This pattern consists of a broad 500 mb trough containing a long ribbon of vortices imbedded in a large thermal gradient aloft. An envelope of vorticity bounded by a 24 x 10-5 s-1 contour can stretch 750-1000 miles or more, and can reasonably be described as a "Tropospheric Vortex River". These patterns may be a favorable setup for the development of long lived supercells that can move inland from the coast into the inland valleys, or even begin in the inland valleys as a long lived supercell. It is thought that since these long vortex rivers can be slow moving events, their extended residence time may allow conditions that produce supercells to persist, thus resulting in increased probabilities of supercell development and possible tornadoes.
Two recent severe weather outbreaks, complete with tornadic supercells accompanying such "vortex rivers" will be investigated and presented. A direct impact of these events on travel in the rapidly urbanizing inland areas will also be presented.
Session 1, Severe Storms Impacts on the Urban Environment: Modeling and Observations
Tuesday, 13 January 2009, 3:30 PM-5:00 PM, Room 123
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