WHAT DOES IT MEAN?
 COMMON WEATHER TERMS

(Referenced from The National Oceanic and Atmospheric Administration’s National Weather Service Internet page at: w1.weather.gov)

Just what do those weather alerts mean?

Common Weather Terms

The National Weather Service uses a variety of weather terms to describe different weather conditions. Do you know what the difference is between a "watch" and a "warning"? What does it mean when there is a "Red Flag Warning" in your area? What are the different wind speeds used to describe tornadoes and hurricanes? Take a look below to find out.

Fire Weather Watch

Critical fire weather conditions are forecast to occur. This type of a Watch may precede a Red Flag Warning.

Flash Flood

A rapid and extreme flow of high water in to a normally dry area, or a rapid water level rise in a stream or creek above a predetermined flood level, beginning within six hours of the causative event (e.g., intense rainfall, dam failure, ice jam). However the actual time threshold may vary in different parts of the country. Ongoing flooding can intensify to flash flooding in cases where intense rainfall results in a rapid surge of rising flood waters.

Flash Flood Watch

Issued to indicate current or developing hydrologic conditions that are favorable for flash flooding in and close to the watch area, but the occurrence is neither certain or imminent.

Flash Flood Warning

Issued to inform the public, emergency management, and other cooperating agencies that flash flooding is in progress, imminent, or highly likely.

Flood Watch

Issued to inform the public and cooperating agencies that current and developing hydrometerological conditions are such that there is a threat of flooding, but the occurrence is neither certain nor imminent.

Flood Warning

In hydrologic terms, a statement issued y the NWS to inform the public of flooding along larger streams in which there is a serious threat to life or property. A flood warning will usually contain river stage (level) forecasts.

Fujita Scale (Enhanced) for Tornado Intensity (From: www.weather.com)

EF-0    65-85 mph winds

Light damage:

Peels surface off some roofs ; some damage to gutters or siding; branches broken off trees; shallow-rooted trees pushed over.

EF-1    85-110 mph winds    

Moderate damage:

Roofs severely stripped; mobile homes overturned or badly damaged; loss of exterior doors; windows and other glass broken.

EF-2    111-135 mph winds

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.

EF-3    136-165 mph winds

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.

EF-4    166-200 mph winds

Devastating damage:

Well-constructed hoses and whole frame houses completely leveled; cars thrown and small missiles generated.

EF-5    >200 mph winds

Incredible damage:

Strong frame houses leveled off foundations and swept away; automobile-sized missiles fly through the air in excess of 100m (109 yards); high rise buildings have significant structural deformation; incredible phenomena will occur (grass being torn from the ground).

Funnel Cloud

A condensation funnel extending from the base of a towering cumulus cloud associated with a rotating column of air that is not in contact with the ground (and therefore different from a tornado). A condensation funnel is a tornado, not a funnel cloud if either 1) it is in contact with the ground or 2) a debris cloud or dust whirl is visible beneath it.

Hurricane Force Wind Watch

A watch or an increased risk of a hurricane force wind event for sustained surface winds, or frequent gusts, of 34 knots (74 mph) or greater, but its occurrence, location, and/or timing is still uncertain.

Hurricane Force Wind Warning

A warning for sustained winds, or frequent gusts, of 64 knots (74 mph) or greater, either predicted or occurring, and not directly associated with a tropical cyclone.

Hurricane Watch

An announcement that hurricane conditions (sustained winds of 74 mph or higher) are possible within the specified coastal area. Because hurricane preparedness activities become difficult once winds reach tropical storm force, the hurricane watch is issued 48 hours in advance of the anticipated onset of tropical-storm-force winds.

Hurricane Warning

An announcement that hurricane conditions (sustained winds of 74 mph or higher) are expected somewhere within the specified coastal area. Because hurricane preparedness activities become difficult once winds reach tropical storm force, the hurricane watch is issued 48 hours in advance of the anticipated onset of tropical-storm-force winds. The warning can remain in effect when dangerously high water or a combination of dangerously high water and waves continue, even though winds may be less than hurricane force.          

Particularly Dangerous Situation (PDS)

Particularly Dangerous Situation (PDS) wording is used in rare situations when long-lived, strong and violent tornadoes are possible. This enhanced wording may also accompany severe thunderstorm watches for intense convective wind storms.

Red Flag Warning

A term used by fire-weather forecasters to call attention to limited weather conditions of particular importance that may result in extreme burning conditions. It is issued when it is an on-going event or the fire weather forecaster has a high degree of confidence that Red Flag criteria will occur within 24 hours of issuance.

Red Flag criteria occurs whenever a geographical area has been in a dry spell for a week or two, or for a shorter period, if before spring green-up or after fall color, and the National Fire Danger Rating System (NFDRS) is high to extreme and the following forecast weather parameters are forecasted to be met:

  • A sustained wind average 15 mph or greater
  • Relative humidity less than or equal to 25% and
  • A temperature of greater than 75 degrees F.

