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The Most Commonly-Issued Weather Watches & Warnings - A Glossary

Updated on July 3, 2017

No matter the time of year, we all live with the best and worst of weather conditions. At times, weather can create adverse conditions. These conditions—depending on both their severity and the extent of their effects—can result in anything from minor disruptions to daily life to threatening the lives of people over a significant area. For this reason, the National Weather Service (NWS) often issues various (types of) weather advisories, watches, and warnings in an effort to keep those living in potentially-affected regions aware of changing weather conditions.

But quite often, a level of confusion arises whenever weather advisories are issued. People may often find themselves asking, What does that mean? What am I expected to be on the lookout for? Am I in Danger? And the like... For these reasons, it becomes important to not only know, but distinguish between the different types of weather advisories, as well as what they imply insofar as weather conditions.

The following is a list of the most commonly issued weather advisories issued by the NWS:

  • A Blizzard Warning is a weather advisory issued by the National Weather Service whenever there is a forecast for conditions consisting of sustained winds (or frequent gusts) of 35 mph (15 meters per second) or greater, along with heavy falling and/or blowing snow for a period of 3 hours or more. A blizzard tends to reduce visibilities to 1/4 of a mile (400 meters) or less.
  • A Blizzard Watch is a weather advisory issued by the National Weather Service whenever there is a potential for winds greater than 35 miles per hour (56 kilometers per hour), falling and/or blowing snow, and visibilities of 1⁄4 mile (0.4 km) or less for a period of 3 + hours. A blizzard watch is usually issued 12 to 48 hours before an expected blizzard event.
  • A Coastal Flood Advisory is issued by the National Weather Service whenever coastal flooding along the coast of the Atlantic Ocean, Pacific Ocean, or the Gulf of Mexico is occurring or imminent (but does not pose a serious threat to lives or property).
  • A Coastal Flood Warning is issued by the National Weather Service whenever coastal flooding is either imminent or occurring along the coast of the Atlantic Ocean, Pacific Ocean, or the Gulf of Mexico. The flooding must be due to water being forced from the nearby body of water onto the land from organized storms such as Nor'easters, hurricanes, tropical storms, and thunderstorms.
  • A Coastal Flood Watch is issued by the National Weather Service whenever coastal flooding along the coast of the Atlantic Ocean, Pacific Ocean, or the Gulf of Mexico is possible. The flooding must be due to water being forced from the nearby body of water onto land, and not from organized storms such as Nor'easters, hurricanes, tropical storms, and thunderstorms.
  • A Dense Fog Advisory is issued by the National Weather Service when widespread fog is expected to reduce visibilities to 1/4 mile (402 meters) or less over a large area for an extended period of time (2 or more hours).
  • A Dust Storm Warning is issued by the National Weather Service when blowing dust is expected to reduce visibility frequently to 1⁄4 mile (400 meters) or less, generally with winds of 25 miles per hour (40 kilometer per hour) or greater. Dust storm warnings are usually issued in areas of the American desert southwest, and parts of the country with similar geographical and capable of producing similar weather conditions.
  • An Excessive Heat Warning is issued by the National Weather Service whenever there is a forecast that indicates a dangerous rise in certain heat index indicators. The criteria for an excessive heath warning include a forecast of 12-hours of the heat index reaching at least 105 °F (40 °C) for more than 3 hours per day for 2 consecutive days, or if the heat index is greater than 115 °F (46 °C) for any period of time. High values of the heat index are caused by temperatures being significantly above normal and high humidity, and such high levels can pose a threat to human life through conditions such as heat stroke, Heat exhaustion, and other heat-related illnesses.
  • An Excessive Heat Watch is issued by the National Weather Service when the heat index is expected to be greater than 105 °F (41 °C) across (the) northern states or 110 °F (43 °C) across the southern states during the day, and/or nighttime low temperature will be at least 75 °F (24 °C) or higher for 2 consecutive days. Note that even with the usual northern/southern criteria, local offices, particularly those with deserts or mountainous terrain, often have their own criteria.
  • A Fire Weather Watch is issued by the National Weather Service for the purpose of alerting fire officials/firefighters in the watch area of potentially dangerous fire weather conditions arriving within the upcoming 24 to 36 hours of the issuance of the watch.
  • A Flash Flood Warning is issued by the National Weather Service when a flash flood is imminent or occurring in the warned area. A flash flood is a sudden, violent flood after a heavy rain, or occasionally after a dam break (rainfall intensity and duration, topography, soil conditions, and ground cover contribute to flash flooding).
  • A Flash Flood Watch is issued by the National Weather Service when conditions are favorable for flash flooding in flood-prone areas, usually when grounds are already saturated from recent rains, or when upcoming rains will have the potential to cause a flash flood. These watches are also occasionally issued when a dam may break in the near future.
