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Meteorological characteristics of heavy precipitation and flash flood events over the western United States
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1980
[PDF-186.91 MB]
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Description:Meteorological characteristics of flash floods and heavy precipitation events over the western United States are often considerably different than those associated with flash floods in the east. A distinct July and August occurrence maximum indicates a strong link with the southwest’s monsoon season. The storms occur during afternoon and evening hours, in contrast to the nocturnal characteristic of the eastern U.S. flash floods, and rain amounts are considerably less than those for eastern U.S. events. Data are compiled and studied for 61 western U.S. flash flood events and attendant meteorological conditions are documented. Events are classified by similar 500 mb flow regimes and four characteristic patterns are identified. Synoptic storms occur in conjunction with both an intense cyclonic surface system and a strong 500 mb trough. The remaining flash floods (49 events) are associated with weak and slow moving 500 mb short-wave troughs. Distinct geographical, seasonal and diurnal characteristics are found for the four basic types of western floods and mean values of important meteorological parameters are computed. It is shown that the National Meteorological Center’s broadscale analyses (surface and standard level charts) are not sufficient for monitoring the subtle features that often interact to produce flash floods. The field forecaster must enhance, or reanalyze, these facsimile charts if he is to identify regions of developing flash flood potential.
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Rights Information:CC0 Public Domain
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