Severe weather terminology (United States)

This article describes severe weather terminology used by the National Weather Service (NWS) in the United States, a government agency operating within the Department of Commerce as an arm of the National Oceanic and Atmospheric Administration (NOAA).

The NWS provides weather forecasts, hazardous weather alerts, and other weather-related products for the general public and special interests through a collection of national and regional guidance centers (including the Storm Prediction Center, the National Hurricane Center and the Aviation Weather Center), and 122 local Weather Forecast Offices (WFO). Each Weather Forecast Office is assigned a designated geographic area of responsibility—also known as a county warning area—that are split into numerous forecast zones (encompassing part or all of one county or equivalent thereof) for issuing forecasts and hazardous weather products.

The article primarily defines precise meanings and associated criteria for nearly all weather warnings, watches, advisories, statements, and other products not associated with hazardous weather issued by the NWS and its sub-organizations (some of which may be specific to certain cities or regions). Related weather scales and general weather terms used by the agency are also addressed.

Definitions of severe weather alerts

thumb|right|400px|An example of weather alerts on a national map from the National Weather Service

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

:* Severe local storms – Short-fused, small-scale hazardous weather or hydrologic events produced by thunderstorms (including large hail, damaging winds, tornadoes, and flash floods).

:* 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.

:* Fire weather – Weather conditions that contribute to an increased risk and help cause the spread of wildfires.

:* Flooding – Hazardous hydrological events resulting in temporary inundation of land areas not normally covered by water, often caused by excessive rainfall.

:* 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.

:* Marine hazards – Hazardous events that may affect marine travel, fishing and shipping interests along large bodies of water, including hazardous seas and freezing spray.

:* 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.

:* 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.

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;
(NPW) — Product event code in parenthetical regular text; used for products that have both standard and Specific Area Message Encoding (SAME) event codes;
SAME product codes assigned to each term for NOAA Weather Radio (NWR) broadcasts are included in products that do not have a specified code are identified where applicable, as defined by NOAA, as:

:** Non-Precipitation Warnings/Watches/Advisories (NPW)

:** Coastal Flood Warnings/Watches/Advisories (CFW)

:** Marine Weather Statement (MWS)

:** Mesoscale Discussion (MCD)

:** Severe Weather Warnings/Watches/Advisories (WSW)

Severe local storms

Tornado watch (yellow box in some select NWS documentation, red box in most other media) – 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 (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.
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 (such as local law enforcement). These warnings are currently issued on a polygonal basis, are usually issued for a duration of 30 minutes (but can run for as long as one hour), 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. (The PDS wording is also incorporated into the boilerplate precautionary/preparedness action statement for tornado emergencies.)
:Tornado emergency – Sent as a "severe weather statement" or as the initial tornado warning, this is a high-end tornado warning issued when a violent tornado is expected to impact a densely 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 path through portions of western Kentucky, including the city of Mayfield) 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.
: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 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.
: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 (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 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 – 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 (as indicated by the most recently updated NEXRAD data) at the time of the statement's issuance. Severe Weather Statements may include notices of cancellation (if the warning is being discontinued entirely, or if sections of counties or county-equivalent jurisdictions are being removed from the continuing warning), or notices of a warning being allowed to expire because the prompting storm has weakened below severe criteria.
: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 (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).
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.
Winter storm warning – Hazardous winter weather conditions that pose a threat to life and/or property are occurring, imminent, or highly likely within 12 to 48 hours. The generic term, Winter Storm Warning, is used for hazardous winter precipitation in the form of heavy snow, freezing rain or sleet, or a combination of two or more precipitation types. The forecast accumulation criteria for each frozen precipitation type vary significantly over different county warning areas. The Winter Storm Warning product was restructured to incorporate additional precipitation-specific criteria previously applied to the deprecated heavy snow warning and sleet warning products beginning with the 2008-09 winter storm season.
Blizzard warning – Sustained winds or frequent gusts of or greater, accompanying heavy snowfall, frequently reducing visibilities to or less is forecast to occur over a period of at least three hours. There are no temperature criteria in the definition of a blizzard, but freezing temperatures of at least and winds will create wind chills of at least . A winter storm watch for blizzard conditions is issued when conditions meeting criteria are forecast to occur within 12 to 48 hours.
Ice storm warning – Heavy ice accumulations that may cause significant disruptions to travel and public utilities, and damage to trees and utility infrastructure impacting life and property are imminent. The criteria for amounts vary over different county warning areas; accumulations range from or more of freezing rain on elevated horizontal flat surfaces. (Hazardous icing conditions are covered and similar warning criteria are used by the Meteorological Service of Canada for their Freezing Rain Warning product.)
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 (which replaced the previously used "Travelers Advisory"), is used for hazardous winter precipitation in the form of snow, freezing rain or freezing drizzle, sleet or blowing snow, or a combination of two or more precipitation types. The forecast accumulation criteria—defined below locally designated warning criteria or based on NWS impact-driven advisory criteria—for at least one of the frozen precipitation elements within a defined 12- or 24-hour period vary significantly over different county warning areas. Originally issued to indicate hazardous travel conditions (usually concurrent with standalone precipitation-specific advisories indicating hazards to life, property and commerce), it was restructured as a general purpose product—deprecating the snow advisory, blowing snow advisory, snow and blowing snow advisory, and sleet advisory products—beginning with the 2008-09 winter storm season (it would later supersede the freezing rain advisory and lake-effect snow advisory products for the 2017-18 winter season).
Lake effect snow warning – Very heavy lake-effect snowfall amounts of generally in 12 hours or less or in 24 hours or less are imminent or highly likely. Lake-effect snow squalls can significantly reduce visibilities with little notice. The NWS had originally discontinued the product, superseded by the winter storm warning for heavy lake-effect snow, on October 15, 2018; however, it reinstated the lake effect snow warning as a standalone product beginning with the 2019–20 winter storm season.
Snow squall warning – An intense, generally limited duration, period of moderate to heavy snowfall has been observed by radar. Usually accompanied by strong, gusty surface winds, significantly reduced visibility up to or less (which may reach levels creating whiteout conditions), and possibly lightning; temperature drops behind an arctic front that are sufficient to produce flash freezes, in conjunction with a significant reduction in visibility from falling and/or blowing snow, may also serve as a warning criteria factor. Snow accumulation may be significant.

