Severe weather terminology (United States) explained

This article describes severe weather terminology used by the National Weather Service (NWS) in the United States. The NWS is a government agency operating as an arm of the National Oceanic and Atmospheric Administration (NOAA) branch. It defines precise meanings for nearly all of its weather terms.

This article describes NWS terminology and related weather scales used by the agency. Some terms may be specific to certain cities or regions. Specific Area Message Encoding (SAME) product codes assigned to each term for NOAA Weather Radio (NWR) broadcasts are included in (following the title of the described alert type if used) products that do not have a specified code are identified where applicable as Non-Precipitation Warnings/Watches/Advisories (NPW), Coastal Flood Warnings/Watches/Advisories (CFW), Marine Weather Statement (MWS), Mesoscale Discussion (MCD) or Severe Weather Warnings/Watches/Advisories (WSW) as defined by NOAA.

Definitions of severe weather alerts

The NWS divides severe weather alerts into several types of hazardous/hydrologic events:

  1. Severe local storms – Short-fused, small-scale hazardous weather or hydrologic events produced by thunderstorms (including large hail, damaging winds, tornadoes, and flash floods).
  1. Winter storms – Weather hazards associated with freezing or frozen precipitation (freezing rain, sleet, and/or snow), or combined effects of winter precipitation and strong winds.
  1. Fire weather – Weather conditions that contribute to an increased risk and help cause the spread of wildfires.
  1. Flooding – Hazardous hydrological events resulting in temporary inundation of land areas not normally covered by water, often caused by excessive rainfall.
  1. Coastal/lakeshore hazards – Hydrological hazards that may affect property, marine or leisure activities in areas near ocean and lake waters including high surf and coastal or lakeshore flooding, as well as rip currents.
  1. Marine hazards – Hazardous events that may affect marine travel, fishing and shipping interests along large bodies of water, including hazardous seas and freezing spray.
  1. Tropical cyclone hazards – Hazardous tropical cyclone events that may affect property in inland areas or marine activities in coastal waters, resulting in wind damage, storm surge, tornadoes and flooding rain.
  1. Non-precipitation hazards – Weather hazards not directly associated with any of the above including extreme heat or cold, dense fog, high winds, and river or lakeshore flooding.

Severe local storms

Particularly dangerous situation tornado watch (TOA) – 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 (EF4 and EF5) 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.[3]

Particularly dangerous situation tornado warning (TOR) – 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. (The PDS wording is also incorporated into the boilerplate precautionary/preparedness action statement for tornado emergencies.)[1] [5]

Tornado emergency (SVS) – 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 (during which the product was conceived by the NWS Forecast Office in Norman); the EF5 tornado that destroyed much of Greensburg, Kansas on May 4, 2007; the EF4 tornado that hit Tuscaloosa, Alabama on April 27, 2011 (one of 16 tornado emergencies issued during the associated regional outbreak, which holds the all-time record for the most tornado emergencies issued in a 24-hour period); 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 (one of which traveled a 165.6miles path through portions of western Kentucky, including the city of Mayfield) on December 10–11, 2021.[6] [7] 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.[5] [1]

Particularly dangerous situation severe thunderstorm watch (SVA) – 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 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.[3] If, however, tornadoes are expected to be a major weather threat in addition to the preceding criteria, then a standard tornado watch (generally not a PDS watch) would be issued instead.[1]

Particularly dangerous situation severe thunderstorm warning (SVR) – 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 (either by a derecho, or from an intense wind core or downburst within a squall line or supercell) containing winds greater than 80 mph (124 km/h or 70 knots), and/or extreme hail of 3inches diameter or larger over a wide area. Specific to this product, the boilerplate PDS wording ("this is a particularly dangerous situation") 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 (SVS) – 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,[10] 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.

Particularly dangerous situation flash flood watch (FFA) – 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.

Particularly dangerous situation flash flood warning (FFW) – 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 (FFS) – 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 (an example is Hurricane Harvey in 2017, during which multiple flash flood emergencies were issued for portions of southeast Texas and southern Louisiana, including the Houston area).

