NCRFC Quantitative Precipitation Forecasts

Introduction

 

The Hydrometeorological Prediction Center (HPC) provides at least 48 hours of gridded Quantitative Precipitation Forecasts (QPF) in six hour time steps four times a day. QPFs are normally prepared twice daily by the HAS function at the North Central River Forecast Center (NCRFC). For each forecast cycle (1200 UTC and 0000 UTC daily), the NCRFC uses the HPC QPF to create a basin average precipitation product which is input into the NCRFC river models.

Creation:

Once the above input is available, the HAS forecaster begins the forecast process. After using all available data such as meteorological models, satellite images, radar precipitation estimates and any WFO input that is available, a 24 hour gridded field of forecast precipitation is created in six hour time steps. If the guidance has differing solutions, which are hydrologically significant, then the HAS may coordinate with the WFOs and/or the HPC to come up with a forecast. This QPF is then used to create basin average precipitation forecasts for each basin within the NCRFC area.

Output:

When all four periods are completed, a 24 hour gridded forecast precipitation field is computed by adding up the four six hour periods. Once this is finished, the final products are created. These include NCRFC area map images and a text file containing precipitation forecast amounts for each of the six hour periods that is used as input into the NCRFC's run of the NWSRFS river hydrologic models.

When it appears that a QPF is not going to verify, the HAS forecaster may update the forecast. Additionally, if heavy precipitation and flooding are expected, the HAS forecaster may use the intermediate QPFs at 1800 UTC or 0600 UTC to produce an updated forecast.

Hydrologic forecasters issue five day river stage forecasts based on observed precipitation and QPFs. Occasionally, a forecast will exceed flood stage based on QPF, but remain below flood stage with zero QPF. For these situations, the hydrologic forecaster will issue a forecast on the expected stage and the time the point will go into flood. The forecaster then issues a Hydrometeorological Coordination Message (HCM) outlining the affected Hydrologic Service Area (HSA), the river system, and the hydrologic forecast point(s). For these locations, the WFO with hydrologic forecasting responsibility may issue a Flood Watch (FFA) or a Flood Warning (FLW) based on the forecast guidance from the NCRFC. 

qpfintro.html -Rev. 06/23/2001-rjw/dml