Deprecated

:*Heavy snow warning – Heavy snowfall amounts are imminent; the criteria for amounts (based on 12-hour and 24-hour minimum accumulations) vary significantly over different county warning areas. Discontinued beginning with the 2008-2009 winter storm season and replaced with the winter storm warning for heavy snow.

:*Sleet warning (alt.: heavy sleet warning) – Heavy sleet accumulations of or more, which may cause significant disruptions to travel or utilities, are imminent or expected to occur within 12 hours. Discontinued beginning with the 2008-2009 winter storm season and replaced by the winter storm warning for heavy sleet.

:*Sleet advisory – Moderate sleet accumulations of are imminent or expected to occur within 12 hours. Because sleet usually occurs with other precipitation types, a Winter Weather Advisory will almost always be used in such cases. Discontinued beginning with the 2008-2009 winter storm season and replaced with the winter weather advisory for sleet.

:*Snow advisory – Moderate snowfall amounts are imminent; the criteria for amounts vary significantly over different county warning areas. Under the former definition, a snow advisory could be warranted if lesser snowfall accumulations were forecast to produce travel difficulties, especially early in the winter season. Discontinued beginning with the 2008-2009 winter storm season and replaced by the winter weather advisory for snow.

:*Blowing snow advisory – Sustained winds or frequent gusts of accompanied by falling and blowing snow, occasionally reducing visibilities to or less, will occur for at least three hours. Discontinued beginning with the 2008-2009 winter storm season and replaced by the Winter Weather Advisory for Blowing Snow.

:*Snow and blowing snow advisory – Sustained winds of are expected to be accompanied by falling and blowing snow, occasionally reducing visibilities to or less for at least three hours. Discontinued beginning with the 2008-2009 winter storm season and replaced by the winter weather advisory for snow and blowing snow.

:*Lake effect snow watch – Significant amounts of lake-effect snow (generally within 12 hours or within 24 hours) are possible in the next 12 to 48 hours. Discontinued on October 2, 2017; a winter storm watch is now issued instead.

:*Lake effect snow advisory – Moderate amounts of lake-effect snow (generally ) are expected or occurring. Discontinued on October 2, 2017; a winter weather advisory for lake-effect snow is now issued instead.

:*Freezing rain advisory (alt.: freezing drizzle advisory) – Freezing rain or freezing drizzle producing ice accretion of up to that may cause significant travel impairments is expected or occurring. Discontinued on October 2, 2017; a winter weather advisory for freezing rain is now issued instead.

:*Blizzard watch – Sustained winds or frequent gusts of or greater, accompanying considerable falling and/or blowing snow, frequently reducing visibilities to or less for a period of three hours or more are possible generally within 12 to 48 hours. The NWS deprecated issuance of blizzard watches in October 2017; a winter storm watch is now issued in its place.