  • A Freezing Rain Advisory is an advisory issued by the National Weather Service when freezing rain or freezing drizzle is expected to cause significant inconveniences, but does not meet warning criteria (typically greater than 1⁄4 inch or 6.4 millimeters of ice accumulation).
  • A Freezing Spray Advisory is issued by the National Weather Service to warn ocean-/lake-/water-going vessels that accumulation of freezing water droplets due to a combination of cold water, wind, cold air, and vessel movement is possible. In most cases, accumulations are not expected to reach rates of no more than 2 centimeters per hour.
  • A Gale Warning is issued by the National Weather Service as an advisory geared primarily toward those in and/or maritime locations that are in jeopardy of (currently or imminently) experiencing winds of gale force on the Beaufort scale. These warnings allow mariners to take precautionary actions to ensure their safety at sea or to seek safe anchorage and ride out the storm on land.
  • A Gale Watch is issued by the National Weather Service when there is an increased risk for a gale force wind event, meaning sustained surface winds (or frequent gusts) of 34 to 47 knots (39 to 54 mph), but the occurrence, location, and/or timing of the event is still uncertain.
  • A Hazardous Seas Warning is issued by the National Weather Service when wave heights and/or wave steepness values reach certain criteria. These criteria are defined by the local forecast office (such tall waves can pose a serious threat to vessels that do not seek shelter).
  • A Hazardous Seas Watch is issued by the National Weather Service when there is an increased threat of high wave heights and/or wave steepness values reach a certain criteria, but the occurrence, timing, and/or location are still uncertain. The criteria are set by the local forecast offices (such tall waves can pose a serious threat to vessels that do not seek shelter).
  • A Heat Advisory is issued by the National Weather Service within 12 hours of the heat index reaching one of two criteria levels. In most areas, an advisory will be issued if there is a heat index of at least 105°F but less than 115°F for less than 3 hours per day and/or if nighttime low temperatures are above 80°F for 2 consecutive days (note that local offices, particularly those where excessive heat is less frequent or in areas with deserts or mountainous terrain, often have their own criteria).
  • A Heavy Freezing Spray Warning is issued by the National Weather Service to warn ocean-/lake-/water-going vessels that accumulation of freezing water droplets due to a combination of cold water, wind, cold air, and vessel movement is likely. This means that accumulation rates of at least 2 centimeters per hour must be possible for a warning to be issued.
  • A Heavy Freezing Spray Watch is issued by the National Weather Service when there is an increased risk to ocean-/lake-/water-going vessels of a heavy spray event that meets the necessary criteria, but the occurrence, timing, and/or location are still uncertain. A watch will be issued when forecasters expect freezing water droplets to be able to accumulate on sea vessels at rates of at least 2 centimeters per hour. This means that accumulation must be caused by an "appropriate combination of cold water, wind, cold air temperature, and vessel movement.
  • A High Wind Watch is issued by the National Weather Service whenever conditions indicate an increased likelihood for sustained winds of at least 40 mph (64 kilometers per hour) or higher for one hour or more. A watch will also be issued conditions indicate an increased likelihood for when wind gusts of 58 mph (93 km/h) or higher for an hour or more.
  • A High Wind Warning is issued by the National Weather Service when conditions are imminent (or occurring) for sustained winds of at least 40 mph (64 kilometers per hour) or higher for one hour or more. A warning will also be issued when conditions for wind gusts of 58 mph (93 km/h) or higher for an hour (or more) are either imminent or occurring.
  • A Hurricane Force Wind Warning is a warning issued by the National Weather Service when sustained winds or frequent gusts of 74 mph (64 knots/ 118 kilometers per hour) or greater are either being observed or are forecast to occur. The winds related to such a warning are not associated with a tropical cyclone, or a hurricane warning will be issued (if winds are lighter than 64 knots, a storm warning or gale warning will be issued instead).
  • A Hurricane Warning is issued by the National Weather Service when sustained winds of at least 64 knots (74 mph/ 118 kilometers per hour) or higher, and associated with a tropical cyclone, are expected in 36 hours or less. These winds may be accompanied by storm surge, coastal flooding, and/or river flooding. 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.
  • A Hurricane Watch will be issued by the National Weather Service whenever conditions are for a tropical cyclone system is possible for a particular region within 48 hours of the watch’s issuance. These conditions include hurricane force winds of 64 knots (74 mph/ 118 kilometers per hour) or higher, the presence of storm surge, coastal flooding, and/or river flooding. The watch does not mean that hurricane conditions will occur; just that they are possible.
  • An Ice Storm Warning is issued by the National Weather Service when freezing rain produces a significant and possibly damaging accumulation of ice on surfaces. The criteria for this warning vary from state to state, but typically an ice storm warning will be issued any time more than 1⁄4 inch (6.4 millimeters) of ice is expected to accumulate in an area; in some areas, the criterion is 1⁄2 inch (13 mm).
