Forecasting Heavy Precipitation in Winter Storms

Despite demonstrable progress in the prediction of cool season middle latitude synoptic-scale cyclones over the last 25 years, progress on predicting the timing, intensity, and location of heavy precipitation associated with these cyclones has been more limited. This more limited progress can be attributed to gaps in our scientific knowledge and understanding of precipitation processes and mechanisms, data limitations and analysis uncertainties, and the inherently mesoscale nature of the precipitation distribution within a cyclone. Progress has also been slowed by challenging technology transfer and communication problems.

This talk will focus on an overview of scientific issues related to forecasting heavy precipitation. An important theme will be the need to assess both upscale and downscale effects when synoptic and mesoscale disturbances interact in winter cyclones. As an example, organized deep convection, triggered by mobile subsynoptic-scale disturbances in the upper troposphere, can significantly impact the ensuing evolution of the synoptic-scale flow as happened in the important cyclogenesis events of 13-14 March 1993 and 24-25 January 2000. Likewise, occasions may occur, such as with the 4 January 1994 storm over eastern North America, where successful synoptic scale cyclone prognoses are deficient in simulating critical mesoscale details in the accompanying precipitation distribution.