Precipitation, being one of the stronger input forcings to hydrologic models, is critical to river forecast accuracy. Beginning in the mid to late 1990s, National Weather Service (NWS) hydrologists have included quantitative precipitation forecasts (QPF) in river level forecasts at all NWS River Forecast Centers (RFC). However, the forecast time horizon used has varied over the 13 RFCs and has resulted in inconsistent input to the river forecast models used. Some of the inconsistencies are justified due to the low confidence in forecasting precipitation during various times of the year and for different geographical regions. For example, it has been found there is more skill in forecasting the timing and location of precipitation during the winter months vs. during the more convective summer months.

This study will compare 6-hourly periods of QPF verification data for the upper Mississippi River and Missouri River basins and attempt to optimize the number of forecast periods used in river forecasts for those RFCs. Seasonal and geographic influences as well as impact of QPF on river forecasts will also be considered.