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Regional weather forecast tool now available to NWS forecasters

June 13, 2014

Accurately predicting short-term regional weather in areas of complex terrain has always been a challenge for forecasters due to limitations in current computer models. Now a new forecast tool, which inputs regional observations and outputs regional forecast data has made its way into NOAA National Weather Service (NWS) weather forecast offices (WFOs) for testing and evaluation. Beginning in May, forecasters at the WFO and California Nevada River Forecast Center (CNFRC) in Sacramento, CA began accessing the Experimental Regional Ensemble Forecast (ExREF) for use in hydro-meteorological forecasts.

With a focus on estimating precipitation at a certain location or across regions such as the western slopes of the northern Sierra Nevada – referred to as quantitative precipitation forecasting (QPF) – HMT has designed unique observation systems (such as ground-based GPS water vapor sensors, wind profilers, snow level measurements, and surface weather stations) to help improve short-term model forecasts. HMT team members from NOAA’s Earth System Research Laboratory (ESRL), along with personnel from the Sacramento WFO and CNRFC, and the NASA Short-term Prediction Research and Transition Center (SPoRT), have worked together for the past several years to develop ExREF, which incorporates the regional information gathered from HMT into the currently-used forecast model through a portable, state-of-the-art data assimilation program, called LAPS.

Forecasters using ExREF will be evaluating its accuracy and usefulness through daily verification methods developed by NWS forecasters (see images below). This process, followed for each available model, will allow results to be compared and hopefully help build confidence that ExREF is comparable to, or provides better guidance than currently available models. Watching the enhanced model perform under a variety of meteorological conditions, may help ExREF "earn" its way into forecasters’ tool set. In addition, forecasters can provide feedback to ExRef developers for future improvements.

HMT staff would like to thank Brad Zavodsky and Jason Burks from NASA SPoRT, William Rasch from WFO Sacramento, Dan Kozlowski, CNRFC, and Ligia Bernardet and Steve Albers from ESRL’s Global Systems Division for their significant contributions in making this effort a success.

Contact: Dave Reynolds

A. ExREF 36–hr forecast of 24-hr QPF
B. Observed 24-hr rainfall utilizing all available rain gauge data and made available by the CNRFC
Difference between A and B above