General Definitions of Product Categories

ADVISORIES	WATCHES	WARNINGS
Advisories are issued when events are expected to remain below the warning criteria, but still cause significant inconvenience. Most common in association with snow events.	A Watch tells you that conditions are favorable and there is a pretty good chance that the event may happen. When a watch is issued begin making preparations for the upcoming event. Listen to your local media to know when warnings are issued. Watches are intended to heighten public awareness of the situation.	A warning means that a certain weather event is IMMINENT. Measures should be taken to safeguard life and property IMMEDIATELY.

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Hazardous Weather Outlook	Special Weather Statement
The Hazardous Weather Outlook will describe potential hazardous weather and hydrologic information of concern in Days 1 through 7. The outlook contains two segments: One segment for the marine zones and adjacent land-based (i.e., coastal) zones and the other segment for the rest of the land-based zones. Each segment of the HWO will contain 3 sections: short term through Day 1, long term for Days 2-7, and spotter information.	The Special Weather Statement is designed to provide critical short term hazardous weather information. The time frame of this information is 6 hours or less. Examples include, but are not limited to: High-Impact, High Resolution Information: Timing and impact information for organized convective storms such as derechos, squall lines, etc. Black ice Timing and impact information for heavy snow bands Heavy rainfall that is forecast to cause nuisance flooding High Heat Indices that are not quite to advisory level Enhanced fire threat that is not quite to warning level.

Hazardous Weather Outlook

Special Weather Statement

The Hazardous Weather Outlook will describe potential hazardous weather and hydrologic information of concern in Days 1 through 7.

The outlook contains two segments: One segment for the marine zones and adjacent land-based (i.e., coastal) zones and the other segment for the rest of the land-based zones. Each segment of the HWO will contain 3 sections: short term through Day 1, long term for Days 2-7, and spotter information.

The Special Weather Statement is designed to provide critical short term hazardous weather information. The time frame of this information is 6 hours or less. Examples include, but are not limited to:

High-Impact, High Resolution Information:
Timing and impact information for organized convective storms such as derechos, squall lines, etc. Black ice
Timing and impact information for heavy snow bands
Heavy rainfall that is forecast to cause nuisance flooding
High Heat Indices that are not quite to advisory level
Enhanced fire threat that is not quite to warning level.

