The National Weather Service at Greenville-Spartanburg's Criteria for Outlooks, Watches, Warnings and Advisories


Hazardous Weather Outlook

  • Issued daily to inform the public, emergency managers, media, and Skywarn Spotters of the potential for winter, fire, convective, or non-precipitation weather, tropical, marine or flood hazards within the next 7 days.

    Products Associated With Precipitation

    WINTER WEATHER

    Winter Storm Watch/Warning/Outlook

    • A Winter Storm Outlook (issued as a Special Weather Statement) is issued when there is a significant possibility of a winter storm beyond the period for which watches are usually issued. This is usually 48 hours or more in the future.
    • A Winter Storm Watch is issued when conditions are favorable for hazardous winter weather conditions to develop during the 2nd, 3rd or 4th periods, but occurrence is still uncertain (generally a 50% or greater chance of meeting/exceeding watch criteria.).
    • A Winter Storm Warning is issued when hazardous or significant winter weather is occurring, imminent or has a very high probability of occurrence. (normally 1st period, can be extended in 2nd, can also be issued for 2nd period, and occasionally 3rd). Warnings are recommended when there is a 80% or greater chance of meeting/exceeding warning criteria.
    • Criteria: Snow accumulating 3 inches across the foothills and piedmont and 4 inches across the NC mountains in a 12-hour period, or 4 inches across the foothills and piedmont or 5 inches across the NC mountains in a 24-hour period, a 1/4" accumulation of ice from freezing rain, or 1" of sleet expected within a 12 hour period. A warning may also be issued based on public impact alone. For example, heavy, wet snow or mixed precip significantly affecting transportation, utilities, etc, can trigger a warning even though snowfall is expected to fall short of criteria.

    Blizzard Warning

    • Blizzard Watches are not issued.
    • Criteria: sustained wind or frequent gusts to 35 mph or more and considerable falling and/or blowing snow reducing visibility to less than 1/4 mile.

    Winter Weather Advisory

    • Issued when winter weather situations are expected to cause significant inconvenience, but do not meet storm criteria (issued for the 1st 12 hours of the forecast, but can extend to 24 hours) Advisory level conditions can cause widespread traffic accidents, for example.
    • Criteria: 1" of snow across the foothills and piedmont or 2" of snow across the NC mountains, or less than 1/4" ice accumulation expected within a 24 hour period. Product can be issued even when lower amounts are expected if the forecaster feels that there will still be significant inconvenience for the public.

    CONVECTIVE EVENTS

    Severe Weather Outlook 

    • Issued when there is a chance for severe convective storms, tornadoes or convectively induced flash flooding from 6 to 24 hours in the future.

    Tornado/Severe Thunderstorm Watch

    • Issued by the Storms Prediction Center (SPC) when there is a chance for severe thunderstorms or tornadoes during the 1st period of the forecast (generally within 8 hours of the present time).
    • Our office does not issue Tornado or Severe Thunderstorm Watches. However, we can extend a watch in time. A watch extension is issued as a Severe Weather Statement. We can also clear the watch for certain counties in our County Warning and Forecast Area (CWA). This product is issued as Special Weather Statement.

    Tornado Warning

    • Issued when there is a radar signature indicative of a tornado, or when a reliable spotter report is received. 

    Severe Thunderstorm Warning

    • Issued when there is a radar signature indicative of a severe thunderstorm, or when a reliable spotter report is received.
    • Criteria: radar signature, or spotter reports, indicate 1) Winds of 58 mph or greater 2) Hail the size of a quarter or larger 3) Or any thunderstorm producing wind or hail damage.
    • The National Weather Service does not issue warnings for lightning.

    The Fujita Scale for Wind Damage - We do not issue a warning with any expectation of Fujita-scale damage. However, as this question is often asked, here are the F-scale rankings for wind/tornado damage:

    F0- Weak - 40-72 mph

    F1- Weak - 73-112 mph

    F2- Strong - 113-157 mph

    F3- Strong - 158-206 mph

    F4- Violent - 207-260 mph

    F5- Violent - 261-318 mph

     

    Products Not Associated With Precipitation

    Frost Advisory/Freeze Warning

    • A Frost Advisory is issued when a frost of sufficient strength to end the growing season is expected. This product is usually issued within 24 hours of an event.
    • A Freeze Warning is issued when temperatures are expected to fall to 32 degrees or below over a large area for a climatologically significant period of time. This product is usually issued within 24 hours of an event.
    • In the Autumn we issue Frost Advisories beginning with the first event when frost (36) is expected for representative areas in a county. We continue issuing those products as needed until that county has experienced a freeze (32). Similarly, Freeze Warnings will begin to be issued when a freeze (32) is first expected for representative areas in a county, and will continue to be issued as needed until a freeze (32) is observed at representative locations in that county. There is no longer a cutoff date for frost advisories and freeze warnings in Autumn.
    • In the Spring, starting with the Spring 2002 season, Frost Advisories (36) and Freeze Warnings (32) will be issued starting on the average last date of freeze (32) for groups of counties. These county groupings will be based on climatology, and determined my local management. The program then continues to be active, until the fall freeze makes it dormant.

