A NOAA national weather forecast

Note: The following was adapted from public domain, official National Weather Service web sites. Some criteria appear to be specific to certain cities or regions and may not apply to your area. Image File history File links Download high resolution version (896x716, 135 KB) File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Image File history File links Download high resolution version (896x716, 135 KB) File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ...

This article describes severe weather terminology used by the U.S. National Weather Service. This includes watches and warnings, such as tornado warning. Related weather terminology and weather scales are also addressed in this article. This article focuses on terminology per se. Additional information can be found by following the indicated links to separate articles. The National Oceanic and Atmospheric Administration (NOAA) is an agency of the United States Department of Commerce. ... A tornado over land. ... Composite satellite image showing the progress of a hurricane weather system approaching the east coast of America Weather comprises all the various phenomena that occur in the atmosphere of a planet. ...

Watches, Warnings and Advisories

The National Weather Service has developed a multi-tier concept for forecasting all types of hazardous weather. These are:

Outlook - A hazardous weather outlook is issued daily to indicate that a hazardous weather or hydrologic event may occur in the next several days. The outlook will include information about potential severe thunderstorms , heavy rain or flooding, winter weather, extremes of heat or cold, etc., that may develop over the next 7 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. A rolling thundercloud over Enschede, The Netherlands. ... Rain falling For other uses see Rain (disambiguation). ... A flood (in Old English flod, a word common to Teutonic languages; compare German Flut, Dutch vloed from the same root as is seen in flow, float) is an overflow of water, an expanse of water submerging land, a deluge. ...

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.

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.

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 cause significant inconvenience and if caution is not exercised, could lead to situations that may threaten life or property.

Table of weather statements

A tornado over land. ... A tornado over land. ... A roll cloud associated with a heavy or severe thunderstorm over Enschede, The Netherlands. ... A roll cloud associated with a heavy or severe thunderstorm over Enschede, The Netherlands. ... Composite satellite image showing the progress of a hurricane weather system approaching the east coast of America Weather comprises all the various phenomena that occur in the atmosphere of a planet. ... A flash flood (also a freshet, considered archaic) is a rapid flooding of low-lying areas, rivers and streams that is caused by the intense rainfall associated with a thunderstorm, or multiple training thunderstorms. ... Look up Flood in Wiktionary, the free dictionary A flood (in Old English flod, a word common to Teutonic languages; compare German Flut, Dutch vloed from the same root as is seen in flow, float) is an overflow of water, an expanse of water submerging land, a deluge. ... Look up Flood in Wiktionary, the free dictionary A flood (in Old English flod, a word common to Teutonic languages; compare German Flut, Dutch vloed from the same root as is seen in flow, float) is an overflow of water, an expanse of water submerging land, a deluge. ... A flash flood (also a freshet, considered archaic) is a rapid flooding of low-lying areas, rivers and streams that is caused by the intense rainfall associated with a thunderstorm, or multiple training thunderstorms. ... Composite satellite image showing the progress of a hurricane weather system approaching the east coast of America Weather comprises all the various phenomena that occur in the atmosphere of a planet. ... If youre looking for the revolutionary communist Weather Underground Organization, see Weathermen Weather forecasting is the science (or some argue that it is an art) of predicting the state of the atmosphere for a future time and location. ... United States of America, showing states, divided into counties. ... Composite satellite image showing the progress of a hurricane weather system approaching the east coast of America Weather comprises all the various phenomena that occur in the atmosphere of a planet. ... A tornado over land. ... A roll cloud associated with a heavy or severe thunderstorm over Enschede, The Netherlands. ... A U.S. state is any one of the 50 states (four of which officially favor the term commonwealth) which, together with the District of Columbia, form the United States of America. ...

Hazardous weather definitions

The hazardous weather warning section of this guide is divided into three types of hazardous weather/hydrologic events.

1. Severe Local Storms - These are short-fused, small scale hazardous weather or hydrologic events produced by thunderstorms, including large hail, damaging winds, tornadoes, and flash floods.
2. Winter Storms - These are weather hazards associated with freezing or frozen precipitation (freezing rain, sleet, snow) or combined effects of winter precipitation and strong winds.
3. Other Hazards - Weather hazards not directly associated with thunderstorms or winter storms including extreme heat or cold, dense fog, high winds, river flooding and lakeshore flooding.

