Performance of Operational Model Precipitation Forecast Guidance during the 2013 Colorado Front-Range Floods

Abstract

uring the period 9?16 September 2013, more than 17 in. (~432 mm) of rainfall fell over parts of Boulder County, Colorado, with more than 8 in. (~203 mm) over a wide swath of Colorado?s northern Front Range. This caused significant flash and river flooding, loss of life, and extensive property damage. The event set a record for daily rainfall (9.08 in., or >230 mm) in Boulder that was nearly double the previous daily rainfall record of 4.8 in. (122 mm) set on 31 July 1919. The operational performance of precipitation forecast guidance from global ensemble prediction systems and the National Weather Service?s global and regional forecast systems during this event is documented briefly in the article and more extensively in online supplemental appendixes. While the precipitation forecast guidance uniformly depicted a much wetter-than-average period over northeastern Colorado, none of the global nor most of the regional modeling systems predicted precipitation amounts as heavy as analyzed. Notable exceptions to this were the Short-Range Ensemble Forecast (SREF) members that used the Advanced Research Weather Research and Forecasting Model (ARW-WRF) dynamical core. These members consistently produced record rainfall in the Front Range. However, the SREF?s record rainfall was also predicted to occur the day before the heaviest actual precipitation as well as the day of the heaviest precipitation.