Boundary Layer Structure and Its Relation to Precipitation Over the St. Louis Area.
ILLINOIS STATE WATER SURVEY URBANA
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Rainfall, wind and temperature data at the surface and winds in the lower 1-2 km for a mesoscale area surrounding St. Louis, Missouri, for 7 summer days in 1975 were used in a study to determine the relationship between the surface kinematic fields and the occurrence and intensity of rainfall, and to determine if the surface kinematic fields are representative of the subcloud layer. It was found that, on some case days, patterns of convergence collocated favorably with raincells, were predictive of rainfall onset, and were positively related with rainfall amount. However, the relationships were nonexistent or negative on other case days. The statistics support the premise of the predictability of rain amount or rain mass based upon the preceding convergence on the cell scale and on the scale of the network, especially if some method that stratifies the convergence-rainfall relations can be found. Subsynoptic andor mesoscale disturbances that tend to increase the potential for convective precipitation were present on all 7 case study days. These disturbances formed over the dense St. Louis surface network on three case study days. Although occurring under different synoptic conditions, these systems were similar structurally, being strongest near the surface and extending through a depth of 550 to 750 meters. Author