NOAA/National Weather Services' storm-based warnings

The National Oceanic and Atmospheric Administration's (NOAA) National Weather Service (NWS) has long issued tornado, severe thunderstorm, and flash flood warnings for entire counties or parishes. For the past several years, these warnings have included information on a smaller “warning polygon” for the area of greatest risk. Issued by latitude and longitude points, these sub-county ‘polygon' warnings are increasingly used by graphical applications for television, the Internet, and even cell phones.

During 2005, several NWS Weather Forecast Offices (WFOs) participated in a test to expand the use of these smaller-than-county areas (polygons) for convective warnings. These offices were asked to put less emphasis on county boundaries and greater emphasis on the polygon. The test demonstrated several positive outcomes of polygon warnings, including reduction in the number of people required to take cover. It also allowed emergency management and other disaster response agencies served by these WFOs to focus their limited resources on smaller areas.

In view of these benefits, NWS plans to move steadily towards polygon implementation over the next 3 years. This paper will discuss the operational impacts associated with this change, including issues related to dissemination, software, and verification. It will also provide the latest proposed schedule for polygon warning implementation.