Investigating the summertime midday precipitation peak in southeast Texas

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Sunday, 17 January 2010
Exhibit Hall B2 (GWCC)
Brad J. Reinhart, Florida State University, Tallahassee, FL; and C. McCaskill, L. J. Hopper Jr., and C. Schumacher

Previous studies of precipitation in southeast Texas have identified a late morning to early afternoon daily maximum in annual rainfall. We analyzed seven years (2002-2008) of hourly gauge data from Easterwood Airport in College Station, Texas, and discovered that this midday maximum is most amplified during summer (June-August). We further separated the gauge data by storm type and found that the midday peak was consistently associated with upper-level disturbances. Other summer storm types (i.e., cold fronts and weakly forced systems) contributed significantly less rain to the summer accumulations and exhibited very different diurnal cycles.

We have two working hypotheses to explain this midday maximum (as opposed to observing a peak at the time of maximum heating). First, based on suppositions made in Winkler et al. (1988), the earlier maximum may be attributed to the inland progression of storms that develop overnight due to the convergence of the land breeze and southerly synoptic flow. Second, the thermodynamic environment associated with upper-level disturbances may create a more moist and conditionally unstable atmospheric column that allows convective temperatures to be reached earlier in the day. Soundings and additional coastal and inland gauges in southeast Texas are analyzed to explore the validity of these hypotheses. Upper-level disturbances are further separated into tropical cyclones, troughs/tails, and fractures to determine the diurnal forcing variability within the upper-level disturbance categorization. Models often have difficulty in simulating the diurnal cycle over land, so this study provides an interesting baseline for evaluating how well models simulate the summertime diurnal cycle of precipitation in southeast Texas compared to regions with a later daytime peak.