Deprecated

Winter precipitation

Deprecated

Fire weather

Extreme red flag warning (FWA) – Conditions for wildland fire combustion, rapid growth and behavior are extremely dangerous, due to very dry fuels, very low humidity levels, and strong winds. Introduced in October 2019, it is analogous to particularly dangerous situation wording for severe weather watches and warnings and superseded such wording occasionally applied to red flag warnings previously.

Flooding

Coastal/lakeshore hazards

Seiche warning (CFW) – Rapid, large fluctuations in water level in the Great Lakes (similar to the sloshing in a bath tub) caused by storms or high winds, resulting in both lakeshore flooding and critically low water levels at different times. Issued as a lakeshore flood warning with reference of being a seiche warning.

Marine hazards

Particularly dangerous situation special marine warning (SMW) – A warning to mariners of hazardous weather conditions that present a considerable threat to life and property.

Small craft advisory for rough bar (SCARB) – Waves in or near harbor or river entrances are expected to be especially hazardous to mariners due to the interaction of swell, tidal and/or river currents in relatively shallow water. Thresholds governing the issuance of this type of small craft advisory vary among local geographic areas, and are based upon locally determined parameters such as wave steepness, wind speed and direction, and local bathymetry.

Small craft advisory for winds (SCAW) – Wind speeds may pose potential hazards for maritime activity. Wave heights must remain below standard small craft advisory criteria to merit the issuance of a wind-based advisory. Thresholds necessitating the issuance of wind-based small craft advisories are determined by the accordant NWS Regional Headquarters.

Brisk wind advisory (NPW) – Sea or lake ice is expected and may be hazardous to small marine craft. May be issued as a Small Craft Advisory with reference of being a brisk wind advisory. This advisory is not issued by WFOs serving the Great Lakes region due to the prevalence of ice floes during winter in the lake bodies.

Temperature

See also Windchill section below.

Windchill

Particularly dangerous situation wind chill warning (NPW) – Extremely low wind chills of -30°F or lower creating an enhanced risk of frostbite, hypothermia and death are imminent or occurring.

Aviation

The following advisories are issued by the National Weather Service Aviation Weather Center (outside of Alaska) or Alaska Aviation Weather Unit. Atmospheric ash plume advisories/warnings are also issued by the United States Geological Survey (Aviation Color Codes).

VAAs are standardized worldwide by the International Civil Aviation Organization.

Tropical weather

Other hazards

Particularly dangerous situation special weather statement (SPS) – An enhanced advisory issued for hazards that do not have a specific code of their own, and pose an exceptionally high risk of damage and loss of life.

Non-meteorological hazards and administrative messages

The National Weather Service also relays messages for non-weather related hazardous events in text products and NOAA Weather Radio broadcasts:[50] [51]

Wind and tropical cyclones

Wind alerting is classified into groups of two Beaufort numbers, beginning at 6–7 for the lowest class of wind advisories. The last group includes three Beaufort numbers, 14–16. The actual alerts can be categorized into three classes: maritime wind warnings, land wind warnings, and tropical cyclone warnings. Advisory-force and gale-force winds will not trigger a separate wind advisory or warning if a Blizzard warning is already in effect. However, as seen with Hurricane Sandy, if widespread high wind warnings are in effect prior to the issuance of a blizzard warning, the high wind warnings may be continued.

Wind alert terms and signals

Wind speed Marine or Beach Hazard Warning Land Warning Tropical Cyclone Warning(s) Flags Lights Beaufort force
25 to 38 mph (22 to 33 knots) Small craft advisory[52] Wind Advisory or Small craft advisory 6–7
39 to 54 mph (34 to 47 knots) Gale warning[53] Tropical storm warning8–9
55 to 73 mph (48 to 63 knots) Storm warning[54] High wind warning Tropical storm warning† 10–11
74–110 mph (64 to 99 knots) Hurricane Force Wind Warning[55] 12–13
Over 110 mph (100+ knots) Hurricane Force Wind Warning Major hurricane warning14–16

*

Hazardous weather risks

The various weather conditions described above have different levels of risk. The National Weather Service uses a multi-tier system of weather statements to notify the public of threatening weather conditions. These statements are used in conjunction with specific weather phenomena to convey different levels of risk. In order of increasing risk, these statements are:

Convective outlook categories

The Storm Prediction Center (SPC) issues Day 1, Day 2, and Day 3 Convective Outlooks depicting forecast areas of general (non-severe) and severe thunderstorm threats across the contiguous United States, along with a text narrative discussion consisting of a plain-language summary of the threat type(s) and timing focused on areas of highest risk, and a technical discussion written in scientific language that usually includes a synoptic overview of convective patterns as well as, if necessary, a geographically specific narrative of meteorological reasoning and justification for the type of coverage and intensity applicable to the severe thunderstorm threat.