In some states, dry lightning and unstable air are criteria.

A Fire Weather Watch may be issued prior to the Red Flag Warning.

Storm Surge

An abnormal rise in sea level accompanying a hurricane or other intense storm, whose height is the difference between the observed level of the sea surface and the level that would have occurred in the absence of the cyclone. Storm surge is usually estimated by subtracting the normal or astronomic tide from the observed storm tide.

Saffir-Simpson Hurricane Wind Scale

Category 1     Sustained Winds of 74-95 mph

Very dangerous winds will produce some damage:

Well-constructed frame homes could have damage to roof, shingles, vinyl siding and gutters. Large branches of trees will snap and shallowly rooted trees may be toppled. Extensive damage to power lines and poles likely will result in power outages that could last a few to several days.

Category 2     Sustained Winds of 96-110 mph

Extremely dangerous winds will cause extensive damage:

Well-constructed frame homes could sustain major roof and siding damage. Many shallowly rooted trees will be snapped or uprooted and block numerous roads. Near-total power loss is expected with outages that could last from several days to weeks.

Category 3     Sustained Winds of 119-129 mph

Devastating damage will occur:

Well-built framed homes may incur major damage or removal of roof decking and gable ends. Many trees will be snapped or uprooted, blocking numerous roads. Electricity and water will be un available for several days to weeks after the storm passes.

Category 4     Sustained Winds of 130-156 mph

Catastrophic damage will occur:

Well-built framed homes can sustain sever damage with loss of most of the roof structure and/or some exterior walls. Most trees will be snapped or uprooted and power poles downed. Fallen trees and power poles will isolate residential areas. Power outages will last weeks to possibly months. Most of the area will be uninhabitable for weeks or months.

Category 5     Sustained Winds of 157 mph or higher

Catastrophic damage will occur:

A high percentage of framed homes will be destroyed, with total roof failure and wall collapse. Fallen trees and power poles will isolate residential areas. Power outages will last weeks to possibly months. Most of the area will be uninhabitable for weeks or months.

Tornado Watch

This is issued by the National Weather Service when conditions are favorable for the development of tornadoes in and close to the watch area. Their size can vary depending on the weather situation. They are usually issued for a duration of 4-8 hours. They normally are issued well in advance of the actual occurrence of severe weather. During the watch, people should review tornado safety rules and be prepared to move to a place of safety if threatening weather approaches.

Tornado Warning

This is issued when a tornado is indicated by the WSR-88D radar or sighted by spotters; therefore, people in the affected area should seek safe shelter immediately. They can be issued without a Tornado Watch being already in effect. They are usually issued for a duration of around 30 minutes.

A Tornado Warning is issued by your local National Weather Service Office (NWFO). It will include where the tornado was located and what towns will be in its path. If the tornado will affect nearshore or coastal waters, it will be issued as the combined product-Tornado Warning and Special Marine Warning. If the thunderstorm which is causing the tornado is also producing torrential rains, this warning may also be combined with a Flash Flood Warning.

After it is has been issued, the affected NWFO will follow it up periodically with Severe Weather Statements. These statements will contain updated information on the tornado and will also let the public know when the warning is no longer in effect.

Tropical Depression

A tropical cyclone in which the maximum 1-minute sustained wind is 33 knots (38 mph) or less.

Tropical Storm

A tropical cyclone in which the maximum 1-minute sustained surface wind ranges from 34-63 knots (39-73 mph) inclusive.

Tropical Storm Watch

An announcement that tropical storm conditions (sustained winds of 39-73 mph) are possible within the specified coastal area within 48 hours.

Tropical Storm Warning

An announcement that tropical storm conditions (sustained winds of 39-73 mph) are possible within the specified coastal area within 36 hours.

Watch

Issued when the risk of a hazardous weather or hydrologic event has increased significantly, but its occurrence, location, and/or timing is still uncertain. It is intended to provide enough lead time so that those who need to set their plans in motion can do so.

Warning

A warning is issued when a hazardous weather or hydrologic event is occurring, is imminent, or has a very high probability of occurring. A warning is used for conditions posing a threat to life or property.

Winter Storm Watch

This product is issued by the National Weather Service when there is a potential for heavy snow or significant ice accumulations, usually at least 24 to 36 hours in advance. The criteria for this watch can vary from place to place.

Winter Storm Warning

This product is issued by the National Weather Service when a winter storm is producing or is forecast to produce heavy snow or significant ice accumulations. The criteria for this watch can vary from place to place.

Winter Weather Advisory

This product is issued by the National Weather Service when a low pressure system produces a combination of winter weather (snow, freezing rain, sleet, etc.) that present a hazard, but does not meet warning criteria.