Fire weather

Fire warning – A major, uncontrolled wildfire or structural fire is currently burning in a populated area and/or near major roadways, and evacuation is recommended by local civil authorities.
Red flag warning – Extreme burning conditions favor the combustion and rapid spread of wildfires within 12 to 24 hours in areas that have not received precipitation for a short period or are experiencing drought conditions, and which the National Fire Danger Rating System (NFDRS) designates as having a high to extreme fire danger. It is issued primarily to alert fire department officials and firefighters of conditions ideal for the combustion and spread of wildfires. The surface relative humidity (RH) and 10-hour fuel moisture criteria meriting a Fire Weather Watch may vary by state based on local vegetation, topography and distance from major water sources, though forecast sustained winds are usually expected to be or greater.
:PDS red flag warning – 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.
Fire weather watch – Conditions expected to become favorable for the rapid spread of wildfires in areas of dry vegetation within 12 to 48 hours or up to 72 hours if the NWS office is reasonably confident that red flag fire conditions will occur. It is issued primarily to alert fire and land management agencies of conditions ideal for the combustion and spread of wildfires. The surface relative humidity and 10-hour fuel moisture criteria meriting a fire weather watch may vary depending by state based on local vegetation, topography and distance from major water sources, though forecast sustained winds are usually expected to be or greater.

Flooding

Areal flood warning – General or areal flooding of streets, low-lying areas, urban storm drains, creeks, and small streams in which there is a serious threat to life or property is occurring, imminent, or highly likely. Flood warnings are usually issued for flooding that occurs more than six hours after the excessive rainfall, or when flooding is imminent/occurring but is not rapid enough to prompt a flash flood warning. These warnings are issued on a polygonal basis by the local Weather Forecast Office and are generally in effect for six to twelve hours.
:River flood warning (formerly flood warning for river forecast point) – Flooding of streams or rivers is occurring, imminent, or highly likely. These warnings are issued either by the River Forecast Centers for the area surrounding affected streams or rivers or on a county by county basis by the local Weather Forecast Office and are generally in effect for an indeterminate period until river gauges in the affected areas record water levels receding below the water body's predetermined flood stage.
Flood statement – A hydrological weather statement issued to provide updated information on ongoing flooding along major streams in which there is not a serious threat to life and/or property active or flood warnings to the public and emergency managers; information will be provided on observed (or if a dam is at risk of breaking, updates on the ongoing threat) flooding within the warning area, and current and forecast flood stages for lakes and rivers at the time of the statement's issuance.
Storm surge watch – Life-threatening inundation from rising water being forced inland by an ongoing or potential tropical, subtropical or post-tropical cyclone is possible within the specified area, generally within 48 hours. Similar criteria included in a Storm Surge Warning for conditions that would limit lead time for undertaking safety precautions and inclusion of areas that may experience isolation from surge inundation also apply to this product. Issued in collaboration between the NHC and local WFOs, storm surge watches are only issued for regions in the Atlantic and Gulf Coasts of the conterminous United States.
Lakeshore flood warning – Lakeshore flooding that poses a serious threat to life and/or property is occurring or is imminent in the next 12 to 24 hours.
:Seiche warning – 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.
Lakeshore flood watch – Lakeshore flooding that could pose a serious threat to life and/or property is possible within the next 12 to 48 hours.
Lakeshore flood advisory – Minor lakeshore flooding that may pose a threat to life and/or property is occurring or is imminent in the next 12 hours.
Lake wind advisory – Sustained wind speeds of are forecast to persist for one hour or longer on area lakes that may cause hazards for maritime travel; wind speeds meeting advisory criteria may vary depending on the county warning area. The usage of this product is locally determined by each Weather Forecast Office.
Hazardous seas warning – Significant wave heights and/or wave steepness values—independent of strong winds—are forecast to cause rough surf in the warned coastal area and adjacent waters, which could pose a serious threat to vessels that do not move to stable waters or dock. Warning criteria may vary depending on the NWS Weather Forecast Office.
Hazardous seas watch – A rough surf event—regardless of forecast wind speeds that may contribute to such an occurrence—is possible in the warned coastal area and adjacent waters, but its occurrence, location, and/or timing remains uncertain. Warning criteria may vary depending on the NWS Weather Forecast Office.
Low water advisory – Critically below average water levels over the Great Lakes, coastal marine zones or other tidal marine area, waterway, or river inlet within or adjacent to a marine zone have been observed, and potentially present a hazard to maritime navigation.
Marine dense fog advisory – Widespread dense fog reducing visibility to less than covering more than half the area of a marine zone is expected for at least two hours over a 12-hour period, creating hazardous navigation conditions for boaters and other marine vessels.
Marine weather statement – The equivalent of a special weather statement at sea, indicating potentially hazardous marine conditions.
Special marine warning – A warning to mariners of short-duration hazardous weather conditions (lasting up to two hours) including thunderstorms or squalls with wind gusts of or more, hail diameter or larger, or waterspouts affecting coastal areas not adequately covered by existing marine warnings. Short-duration mesoscale events (such as a strong cold front, gravity wave or squall line) expected to last two hours or less and produce criteria wind speeds, or volcanic ashfall may also warrant issuance.
:Particularly dangerous situation special marine warning – A warning to mariners of hazardous weather conditions that present a considerable threat to life and property.
Small craft advisory – A warning to mariners of high sustained winds or frequent gusts and/or significant sea or wave heights that may damage or capsize small boats. Only issued by WFOs in coastal regions and the Great Lakes for areas included in the Coastal Waters Forecast or Nearshore Marine Forecast products. Thresholds necessitating the issuance of small craft advisories are determined by the accordant NWS Regional Headquarters.
:Small craft advisory for hazardous seas – An advisory to mariners of wave or sea conditions that are potentially hazardous to small boats because of wave height, wave period, steepness, or swell direction, even if wind speeds are expected to fall below locally defined small craft advisory criteria. Only issued by WFOs in coastal regions and the Great Lakes for areas included in the Coastal Waters Forecast or Nearshore Marine Forecast products. Thresholds necessitating the issuance of this type of small craft advisory vary among geographic areas within each NWS Regional Headquarters.
:Small craft advisory for rough bar – 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 – 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 – 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

