Blizzard Watch/Warning
Sustained winds or frequent gusts to 35 mph or greater and falling and/or blowing snow and visibility reduced to 1/4 mile or less for at least 3 hours.
Dense Fog Advisory
A Dense Fog Advisory is issued when fog reduces visibility to 1/8 mile or less over a widespread area.
Derecho
A derecho is a widespread, long-lived wind storm. Derechos are associated with bands of rapidly moving showers or thunderstorms variously known as bow echoes, squall lines, or quasi-linear convective systems. By definition, if the wind damage swath extends more than 240 miles (about 400 kilometers) and includes wind gusts of at least 58 mph (93 km/h) or greater along most of its length, then the event may be classified as a derecho.
Excessive Heat Warning
An Excessive Heat Warning is issued within 12 hours of the onset of the following criteria: heat index of at least 105°F for more than 3 hours per day for 2 consecutive days, or heat index more than 115°F for any period of time.
Excessive Heat Watch
An Excessive Heat Watch is issued by the National Weather Service when heat indices in excess of 105ºF during the day combined with nighttime low temperatures of 80ºF or higher are forecast to occur for two consecutive days.
Flash Flood Warning
A Flash Flood Warning is issued to inform the public, emergency management, and other cooperating agencies that flash flooding is in progress, imminent, or highly likely.
Flash Flood Watch
A Flash Flood Watch is 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.
Flood Warning
A Flood Warning is issued 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.
Flood Watch
A Flood Watch is issued to inform the public and cooperating agencies that current and developing hydrometeorological conditions are such that there is a threat of flooding, but the occurrence is neither certain nor imminent.
Freeze Warning
A Freeze Warning is issued during the growing season when surface temperatures are expected to drop below freezing over a large area for an extended period of time, regardless whether or not frost develops.
Freeze Watch
A Freeze Watch is issued when there is a potential for significant, widespread freezing temperatures within the next 24-36 hours.
Freezing Fog Advisory
Light ice accumulation from freezing fog.
Freezing Rain Advisory
A Freezing Rain Advisory is issued when freezing rain or freezing drizzle is forecast but a significant accumulation is not expected. However, even small amounts of freezing rain or freezing drizzle may cause significant travel problems. Ice accumulation of under 1/4 inch.
Frost Advisory
A Frost Advisory is issued during the growing season when widespread frost formation is expected over an extensive area. Surface temperatures are usually in the mid 30s Fahrenheit.
Hard Freeze Warning
Widespread temperatures at or below 28°F (−2 °C) during the growing season. A hard freeze may occur with or without frost. -No official definition.
Hard Freeze Watch
Widespread temperatures at or below 28°F (−2 °C) during the growing season are possible within the next 24-36 hours. -No official definition.
Heat Advisory
A Heat Advisory is issued within 12 hours of the onset of the following conditions: heat index of at least 105°F but less than 115°F for less than 3 hours per day, or nighttime lows above 80°F for 2 consecutive days.
High Wind Warning
A High Wind Warning is issued when high wind speeds may pose a hazard or is life threatening. The criteria for this warning varies from state to state. In Michigan, the criteria is sustained non-convective (not related to thunderstorms) winds greater than or equal to 40 mph lasting for one hour or longer, or winds greater than or equal to 58 mph for any duration.
High Wind Watch
A High Wind Watch is issued when there is the potential of high wind speeds developing that may pose a hazard or is life threatening. The criteria for this watch varies from state to state.
Ice Storm Warning
An Ice Storm Warning is issued when freezing rain produces a significant and possibly damaging accumulation of ice. The criteria for this warning varies from state to state, but typically will be issued any time more than 1/4" of ice is expected to accumulate in an area. Ice accumulation of 1/4 inch or greater in 24 hours.
Lake Effect Snow Advisory
A Lake Effect Snow Advisory is issued when pure lake effect snow (this is where the snow is a direct result of lake effect snow and not because of a low pressure system) may pose a hazard or it is life threatening. The criteria for this advisory varies from area to area.
Lake Effect Snow Warning
A Lake Effect Snow Warning is issued when pure lake effect snow (this is where the snow is a direct result of lake effect snow and not because of a synoptic storm or low pressure system) may pose a hazard or it is life threatening.
