A 26 year high-resolution dynamical downscaling over the wasatch mountains: Synoptic effects on winter precipitation performance

Abstract

26 year high-resolution dynamical downscaling over the Wasatch Mountains of Utah, USA, was performed using the Weather Research and Forecasting model with initial and boundary conditions derived from Climate Forecast System Reanalysis. Precipitation validation was conducted on the inner (4 km resolution) domain with Snowpack Telemetry (SNOTEL) and Parameter-elevation Regressions on Independent Slopes Model data sets. Analysis of seasonal performance reveals the model’s overall good skill at reproducing the spatial distribution of precipitation. Annual precipitation validates within ~20% of SNOTEL. The largest monthly biases occurred in December-January (~+30%) stemming from a small set of high-precipitation events. Composite analysis of cold season days with large positive or negative precipitation biases reveals two distinct synoptic regimes with significantly different moisture, temperature, and circulation patterns that respectively enhanced geopotential height and moisture biases consistent with the sign of their mean precipitation biases. The number of cold season days with large (>5 mm) positive precipitation bias was negatively correlated with El Niño (r = -0.55), indicating storm track-related effects on the sign of the bias consistent with the distinct synoptic regimes revealed by the above-noted composite analyses.