The categorical forecast in the Day 1-3 Convective Outlooks—which estimates a severe weather event occurring within 25miles of a point and derives the attendant risk areas from probability forecasts of tornadoes, damaging winds, and large hail on Days 1 and 2, and a combined severe weather risk on Day 3—specifies the level of overall severe thunderstorm risk via numbers, descriptive labeling, and colors as follows: (The Day 4-8 Convective Outlook assesses the percentile probability of severe thunderstorm activity during that period at the 15% and 30% likelihood.)[62]

Convective thunderstorm risk categories
Risk categoryMap codeDescription
General or non-severe thunderstormsTSTM Delineates, to the right of a line, where a 10% or greater probability of thunderstorms is forecast during the valid period. While severe weather is not anticipated, thunderstorms occurring in areas under general risk can occasionally reach severe intensity.
Marginal1-MRGL An area of severe storms of either limited organization and longevity, or very low coverage and marginal intensity.
Slight2-SLGT An area of organized severe storms, which is not widespread in coverage with varying levels of intensity.
Enhanced3-ENH An area of greater (relative to Slight risk) severe storm coverage with varying levels of intensity.
Moderate4-MDT An area where widespread severe weather with several tornadoes and/or numerous severe thunderstorms is likely, some of which should be intense. This risk is usually reserved for days with several supercells producing intense tornadoes and/or very large hail, or an intense squall line with widespread damaging winds.
High5-HIGH An area where a severe weather outbreak is expected from either numerous intense and long-tracked tornadoes or a long-lived derecho-producing thunderstorm complex that produces hurricane-force wind gusts and widespread damage. This risk is reserved for when high confidence exists in widespread coverage of severe weather with embedded instances of extreme severe (i.e., violent tornadoes or very damaging convective wind events).

Warning impact statements

Many of the National Weather Service's Weather Forecast Offices—primarily those located within the Central and Southern Region Headquarters—use a multi-tier impact-based warning (IBW) system of impact statements to notify the public and emergency management officials of the severity of specific severe weather phenomena. The impact statement system—initially used only for tornado and severe thunderstorm warnings—was first employed by the WFOs in Wichita and Topeka, Kansas, and Springfield, St. Louis and Kansas City/Pleasant Hill, Missouri beginning with the 2012 Spring severe weather season, eventually expanded to include 33 additional National Weather Service Weather Forecast Offices within the Central Region Headquarters in 2013, and then to eight additional offices within the Eastern, Southern and Western Regions in the spring of 2014.[5] Since July 28, 2021 (or as late as August 2 in certain County Warning Areas), the NWS has incorporated categorical “CONSIDERABLE” and “DESTRUCTIVE" damage threat indicators (similar to those incorporated into tornado warning products since the implementation of the Impact Based Warning system) at the bottom of the product text of certain severe thunderstorm warnings and related Severe Weather Statements to indicate higher-end hail and/or wind events caused by the parent storm cell.[63] [64]

Under this system, the warning product will include text denoting the specific hazard (i.e., 60 mph wind gusts and quarter size hail) and applicable sourcing (either via indication from Doppler weather radar, or visual confirmation from storm spotters or other emergency management officials) and the level of impact to life and/or property. In order of increasing risk by warning type, these statements—which may be modified at the discretion of the regional forecast office—are:[65]

