Severe weather terminology (United States)

Definitions of severe weather alerts

Legend

• — Designated color codes used to identify watches, warnings, advisories or other products in NWS hazard maps and other internal products are indicated alongside the event code;
• — Off-white background indicates product does not have an assigned color code
• SVR — Product event code in bold text; all event codes are indicated following the title of each listed product;
• — Product event code in parenthetical regular text; used for products that have both standard and Specific Area Message Encoding event codes;
• *SAME product codes assigned to each term for NOAA Weather Radio broadcasts are included in products that do not have a specified code are identified where applicable, as defined by NOAA, as:

  Severe local storms

• 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 capable of producing 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 strong to violent tornadoes exists. Usually only reserved for forecast "high-end" severe weather events, this type of watch is usually valid for a longer period of time and issued for a larger area by the Storm Prediction Center in Norman, Oklahoma, than a typical tornado watch.
• Tornado warning – Strong rotation in a thunderstorm has been indicated by Doppler weather radar or a tornado has been sighted by Skywarn spotters or other persons. These warnings are currently issued on a polygonal basis, are usually issued for a duration of 30 minutes, and can be issued without either a tornado watch or a severe thunderstorm watch being already in effect. Tornado warnings may be issued in combination with a Special Marine Warning if the storm affects nearshore or coastal waters.
• :Particularly dangerous situation tornado warning – A large tornado has been confirmed to be producing damage and is moving into and through the warned area. The PDS wording can be incorporated into the text of a tornado warning, either upon its initial issuance or in a "severe weather statement" providing updated information on the storm, when a considerable tornado debris signature is detected on radar or a large tornado is visually observed.
• :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, among other significant tornado events, the F5-rated tornado that destroyed much of Bridge Creek, Moore and portions of southeastern Oklahoma City, Oklahoma on May 3, 1999 ; the EF5 tornado that destroyed much of Greensburg, Kansas on May 4, 2007; the EF4 tornado that hit Tuscaloosa, Alabama on April 27, 2011 ; the EF5 tornado that affected Moore and adjacent southern portions of the Oklahoma City area on May 20, 2013; the May 31, 2013 tornado system that went over the Oklahoma City area through portions of Canadian County near and south of the densely populated city of El Reno; the EF4 tornado that affected western portions of the Kansas City area on May 28, 2019; the EF4 tornado that affected several areas in Mississippi on April 12, 2020; and two long-track EF4 tornadoes that affected the Mid-South region on December 10–11, 2021. This enhanced form of a tornado warning is issued mainly by Weather Forecast Offices within the National Weather Service's Central and Southern Region Headquarters; a tornado emergency is the highest level of a three-tiered Impact Based Warning system for tornadoes used by all WFOs within the Central Region Headquarters, and eight others within the Eastern, Southern and Western Regions.
• 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 diameter or larger, and/or damaging winds greater than 58 mph 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 is the mostly likely reason for a PDS severe thunderstorm watch to be issued, with widespread winds greater than 90 mph possible. These watches are usually valid for a longer period of time and are issued for a larger area by the Storm Prediction Center in Norman, Oklahoma than a typical severe thunderstorm watch. This type of watch is usually only reserved for forecast "high-end" severe weather events. If, however, tornadoes are expected to be a major weather threat in addition to the preceding criteria, then a standard tornado watch would be issued instead.
• Severe thunderstorm warning – A severe thunderstorm is indicated by Doppler weather radar or sighted by Skywarn spotters or other persons, such as local law enforcement. A severe thunderstorm contains large damaging hail of in diameter or larger, and/or damaging winds of or greater. These warnings are currently issued on a polygonal basis, are usually issued for a duration of 30 minutes to one hour, and can be issued without a severe thunderstorm watch or a tornado watch being already in effect. Because severe thunderstorms can produce tornadoes with little or no advance warning, a severe thunderstorm warning may be upgraded to a tornado warning if strong rotation is indicated or a tornado is sighted. Lightning frequency is not a criterion for issuing a severe thunderstorm warning. Severe thunderstorm warnings may be issued in combination with a special marine warning if the storm affects nearshore or coastal waters.
• :Particularly dangerous situation severe thunderstorm warning – Issued within the initial severe thunderstorm warning or as a complete re-issuance of the previously issued warning, a PDS severe thunderstorm warning indicates a significant severe thunderstorm has been detected by Doppler weather radar and/or observed by Skywarn spotters or other civil defense personnel, and is moving into and through the warned area with the capability of causing significant property damage, and severe injury or fatality to people or animals caught in the storm's path. These may be issued for an ongoing severe wind event containing winds greater than 80 mph, and/or extreme hail of diameter or larger over a wide area. Specific to this product, the boilerplate PDS wording placed between the storm summary and hazard information in the warning text was replaced in July 2021 with the notation "this is a destructive storm for," highlighting specific locations under greatest threat from extreme winds or hail accompanying the warned storm.
• :Severe thunderstorm emergency – Sent as a "severe weather statement" or a complete re-issuance of the severe thunderstorm warning, this is an unofficial, high-end severe thunderstorm warning that is occasionally issued when a significant severe thunderstorm is imminent or impacting a highly populated area. First issued by the National Weather Service office in Cheyenne, Wyoming on August 16, 2019, the National Weather Service does not currently maintain a concrete criterion for issuance, although Weather Forecast Offices that issue or have issued such warnings may use the same criteria meriting a PDS Severe Thunderstorm Warning to indicate life-threatening severe weather conditions that will impact a densely populated area.
• Severe weather statement – A statement issued to provide updated information for active severe thunderstorm and tornado warnings to the public and emergency managers, with revised information including reports of observed severe weather and the approximate location of the storm cell at the time of the statement's issuance. Severe Weather Statements may include notices of cancellation, or notices of a warning being allowed to expire because the prompting storm has weakened below severe criteria.
• Flash flood watch – Conditions are favorable for flash flooding or urban flooding in and close to the watch area within the next 36 hours. These watches are issued by the Weather Forecast Office and are usually issued six to 24 hours in advance of expected flood potential.
• :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 typical flash flood watches, which often span multiple county warning areas, and are usually valid for a longer period of time. This type of watch is usually only reserved for forecast "high-end" flash flood events.
• Flash flood warning – Flash flooding—either indicated by Doppler weather radar or stream gauges, or reported by Skywarn spotters or local emergency officials—is occurring, imminent, or highly likely in the short term. A flash flood is a flood that occurs within six hours of excessive rainfall and poses a threat to life and/or property, especially in low-lying or flood prone areas ; 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 two to six hours, although particularly during tropical cyclones a warning may last for a longer period of time, and occasionally last shorter than two hours.
• :Particularly dangerous situation flash flood warning – Issued within the initial flash flood warning or as a complete re-issuance of the previously issued warning, this indicates widespread, life-threatening flash flooding—caused by excessive rainfall, ice jams or imminent dam failures—has been indicated by Doppler weather radar, emergency personnel or trained observers over a broadly populated area.
• :Flash flood emergency – A flash flood emergency is a high-end usage of the flash flood warning. The flash flood emergency term is used when widespread flooding is occurring, and either, multiple water rescues have been reported in the past few hours, or if highly populated regions are undergoing significant flash flooding likely to cause loss of life and property. This terminology is more widely used during hurricanes with high amounts of moisture.
• Flash flood statement – A hydrological weather statement issued to provide updated information on active flash flood watches and warnings to the public and emergency managers.