Cool-season intermittent precipitation cells in the Pacific Northwest

Precipitation is enhanced over the mountainous U.S. West Coast as the low-level flow and moisture from land-falling storms interacts with the coastal terrain. While much of the previous work on orographic precipitation has focused on steady-state processes, little work has been done on intermittent precipitation cells. Current linear models and non-linear mesoscale forecast models such as MM5 and WRF can reproduce small scale precipitation patterns over individual terrain ridges in some cases but not others. We hypothesize that these problems are in part a result of errors in the representation of intermittent processes within models, especially convective cells embedded within stratiform precipitation regions. This study examines the spatial patterns and life-cycle statistics for tracks of convective cells observed by the operational WSR-88D radar at Portland, Oregon during cool-season storms. The cell tracking algorithm determines the most probable path among many possibilities based on cell speed and direction. Cell track information is part of our developing methodology to objectively characterize the intermittency of precipitation in this region and to develop feature-based comparison metrics that can be applied to both observations and model output.