Tornado Warning
Tornado impact attributeImpact statement(s)
Landspout / weak tornado
  • Expect damage to mobile homes, roofs, and vehicles.
  • Alternate wording: Expect damage to mobile homes, roofs, screen enclosures, carports, vehicles and trees along the path of the tornado.
"Base" (default)
  • Flying debris will be dangerous to those caught without shelter.
  • Mobile homes will be damaged or destroyed.
  • Damage to roofs, windows and vehicles will occur.
  • Tree damage is likely.
Considerable
  • You are in a life-threatening situation.
  • Flying debris may be deadly to those caught without shelter.
  • Mobile homes will be destroyed.
  • Considerable damage to homes, businesses, and vehicles is likely and complete destruction is possible.
Catastrophic
  • You are in a life-threatening situation.
  • Flying debris may be deadly to those caught without shelter.
  • Mobile homes will be destroyed.
  • Considerable damage to homes, businesses, and vehicles is likely and complete destruction is possible.
Severe Thunderstorm Warning
Thunderstorm attributeImpact statement(s)
Wind (60 mph)
  • 1) Expect damage to roofs, siding, and trees.


Alternate wording:

  • 1) Tree and power line damage is likely.
  • 2) Expect damage to some roofs, siding, carports, and fences.
Wind (70 mph)
  • 1) Expect considerable tree damage.
  • 2) Damage is likely to mobile homes, roofs, and outbuildings.


Alternate wording:

  • 1) Expect considerable tree and power line damage.
  • 2) Damage is likely to mobile homes, roofs, screen enclosures, carports, and outbuildings.
Wind (80 mph)
  • 1) Flying debris will be dangerous to those caught without shelter.
  • 2) Mobile homes will be heavily damaged.
  • 3) Expect considerable damage to roofs, windows, and vehicles.
  • 4) Extensive tree damage and power outages are likely.


Alternate wording:

  • 1) Flying debris will be dangerous to those caught without shelter.
  • 2) Mobile homes will likely be heavily damaged.
  • 3) Considerable damage to roofs, windows, and vehicles is likely.
  • 4) Expect considerable tree and power line damage.
Wind (90 mph)
  • 1) You are in a life-threatening situation.
  • 2) Flying debris may be deadly to those caught without shelter.
  • 3) Mobile homes will be heavily damaged or destroyed.
  • 4) Homes and businesses will have substantial roof and window damage.
  • 5) Expect extensive tree damage and power outages.


Alternate wording:

  • 1) You are in a life-threatening situation.
  • 2) Flying debris may be deadly to those caught without shelter.
  • 3) Mobile homes will be heavily damaged or destroyed.
  • 4) Homes and businesses will likely have substantial roof and window damage.
  • 5) Expect extensive tree damage and power line damage with widespread power outages.
Wind (100 mph+)
  • 1) You are in a life-threatening situation.
  • 2) Flying debris may be deadly to those caught without shelter.
  • 3) Mobile homes will be destroyed.
  • 4) Expect considerable damage to homes and businesses.
  • 5) Expect extensive tree damage and power outages.


Alternate wording:

  • 1) You are in a life-threatening situation.
  • 2) Flying debris may be deadly to those caught without shelter.
  • 3) Mobile homes will be heavily damaged or destroyed.
  • 4) Homes and businesses will likely have substantial roof and window damage.
  • 5) Expect extensive tree damage and power line damage with widespread power outages.
Hail (1.00" to 1.25")
  • Damage to vehicles is expected.


Alternate wording: Damage to vehicles is likely.

Hail (1.50" to 2.50")
  • 1) People and animals outdoors will be injured.
  • 2) Expect damage to roofs, siding, windows, and vehicles.


Alternate wording:

  • 1) People and animals outdoors will likely be injured.
  • 2) Expect damage to roofs, siding, screen enclosures, windows, and vehicles.
Hail (2.75"+)
  • 1) People and animals outdoors will be severely injured.
  • 2) Expect shattered windows, extensive damage to roofs, siding, and vehicles.


Alternate wording:

  • 1) Severe injuries are likely with hail this size.
  • 2) Expect shattered windows, extensive damage to roofs, siding, screen enclosures, and vehicles.

