Public Severe Thunderstorm Watch Notification Message. AC 00-45H Chap 5

5.6.2.2 Public Severe Thunderstorm Watch Notification Message.

The SPC issues a Public Severe Thunderstorm Watch Notification Message when forecasting six or more hail events of 1 in (quarter sized) diameter or greater or damaging winds of 50 kts (58 mph) or greater. The forecast event minimum threshold is at least 2 hours over an area of at least 8,000 mi2. Below these thresholds, the SPC, in collaboration with affected NWS offices, may issue a watch for smaller areas and for shorter periods of time when conditions warrant, and for Convective watches along coastlines, near the Canadian border, and near the Mexican border.

A Public Severe Thunderstorm Watch Notification Message contains three bulleted blocks of information:

• The geographic area of the watch,

• The valid time of the watch, and

• A description of the primary threats anticipated within the watch.

A plain text watch summary is included beneath the bulleted information followed by a more detailed description of the area and axis of the watch.

The SPC includes the term “adjacent coastal waters” when the watch affects coastal waters adjacent to the Pacific/Atlantic coast, the Gulf of Mexico, or the Great Lakes. Adjacent coastal waters refers to a WFO’s near-shore responsibility (out to 20 NM for oceans), except for Convective watches, which include portions of the Great Lakes.

The SPC issues a watch cancellation message when no counties, parishes, independent cities and/or marine zones remaining are in the watch area prior to the expiration time. The text of the message will specify the number and area of the canceled watch.