Extreme heat warning – Maximum Heat Index (HI) values are forecast to meet or exceed locally defined warning criteria for more than three hours over at least two consecutive days. Excessive Heat Warnings are issued within 12 hours of the onset of the defined heat index criteria. Specific criteria vary among local Weather Forecast Offices, due to climate variability and the effect of excessive heat on the local population. Typical HI values are maximum daytime temperatures above for up to three hours per day, with minimum nighttime temperatures above (criteria may vary slightly by county warning area) for two consecutive days. Warning criteria may be lowered by the issuing WFO if the heat event occurs early in the season, during a multi-day heat wave or during a widespread power outage occurs during a heat event due to severe weather phenomena (such as high winds, severe thunderstorms, or a derecho). This product was previously known as an Excessive Heat Warning until March 4, 2025.
Extreme heat watch – Conditions are favorable for an excessive heat event with extreme Heat Index values during the day, combined with nighttime low temperatures of or higher that limit perspiration recovery, are forecast to occur to meet or exceed local Excessive Heat Warning criteria in the next 24 to 72 hours. and was reinstated for use by the Alaskan Region WFOs in 2018 as a consolidation of the previously separate Extreme Cold Warning and Wind Chill Warning products. Elsewhere, Extreme Cold Warnings could be issued by local Weather Forecast Offices in the mainland United States as an experimental product using locally appropriate thresholds, usually with little or no wind as a factor. Both this and the Wind Chill Warning product were to have been consolidated into a singular Extreme Cold Warning product for use by WFOs in the rest of the conterminous United States in 2021, accounting for NWS software upgrades; the Extreme Cold Warning formally superseded the Wind Chill Warning in October 2024.
Extreme cold watch – Dangerously cold temperatures are possible for a prolonged period of time. Frostbite and hypothermia are likely if exposed to these temperatures. This product replaced the Wind Chill Watch in October 2024.
Freeze watch – Issued during the locally defined growing season when conditions are favorable for a freeze event that may damage or kill crops to meet or exceed Freeze Warning criteria within 24 to 48 hours.
Heat advisory – High Heat Index (HI) values are forecast to meet or exceed locally defined warning criteria for one or two days. Specific criteria vary over different county warning areas, due to climate variability and the effect of excessive heat on the local population. Usually issued within 12 hours of the onset of conditional advisory criteria, typical HI values are maximum daytime temperatures above for up to three hours per day, with minimum nighttime temperatures falling within or above the range of (depending on county warning area criteria) for two consecutive days. Warning criteria may be lowered by the issuing WFO if the heat event occurs early in the season, during a multi-day heat wave or during a widespread power outage occurring during a heat event due to severe weather phenomena (such as high winds, severe thunderstorms, or a derecho). This product was intended to be deprecated sometime in 2021, and superseded by the Extreme Cold Warning product, which was to have included dual criteria for extreme wind chill and actual temperature values, and have its use expanded to WFOs elsewhere in the conterminous United States; the Wind Chill Warning was finally deprecated in October 2024.
SIGMET (significant meteorological information) – Advises of weather that is potentially hazardous to all aircraft and is affecting or is forecast to affect at least .

VAAs are standardized worldwide by the International Civil Aviation Organization.

