Sunday, 11 January 2009
Precipitation distributions for storm types in southeast Texas
Phoenix Convention Center
Large seasonal and interannual variations in precipitation occur in southeast Texas, a subtropical region affected by both mid-latitude and tropical influences. Precipitation in this region is primarily caused by fronts in over half of the cases and upper-level disturbances in about one-third, while weak synoptic forcing (e.g., sea breeze) and drylines account for the rest. Six years (March 2002-February 2008) of hourly rain gauge data from Easterwood Airport in College Station, Texas, is matched with NEXRAD radar images to determine each storm's total precipitation. Storms are included if at least 0.02 inches of precipitation occur in a 1-hour period or if 0.05 inches occur in a 24-hour period. New storms are identified if no precipitation is recorded for five consecutive hours.
Hourly and storm total histograms for each storm type are created and analyzed for interannual and seasonal variations. Surrounding daily rain gauge data will be used to corroborate each storm type's contribution to annual rainfall. We hypothesize that warm fronts produce the most precipitation per storm, comprising a relatively large fraction of annual precipitation despite occurring less frequently than most other storm types. Spatial variations may also be examined by performing a similar analysis for a site in Houston, Texas. In addition to outlining a methodology that may be extended to other subtropical regions for comparison, this study will provide empirically based histograms to assist forecasters when making quantitative precipitation forecasts (QPFs) for southeast Texas.