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WWA
Definitions

NWS Norman Watch, Warning and Advisory Criteria

Important Note: These criteria are for the National Weather Service Forecast Office in Norman, Oklahoma. These values do not necessarily apply to other offices around the country.

Winter Season Watches, Warnings and Advisories

Snow Advisory
Issued when accumulating snow of 2 to 4 inches is expected. An advisory may still be warranted if lesser accumulations will produce travel difficulties, especially early in the winter season.

Blowing Snow Advisory
Issued when blowing snow is expected to occasionally reduce visibilities to 1/4 mile or less with winds generally 25 to 34 mph. The event should last at least 3 hours.

Snow and Blowing Snow Advisory
Issued when winds of 25 to 34 mph are expected to be accompanied by falling snow and blowing snow, occasionally reducing the visibility to 1/4 mile or less. The event should last at least 3 hours.

Freezing Rain/Drizzle Advisory
Issued for freezing rain when ice accumulations are expected to cause travel problems, but not exceed 1/4".

Sleet Advisory
Issued for accumulating sleet of 1/4" to 1". Because sleet usually occurs with other precipitation types, a winter weather advisory will almost always be used in such cases.

Winter Weather Advisory
Issued for a winter weather event in which there is more than one hazard present, but all precipitation is expected to remain below warning criteria. For example, it would be issued if 2 inches of snow were expected with a small amount of sleet mixing in at times.

Wind Chill Advisory
Issued when wind chill values will reach -5°F to -19°F, with wind speeds around 10 mph or more.

Wind Chill Warning
Issued when wind chill values will reach -20°F or colder, with wind speeds around 10 mph or more. A Wind Chill Watch is issued when these conditions may be met 12 to 48 hours in the future.

Ice Storm Warning
Issued when a period of freezing rain is expected to produce ice accumulations of 1/4" or greater, or cause significant disruptions to travel or utilities.

Heavy Sleet Warning
Issued when a period of sleet is expected to produce ice accumulations of 1" or greater, or cause significant disruptions to travel or utilities.

Heavy Snow Warning
Issued when snow is expected to accumulate 4 inches or more in 12 hours, or 6 inches or more in 24 hours.

Winter Storm Warning
Issued for a winter weather event in which there is more than one hazard present, and one of the warning criteria listed above is expected to be met. For example, it would be issued if 5 inches of snow were expected in 12 hours, with some sleet mixing in at times. It is commonly issued for heavy snow with strong winds of 25-34 mph that will cause blowing and drifting of the snow. A Winter Storm Watch is issued when these conditions may be met 12 to 48 hours in the future.

Blizzard Warning
Issued for sustained wind or frequent gusts greater than or equal to 35 mph accompanied by falling and/or blowing snow, frequently reducing visibility to less than 1/4 mile for three hours or more. A Blizzard Watch is issued when these conditions may be met 12 to 48 hours in the future.

Severe Weather Watches, Warnings and Advisories

Severe Thunderstorm Warning
Issued when there is evidence based on radar or a reliable spotter report that a thunderstorm is producing, or about to produce, wind gusts of 58 mph or greater, structural wind damage, and/or hail 1 inch in diameter or greater.

Severe Thunderstorm Watch
Is issued by the Storm Prediction Center when conditions are favorable for the development of severe thunderstorms over a larger-scale region. Tornadoes are not expected in such situations, but isolated tornado development cannot be ruled out.

Tornado Warning
Issued when there is evidence based on radar or a reliable spotter report that a tornado is imminent or occurring.

Tornado Watch
Is issued by the Storm Prediction Center when conditions are favorable for the development of severe thunderstorms and tornadoes over a larger-scale region.

Significant Weather Advisory
Issued for strong thunderstorms that are below severe levels, but still may have some adverse impacts. Usually issued for the threat of wind gusts of 40-58 mph or hail up to 1 inch in diameter.

Flooding Watches, Warnings and Advisories

Flash Flood Watch
Issued generally when there is the possibility of flash flooding or urban flooding over an area within the next 36 hours.

Flash Flood Warning
Issued when flash flooding is imminent, generally within the next 1 to 3 hours. Usually issued based on observed heavy rainfall (measured or radar estimated), but may also be issued for significant dam breaks that have occurred or are imminent.

Flood Watch
Issued when there is the possibility of widespread general flooding over an area within the next 36 hours.

Flood Warning for River Forecast Point
Issued when a river gauge has exceeded, or is forecast to exceed, a predetermined flood stage.

Flood Advisory
Issued when flooding is imminent or occurring, generally within the next 1 to 3 hours, but is not expected to substantially threaten life and property.

Non-Precipitation Watches, Warnings and Advisories

Wind Advisory
Issued when sustained winds of 30 to 39 mph are expected for 1 hour or longer.

High Wind Warning
Issued when sustained winds of 40 mph or more are expected for 1 hour or longer, or for wind gusts of 58 mph or more with no time limit. A High Wind Watch is issued when these conditions may be met 12 to 48 hours in the future.

Dense Fog Advisory
Issued when fog is expected to reduce visibilities to 1/4 mile or less.

Heat Advisory
Issued when maximum daytime heat index values are expected to reach or exceed 105°F on at least 2 consecutive days, with intermediate low temperatures of 75°F or higher.

Excessive Heat Warning
Issued when maximum daytime heat index values are expected to reach or exceed 110°F on at least two consecutive days, with intermediate low temperatures of 75°F or higher. An Excessive Heat Watch is issued when these conditions may be met 12 to 48 hours in the future.

Frost Advisory
Issued when nighttime minimum temperatures are expected to range from 33°F to 36°F in the growing season.

Freeze Warning
Issued when nighttime minimum temperatures are expected to reach 32°F or lower in the growing season. They are usually issued to highlight the first few freezes of the fall, or unusually late freezes in the spring. A Freeze Watch is issued when these conditions may be met 12 to 48 hours in the future.

Air Stagnation Advisory
Issued only at the request of the Environmental Protection Agency (EPA), whenever atmospheric conditions are stable enough to cause air pollutants to accumulate in a given area.

Blowing Dust Advisory
Issued when blowing dust is expected to reduce visibility to between 1/4 and 1 mile, generally with winds of 25 mph or greater.

Dust Storm Warning
Issued when blowing dust is expected to reduce visibility frequently to 1/4 mile or less, generally with winds of 25 mph or more.

Dense Smoke Advisory
Issued when smoke is expected to reduce visibility to 1/4 mile or less.

Fire Weather Watch
Issued when dry vegetation and conditions favoring extreme fire danger are expected 12 to 72 hours in the future.

Red Flag Warning
Issued when dry vegetation and conditions favoring extreme fire danger are expected, generally within 24 hours.


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