Tropical weather

Tropical storm warning – Tropical storm conditions (gale- and storm-force sustained winds of ) are expected within the specified coastal or inland area within 36 hours (24 hours for Guam, as locally defined by the NWS Forecast Office in Barrigada) in advance of the forecast onset of tropical-storm-force winds. These winds may be accompanied by storm surge, and coastal and/or river flooding. Tropical Storm Warnings may also be issued in association with a subtropical or post-tropical cyclone.
Extreme wind warning – An extreme wind event producing sustained surface winds of or greater, associated with the eyewall of a major hurricane (Category 3 or higher on the Saffir-Simpson Scale), non-convective winds, downslope winds or a derecho is occurring or expected to occur in the specified coastal or inland area within one hour. Extreme Wind Warnings—which should be issued no prior than two hours before the onset of extreme winds—are not issued by WFOs located within the Pacific basin.
Freezing fog advisory – Widespread dense fog reducing visibility to less than that occurs in a sub-freezing environment, producing very light glazed ice accumulations on exposed surfaces.
Dense smoke advisory – Widespread or localized smoke reducing visibilities to or less (up to for marine-based advisories, depending on locally defined criteria) is occurring; minimum visibility criteria may be defined by the accordant NWS Regional Headquarters or local Weather Forecast Office.
:Particularly dangerous situation special weather statement – 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.
Storm warning – Sustained surface winds or frequent gusts of is either predicted within 36 hours or occurring. Expected wind speeds are likely to cause significant navigational impairment and/or damage to commercial and recreational boating within the warned area. The wind speeds must not be directly associated with a tropical cyclone.
Storm watch – Sustained surface winds or frequent gusts of are forecast to occur, but its occurrence, location and/or timing remains uncertain. Expected wind speeds may cause significant navigational impairment and/or damage to commercial and recreational boating. The wind speeds must not be directly associated with a tropical cyclone.
Wind advisory – Strong sustained winds of for one hour or longer and/or wind gusts of for any duration are expected within the next 12 to 24 hours. Wind speeds may pose a hazard to pedestrian and vehicular travel, topple and/or create flying debris from unsecured outdoor objects, and potentially disrupt public utilities and down electrical lines. Advisory criteria may vary by county warning area depending on local climatology; winds of the standard criteria magnitude occurring over an area that frequently experiences such wind speeds will not necessarily trigger a wind advisory.
911 telephone outage emergency – Issued when 911 telephone service experiences a network outage over a geographic area or telephone exchange. Alternative phone numbers in which to reach 911 or dispatch emergency personnel will be provided to the public.
Administrative message – A non-emergency message providing updated information about an event that is either in progress, has expired or concluded early, pre-event preparation or mitigation activities, post-event recovery operations, or other Emergency Alert System-related administrative matters.
Avalanche watch – Indicates conditions are forecast to favor natural or human-induced avalanches that could affect roadways, structures, or backcountry activities.
Avalanche warning – Avalanche activity—either natural or human-induced—is ongoing or imminent, and likely to affect roadways, structures or backcountry activities and threaten the lives of people within the avalanche's path. Safety precautions will be recommended or ordered as dictated by state law or local ordinance.
Avalanche Advisory – Indicates that conditions may be favorable for the development of avalanches in mountainous regions.
Blue alert – Issued by state and local authorities to warn the public of information relating to a law enforcement officer who is missing, seriously injured or was killed in the line of duty, or if there is an imminent, credible threat to an officer. Information on the suspect and safety instructions for if the suspect has been spotted within a specific community may be included. The NWS added the ability to convey these messages to its WFOs on a phased basis beginning in late 2019.
Child abduction emergency – An emergency message, usually issued in accordance with an Amber alert, informing the public and law enforcement about a missing child believed to have been abducted. Local or state law enforcement agencies investigating the abduction will provide descriptions of the missing child, suspect or vehicle used by the suspect, and ask the public to notify the requesting agency if they have information on the child's or suspect's whereabouts.
Civil danger warning – Assigned a higher priority than a Local Area Emergency, this indicates a hazardous event (such as the contamination of local water supply or a military or terrorist attack that is imminent or ongoing) presenting a danger to a significant civilian population, requiring specific protective action (such as evacuation or sheltering in place).
Civil emergency message – A message intended to warn the public of an in-progress or imminent significant threat(s) to public safety and/or property. Although the hazard that warrants such a message to be issued is less specific than that meriting a Civil Danger Warning, it is given higher priority than the Local Area Emergency.
Demonstration Message – A demonstration or test message used for particular purposes in established state, local, tribal or territorial EAS plans. Purposes may include testing of a siren system, audio quality checks or alert origination system and pathway demonstration.
Earthquake warning – Indicates earthquake activity is ongoing or imminent.
Evacuation immediate – Warns the public that immediate evacuation for a long-duration emergency event (such as for an approaching tropical cyclone, a wildfire or the release of flammable or explosive gas) has been recommended or ordered by state and/or local law enforcement.
Hazardous materials warning – Warns the public of the release of non-radioactive hazardous material (such as a flammable gas, toxic chemical, or biological agent) that may necessitate recommendations of evacuation (for an explosion, fire or oil spill hazard) or sheltering in place (for a toxic fume hazard).
Law enforcement warning – Issued by authorized law enforcement agencies to warn the public of a bomb explosion, riot, or other criminal event (e.g., a jailbreak) that may result in the blockade roads, waterways, or facilities, the evacuation or denial of access to affected areas, and the arrest of violators or suspicious persons.
Local area emergency – An emergency message that defines an event of insignificant threat to public safety and/or property, which could escalate, contribute to more serious events, or disrupt critical public safety services (such as a disruption in water, electric or natural gas service, snowfall-induced road closures, or a potential terrorism threat).
Nuclear power plant warning – Warns of a hazardous materials event at a nuclear power plant classified as a Site Area Emergency (a hazardous event confined to the plant site) or General Emergency (an event affecting a less than radius around the plant) under Nuclear Regulatory Commission (NRC) guidelines. Authorized officials may recommend evacuation or medical treatment of exposed persons in nearby areas.
Radiological hazard warning – Indicates the loss, discovery, theft or release of a radiological hazard.
Shelter in place warning – Indicates an event (such as the release of hazardous materials containing toxic fumes or radioactivity harmful to residents in the warning area) in which the public is recommended to shelter in place and take necessary safety precautions.
Tsunami watch – A tsunami is forecast to impact the specified area.
Tsunami warning – A tsunami with the potential of causing widespread coastal flooding accompanied by powerful currents and inundation and/or significant damage to adjacent property is imminent, expected or occurring and may continue for several hours after the wave's initial arrival, issued by the National Tsunami Warning Center.
Tsunami advisory – A tsunami with the potential to generate strong currents or waves dangerous to those in or very near the water is imminent, expected, or occurring. The threat may continue for several hours after initial arrival, but significant inundation of land and adjacent property is not expected.
Volcano warning – Indicates volcanic activity that is ongoing or imminent.

