Determing Quantitative Precipitation Forecast Duration to Optimize River Forecast Services

The two NOAA's National Weather Service (NWS) Central Region River Forecast Centers investigated the errors in quantitative precipitation forecasts (QPF) as well as the impact of QPF on river forecast accuracy in order to determine the optimum number of hours of QPF to use in river forecasts. This study spans 13 months from June 1, 2009 through June 30, 2010. The study was divided into three parts. The first two parts look only at QPF errors using individual 6-hour time step precipitation data, accumulated precipitation data from six hours up to 72 hours, and 24-hour daily precipitation totals out to three days in the analyses. In Part 3, both precipitation and river forecast errors resulting from various QPF durations are analyzed. The methods used in the statistical analysis are hypothesis testing (Student's t-Test), accuracy “error statistics” (mean absolute error (MAE), mean error (ME)), and categorical statistics (probability of detection (POD) and hydrologic false alarm ratio (HFAR)).