Media distribution

Hazardous weather forecasts and alerts are provided to the public using the NOAA Weather Radio All Hazards system and through news media such as television, radio and internet sources. Many local television stations have overlay graphics which will either show a map or a list of the affected areas. The most common NWS weather alerts to be broadcast over NOAA Weather Radio using SAME technology are described in the following table:

Common NWS weather alerts
Event nameCodeDescription
Tornado watch TOA Also known as a red box. Conditions are favorable for the development of severe thunderstorms producing tornadoes in and close to the watch area. Watches are usually in effect for several hours, with six hours being the most common (also automatically indicates a Severe Thunderstorm Watch).
Tornado warning TOR A tornado is indicated by radar or sighted by storm spotters. The warning will include where the tornado is and what locations will be in its path (also automatically indicates a Severe Thunderstorm Warning).
Severe thunderstorm watch SVA Also known as a yellow box or blue box. 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 six hours being the most common.
Severe thunderstorm warning SVR Issued when a thunderstorm produces hail 1inches or larger in diameter and/or winds which equal or exceed 58mph. Severe thunderstorms can result in the loss of life and/or property. Information in this warning includes: where the storm is, what locations will be affected, and the primary threat(s) associated with the storm. Tornadoes can also and do develop in severe thunderstorms without the issuance of a tornado warning.
Severe weather statement SVS Issued when the forecaster wants to follow up a warning with important information on the progress of severe weather elements.
Special marine warning SMW Issued when a thunderstorm over water produces hail 1inches or larger in diameter, causes winds which equal or exceed 39mph, or is capable of producing or currently producing a waterspout. Information in this warning includes: where the storm is, what waters will be affected, and the primary threat associated with the storm.
Flood watch FLA Issued as either a Flood Watch or a River Flood Watch. Indicates that flooding is possible in and close to the watch area. Those in the affected area are urged to be ready to take action if a flood warning is issued or flooding is observed.
Flood warning FLW Issued as either a Flood Warning or a River Flood Warning. Indicates that flooding is imminent or occurring in the warned area.
Flash flood watch FFA Also known as a green box. 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 FFW 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.
Blizzard watch BZA An announcement for specific areas that blizzard conditions are possible.
Blizzard warning BZW A warning that sustained winds or frequent gusts of 30 kn (35 mph or 56 km/h) or higher and considerable falling and/or blowing snow reducing visibilities to NaNmiles or less are expected in a specified area. A blizzard warning can remain in effect when snowfall ends but a combination of strong winds and blowing snow continue, even though the winter storm itself may have exited the region (also automatically indicates a Winter Storm Warning for Heavy Snow and Blowing Snow).
Tropical storm watch TRA An announcement for specific areas that tropical storm conditions are possible within 48 hours.
Tropical storm warning TRW A warning that sustained winds within the range of 34 to 63 kn (39 to 73 mph or 63 to 117 km/h) associated with a tropical cyclone are expected in a specified area within 36 hours or less.
Hurricane watchHUA An announcement for specific areas that hurricane conditions are possible, and tropical storm conditions are possible within 48 hours.
Hurricane warning HUW A warning that sustained winds 64 kn (74 mph or 118 km/h) or higher associated with a hurricane are expected, and tropical storm conditions are expected within 36 hours in a specified area. A hurricane warning can remain in effect when dangerously high water or a combination of dangerously high water and exceptionally high waves continue, even though winds may be less than hurricane force (also automatically indicates a Tropical Storm Warning).

Related weather scales as defined by the NWS

The NWS uses several scales in describing weather events or conditions. Several common scales are described below.

Hail diameter sizes

See main article: Hail. The size of individual hailstones that reach surface level is determined by speed of the updraft which create the individual ice crystals at atmospheric levels. Larger hailstones are capable of producing damage to property, and particularly with very large hailstones, resulting in serious injury or death due to blunt-force trauma induced by the impact of the hailstones. Hailstone size is typically correspondent to the size of an object for comparative purposes.

Hailstone size Measurement (in) Measurement (cm) Updraft Speed (mph) Updraft Speed (m/s)
0.25 0.6 40 18
0.75 1.9 44 20
quarter1.00 2.5 49 22
1.25 3.2 54 24
1.50 3.8 60 27
1.75 4.4 64 29
hen egg† 2.00 5.1 69 31
2.50 6.4 77 34
2.75 7.0 81 36
3 7.6 84 38
4 10.1 98 44
4.50 11.4 103 46
Computer CD/DVD512.7

* Begins hail sizes within the severe hail criterion.
Begins hail sizes within the Storm Prediction Center's significant severe criterion.

Beaufort wind scale

See main article: Beaufort scale.