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

{| class="wikitable"

| 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|| Wind advisory || Wind advisory or small craft advisory || File:Small craft warning (USA).jpg || File:smallcraftlights.gif || 6–7

| 39 to 54 mph (34 to 47 knots) || Gale warning|| High wind warning || Tropical storm warning* || File:Gale warning (USA).jpg || File:galelights.gif || 8–9

| 55 to 73 mph (48 to 63 knots) || Storm warning|| High wind warning || Tropical storm warning† || File:Storm warning (USA).jpg || File:stormlights.gif || 10–11

| 74–110 mph (64 to 99 knots) || Hurricane force wind warning|| High wind warning || Hurricane warning || File:Hurricane warning (USA).jpg || File:hurricanelights.gif || 12–13

| Over 110 mph (100+ knots) || Hurricane force wind warning || Extreme wind warning || Major hurricane warning‡ || File:Hurricane warning (USA).jpg || File:hurricanelights.gif || 14–16

†

‡

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:

Outlook – Outlooks are issued to provide contextual forecasts of potential hazardous weather events:
A Hazardous Weather Outlook is issued daily to outline hazardous weather or hydrologic events that may occur in the next seven days within each Weather Forecast Office’s area of responsibility. Each segment of the product will contain sections outlining hazardous weather in the short term (through Day 1) and long term (for Days 2-7), and spotter activation information. The outlook will include information about any potential hazards to life, property or travel (severe or strong thunderstorms, heavy rain or flooding, winter weather, tropical cyclones, extremes of heat or cold, and/or fire weather conditions) that may take place over the next seven days with an emphasis on the first 24 hours of the forecast. It is intended to provide information to those who need considerable lead time to prepare for the event (such as emergency management agencies, Skywarn spotters and media outlets). If issued for a coastal area, the outlook will contain two segments: one for the marine zones and adjacent land-based (i.e., coastal) zones, and the other for the remainder of the land-based zones. In August 2021, the Graphical Hazardous Weather Outlook (GHWO)—originally known as the Enhanced Hazardous Weather Outlook (EHWO)—was introduced as an experimental product, providing color-coded graphical depictions of potential weather hazards within each WFO’s area of responsibility over the seven-day forecast period, compiled utilizing data collected from the Storm Prediction Center and the Weather Prediction Center; beginning with its elimination by the Eureka, California and Corpus Christi, Texas offices in August 2023, NWS Forecast Offices will gradually discontinue the text-based Hazardous Weather Outlook product in favor of utilizing the GHWO to outline weather hazards within each forecast area and the Area Forecast Discussion product to convey regionally specific hazard information.
A Hydrologic Outlook is issued daily solely to outline possible hydrologic events occurring in the next seven days within each WFO’s area of responsibility. The outlook, which follows a similar structure to the Hazardous Weather Outlook, will include information on an as-needed basis about potential flooding more than 24 hours from the event and long-term forecast information (such as water supply forecasts and probabilistic analyses).
A Short-Term Forecast (alt., NOWcast) is an event-driven narrative outlook of near-term weather conditions within the Weather Forecast Office’s area of responsibility, typically valid for a three- to seven-hour period. The product outlines any ongoing or recently occurring conditions—based on radar analysis, satellite imagery and other forms of remote observation—that provide a basis for, or an enhancement to, the forecast. During severe weather events, the product can be used to describe the progress of severe weather and/or rainfall capable of producing flash flooding.
Mesoscale discussions (MDs) are event-driven narrative outlooks of near-term severe weather and hydrological conditions over the continental United States, typically valid for a one- to seven-hour period, usually preceding the onset of an event. The Storm Prediction Center issues Mesoscale Convective Discussions (MCD) to provide short-term analysis highlighting the development and/or evolution of potential or ongoing severe thunderstorm and hazardous winter weather activity. In severe weather situations, discussions illustrate forecaster reasoning for whether a watch is warranted (based on probabilities ranging from 5% to 95%), to provide analysis of ongoing convection (often to update information on ongoing watches and sometimes to provide reasoning for a watch cancellation), or are used as advance notice of a categorical upgrade in a forthcoming convective outlook update. During winter weather events, they provide analysis of expected heavier rates of winter precipitation over a specific time span or elevation, short-term blizzard conditions; or climatologically anomalous or unexpected events below defined criteria. The Weather Prediction Center issues mesoscale precipitation discussions (MPDs) as flash flood guidance for National Weather Service forecast offices, NWS River Forecast Centers, the media, emergency managers and other users, containing technical discussions concerning forecasted heavy rainfall events and expected impacts relating to potential flooding.