A large hailstone Hail is a type of graupel (a form of precipitation) composed of spears or irregular lumps of ice. ... For the 1928 film, see The Wind. ... Freezing rain begins as snow falling from a cloud towards earth. ... Whereas hail forms within clouds, sleet begins as snow falling to earth after having left its originating cloud. ... This page is about the form of precipitation. ... Giuseppe Arcimboldo, Winter, 1573. ... A red-hot iron rod cooling after being worked by a blacksmith. ... Cold can have the following meanings: Low temperatures, and/or the absence of heat Common cold, an infectious disease of the nose and throat Cold (band), a hard rock band Abbreviation for Computer Output to Laser Disk, see Enterprise Report Management (ERM) A James Bond novel, COLD by John Gardner... Early morning fog obscures the surface of this lake in Carrollton, Georgia, but the sky remains clear. ... For the Second World War frigate class, see River class frigate The Murray River in Australia A river is a large natural waterway. ... Look up Flood in Wiktionary, the free dictionary A flood (in Old English flod, a word common to Teutonic languages; compare German Flut, Dutch vloed from the same root as is seen in flow, float) is an overflow of water, an expanse of water submerging land, a deluge. ...

Severe Local Storms

Tornado Watch - Conditions are favorable for the development of severe thunderstorms and tornadoes in and close to the watch area. These watches are issued for large areas by the Storm Prediction Center in Norman, Oklahoma, and are usually valid for four to six hours. A roll cloud associated with a heavy or severe thunderstorm over Enschede, The Netherlands. ... A tornado over land. ... The Storm Prediction Center is part of the National Centers for Environmental Prediction (NCEP), operating under the control of the National Weather Service, which in turn is part of the National Oceanic and Atmospheric Administration (NOAA) of the U.S. government. ... Bizzel Library, University of Oklahoma Norman is a major city located in Cleveland County, Oklahoma and is part of the Oklahoma City Metropolitan Area. ...

Tornado Warning - Strong rotation in a thunderstorm is indicated by Doppler radar or a tornado is sighted by skywarn spotters. These warnings are issued on a county by county basis. Doppler radar uses the Doppler effect to return additional information from a radar system. ... In general, a spotter is someone trained to look for or spot something. ...

Severe Thunderstorm Watch - Conditions are favorable for the development of severe thunderstorms 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 four to six hours.

Severe Thunderstorm Warning - A severe thunderstorm is indicated by Doppler radar or sighted by skywarn spotters. A severe thunderstorm contains large damaging hail, 3/4 inch diameter or larger, and/or damaging winds of around 60 mph or greater. These warnings are issued on a county by county basis.

Flood Watch - Conditions are favorable for flash flooding in and close to the watch area. These watches are issued by the Weather Forecast Office and are usually for the first 12 to 24 hours of a forecast.

Flash Flood Warning - Flash flooding is occurring, imminent or highly likely. A flash flood is a flood that occurs within 6 hours of excessive rainfall and that poses a threat to life and/or property. Ice jams and dam failures can also cause flash floods. These warnings are issued on a county by county basis by the local Weather Forecast Office and are generally in effect for up to 6 hours.

Flood Warning - General or areal flooding of streets, low-lying areas, urban storm drains, creeks and small streams is occurring, imminent, or highly likely. Flood warnings are issued for flooding that occurs more than 6 hours after the excessive rainfall. These warnings are issued on a county by county basis by the local Weather Forecast Office and are generally in effect for 6 to 12 hours.

Special Marine Warning - A warning to mariners of hazardous thunderstorms or squalls with wind gusts of 34 knots or more, hail 3/4 inch diameter or larger, or waterspouts.

Winter Storms

Winter Storm Watch - Conditions are favorable for hazardous winter weather conditions including heavy snow, blizzard conditions, or significant accumulations of freezing rain or sleet. These watches are issued by the Weather Service Forecast Office and are usually issued 12 to 36 hours in advance of the event. Blizzards are characterized by high winds and blinding precipitation Sudden blizzards can cause terrible damage to infrastructure as well as danger to human life. ...

Winter Storm Warning - Hazardous winter weather conditions that pose a threat to life and/or property are occurring, imminent or likely. The generic term, winter storm warning, is used for a combination of two or more of the following winter weather events; heavy snow, freezing rain, sleet and strong winds. The following event-specific warnings are issued for a single weather hazard:

• Blizzard Warning - Sustained winds or frequent gusts of 35 mph or greater, considerable falling and/or blowing snow reducing visibility frequently to 1/4 mile or less for a period of three hours or more. There are no temperature criteria in the definition of a blizzard but freezing temperatures and 35 mph winds will create sub-zero wind chills.

• Heavy Snow Warning - Snowfall of 6 inches or more in 12 hours or less, or 8 inches or more in 24 hours or less.

• Lake Effect Snow Warning - Lake effect snowfall of 6 inches or more in 12 hours or less, or 8 inches or more in 24 hours or less.

• Ice Storm Warning - Accumulations of 1/4 inch or more of freezing rain.

• Heavy Sleet Warning - Accumulations of 1/2 inch or more of sleet.