The Beaufort scale is an empirical measure that correlates wind speed to observed conditions at sea or on land.

Wind category Beaufort number Wind speed Conditions
Advisory-force 6 25–31 mph
(40–50 km/h)
Large branches in motion; whistling in telephone wires.
Advisory-force 7 32–38 mph
(51–62 km/h)
Whole trees in motion; inconvenience felt walking against wind.
Gale-force 8–9 39–54 mph
(63–88 km/h)
Twigs break off trees; wind generally impedes progress. Tropical storm criteria begin.
Storm-force 10–11 55–73 mph
(89–117 km/h)
Damage to chimneys and television antennas; pushes over shallow-rooted trees. Severe thunderstorm criteria begin (58 mph (93 km/h)).
Hurricane-force 12–13 74–112 mph
(118–181 km/h)
Peels shingles off roofs; windows broken if struck by debris; trees uprooted or snapped; mobile homes severely damaged or overturned; moving cars pushed off-road. Hurricane criteria begin.
14–16 113–237 mph
Roofs torn off houses; cars lifted off ground; trees defoliated and sometimes debarked. Major hurricane criteria begin.

:Beaufort levels above 12 are non-standard in the United States. Instead, the Saffir–Simpson hurricane scale (Category 1, Category 2, etc.) is used.

Enhanced Fujita tornado intensity scale

See main article: Enhanced Fujita scale. The Enhanced Fujita scale, an updated version of the original Fujita scale that was developed by Ted Fujita with Allen Pearson, assigns a numerical rating from EF0 to EF5 to rate the damage intensity of tornadoes. EF0 and EF1 tornadoes are considered "weak" tornadoes, EF2 and EF3 are classified as "strong" tornadoes, with winds of at least major hurricane force, where EF4 and EF5 are categorized as "violent" tornadoes, with winds corresponding to category 5 hurricane winds and rising to match or exceed the strongest tropical cyclones on record. The EF scale is based on tornado damage (primarily to buildings), which makes it difficult to rate tornadoes that strike in sparsely populated areas, where few man-made structures are found. The Enhanced Fujita scale went into effect on February 1, 2007.

EF number Wind speed Comparable hurricane winds Damage Examples
EFU N/A N/A No surveyable damage. Intensity cannot be determined due to a lack of information. This rating applies to tornadoes that traverse areas where no structures or trees were impacted to allow a damage indicator to be assigned, cause damage in an area that cannot be accessed by a survey, or cause damage that cannot be differentiated from that of another tornado.[66] N/A
EF0 65–85 mph (105–137 km/h) Severe tropical storm – Category 1 Light damage. Peels surface off some roofs; some damage to gutters or siding; branches broken off trees; shallow-rooted trees pushed over. Philadelphia (1999); Jacksonville (2004); St. Louis (2007); Windsor, Ontario (2009); Minneapolis (2009)
EF1 86–110 (138–178 km/h) Category 1–2 Moderate damage. Roofs severely stripped; mobile homes overturned or badly damaged; loss of exterior doors; windows and other glass broken. Houston, (1992), Miami (1997), Bronx, New York (2010); Brooklyn and Queens, New York (2010); Minneapolis (2011)
EF2 111–135 (179–218 km/h) Category 3 Considerable damage. Roofs torn off well-constructed houses; foundations of frame homes shifted; mobile homes completely destroyed; large trees snapped or uprooted; light-object missiles generated; cars lifted off ground. Salt Lake City (1999); Brooklyn (2007); Atlanta (2008); Vaughan, Ontario (2009); Mobile (2012)
EF3 136–165 (219–266 km/h) Category 4–5 Severe damage. Entire stories of well-constructed houses destroyed; severe damage to large buildings such as shopping malls; trains overturned; trees debarked; heavy cars lifted off the ground and thrown; structures with weak foundations blown away some distance. St. Louis (1871); Miami (1925); Pine Lake, Alberta (2000); Springfield, Massachusetts (2011); El Reno, Oklahoma (2013)
EF4 166–200 (267–322 km/h) Strong category 5 Devastating damage. Well-constructed houses and whole frame houses completely leveled; cars thrown and small missiles generated. St. Louis (1896); Regina, Saskatchewan (1912); Worcester (1953); Jackson (2003); Tuscaloosa and Birmingham, Alabama (2011)
EF5 >200 (>322 km/h) Explosive damage. Strong frame houses leveled off foundations and swept away; automobile-sized missiles fly through the air in excess of 100 m (300 ft); steel reinforced concrete structures badly damaged; high-rise buildings have significant structural deformation; incredible phenomena will occur. Waco (1953); Birmingham (1977); Moore, Oklahoma (1999); Joplin (2011); Moore, Oklahoma (2013)

Saffir–Simpson hurricane category scale

See main article: Saffir–Simpson scale.

