It is very important to understand the difference between a severe weather WATCH and WARNING. WATCHES and WARNINGS are issued for Tornadoes, Severe Thunderstorms, and Flash Floods.
The term WATCH implies that people should be alert for the possibility of severe weather or flash flooding, and have a plan of action in case a storm threatens.
When a WARNING is issued by the National Weather Service, this means that a tornado, severe thunderstorm, or flash flood has been detected by radar or observed by trained storm spotters or public officials. These warnings are for short-fuse events that only last an hour or so. People in the path of the storm are expected to take action to protect life and property when the term WARNING is heard.
Winter Storm Warning: Issued when a combination of heavy snow, heavy freezing rain, or heavy sleet is expected. Winter Storm Warnings are usually issued 6 to 24 hours before the event is expected to begin.
Winter Storm Watch: Alerts the public to the possibility of a blizzard, heavy snow, freezing rain, or heavy sleet. Winter Storm Watches are usually issued 12 to 36 hours before the beginning of a Winter Storm.
Winter Storm Outlook: Issued prior to a Winter Storm Watch. The outlook is given when forecasters believe winter storm conditions are possible and are usually issued 48 to 60 hours in advance of a winter storm.
Blizzard Warning: Issued for sustained or gusty winds of 35 mph or more, and falling or blowing snow creating visibilities at or below 1/4 mile; these conditions should persist for at least three hours.
Wind Chill Warning: Issued when wind chill temperatures are life threatening, and expected to be less than 34 degrees below zero.
Wind Chill Advisory: Issued when wind chill temperatures could be life threatening if action is not taken and expected to be between 20 below and 34 degrees below zero.
Winter Weather Advisories: Issued for accumulations of snow, freezing rain, freezing drizzle, and sleet which will cause significant inconvenience and moderately dangerous conditions.
Dense Fog Advisory: Issued when fog will reduce visibility to 1/4 mile or less over a widespread area.
Snow Flurries: Light snow falling for short durations. No accumulation or light dusting is all that is expected.
Snow Showers: Snow falling at varying intensities for brief periods of time. Some accumulation is possible.
Snow Squalls: Brief, intense snow showers accompanied by strong, gusty winds. Accumulation may be significant. Snow squalls are best known in the Great Lakes region.
Blowing Snow: Wind-driven snow that reduces visibility and causes significant drifting. Blowing snow may be snow that is falling and/or loose snow on the ground picked up by the wind.
Sleet: Rain drops that freeze into ice pellets before reaching the ground. Sleet usually bounces when hitting a surface and does not stick to objects. However, it can accumulate like snow and cause a hazard to motorists.
Freezing Rain: Rain that falls onto a surface with a temperature below freezing. This causes it to freeze to surfaces, such as trees, cars, and roads, forming a coating or glaze of ice. Even small accumulations of ice can cause a significant hazard.
Tornado Watch: Conditions are favorable for the development of tornadoes in and close to the watch area. Watches are usually in effect for several hours, with 6 hours being the most common.
Tornado Warning: Tornado is indicated by radar or sighted by storm spotters. The warning will include where the tornado is and what towns will be in its path.
Severe Thunderstorm Watch: Conditions are favorable for the development of severe thunderstorms in and close to the watch area. Watches are usually in effect for several hours, with 6 hours being the most common.
Severe Thunderstorm Warning: Issued when a thunderstorm produces hail 1 inch or larger in diameter and/or winds which equal or exceed 58 mph. Severe thunderstorms can result in the loss of life and/or property. Information in this warning includes: where the storm is, what towns will be affected, and the primary threat associated with the storm.
Severe Weather Statement: Issued when the forecaster wants to follow up a warning with important information on the progress of severe weather elements.
Flash Flood Watch: Indicates that flash flooding is possible in and close to the watch area. Those in the affected area are urged to be ready to take quick action if a flash flood warning is issued or flooding is observed.
Flash Flood Warning: Signifies a dangerous situation where rapid flooding of small rivers, streams, creaks, or urban areas are imminent or already occurring. Very heavy rain that falls in a short time period can lead to flash flooding, depending on local terrain, ground cover, degree of urbanization, degree of man-made changes to river banks, and initial ground or river conditions.
Urban and Small Stream Flood Advisory: Alerts the public to flooding which is generally only an inconvenience and does not pose a threat to life and/or property. Issued when heavy rain will cause flooding of streets and low-lying places in urban areas, or if small rural or urban streams are expected to reach or exceed bankfull.
Flash Flood Statement: Used as a follow-up to Flash Flood Warnings and Watches. The statement will contain the latest information on the event.
Special Weather Statement: Issued to convey update information about severe weather.
Short Term Forecast (Nowcast): A short term forecast designed to give specific, detailed forecast information for the next 1 to 6 hours on a county-by-county basis. Both routine and near-severe information are contained in these forecasts which are routinely issued several times per day, and more often during busy weather periods.
Local Storm Report: Used to distribute severe weather reports to the media, emergency managers, and other NWS offices. It is issued as reports are received, and may also be issued as a collection of all reports received after an event is over. Delayed reports are disseminated after an event is over as well.
Weather Watch Redefining Statement: Issued for every tornado and severe thunderstorm watch that affects a state. It lists the type of watch, its corresponding number, the ending time of the watch, all counties included in the watch, and large cities and towns in the watch area.
This and more information can be found at the National Oceanic and Atmospheric Administration Web site at www.noaa.gov