Weather Type:	Advisory	Watch	Warning
Dense Fog	A Dense Fog Advisory is issued when widespread fog is expected to reduce visibilities to 1/4 mile or less over a large area for an extended period of time (2 or more hours).	n/a	n/a
Freezing Rain	A Freezing Rain Advisory is issued when freezing precipitation is expected, however ice accumulations are anticipated to be less than 1/4 inch. These are generally issued 12 to 24 hours prior to the expected start of the event.	n/a	n/a
Ice Storm	n/a	n/a	An Ice Storm Warning is issued when freezing precipitation is expected with 1/4 inch or more of ice accumulation. These are generally issued 12 to 24 hours prior to the expected start of the event.
Winter Weather	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.	n/a	n/a
Winter Storm	n/a	Conditions are favorable for hazardous winter weather conditions including heavy snow, blizzard conditions, or significant accumulations of freezing rain or sleet. These watches are usually issued 12 to 36 hours in advance of the event. Specific criteria are subjective based on region, however generally speaking significant and hazardous winter weather is defined as a combination of: 1) 4 inches or more of snow/sleet within a 12-hour period or 7 inches or more of snow/sleet within a 24-hour period AND/OR 2) Enough ice accumulation to cause damage to trees or powerlines. AND/OR 3) A life threatening or damaging combination of snow and/or ice accumulation with wind.	A Winter Storm Warning is issued when a significant combination of hazardous winter weather is occurring or imminent. Specific criteria are subjective based on region. The criteria listed below are consistent with the Chicago, IL (NWS) Office: 1) Heavy snow of 6 inches or greater. AND/OR 2) Heavy sleet of half inch or more. AND/OR 3) Conditions meet the criteria for two or more separate warnings. Example: If you have Heavy Snow Warning conditions along with Wind Chill Warning conditions, a Winter Storm Warning will be issued.
Blizzard	n/a	n/a	A Blizzard Warning means that the following conditions are occurring or expected for 3 hours or longer within the next 12 to 18 hours. 1) Snow and/or blowing snow reducing visibility to 1/4 mile or less. AND 2) Sustained winds of 35 mph or greater or frequent gusts to 35 mph or greater. There is no temperature requirement that must be met to achieve blizzard conditions.
Snow Advisory*	A Snow Advisory will be issued when 3-5 inches is expected to fall.	n/a	n/a
Lake Effect Snow	n/a	n/a	Lake effect snowfall of 6 inches or more in 12 hours or less, or 8 inches or more in 24 hours or less.
Heavy Snow	n/a	n/a	A Heavy Snow Warning will be issued if 6 or more inches of snow is expected in a 12 hour period.
Blowing Snow	A Blowing Snow advisory will be posted for events in which visibility is intermittently 1/4 mile or less.	n/a	n/a
Frost	A Frost Advisory is issued when the minimum temperature is forecast to be 33 to 36 degrees on clear and calm nights or generally with frost is expected to occur during the growing season. The growing season in the US is generally defined as the period of time between the last occurance of a frost or freeze in the Spring and the first occurance of a frost or freeze in the Autumn.	n/a	n/a
Freeze	n/a	A Freeze Watch is issued during the growing season when there is a potential for significant, widespread freezing temperatures within the next 24-36 hours. See 'Frost Advisory' definition of the growing season.	A Freeze Warning is issued when significant, widespread freezing temperatures are occuring during the growing season. See 'Frost Advisory' definition of the growing season.
Wind Chill**	A Wind Chill Advisory will be issued when the wind chill is less than or equal to -20°F AND the winds are greater than or equal to 10 mph. See NWS Wind Chill Chart to calculate wind chill.	n/a	A Wind Chill Warning is issued when the wind chill will be less than or equal to -30°F AND the winds are greater than or equal to 10 mph. See NWS Wind Chill Chart to calculate wind chill.

*The values for snowfall are accurate for the Chicago area. Check with your NWS office for local snowfall requirements.

**The values for the wind chill products are accurate for the Chicago area. Check with your local National Weather Service office for the warning/advisory criteria where you live.