The Saffir–Simpson hurricane wind scale, assigns a numerical classification of hurricanes into five categories distinguished by the intensities of their sustained winds. The scale spans from Category 1 (winds of at least 74mph) to Category 5 (exceeding 156mph). Unlike the Enhanced Fujita Scale, which assigns ratings for tornadoes after damage has been incurred and thoroughly assessed, categories on the Saffir-Simpson scale are assigned to most active cyclones that reach the minimum hurricane threshold, even before landfall.

Category Sustained winds Potential damage Example(s)
33–42 m/s
74–95 mph
64–82 knot
119–153 km/h
4–5 ft
1.2–1.5 m
28.94 inHg
980 mbar
No real damage to building structures. Damage primarily to unanchored mobile homes, shrubbery, and trees. Also, some coastal flooding and minor pier damage.[67] Jerry (1989)
Ismael (1995)
Danny (1997)
Gaston (2004)
Kate (2015)
43–49 m/s
96–110 mph
83–95 kn
154–177 km/h
6–8 ft
1.8–2.4 m
28.50–28.91 inHg
965–979 mbar
Some roofing material, door, and window damage. Considerable damage to vegetation, mobile homes, etc. Flooding damages piers and small craft in unprotected anchorages may break their moorings.Carol (1954)
Diana (1990)
Erin (1995)
Marty (2003)
Juan (2003)
50–58 m/s
111–129 mph
96–113 kn
178–209 km/h
9–12 ft
2.7–3.7 m
27.91–28.47 inHg
945–964 mbar
Some structural damage to small residences and utility buildings, with a minor amount of curtainwall failures. Mobile homes are destroyed. Flooding near the coast destroys smaller structures with larger structures damaged by floating debris. Terrain may be flooded well inland.Alma (1966)Alicia (1983)
Roxanne (1995)
Fran (1996)
Isidore (2002)
Sandy (2012)
59–69 m/s
130–156 mph
114–135 kn
210–249 km/h
13–18 ft
4.0–5.5 m
27.17–27.88 inHg
920–944 mbar
More extensive curtainwall failures with some complete roof structure failure on small residences. Major erosion of beach areas. Terrain may be flooded well inland. "Galveston" (1900)
Hazel (1954)
Iniki (1992)
Iris (2001)
Harvey (2017)
Laura (2020)
Ian (2022)
70 m/s
157 mph
136 kn
250 km/h
19 ft
5.5 m
<27.17 inHg
<920 mbar
Complete roof failure on many residences and industrial buildings. Some complete building failures with small utility buildings blown over or away. Flooding causes major damage to lower floors of all structures near the shoreline. Massive evacuation of residential areas may be required."Labor Day" (1935)
Camille (1969)
Gilbert (1988)
Andrew (1992)
Wilma (2005)
Irma (2017)
Michael (2018)Dorian (2019)

See also

External links

Notes and References

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  6. Web site: December 11, 2021. Many trapped, two dead as tornado hits nursing home in Arkansas -media. December 11, 2021. reuters.com. en. December 11, 2021. https://web.archive.org/web/20211211042134/https://www.reuters.com/markets/commodities/many-trapped-two-dead-tornado-hits-nursing-home-arkansas-media-2021-12-11/. live.
  7. News: 'Quad-State Tornado' crossed four states in four hours, a rare December tornado. Kathryn Prociv. Nicole Acevedo. NBC News. December 11, 2021. December 12, 2021. December 12, 2021. https://web.archive.org/web/20211212005805/https://www.nbcnews.com/news/weather/quad-state-tornado-crossed-four-states-four-hours-leaving-trail-death-rcna8465. live.
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