Flash Flood Guidance enhancement at the Middle Atlantic River Forecast Center

This poster will describe and present test results from several methodologies being investigated to improve Flash Flood Guidance (FFG). Recognizing the need to improve its FFG products to better conform in scale and accuracy to the gridded precision required by NOAA/National Weather Service (NWS) Weather Forecast Office (WFO) flash flood diagnostic software, the NWS Middle Atlantic River Forecast Center (MARFC) in State College, PA has undertaken an in house effort to address several known assumptions and limitations in the national FFG system methodology.

Among the areas being explored are: 1) development of a process that allows each gridded FFG value to vary independently based on the analogous gridded Multisensor Precipitation Estimator (MPE) data, rather than all grids within larger hydrologic areas being assigned the same value; 2) addressing the "empty channel assumption" by investigating statistical approaches to reasonably estimate the amount of water already in small ungauged stream channels prior to an event; 3) analyzing rainfall recurrence intervals to develop and implement realistic maximum FFG value limits with regional and topographic relevance, rather than the present one-size-fits-all limits covering the entire MARFC area; and 4) compiling small stream channel information from site visits and other sources in order to develop threshold runoffs more appropriate for the gridded scale.

All of these areas of investigation are in various levels of development, testing, and implementation, including a collaborative arrangement with WFO State College, PA. It is hoped that enhancements to MARFC's FFG products will help the WFOs in our service area to improve lead times and accuracy in their respective flash flood programs, and will serve as a useful transition toward the eventual development of a national distributed modeling approach to hydrologic forecasting.