Red Flag Warning
A Red Flag Warning is issued 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:
1) a sustained wind average 15 mph or greater
2) relative humidity less than or equal to 25 percent and
3) 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.
Severe Thunderstorm Warning
A Severe Thunderstorm Warning is issued when either a severe thunderstorm is indicated by the WSR-88D radar or a spotter reports a thunderstorm producing hail one inch or larger in diameter and/or winds equal or exceed 58 miles an hour; therefore, people in the affected area should seek safe shelter immediately. Severe thunderstorms can produce tornadoes with little or no advance warning. Lightning frequency is not a criteria for issuing a severe thunderstorm warning. They are usually issued for a duration of one hour. They can be issued without a Severe Thunderstorm Watch being already in effect.
Severe Thunderstorm Watch
A Severe Thunderstorm Watch is issued when conditions are favorable for the development of severe thunderstorms in and close to the watch area. A severe thunderstorm by definition is a thunderstorm that produces one inch hail or larger in diameter and/or winds equal or exceed 58 miles an hour. The size of the watch can vary depending on the weather situation. They are usually issued for a duration of 4 to 8 hours. They are normally issued well in advance of the actual occurrence of severe weather. During the watch, people should review severe thunderstorm safety rules and be prepared to move a place of safety if threatening weather approaches.
Storm Warning
A Storm Warning is issued as a warning of sustained surface winds, or frequent gusts, in the range of 48 knots (55 mph) to 63 knots (73 mph) inclusive, either predicted or occurring, and not directly associated with a tropical cyclone.
Storm Watch
A Storm Watch is issued for an increased risk of a storm force wind event for sustained surface winds, or frequent gusts, of 48 knots (55 mph) to 63 knots (73 mph), but its occurrence, location, and/or timing is still uncertain.
Tornado Emergency
In exceedingly rare situations, when a severe threat to human life and catastrophic damage from a tornado is imminent or ongoing. (May be included in a Tornado Warning.)
Tornado Warning
A Tornado Warning 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.
Tornado Watch
A Tornado Watch is issued 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 to 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 a place of safety if threatening weather approaches.
Wind Advisory
A Wind Advisory is issued when sustained winds 31 to 39 mph and/or gusts of 46 to 57 mph are present or expected. Issuance is normally site specific. However, winds of this magnitude occurring over an area that frequently experiences such winds.
Wind Chill Advisory
A Wind Chill Advisory is issued when the wind chill could be life threatening if action is not taken. The criteria for this warning varies from state to state. Wind Chill of -10ºF to -24ºF with wind of 10 MPH or greater.
Wind Chill Warning
A Wind Chill Warning is issued when the wind chill is life threatening. The criteria for this warning varies from state to state. Wind Chill of -25ºF or less with wind of 10 MPH or greater.
Winter Storm Warning
A Winter Storm Warning is issued when a winter storm is producing or is forecast to produce heavy snow or significant ice accumulations. The criteria for this warning can vary from place to place.
Champaign-Clark-Delaware-Franklin-Greene-Licking-Madison-Union
6 inches of snow or 1/2 inch of sleet in 12 hours or 8 inches of snow in 24 hours.
Fairfield-Fayette-Hocking-Pickaway
4 inches of snow or 1/2 inch of sleet in 12 hours or 6 inches of snow in 24 hours.
Winter Storm Watch
A Winter Storm Watch is issued 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. Refer to the Winter Storm Warning definition.
Winter Weather Advisory
A Winter Weather Advisory is issued 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.
Champaign-Clark-Delaware-Franklin-Greene-Licking-Madison-Union
3 inches of snow or under 1/2 inch of sleet in 12 hours or falling and/or blowing snow reducing visibility to 1/4 mile or less, with winds of 34 mph or less or significant black ice conditions.
Fairfield-Fayette-Hocking-Pickaway
2 inches of snow or under 1/2 inch of sleet in 12 hours or falling and/or blowing snow reducing visibility to 1/4 mile or less, with winds of 34 mph or less or significant black ice conditions.