  • A Lake Effect Snow Advisory is issued by the National Weather Service when lake effect snow may pose a hazard or is life-threatening. The snow must be completely caused by a convective snow development over a lake (or similarly large body of water) and not by a low pressure system.
  • A Lake Effect Snow Warning is a bulletin issued by the National Weather Service to warn areas near large lakes and/or similar body of water of imminent heavy snowfall amounts from convective snow generated by very cold air mass passing over unfrozen lakes (lake effect snow).
  • A Lake Effect Snow Watch is a bulletin issued by the National Weather Service to warn areas near large lakes and/or similar body of water of the possibility of heavy snowfall amounts from convective snow generated by cold air masses passing over unfrozen lakes (lake effect snow).
  • A Particularly Dangerous Situation (PDS) is a type of enhanced weather advisory used by the Storm Prediction Center (an arm of the National Weather Service) on certain severe weather watches. It is issued at the discretion of the forecaster composing the watch and implies that there is an enhanced risk of very severe and life-threatening weather, usually a predicted major tornado outbreak or—much less often—a long-lived, extreme derecho or severe thunderstorm-related event.
  • A Red Flag Warning, also known as a Fire Weather Warning, is a forecast warning issued by the National Weather Service to inform area firefighting and land management agencies that conditions are ideal for wildfire combustion, and its rapid spread. These conditions include drought, very low humidity levels, high or erratic winds, and the possibility of lightning. When all or a significant combination of these factors are present, the Red Flag Warning becomes a critical statement for firefighting agencies.
  • A Fire Weather Watch is issued by the National Weather Service to alert firefighting and land management agencies to the possibility that Red Flag conditions may exist beyond the first forecast period (12 hours). The watch is issued generally 12 to 48 hours in advance of the expected conditions, but can be issued up to 72 hours in advance if the NWS agency is reasonably confident.
  • A Severe Thunderstorm Warning is issued by the National Weather Service whenever official storm spotters (volunteers trained by the NWS) or a Doppler weather radar indicate that a thunderstorm is either producing, or will soon produce dangerously large hail or high winds, capable of causing significant damage. Severe thunderstorms are defined as thunderstorms that produce winds of at least 58 mph (93 km/h) and hail of at least 1 inch (2.54 centimeters) in diameter.
  • A Severe Thunderstorm Watch is issued by the National Weather Service when weather conditions are favorable for the development of severe thunderstorms in the watch area. A watch means that severe thunderstorms capable of producing winds of at least 58 mph (93 km/h) and hail of at least 1 inch (2.54 centimeters) in diameter are possible in the watch area.
  • A Small Craft Advisory is a type of warning issued by the National Weather Service, primarily around coastal areas and the waters of the Great Lakes. A small craft advisory is issued when winds have reached, or are expected to reach (within 12 hours) a speed marginally less than gale force (less than 28 knots/32 mph/52 km/h). A Small Craft Advisory may also be issued when sea or lake ice exists that could be hazardous to small boats.
  • A Special Marine Warning is a warning issued by the National Weather Service for potentially hazardous marine weather conditions. These conditions are usually of short duration (up to 2 hours), but can potentially produce sustained marine thunderstorm winds (or associated gusts of at least 39 miles per hour/34 knots/ 62 kilometers per hour), hail of at least 3/4 inch (19 millimeters), and/or possible waterspouts. It is also used for short duration weather events such as a strong cold front, gravity wave, squall line, etc., lasting less than 2 hours and producing winds or gusts of 39 mph or greater.
  • At sea, a Storm Warning is a warning issued by the National Weather Service when winds between 48 knots (89 km/h, 55 mph) and 63 knots (117 km/h, 73 mph) are occurring or predicted to occur soon. The winds must not be associated with a tropical cyclone. If the winds are associated with a tropical cyclone, a tropical storm warning will be substituted for the storm warning and less severe gale warning.
  • A Tornado Emergency is an enhanced version of the tornado warning used by the National Weather Service during a significant tornado event in highly populated areas. Although a rarely-issued warning, a tornado emergency generally means that significant, widespread damage is expected to occur, and that there is a high likelihood of numerous casualties expected with a large, strong to violent tornado. A tornado emergency may also be issued when computer models predict a 100% chance that a powerful tornado will strike a populated area.
  • A Tornado Warning is an alert issued by National Weather Service to warn the public that severe thunderstorms with tornadoes are possible, imminent, or occurring. Tornado warnings are issued whenever official storm spotters (volunteers trained by the NWS), storm chasers, or local first-responders (e.g., law enforcement of fire fighters) observe either an actual tornado or funnel cloud. A warning may also be issued if local weather radar(s) indicate the presence of a severe thunderstorm with a high likelihood of producing a tornado, or if local radar indicates that an active tornado either occurring or forming—even if one is not actually observed by emergency officials.