Winter Weather Advisory - Hazardous winter weather conditions are occurring, imminent or likely. Conditions will cause a significant inconvenience and if caution is not exercised, will result in a potential threat to life and/or property. The generic term, winter weather advisory, is used for a combination of two or more of the following events; snow, freezing rain or drizzle, sleet, blowing snow. The following event-specific advisories are issued for these single weather hazards:

• Snow Advisory - Snowfall of 3 to 5 inches.

• Lake Effect Snow Advisory - Lake effect snowfall of 3 to 5 inches.

• Freezing Rain Advisory - Accumulations of less than 1/4 inch of freezing rain or freezing drizzle.

• Sleet Advisory - For accumulations of less than 1/2 inch of sleet.

• Snow and Blowing Snow Advisory - Sustained winds or frequent gusts of 25 to 35 mph accompanied by falling and blowing snow, occasionally reducing visibility to 1/4 mile or less.

Other Hazards

Wind Chill Warning - Extreme wind chills of -30oF or colder.

Wind Chill Advisory - Dangerous wind chills of -20oF to -30oF.

Excessive Heat Warning - Extreme values of the heat index.

Heat Advisory - Maximum heat index of 105 to 110oF with a minimum of 75oF for two or more consecutive days.

High Wind Warning - Sustained winds of 40 mph or greater for a duration of one hour or longer or gusts to 58 mph or greater.

Wind Advisory - Sustained winds of 30 mph or greater or gusts to 45 mph or greater for a duration of one hour or longer.

Dense Fog Advisory - Widespread dense fog reducing visibility to less than 1/4 mile.

Flood Warning (river flood)- A warning for specific communities or areas along a river where flooding is imminent or occurring. Flood warnings normally give specific crest forecasts.

Freeze Warning - Widespread temperatures at or below 32oF during the growing season. A freeze may occur with or without frost. A hard freeze occurs with temperatures below 28oF. Growing season is based on the average date of first and last freeze at O'Hare. It begins April 17 and ends October 27.

Frost Advisory - Widespread frost during the growing season. Frost generally occurs with fair skies and light winds.

Lakeshore Warning - Lakeshore flooding that is occurring or is imminent in the next 12 hours, which poses a serious threat to life and/or property. A seiche warning is issued for rapid and large fluctuations in water level in Lake Michigan usually caused by a strong line of thunderstorms moving rapidly southeast across the lake.

Blowing Snow Advisory - Widespread blowing snow with winds 25 to 35 mph, occasionally reducing visibility to 1/4 mile or less.

Other weather terminology and scales

Hail diameter sizes

A large hailstone Hail is a type of graupel (a form of precipitation) composed of spears or irregular lumps of ice. ...

Beaufort wind scale

Main article Beaufort scale. The Beaufort scale is an empirical measure for the intensity of the wind based mainly on sea-state or wave conditions. ...

Fujita tornado intensity scale

Main article Fujita scale The Fujita scale rates a tornados intensity by the damage it inflicts on human-built structures. ...

The Fujita scale, developed by Dr. Theodore Fujita, assigns a numerical rating from F0 to F5 to rate the intensity of tornadoes. F0 and F1 tornadoes are considered "weak" tornadoes, F2 and F3 are classified as "strong" tornadoes, where F4 and F5 are categorized as "violent" tornadoes. The F scale is based on tornado damage (primarily to buildings), so there is some ambiguity in the scale, but nonetheless, it provides a good baseline for classifying tornadoes according to their intensity. The Fujita scale rates a tornados intensity by the damage it inflicts on human-built structures. ...

Precipitation probabilities

Technically, the probability of precipitation (PoP) is defined as the likelihood of occurrence (expressed as a percent) of a measurable amount (.01 inch or more) of liquid precipitation (or the water equivalent of frozen precipitation) during a specified period of time at any given point in the forecast area. Forecasts are normally issued for 12-hour time periods. Descriptive terms for uncertainty and areal coverage are used as follows: The word probability derives from the Latin probare (to prove, or to test). ...

The following terms of duration imply a high probability (80-100%) of occurrence: brief, periods of, occasional, intermittent, frequent.

Sky condition

Wind terms

General weather terms

These terms were adapted from the National Weather Service. Many terms have separate Wikipedia articles as indicated.

Cold air funnel - A funnel cloud or (rarely) a small relatively weak tornado that can develop from a small shower or thunderstorm when the air aloft is unusually cold. They are much less violent than other types of tornadoes.

Crest - The highest level of a flood wave as it passes a point.

Degree Day - Gauges the amount of heating or cooling needed for a building using 65 degrees as a baseline. To compute degree days, the average temperature for a day is taken and referenced to 65. An average temperature of 50 yields 15 heating degree days, while an average temperature of 75 would yield 10 cooling degree days.

Dew Point - A measure of atmospheric moisture. It is the temperature to which air must be cooled in order to reach saturation (assuming pressure and moisture content are constant). The dew point or dewpoint of a given parcel of air is the temperature to which the parcel must be cooled, at constant barometric pressure, for the water vapor component to condense into water, called dew. ...