Advisory – An advisory is issued when a hazardous weather or hydrologic event is occurring, imminent, or likely. Advisories are for "less serious" conditions than warnings that may cause significant inconvenience, and if caution is not exercised could lead to situations that may threaten life or property. The National Weather Service may activate weather spotters in areas affected by advisories to help them better track and analyze the event.
Emergency – An Emergency is issued when an event that by itself cannot pose a threat to life or property, but may indirectly cause other events to happen that may pose a threat to life or property. An example of this would be a power outage, which although not directly posing a hazard, may threaten public safety and critical services. The only existing exceptions to this are the tornado emergency and flash flood emergency, which are issued to get the attention of the public to a major tornado or flash flood.
Watch – A watch is used when the risk of a hazardous weather or hydrologic event has increased significantly, but its occurrence, location, or timing is still uncertain. It is intended to provide enough lead time so those who need to set their plans in motion can do so. A watch means that hazardous weather is possible. People should have a plan of action in case a storm threatens and they should listen for later information and possible warnings especially when planning travel or outdoor activities. The National Weather Service may activate weather spotters in areas affected by watches to help them better track and analyze the event.
Warning – A warning is issued when a hazardous weather or hydrologic event is occurring, imminent, or likely. A warning means weather conditions pose a threat to life or property. People in the path of the storm need to take protective action. The National Weather Service may activate weather spotters in areas affected by warnings to help them better track and analyze the event.
Statement – A statement is either issued as a follow-up message to a warning, watch, or emergency, that may update, extend, or cancel the message it is following up or a notification of significant weather for which no type of advisory, watch, or warning exists.

{| class="wikitable"

|+ Convective thunderstorm risk categories

! scope="col" | Risk category

! scope="col" | Map code

! scope="col" | Description

! scope="row" style="background:#b7eab7" | General or non-severe thunderstorms

| style="text-align: center;" width="80px"|TSTM || 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.

! scope="row" style="background:#008000" | Marginal

| style="text-align: center;" width="80px"|1-MRGL || An area of severe storms of either limited organization and longevity, or very low coverage and marginal intensity.

! scope="row" style="background:#ffff00" | Slight

| style="text-align: center;" width="80px"|2-SLGT || An area of organized severe storms, which is not widespread in coverage with varying levels of intensity.

! scope="row" style="background:#ffa500" | Enhanced

| style="text-align: center;" width="80px"|3-ENH || An area of greater (relative to slight risk) severe storm coverage with varying levels of intensity.

! scope="row" style="background:#ff0000" | Moderate

| style="text-align: center;" width="80px"|4-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.

! scope="row" style="background:#ff00ff" | High

| style="text-align: center;" width="80px"|5-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).

The attendant risk areas are derived from probability forecasts of tornadoes, damaging winds, and large hail occurring within 25 miles of any point during each day of the outlook period. For the Day 1 and Day 2 Convective Outlooks, the risk areas are determined by the probability of any individual severe weather hazard, ranging from 2% to 60%, derived from odds greater than the statistical average that any one location may be impacted by severe weather hazards. (For example, a 15% tornado probability indicates 15 times the average odds that a tornado will be reported within 25 miles of a point.) Probabilities for severe-criteria wind and hail are typically assigned higher numbers than for tornadoes, since there is a greater likelihood of occurrence in comparison.

