Know Your Severe Weather Advisories

March 3, 2017

Tornado Watch — Conditions are favorable for the development of severe thunderstorms and tornadoes in and close to the watch area. These watches are issued for large areas by the Storm Prediction Center in Norman, Oklahoma, and are usually valid for five to eight hours.
Particularly dangerous situation Tornado Watch – Conditions are favorable for the development of severe thunderstorms and destructive tornadoes in and close to the watch area. These watches are occasionally issued, and usually mean that a major tornado outbreak is possible, where the potential for multiple violent (EF-4 and EF-5) tornadoes exists. These watches are usually issued for a larger area by the Storm Prediction Center in Norman, Oklahoma than a regular Tornado Watch, and are usually valid for a longer period of time than a regular Tornado Watch. This type of watch is usually only reserved for forecast “high-end” severe weather events.

Tornado Warning — Strong rotation in a thunderstorm is indicated by Doppler weather radar or a tornado is sighted by Skywarn spotters. These warnings are currently issued on a polygonal basis.
Particularly dangerous situation Tornado Warning – A Large tornado has been confirmed to be producing damage and is moving into and through the warned area. It is usually issued as the initial tornado warning or as a complete re-issuance of the previous tornado warning. These may also include wording for a Tornado Emergency.

Tornado Emergency — Sent as a “severe weather statement” or a complete re-issuance of the tornado warning, this is an unofficial, high end tornado warning issued when a violent tornado is expected to impact a heavily populated area. Such warnings have been issued for the 1999 F5 Moore, Oklahoma tornado, the 2007 EF5 Greensburg, Kansas tornado, and the 2011 EF4 Tuscaloosa, Alabama tornado.

Severe Thunderstorm Watch — Conditions are favorable for the development of severe thunderstorms in and close to the watch area. A severe thunderstorm contains large damaging hail of 1 inch (2.7 cm) diameter or larger, and/or damaging winds greater than 58 mph (95 km/h or 50 knots) or greater. Isolated tornadoes are also possible but not expected to be the dominant severe weather event. These watches are issued for large areas by the Storm Prediction Center in Norman, Oklahoma, and are usually valid for five to eight hours.
Particularly dangerous situation Severe Thunderstorm Watch – Conditions are favorable for the development of severe thunderstorms in and close to the watch area. Isolated tornadoes are possible but not expected to be the dominant severe weather event, hence these watches are very rarely issued. An expected severe wind event (derecho) is the mostly likely reason for a PDS Severe Thunderstorm Watch to be issued, with widespread winds greater than 90 mph (150 km/h or 80 knots) possible. These watches are usually issued for a larger area by the Storm Prediction Center in Norman, Oklahoma than a regular Severe Thunderstorm Watch, and are usually valid for a longer period of time than a regular Severe Thunderstorm Watch. This type of watch is usually only reserved for forecast “high-end” severe weather events.

Severe Thunderstorm Warning — A severe thunderstorm is indicated by Doppler weather radar or sighted by Skywarn spotters. A severe thunderstorm contains large damaging hail of 1 inch in diameter or larger, and/or damaging winds of 58 mph (93 km/h) or greater. These warnings are currently issued on a polygonal basis.
Significant Weather Advisory – A strong thunderstorm is indicated by Doppler weather radar, containing small hail below 1 inch (2.5 cm) diameter, and/or strong winds of 39–57 miles per hour (63–92 km/h). These advisories are issued on a county by county basis. These are issued as special weather statements written in the style of severe thunderstorm warnings, rather than being an official product itself.

Flash Flood Watch — Conditions are favorable for (flash) flooding in and close to the watch area. These watches are issued by the Weather Forecast Office and are usually issued six to twenty-four hours in advance of expected flood potential. In Canada, a Heavy Rainfall Warning has a similar meaning.
Particularly dangerous situation Flash Flood Watch – Conditions are favorable for an extremely elevated level of severe and life-threatening flash flooding beyond the level of a normal flash flood watch in and close to the watch area. These watches are usually issued for a smaller area by the local WFOs than a regular Flash Flood Watches, which often span multiple county warning areas, and are usually valid for a longer period of time than a regular Flash Flood Watch. This type of watch is usually only reserved for forecast “high-end” flash flood events.