Doppler Radar - Radar that can measure radial velocity, the instantaneous component of motion parallel to the radar beam (i.e., toward or away from the radar). Doppler radar uses the Doppler effect to return additional information from a radar system. ...

Downburst - A strong downdraft from a thunderstorm resulting in an outward burst of damaging winds on or near the ground. Downburst winds are often 50 to 100 mph and in a few cases, 100 to 150 mph. They can do as much damage as a small tornado.

Microburst - a small downburst affecting an area less than 2 1/2 miles in diameter with peak winds lasting generally less than five minutes. A microburst is a very localized column of sinking air, producing damaging straight-line winds similar to, but distinguishable from tornadoes. ...

Macroburst - a large downburst affecting an area greater than 2 1/2 miles in diameter with peak winds generally lasting five minutes or longer.

Flood Stage - The level or stage at which a stream overflows its banks or the stage at which the overflow of a stream begins to cause damage. Look up Flood in Wiktionary, the free dictionary A flood (in Old English flod, a word common to Teutonic languages; compare German Flut, Dutch vloed from the same root as is seen in flow, float) is an overflow of water, an expanse of water submerging land, a deluge. ...

Freezing Rain/Freezing Drizzle - Rain or drizzle which falls in liquid form and freezes on impact with cold surfaces to form a glaze on the ground and exposed objects.

Funnel Cloud - A rotating column of air, extending from a towering cumulus or cumulonimbus cloud, that is not in contact with the ground. A funnel cloud. ...

Gustnado - A gust front tornado. A small, weak, short-lived tornado that occurs along a gust front - the leading edge of a thunderstorm, caused by rain-cooled air flowing out from the storm's downdraft. A gustnado is often visible as a debris cloud or dust whirl.

Hail - Precipitation in the form of lumps of ice that form during some thunderstorms. A large hailstone Hail is a type of graupel (a form of precipitation) composed of spears or irregular lumps of ice. ...

Heat Index - The apparent temperature that describes the combined effect of high temperatures and high levels of humidity, which reduces the body's ability to cool itself. Heat Index (HI) is an index that combines air temperature and relative humidity to determine an apparent temperature — how hot it actually feels. ...

Lake Breeze - A local wind blowing from the cooler surface of Lake Michigan to warmer inland areas, usually during the afternoon in spring and summer.

Lake Effect Snow - Snow that occurs to the lee of the Great Lakes when cold air moves across relatively warm waters of the lakes.

Rain/Showers - Rain is a nearly steady and uniform fall of precipitation over an area. Showers are intermittent and/or scattered convective rainfall of varying intensity.

Seiche - An oscillation of the surface of southern Lake Michigan usually caused by a squall line moving rapidly south-southeast down the Lake. Rapid changes in the lake level pose a serious threat to marinas and people on piers and breakwaters.

Relative Humidity - The ratio of the amount of water vapor actually present in the air to the greatest amount possible at the same temperature. Relative humidity is the ratio of the current vapor pressure of water in any gas (especially air) to the vapor pressure at which the gas would become saturated at the current temperature, normally expressed as a percentage (of what to what?). Equivalently, it is the ratio of the current mass...

Sleet - Sleet or ice pellets are solid grains of ice formed from the freezing of rain or the refreezing of melted snow, which bounce off the ground and other objects. Whereas hail forms within clouds, sleet begins as snow falling to earth after having left its originating cloud. ...

Squall line - A line of thunderstorms or squalls which may extend over several hundred miles. A squall or squall line is a line of thunderstorms with a common leading convection line, or mesocyclone, which tends to create a powerful gust front. ...

Tornado - A violently rotating column of air, from a thunderstorm, in contact with the ground. A tornado over land. ...

Waterspout - In general, a tornado occurring over water. Specifically, it refers to a small, relatively weak rotating column of air over water beneath a towering cumulus or cumulonimbus cloud. They occasionally occur over Lake Michigan in late summer with unusually cold air aloft. A waterspout off the Florida Keys A waterspout is most frequent in tropical regions. ...

Wind Chill - An apparent temperature that describes the combined effect of wind and low temperature on exposed skin. Wind chill is the apparent temperature felt on the exposed human (or animal) body due to the combination of air temperature and wind speed. ...

See also

• Weatheradio
• Emergency Alert System
• National Weather Service

Weatheradio is a special radio service available over much of North America that transmits weather warnings and forecasts 24 hours a day. ... The Emergency Alert System (EAS), is a national system in the U.S. put into place in 1997, superseding the Emergency Broadcast System and administered by the Federal Communications Commission (FCC). ... The National Oceanic and Atmospheric Administration (NOAA) is an agency of the United States Department of Commerce. ...

References

• National Weather Service, Louisville, KY
• National Weather Service, Chicago, IL