  • A Tornado Watch is an advisory issued by the National Weather Service whenever weather conditions are favorable for the development of severe thunderstorms that are capable of producing tornadoes. A tornado watch usually implies that it is also a severe thunderstorm watch. A tornado watch must not be confused with a tornado warning. In most cases, the potential exists for large hail and/or damaging winds in addition to tornadoes.
  • A Tropical Storm Watch is issued by the National Weather Service whenever a tropical cyclone containing winds of between 39 and 73 mph (between 34 and 63 knots/62 and 117 km/h) poses a possible threat, generally within 48 hours of the issuance of the watch. These winds may be accompanied by storm surge, coastal flooding, and/or river flooding. The watch does not mean that tropical storm conditions will occur, just that these conditions are possible.
  • A Tropical Storm Warning is issued by the National Weather Service whenever a tropical cyclone containing winds of between 39 and 73 mph (between 34 and 63 knots/ 62 and 117km/h) are expected, usually within 36 hours (or less). These winds will typically be accompanied by storm surge, coastal flooding, and/or river flooding.
  • An Urban and Small Stream Flood Advisory is issued by the National Weather Service when ponding of water in streets, along low-lying areas, on highways, under overpasses, in urban storm drains, as well as the elevation of creek and small stream levels is occurring or imminent. Urban and small stream flood advisories are issued for flooding expected to occur within 3 hours after excessive rainfall. These advisories are issued on a county by county basis by the local weather forecast offices, and generally remain in effect for 3 to 4 hours.
  • A Wind Advisory is generally issued by the National Weather Service when weather conditions indicate the imminent or actual presence of sustained winds between 31 and 39 miles per hour (50 and 63 km/h,) and/or gusts of between 46 and 57 miles per hour (74 and 92 km/h) over land. This advisory is predicated on changing weather based on the presence of active weather system. As such, winds of this magnitude occurring over an area that frequently experiences such wind speeds will not trigger a wind advisory.
  • A Wind Chill Advisory is issued by the National Weather Service when the wind chill (the apparent temperature felt on exposed skin, which is a function of the air temperature and wind speed) is low enough that it poses a threat to human health and life if adequate protection is not taken against hypothermia and frostbite. The exact definition varies from state to state, and areas prone to colder temperatures such as areas in the Northern U.S. will often require the wind chill to be lower before issuing an advisory.
  • A Wind Chill Warning is issued by the National Weather Service when wind chills (the apparent temperature felt on exposed skin, which is a function of the air temperature and wind speed) of -20 ⁰F (-28.9 ⁰C) or lower are expected.
  • A Wind Chill Watch is issued by the National Weather Service when the wind chill (the apparent temperature felt on exposed skin, which is a function of the air temperature and wind speed) could reach dangerous levels (-20 ⁰F /-28.9 ⁰C or lower) within 12 to 48 hours of the issuance of the watch.
  • A Winter Storm Warning is issued by the National Weather Service when weather conditions indicate the imminent arrival (or active occurrence) of a winter storm. In the case of an expected winter storm, the warning is typically issued with the understanding that the storm is expected to occur within 36 hours of the issuance of the warning. Generally, a winter storm warning is issued if at least the criteria—usually between 4 inches (10 cm) to 7 inches (18 cm) or more of snow levels of or 3 inches (7.6 cm)—is forecast. Additionally, a warning will be issued for an expected large accumulation of snow—of indeterminate levels—along with ice is forecast. In the Southern United States, where severe winter weather is much less common, the criteria for a winter storm warning are lower (as low as 1 inch/2.5 cm) in the southernmost areas.
  • A Winter Storm Watch is issued by the National Weather Service when there is a potential for heavy snow or significant ice accumulations for a particular region. The watch is usually issued 12 to 48 hours before the storm's arrival in the area.
  • A Winter Weather Advisory is issued by the National Weather Service when a low pressure system produces a combination of winter weather (snow, freezing rain, or sleet) that presents a hazard, but does not meet warning criteria. It also applies hazardous conditions that linger after a substantial winter event (e.g., a winter storm or a blizzard).

The various different types of weather watches and warnings used at the NWS website
The various different types of weather watches and warnings used at the NWS website

The purpose for the NWS in issuing these weather advisories is not to alarm the public, but to keep people advised of changing weather conditions. They are also issued so as to afford basic information about the weather, so that individuals can plan their day-to-day activities with the least amount of disruption. Finally, and in the worst-cases, they are issued to warn the public of hazardous and life-threatening weather condition, so that people can take steps to protect themselves from the most dangerous aspects of the weather.

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