Severe thunderstorm watch
Depending on storm cell intensity, severe thunderstorms can cause damage to structures or vehicles; impairment of vehicle and pedestrian travel; flooding to streets, populated neighborhoods, farmlands and other areas of poor drainage; and in extreme cases, injury or possible fatality to people and animals exposed outdoors (from either repeated hail-induced blunt trauma, wind-generated debris or intense flooding).Residents and travelers in the watch area are advised to immediately undertake safety preparations ahead of the arrival of severe weather.PDS severe thunderstorm watches usually suggest conditions over the approximate area present a widespread threat of destructive hail greater than two inches (5.1 cm) in diameter and winds greater than 75 mph (121 km/h) being generated from the thunderstorm convection, or that downstream conditions favor the development and intensification of a bow echo or derecho moving at 55 mph (89 km/h) or faster.[8][9] SPC meteorologists utilize WarnGen software integrated into the National Centers Advance Weather Interactive Processing System (N-AWIPS) and/or the SPC Product Generator (PRODGEN) to generate the watch statement, which is disseminated through various communication routes accessed by the media and various agencies, on the internet, to NOAA satellites, and over NOAA Weather Radio.The graphical and text Public Watch products—in addition to outlining the approximate affected area, valid time, meteorological and aviation discussions, and other pertinent information—includes language specifying the forecast severe weather threat (e.g., "widespread large hail and isolated very large hail events to 3 inches in diameter likely, scattered damaging wind gusts to 70 mph likely, a tornado or two possible") in the primary hazards list.[7][10][9] The SPC issues Watch Status Messages to designate areas considered to have a continuing severe weather threat, based primarily on the position of surface features (such as cold fronts and drylines)—and the NWS offices decide what counties to remove from the watch (the local offices will almost always follow the SPC recommendation on the status messages).
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