Flash Flood Warning — Flash flooding is occurring, imminent, or highly likely. A flash flood is a flood that occurs within 6 hours of excessive rainfall and that poses a threat to life and/or property. Ice jams and dam failures can also cause flash floods. These warnings are issued on a county by county basis by the local Weather Forecast Office and are generally in effect for up to 6 hours.

Blizzard Warning — Sustained winds or frequent gusts of 35 mph (56 km/h) or greater, considerable falling, and/or blowing snow reducing visibility frequently to 1/4 mile (0.4 km) or less for a period of three hours or more. There are no temperature criteria in the definition of a blizzard but freezing temperatures and 35 mph (56 km/h) winds will create sub-zero (below -18°C) wind chills.

Blizzard Watch — Sustained winds or frequent gusts of 35 mph (56 km/h) or greater, considerable falling, and/or blowing snow reducing visibility frequently to 1/4 mile (0.4 km) or less for a period of three hours or more are possible generally within the next 48 hours.

Winter Storm Warning — Hazardous winter weather conditions that pose a threat to life and/or property are occurring, imminent, or highly likely. The generic term, winter storm warning, is used for a combination of two or more of the following winter weather events; heavy snow, freezing rain, sleet, and strong winds.[10] The Heavy Snow Warning and Sleet Warning have been deprecated in favor of issuing the Winter Storm Warning for Heavy Snow and Winter Storm Warning for Heavy Sleet, respectively.

Winter Storm Watch — Hazardous winter weather conditions including significant accumulations of snow and/or freezing rain and/or sleet are possible generally within 48 hours. These watches are issued by the Weather Service Forecast Office.

Winter Weather Advisory — Hazardous winter weather conditions are occurring, imminent, or likely. Conditions will cause a significant inconvenience and if caution is not exercised, may result in a potential threat to life and/or property. The generic term, winter weather advisory, is used for a combination of two or more of the following events; snow, freezing rain or freezing drizzle, sleet, and blowing snow.[12] The Snow Advisory, and Blowing Snow Advisory have been deprecated in favor of issuing the Winter Weather advisory for Snow and the Winter Weather Advisory for Snow and Blowing Snow, respectively.

Red Flag Warning — A warning issued when conditions are favorable for the rapid spread of wildfires.

Fire Weather Watch — Conditions are expected to become favorable for the rapid spread of wildfires.

Excessive Heat Warning — Extreme heat index making it feel very hot, typically above 105 °F (41 °C) for 3 hours or more during the day for two consecutive days or above 115 °F (46 °C) at any time. Specific criteria vary over different county warning areas.

Heat Advisory — Extreme heat index making it feel hot, typically between 105 and 110 °F (41 and 43 °C) for up to 3 hours during the day and at or above 80 °F (27 °C) at night for two consecutive nights. Specific criteria vary over different county warning areas.

Hard Freeze Warning — Widespread temperatures at or below 28 °F (−2 °C) during the growing season. A hard freeze may occur with or without frost.

Freeze Warning — Widespread temperatures at or below 32 °F (0 °C) during the growing season. A freeze may occur with or without frost.

Frost Advisory — Widespread frost during the growing season. Frost generally occurs with fair skies and light winds at temperatures at or below 36 °F (2 °C).

Dust Storm Warning — Gale-force winds and considerable blowing sand or dust reducing visibilities to 1/4 mile or less.

Blowing Dust Advisory — Strong winds and considerable blowing sand or dust reducing visibilities.

Dense Fog Advisory — Widespread dense fog reducing visibility to less than 1/4 mile (400 m).

Special Weather Statement — An advisory issued when a hazard is approaching advisory level.

**Source — National Weather Service

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