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 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 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
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
- 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.
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
- 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
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
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).
- 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
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
- 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.
- 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...
- 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.
- 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
Page updated 02/20/2003 by
Original Page Layout by Chris
Document reviewed by Laurence Lee and