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Pennsylvania State Univ.: "A study of lake-effect rain events downwind of Lake Erie"

Final Report

The primary objective of this COMET project was to complete a study of Lake Erie-effect precipitation (primarily rain) to determine its frequency and magnitude which to date has received very little attention, compared to wintertime lake-effect snow. Based upon examination of radar-observed precipitation, it was found that lake-effect precipitation occurs throughout the entire autumn season. The frequency of lake-effect precipitation was measured by compiling both lake-effect days and lake-effect events. An analysis of long-term regional precipitation climatologies confirms the radar study and indicates that lake-effect precipitation begins in earnest by September and reaches a maximum during November. While lake-effect precipitation events probably occur more often in early winter, the climatological precipitation patterns suggest that the peak in lake-effect precipitation amount precedes the peak in event frequency.

Another finding is that mean lake-effect rain analyses show considerable similarities to snow events, when the environments of the individual events are averaged at certain states in their life-cycles. The similarities are most notable in the general position of surface and upper air features, in addition to the near uniform west to southwest tropospheric flow. Differences between rain and snow environments are manifested primarily in the thermodynamic profile of the lower to middle troposphere. In contrast to most lake-effect snow events, the conditionally unstable layer for lake-effect rain events is much deeper. This finding led the forecast office to amend the on-station lake-effect guidance products to incorporate higher sigma levels to diagnose the higher steering level of lake-effect rain in Western New York. In addition, the shortcomings of diagnosing lake-effect rain intensity via the old on-station thermodynamic charts at the NWS Buffalo have been highlighted and corrected to better account for the profiles in which lake-effect rain occurs.