MRMS QPE Performance West of the Rockies during the 2013-2014 Cool and Warm Seasons

Abstract: Multiple Radar-Multiple Sensor (MRMS) Quantitative Precipitation Estimate (QPE) Radar Only (Q3RAD), Q3RAD Local Gauge Corrected (Q3gc), Dual Pol and legacy Precipitation Processing System (PPS) product performance was evaluated for data collected during the 2013-2014 cool and 2014 warm seasons. Precipitation events from 34 calendar days affecting 14 radars were collected with reference to single radars to highlight the advantages of a mosaic vs. single radar QPE. Product performance was evaluated at a range of 230 km and 100 km from the radar location, the latter distance functioning as a proxy for a best-case scenario mosaic for DPR and PPS estimates. Performance was assessed via the comparison of precipitation estimates to Community Collaborative Rain, Hail and Snow Network (CoCoRaHS) twenty-four hour accumulation gauge data while hourly automated gauge data (with quality controlled measures applied) were used for spatial and time series analysis. QPE data were evaluated over two regions: the U.S. West Coast and the U.S. Inter-mountain region.

During the cool season and early warm season, precipitation was primarily associated with passing frontal systems that produced stratiform rain along the coast and snow in the coastal mountains. All the precipitation products were substantially impacted by terrain blockage, radar beam overshoot and gauge undercatch. However, Q3RAD clearly outperformed Dual Pol and PPS estimates both at 230 and 100 km from the radar due to 1) MRMS applied a bright band correction for reflectivity in the melting layer which improved estimates and 2) the extra information provided by neighboring radars in a MRMS reflectivity mosaic mitigated terrain blockage/beam overshoot. During the summer, precipitation was mostly due to monsoonal convection over the inter-mountain regions where overlapping regions of radar data is sparse reducing the advantages of a mosaic. In this region, Dual Pol performed slightly better than PPS and Q3RAD, likely because 1) the precipitation was mostly convective and 2) the additional hydro-meteor information provided by Dual Pol variables improved the estimates. In both warm and cool seasons, Q3gc estimates provided some improvement upon the Q3RAD estimates although the magnitude was less than seen east of the Rockies, likely due to the sparsity of gauges in the regions.