    Wind Chill Warning/Advisory

    • A Wind Chill Warning is issued when wind chill values are forecast to fall to  -15F in the lower elevations of our CWA, to -20F in the higher elevations, including the mountains and northern foothills. This product is usually issued within 12 hours of an event.
    • A Wind Chill Advisory is issued when wind chill values are forecast to fall to 0F in the lower elevations of our CWA, to -5F in the higher elevations, including the mountains and northern foothills. This product is usually issued within 12 hours of an event.

    High Wind Outlook/Watch/Warning

    • A High Wind Outlook is issued when there is a significant possibility of non-thunderstorm high winds beyond the period for which watches are usually issued. This is usually 48 hours or more in the future.
    • A High Wind Watch is issued when non-thunderstorm high winds are expected to develop during the 2nd-4th periods of the forecast (12-48 hours). An outlook is issued when high winds are expected beyond the 3rd period.
    • A High Wind Warning is issued when non-thunderstorm high winds are expected during the 1st, and occasionally the 2nd period of the forecast. (0-24 hours)
    • Criteria: Sustained non-thunderstorm winds of at least 40 mph for 1 hour or more, or frequent gusts to 58 mph or greater. An Inland High Wind Watch for Hurricane Force Winds can also be issued, but only when sustained winds of 74 mph or greater are expected (a very rare occurrence in our CWA).

    Wind Advisory

    • Issued during the 1st period, but can occasionally be extended into the second period (0-24 hours).
    • Criteria: Sustained wind of 31-39 mph for at least 1 hour, or frequent gusts 46-57 mph.

    Wind Advisory For Area Lakes

    • Issued when conditions are expected to be hazardous for boaters on area lakes. Can be thought of as an inland version of a Small Craft Advisory. This product is only issued for the 1st period of the forecast (0-12 hours).
    • Criteria: Sustained wind of 25 mph, or frequent gusts to 40-45 mph.

    Excessive Heat Outlook/Watch/Warning

    • An Excessive Heat Outlook is issued from the 3rd period of the forecast outward (36 hours or more). An Excessive Heat Watch is issued mainly for the 2nd period of the forecast (12-24 hours). An Excessive Heat Warning is issued only for the 1st period of the forecast (0-12 hours).
    • Criteria: a daytime heat index of 110F or more is expected for any length of time. The nighttime minimum and consecutive days criteria has been dropped.

    Heat Advisory

    • A Heat Advisory is issued only for the 1st period (0-12 hours).
    • Criteria: daytime heat index reaches 105F or more for 3 hours or more, but remains below warning criteria.

    Dense Fog Advisory

    • Usually issued during the 1st period (0-12 hours).
    • Criteria: fog reducing visibility to 1/4 mile or less over a large area.

     

    Hydrometeorological Products

    Hydrologic Outlook

    • Issued beyond the period when a Flood Watch is issued. This is usually more than 36 hours in the future. The product is also issued to detail the severity of droughts and for other water resource issues.
    • The product can have the following headlines:
      • ...FLOOD POTENTIAL OUTLOOK...
      • ...WINTER/SPRING FLOOD OUTLOOK...
      • ...DROUGHT/WATER RESOURCE STATEMENT...

    Flood Watch

    • Issued when hydrometeorological conditions that could result in flooding are expected in the 1st 36 hours of the forecast period.

    Flash Flood Warning

    • A Flash Flood Warning is issued for flooding which occurs within 6 hours of the onset of precipitation.
    • Criteria: Issued when rapid increases in water levels along creeks, streams, and non main-stem rivers is imminent that create a serious hazard to life and property. This is an event that is more than just standing water on roads, water is usually quite deep or is moving rapidly. A flash flood typically describes an event in which flood waters rise to dangerous levels in a short period of time. Flash flood warnings are also issued for dam failures. The product is issued for counties, parts of counties, well-known geographical areas, or river basins.

    Flood Warning.

    • A Flood Warning is issued for flooding which occurs beyond 6 hours of the onset of precipitation.
    • Criteria: Flooding does not occur rapidly and lasts longer than 6 hours, though it is still not associated with main-stem rivers. Because this type of flooding can be widespread and flood waters do not subside quickly, it can be considered a possible hazard to life and/or property. They product is issued for counties, parts of counties, areas along rivers and streams, or hydro forecast points.

    Flash Flood Statement.

    • A Flash Flood Statement is now issued to provide supplemental info on Flash Flood Warnings only. Also issued to cancel or expire a Flash Flood Warning.

    Criteria for all other hydrologic products are found on our hydrology page


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    Page created 1/23/2001 by Bryan McAvoy
    Page updated 02/20/2003 by Webmaster
    Original Page Layout by Chris Horne
    Document reviewed by Laurence Lee and Wayne Jones