Sustained winds or frequent gusts to 35 mph or greater and falling and/or blowing snow and visibility reduced to 1/4 mile or less for at least 3 hours.
Dense Fog Advisory
A Dense Fog Advisory is issued when fog reduces visibility to 1/8 mile or less over a widespread area.
Derecho
A derecho is a widespread, long-lived wind storm. Derechos are associated with bands of rapidly moving showers or thunderstorms variously known as bow echoes, squall lines, or quasi-linear convective systems. By definition, if the wind damage swath extends more than 240 miles (about 400 kilometers) and includes wind gusts of at least 58 mph (93 km/h) or greater along most of its length, then the event may be classified as a derecho.
Excessive Heat Warning
An Excessive Heat Warning is issued within 12 hours of the onset of the following criteria: heat index of at least 105°F for more than 3 hours per day for 2 consecutive days, or heat index more than 115°F for any period of time.
Excessive Heat Watch
An Excessive Heat Watch is issued by the National Weather Service when heat indices in excess of 105ºF during the day combined with nighttime low temperatures of 80ºF or higher are forecast to occur for two consecutive days.
Flash Flood Warning
A Flash Flood Warning is issued to inform the public, emergency management, and other cooperating agencies that flash flooding is in progress, imminent, or highly likely.
Flash Flood Watch
A Flash Flood Watch is 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.
Flood Warning
A Flood Warning is issued 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.
Flood Watch
A Flood Watch is issued to inform the public and cooperating agencies that current and developing hydrometeorological conditions are such that there is a threat of flooding, but the occurrence is neither certain nor imminent.
Freeze Warning
A Freeze Warning is issued during the growing season when surface temperatures are expected to drop below freezing over a large area for an extended period of time, regardless whether or not frost develops.
Freeze Watch
A Freeze Watch is issued when there is a potential for significant, widespread freezing temperatures within the next 24-36 hours.
Freezing Fog Advisory
Light ice accumulation from freezing fog.
Freezing Rain Advisory
A Freezing Rain Advisory is issued when freezing rain or freezing drizzle is forecast but a significant accumulation is not expected. However, even small amounts of freezing rain or freezing drizzle may cause significant travel problems. Ice accumulation of under 1/4 inch.
Frost Advisory
A Frost Advisory is issued during the growing season when widespread frost formation is expected over an extensive area. Surface temperatures are usually in the mid 30s Fahrenheit.
Hard Freeze Warning
Widespread temperatures at or below 28°F (−2 °C) during the growing season. A hard freeze may occur with or without frost. -No official definition.
Hard Freeze Watch
Widespread temperatures at or below 28°F (−2 °C) during the growing season are possible within the next 24-36 hours. -No official definition.
Heat Advisory
A Heat Advisory is issued within 12 hours of the onset of the following conditions: heat index of at least 105°F but less than 115°F for less than 3 hours per day, or nighttime lows above 80°F for 2 consecutive days.
High Wind Warning
A High Wind Warning is issued when high wind speeds may pose a hazard or is life threatening. The criteria for this warning varies from state to state. In Michigan, the criteria is sustained non-convective (not related to thunderstorms) winds greater than or equal to 40 mph lasting for one hour or longer, or winds greater than or equal to 58 mph for any duration.
High Wind Watch
A High Wind Watch is issued when there is the potential of high wind speeds developing that may pose a hazard or is life threatening. The criteria for this watch varies from state to state.
Ice Storm Warning
An Ice Storm Warning is issued when freezing rain produces a significant and possibly damaging accumulation of ice. The criteria for this warning varies from state to state, but typically will be issued any time more than 1/4" of ice is expected to accumulate in an area. Ice accumulation of 1/4 inch or greater in 24 hours.
Lake Effect Snow Advisory
A Lake Effect Snow Advisory is issued when pure lake effect snow (this is where the snow is a direct result of lake effect snow and not because of a low pressure system) may pose a hazard or it is life threatening. The criteria for this advisory varies from area to area.
Lake Effect Snow Warning
A Lake Effect Snow Warning is issued when pure lake effect snow (this is where the snow is a direct result of lake effect snow and not because of a synoptic storm or low pressure system) may pose a hazard or it is life threatening.