! scope="col" | Outlook probability

! scope="col" | TORN

! scope="col" | WIND

! scope="col" | HAIL

| scope="row" style="background:green;”|2% || scope="row" style="background:lime;”|MRGL || ||

| scope="row" style="background:brown;"|5% || scope="row" style="background:yellow;"|SLGT || scope="row" style="background:lime;"|MRGL || scope="row" style="background:lime;"|MRGL

| scope="row" style="background:yellow;"|10% || scope="row" style="background:orange;"|ENH || ||

| scope="row" style="background:yellow;"|10% Sig. Severe || scope="row" style="background:orange;"|ENH || ||

| scope="row" style="background:red;"|15% || scope="row" style="background:orange;"|ENH || scope="row" style="background:yellow;"|SLGT || scope="row" style="background:yellow;"|SLGT

| scope="row" style="background:red;"|15% Sig. Severe || scope="row" style="background:red;"|MDT || scope="row" style="background:yellow;"|SLGT || scope="row" style="background:yellow;"|SLGT

| scope="row" style="background:magenta;"|30% || scope="row" style="background:red;"|MDT || scope="row" style="background:orange;"|ENH || scope="row" style="background:orange;"|ENH

| scope="row" style="background:magenta;"|30% Sig. Severe || scope="row" style="background:magenta;"|HIGH || scope="row" style="background:orange;"|ENH || scope="row" style="background:orange;"|ENH

| scope="row" style="background:#912CEE;"|45% || scope="row" style="background:magenta;"|HIGH || scope="row" style="background:orange;"|ENH || scope="row" style="background:orange;"|ENH

| scope="row" style="background:#912CEE;"|45% Sig. Severe || scope="row" style="background:magenta;"|HIGH || scope="row" style="background:red;"|MDT || scope="row" style="background:red;"|MDT

| scope="row" style="background:#104E8B; color:white;"|60% || scope="row" style="background:magenta;"|HIGH || scope="row" style="background:red;"|MDT || scope="row" style="background:red;"|MDT

| scope="row" style="background:#141414; color:white;"|60% Sig. Severe || scope="row" style="background:magenta;"|HIGH || scope="row" style="background:magenta;"|HIGH || scope="row" style="background:red;"|MDT

| colspan="4"|Day 3 probability to categorical outlook conversion

Under this system, the existing SPC significant severe hazard grids for tornado, wind, hail and total severe will continue to be disseminated, with additional probability thresholds for discrete severe thunderstorms being added to the existing 10% significant severe threshold, represented as a sequence of even numbers (e.g., 2%, 4%), and unconditional probabilities of significant severe hazards based on potential tornado intensity, maximum hail size and maximum wind speeds. The maximum threshold for the Day 1 and Day 2 probabilistic severe wind forecasts will also be increased with the introduction of two additional probability categories (75% and 90%).

{| class="wikitable"

! scope="row" colspan="3" style=background:#DCDCDC; color:#000000; border: 2px solid #D33A5D|Tornado Warning || N/A

| style="background: #" | 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)

| style="background: #" | 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)

| style="background: #" | 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)

| style="background: #" | 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)

| style="background: #" | 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); Mayfield (2021); Greenfield (2024)

| style="background: #" | EF5 || >200 (>322 km/h) || Hurricane Patricia || 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

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 ) to Category 5 (exceeding ). 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.

<!--

PLEASE NOTE: Intensity of example hurricanes is at time of landfall AND peak intensity. Choose your examples carefully to avoid confusion.

For instance: DO NOT ADD HURRICANE KATRINA AS AN EXAMPLE.

Katrina is not a good example of either a Cat 3, Cat 4, or a Cat 5 since "officially" it was a Cat 3, it was operationally a Cat 4,

but in pressure, surge, and damage most people will think of it as a Cat 5, which will be confusing for the reader.

Don't add any other storms with disputed categories (i.e. Ivan, Frederic).

Also, don't add linebreaks below this comment markup.

-->{| class="wikitable" style="text-align: right;"

! Category !! Sustained winds !! Storm surge !! Central pressure !! Potential damage !! style="width: 9em;"|Example(s)

! style="background: #;" | 50px

| 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

| style="text-align: left;" | No real damage to building structures. Damage primarily to unanchored mobile homes, shrubbery, and trees. Also, some coastal flooding and minor pier damage.

| Jerry (1989)

Ismael (1995)

Danny (1997)

Gaston (2004)

Kate (2015)

! style="background: #;" | 50px

| 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

| style="text-align: left;" | 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.