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Saint Louis University: "Study of mesoscale precipitation systems"

Final Report

During the warm season (April-September) Mesoscale Precipitation Systems (MPS) are basically equivalent to Mesoscale Convective Systems (MCS), i.e., precipitation systems on spatial scales from 20-500 km and temporal scales of 3-12 hours that include deep convection during some part of their lifetimes. In the cold season (October-March), MPS's are usually associated with elevated convection (i.e., convection based on a frontal inversion) which is typically shallow with echo tops below 30,000 feet. These latter systems often form in regions of conditional symmetric instability which is conducive to "slantwise convection".

The objective of this project was to identify those physical processes responsible for the initiation and propagation of cold and warm season MPS's. For wintertime MPS's, the researchers looked at elevated convection, conditional symmetric instability, frontogenetical circulations, and jet streak interactions, as well as slantwise convection. Guidelines for the short-term (0-6 hr) forecasting of MPS's were tested, and strategies for anticipating MPS production and movement were developed. The study also tested other forecast guidelines, while emphasizing the differences between cold and warm season MPS behavior. For the MCS's during the warm season, it was found that the magnitude and orientation of the CAPE, 850 mb theta-e, low-level boundaries, and low-level jet were critical for MCS propagation.

Two preprint articles, two journal articles, and several presentations summarize the results of the project.