SUPPLEMENTAL INFORMATION...IN GREATER DEPTH

Tuesday, 21 November 2017

PUBLIC WATCHES and WARNINGS:
SEVERE LOCAL STORM TERMINOLOGY


Note: This document is a repeat of that appearing as a Supplementary Information File for last Tuesday, 14 November 2017.


The National Weather Service is mandated by Federal law to monitor, predict and provide necessary information to the public on impending destructive weather or hydrologic events. These events can be grouped into local convective or severe weather, tropical, marine, winter storm and other non-precipitation events. Public statements issued for various winter storm events were previously described in the Week 10 Tuesday Concept for the Day. These statements conform to a specific wording that the National Weather Service uses to alert the public to various hazardous events. In general, the following terms are used:

Most of the watches for the country, to include all severe local storms, are currently issued by the Storm Prediction Center in Norman, OK. Watches for tropical weather events are issued from the National Hurricane Center near Miami, FL. However, warnings for specific local weather events are issued by the local Weather Service Offices when hazardous weather events are occurring in their area of responsibility. The National Weather Service also alerts the public to those windy conditions not associated with thunderstorms with special advisories, watches and warnings as described in Monday's Supplemental Information…In Greater Depth.

The following list includes terminology used by the National Weather Service for those public statements pertaining specifically to severe local storms. These storms are usually convective and contain severe weather with large hail (one-inch diameter or larger) and/or strong winds (58 miles per hour or greater) meeting the specific criteria, as well as tornadoes and flash flooding due to excessive precipitation in thunderstorms. (NOTE: In January 2010, the National Weather Service changed the minimum hail size criterion for severe thunderstorms from three-quarters of an inch to one inch.) A description of those statements used to alert the public for flash floods will accompany Thursday's concept. The other pertinent terms are given:

The Storm Prediction Center issues Convective Outlooks and Second Day Severe Weather Outlooks that are primarily for internal use and outline the geographic regions where severe weather may develop. However, some of the information contained in these guidance products is used on television weathercasts. These Outlooks include levels of risk, ranging from slight to moderate to high.


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Prepared by Edward J. Hopkins, Ph.D., email hopkins@aos.wisc.edu
© Copyright, 2017, The American Meteorological Society.