Restructuring the National Weather Service Quantitative Precipitation Forecast process

On February 25, 1999, the National Weather Service (NWS) Director commissioned nine individuals from diverse components of the organization to review the Quantitative Precipitation Forecast (QPF) process to support the NWS River Forecast System. The Director's charge to the team was to determine whether the existing QPF process constituted the most effective use of human resources to produce quality QPF information critical for hydrologic services. The human resources involved in this important forecast process, include meteorologists from the Hydrometeorological Prediction Center (HPC) of the National Centers for Environmental Prediction, field forecasters at the Weather Forecast Offices (WFOs), and personnel who comprise the Hydrometeorological Analysis and Support (HAS) function at the River Forecast Centers (RFCs). Nationwide, 13 diverse RFCs, which vary significantly in size, topography, and prevailing climate, depend upon the QPF output to generate accurate hydrologic forecasts.

In less than four months, the team gathered information related to the utility of the QPF products via their painstaking examination of several heavy precipitation events and by the generation and expert analysis of verification data. By producing a comprehensive suite of comparative verification data, they accelerated the implementation of the inaugural prototype for the national QPF verification system. Additionally, the participants in the QPF process were surveyed nationwide and these detailed results were carefully scrutinized.

The team uncovered substantial inefficiency and unnecessary complexity in the existing QPF process east of the Continental Divide. Recommendations to simplify and improve the QPF process were communicated via briefings to the NWS Director and the Corporate Board, and by dissemination of a detailed report. A recommendation for areas west of the Continental Divide was deferred until additional information could be gathered.

The ensuing analysis for the Western U.S. based on data from the period November 1999 through March 2000, revealed an overall lack of meaningful difference in QPF skill between the WFOs and HPC out through Day 3. This was primarily due to the rather large errors associated with both sets of forecasts for the precipitation categories and 6-h time intervals examined. Hence, the team recommended streamlining the QPF process west of the Continental Divide to rely on the QPF products provided by HPC. Additional and important supporting recommendations from the assessment include:

• HPC and HAS personnel will produce QPF products for input to river forecast models for all RFCs located within the conterminous United States; • the RFC HAS function must take an active role in the QPF process, especially for the provision of updates for the first 6 hours of each forecast cycle; • any WFO may produce QPF for other (internal and external) local uses.

On June 14, 2000, the NWS Corporate Board adopted these recommendations. The presentation will provide an overview of the entire assessment effort.