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.

Geographic coverage of severe thunderstorm watches (which ranges from 20,000–40,000 square miles [52,000–104,000 km2] on average, encompassing portions of one or more states) vary based on the size of the land area under threat, the duration of severe weather risk, and the forward motion of the parent storm system and associated surface boundaries.

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 Storm Prediction Center, in conjunction with local NWS Weather Forecast Offices, issues component watch products to communicate the approximate area, primary hazards and other pertinent information about the severe thunderstorm watch to the public, NOAA meteorologists, emergency management and aviation personnel.

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).

[14] Watches are disseminated to the public through terrestrial television and radio stations,[15] and online media outlets.