Flash flooding can occur on a small horizontal and short temporal scale. The National Weather Service (NWS) Weather Forecast Office in Sterling, VA is charged with issuing Flash Flood Warnings (FFWs) and follow-up Flash Flood Statements (FFSs) for the purpose of saving life and property for a large portion of the Mid-Atlantic Region.

The primary method for issuing FFWs is with the NWS NEXRAD radars (or WSR-88Ds). Due to inherent limitations with radar sampling of flash-flood producing storms (e.g., earth curvature with distance and beam blockage), flash flood prediction and detection can be problematic within certain areas of the radar sampling volume.

To counteract the limitations of radar, a comprehensive survey was developed and sent to emergency management officials within the NWS Sterling warning area. These officials have compiled detailed listings or maps of flood-prone areas, which include waterways that overflow their banks (where they inundate) and common road closures due to flash flooding and high water from storm runoff.

A graphical “shape” file (or overlay) of these local flood-prone small areas was developed for use in AWIPS. When overlain on radar imagery, forecasters are more cognizant of known flash flood-prone areas in relation to storms.

Testing is underway for ingesting the flash flood-prone sites into the WarnGen database, which will allow for automated inclusion of text for these locations in FFWs and FFSs.