Weather Type:	Advisory	Watch	Warning
Severe Thunderstorm	n/a	A Severe Thunderstorm Watch is issued for a large area (roughly on the order of 100 square miles or more) by the Storm Prediction Center (SPC) when severe thunderstorms are possible in and near the watch area. Severe thunderstorms are defined as follows: 1) Winds of 58 mph or higher AND/OR 2) Hail 1 inch in diameter or larger. A Severe Thunderstorm Watch may also come with a qualifier that labels it as a "Particularly Dangerious Situations" (PDS). A PDS watch is issued at the discretion of the forecaster and is meant to emphasize an enhanced risk of extraordinary severe and life-threatening weather.	A Severe Thunderstorm Warning is issued by the National Weather Service (NWS) when severe thunderstorms are occurring or imminent for a localized area specific to the storm and the areas expected to be impacted. Severe thunderstorms are defined as follows: 1) Winds of 58 mph or higher AND/OR 2) Hail 1 inch in diameter or larger. AND/OR 3) A tornado is occuring or has recently occured with this thunderstorm*.
Tornado	n/a	A Tornado Watch is issued for a large area (roughly on the order of 100 square miles or more) by SPC when severe thunderstorms capable of producing tornadoes are possible in and near the watch area. Severe thunderstorms are defined as follows: 1) Winds of 58 mph or higher AND/OR 2) Hail 1 inch in diameter or larger. A Tornado Watch may also come with a qualifier that labels it as a "Particularly Dangerious Situations" (PDS). A PDS watch is issued at the discretion of the forecaster and is meant to emphasize an enhanced risk of extraordinary severe and life-threatening weather.	A Tornado Warning is issued by the NWS when a tornado is occurring or imminent. The area warned is a localized area specific to the storm producing the tornado and the areas expected to be impacted. When a tornado warning is issued, seek safe shelter immediately.
Tornado Emergency	n/a	n/a	A Tornado Emergency is a more notorious version of Tornado Warning issued (rarely) at the discretion of the NWS during significant tornado occurrences in highly populated areas. A Tornado Emergency generally means that significant, widespread damage is expected to continue and a high likelihood of numerous fatalities is expected with a large, strong to violent tornado.
Wind	A Wind Advisory is issued when the following conditions are expected for 3 hours or longer. 1) Sustained winds of 31 to 39 mph AND/OR 2) Wind gusts of 46 to 57 mph.	n/a	n/a
High Wind	n/a	A High Wind Watch is issued when the following conditions are possible: 1) Sustained winds of 40 mph or higher for one hour or more OR 2) Wind gusts of 58 mph or higher for one hour or more.	A High Wind Warning is issued when the following conditions are occuring or imminent: 1) Sustained winds of 40 mph or higher for one hour or more OR 2) Wind gusts of 58 mph or higher for one hour or more.
Extreme Wind	n/a	n/a	An Extreme Wind Warning is issued for surface winds of 100 knots (115 MPH) or greater associated with non-convective, downslope, derecho (NOT associated with a tornado), or sustained hurricane winds are expected to occur within one hour.
Dense Fog	A Dense Fog Advisory is issued when widespread fog is expected to reduce visibilities to 1/4 mile or less over a large area for an extended period of time (2 or more hours).	n/a	n/a

*This is mainly for verification purposes. Should a Severe Thunderstorm Warning be issued for a particular storm and neither condition 1 or 2 occured but a tornado occured, then by definition the storm is considered to be 'Severe'.

Weather Type:	Advisory	Watch	Warning
Tropical Storm	n/a	A Tropical Storm Watch is issued when a tropical cyclone containing winds of 34 to 63 kt (39 to 73 mph) or higher poses a possible threat, generally within 48 hours. These winds may be accompanied by storm surge, coastal flooding, and/or river flooding.	A Tropical Storm Warning is issued when sustained winds of 34 to 63 kt (39 to 73 mph) or higher 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.
Hurricane	n/a	A Hurricane Watch is issued when a tropical cyclone containing winds of 64 kt (74 mph) or higher poses a possible threat, generally within 48 hours. These winds may be accompanied by storm surge, coastal flooding, and/or river flooding.	A Hurricane Warning is issued when sustained winds of 64 kt (74 mph) or higher 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.

Weather Type:	Advisory	Watch	Warning
Fire Weather	n/a	A Fire Weather Watch is issued by the National Weather Service (NWS) when potentially dangerous fire weather conditions are expected within the next 24 to 72 hours. Specific fire weather criteria needing to be met for a Fire Weather Watch to be issued are subjective based on region. The following are the criteria needed for Northern Illinois and Northwest Indiana: 1) Sustained winds of 20 mph or higher. 2) Afternoon relative humidity less than 25%. 3) 10 hour fuel moisture at 8% or less for one day.	n/a
Red Flag	n/a	n/a	A Red Flag Warning is issued to alert fire officials and firefighters of potentially dangerous fire weather conditions within the next 24 hours. Specific fire weather criteria needing to be met for a Red Flag Warning to be issued are subjective based on region. The following are the criteria needed for Northern Illinois and Northwest Indiana: 1) Sustained winds of 20 mph or higher. 2) Afternoon relative humidity less than 25%. 3) 10 hour fuel moisture at 8% or less for one day.