Red Flag Warning
A Red Flag Warning is issued 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:
1) a sustained wind average 15 mph or greater
2) relative humidity less than or equal to 25 percent and
3) 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.
Severe Thunderstorm Warning
A Severe Thunderstorm Warning is issued when either a severe thunderstorm is indicated by the WSR-88D radar or a spotter reports a thunderstorm producing hail one inch or larger in diameter and/or winds equal or exceed 58 miles an hour; therefore, people in the affected area should seek safe shelter immediately. Severe thunderstorms can produce tornadoes with little or no advance warning. Lightning frequency is not a criteria for issuing a severe thunderstorm warning. They are usually issued for a duration of one hour. They can be issued without a Severe Thunderstorm Watch being already in effect.
Severe Thunderstorm Watch
A Severe Thunderstorm Watch is issued when conditions are favorable for the development of severe thunderstorms in and close to the watch area. A severe thunderstorm by definition is a thunderstorm that produces one inch hail or larger in diameter and/or winds equal or exceed 58 miles an hour. The size of the watch can vary depending on the weather situation. They are usually issued for a duration of 4 to 8 hours. They are normally issued well in advance of the actual occurrence of severe weather. During the watch, people should review severe thunderstorm safety rules and be prepared to move a place of safety if threatening weather approaches.
Storm Warning
A Storm Warning is issued as a warning of sustained surface winds, or frequent gusts, in the range of 48 knots (55 mph) to 63 knots (73 mph) inclusive, either predicted or occurring, and not directly associated with a tropical cyclone.
Storm Watch
A Storm Watch is issued for an increased risk of a storm force wind event for sustained surface winds, or frequent gusts, of 48 knots (55 mph) to 63 knots (73 mph), but its occurrence, location, and/or timing is still uncertain.
Tornado Emergency
In exceedingly rare situations, when a severe threat to human life and catastrophic damage from a tornado is imminent or ongoing. (May be included in a Tornado Warning.)
Tornado Warning
A Tornado Warning 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.
Tornado Watch
A Tornado Watch is issued 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 to 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 a place of safety if threatening weather approaches.
Wind Advisory
A Wind Advisory is issued when sustained winds 31 to 39 mph and/or gusts of 46 to 57 mph are present or expected. Issuance is normally site specific. However, winds of this magnitude occurring over an area that frequently experiences such winds.
Wind Chill Advisory
A Wind Chill Advisory is issued when the wind chill could be life threatening if action is not taken. The criteria for this warning varies from state to state. Wind Chill of -10ºF to -24ºF with wind of 10 MPH or greater.
Wind Chill Warning
A Wind Chill Warning is issued when the wind chill is life threatening. The criteria for this warning varies from state to state. Wind Chill of -25ºF or less with wind of 10 MPH or greater.
Winter Storm Warning
A Winter Storm Warning is issued when a winter storm is producing or is forecast to produce heavy snow or significant ice accumulations. The criteria for this warning can vary from place to place.
Champaign-Clark-Delaware-Franklin-Greene-Licking-Madison-Union
6 inches of snow or 1/2 inch of sleet in 12 hours or 8 inches of snow in 24 hours.
Fairfield-Fayette-Hocking-Pickaway
4 inches of snow or 1/2 inch of sleet in 12 hours or 6 inches of snow in 24 hours.
Winter Storm Watch
A Winter Storm Watch is issued 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. Refer to the Winter Storm Warning definition.
Winter Weather Advisory
A Winter Weather Advisory is issued 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.
Champaign-Clark-Delaware-Franklin-Greene-Licking-Madison-Union
3 inches of snow or under 1/2 inch of sleet in 12 hours or falling and/or blowing snow reducing visibility to 1/4 mile or less, with winds of 34 mph or less or significant black ice conditions.
Fairfield-Fayette-Hocking-Pickaway
2 inches of snow or under 1/2 inch of sleet in 12 hours or falling and/or blowing snow reducing visibility to 1/4 mile or less, with winds of 34 mph or less or significant black ice conditions.
Source: The National Oceanic and Atmospheric Administration's National Weather Service.