Weather Type:	Advisory	Watch	Warning
Coastal Flood	A Coastal Flood Advisory is issued when minor or nuisance coastal flooding is occurring or imminent.	A Coastal Flood Watch is issued when moderate to major coastal flooding is possible. Such flooding would potentially pose a serious risk to life and property.	A Coastal Flood Warning is issued when moderate to major coastal flooding is occurring or imminent. This flooding will pose a serious risk to life and property..
Flood	n/a	A Flood Watch is issued when conditions are favorable for flooding.	A Flood Warning is issued when flooding is imminent or occurring.
Urban and Small Stream Flood	An Urban and Small Streams Flood Advisory is issued when flooding of small streams, streets, and low-lying areas, such as railroad underpasses and urban storm drains, is imminent or occuring.	n/a	n/a
Flash Flood	n/a	A Flash Flood Watch is issued when conditions are favorable for flash flooding. Flash Flood watch covers flash flooding, widespread urban and small stream, and headwater flood events.	A Flash Flood Warning is issued when flash flooding is imminent or occurring. Situations resulting in a Flash Flood include but are not limited to locally heavy rainfall, a dam or levee failure, or water released from an ice jam rapidly flooding nearby land.
River Flood	n/a	A River Flood Watch is issued when river flooding is possible at one or more forecast points along a river.	A River Flood Warning is issued when river flooding is occurring or imminent at one or more forecast points along a river.

Weather Type:	Advisory	Watch	Warning
Heat	A Heat Advisory is issued when the heat index value is expected to reach 105 degrees within the next 12 to 24 hours along with a nighttime low not forecast to fall below 80F. A Heat Advisory may be issued for lower criteria if it is early in the season or during a multi-day heat wave.	n/a	n/a
Excessive Heat	n/a	An Excessive Heat Watch is issued when there is a potential for the following criteria to occur in the next 24 to 48 hours. 1) Heat Index ≥ 115°F for 3 hours AND/OR 2) Heat Index ≥ 105°F for 3 days These criteria are subjective based on region. The values listed above are based on the NWS standard for the U.S.	An Excessive Heat Warning is issued when it is likely that the following criteria will be met within the next 12 to 24 hours. 1) Heat Index ≥ 115°F for 3 hours AND/OR 2) Heat Index ≥ 105°F for 3 days An Excessive Heat Warning may be issued for lower criteria if it is early in the season or during a multi-day heat wave. These criteria are subjective based on region. The values listed above are based on the NWS standard for the U.S.

Weather Type:	Advisory	Watch	Warning
Small Craft	Small Craft Advisories are issued when one or both of the following conditions is expected to begin within 36 hours: 1) Sustained winds of 25 - 33 knots OR 2) Waves of 7 feet or higher Criteria are subjective based on region and issuing office. The values listed above are consistent with the Chicago, IL NWS for lower Lake Michigan.	n/a	n/a
Gale	n/a	n/a	Gale Warnings are issued when sustained winds of 34 - 47 knots not directly associated with a tropical cyclone are predicted or occuring. Gale Warning criteria are subjective and may vary based on region or issuing office. The values listed above are consistent with the Chicago, IL NWS for lower Lake Michigan.
Storm	n/a	n/a	Storm Warnings are issued for when sustained winds >47 knots not directly associated with a tropical cyclone are predicted or occuring. Storm Warning criteria are subjective and may vary based on region or issuing office. The values listed above are consistent with the Chicago, IL NWS for lower Lake Michigan.
Hurricane Force Wind	n/a	n/a	Hurricane Force Wind Warnings are issued sustained winds > 63 knots not directly associated with a tropical cyclone are predicted or occuring.
Special Marine	n/a	n/a	A warning of potentially hazardous weather conditions of short duration (up to 2 hours) affecting areas included in a CWF that are not adequately covered by existing marine warnings and producing one or more of the following: 1) Sustained marine convective winds (showers/thunderstorms) or associated gusts of 34 knots or greater AND/OR 2) Hail three quarters of an inch or more in diameter AND/OR 3) Waterspouts

U.S. Severe Weather Terminology (The Complete Guide)

General Definitions of Product Categories

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