An Outlook is used to indicate that hazardous winter weather
may develop. It is intended to provide information to those
who need considerable lead time to prepare for the event.
A Winter Storm Outlook is needed when there is 30% confidence
that a hazardous winter weather event could threaten life
or property. This typically pertains to the day 3 through
day 7 period- when confidence in a warning event is usually
quite low. Outlooks will normally be very broad- often encompassing
the entire forecast area unless there is very good reason
to exclude any sections. The Winter Storm Outlook information
is disseminated through the Hazardous Weather Outlook (CAEHWOGSP).
WFO GSP will issue winter weather Watches when conditions
are favorable for a hazardous winter weather event to develop
over part, or all, of the forecast area, but the occurrence
is uncertain. This 50% confidence threshold is typically
first met within 48 hours of an approaching winter storm.
Winter weather Watches are, thus, usually issued for events
falling in periods 2 through 4 of the current forecast cycle.
Watches should usually encompass areas slightly larger than
the main winter event threat locations in order to allow for
some uncertainty with the forecast. Watches should also be
issued as soon as confidence thresholds are met, and coordination
allows, in order to achieve the longest lead time possible.
WFO GSP will use CAEWSWGSP to issue
the following types of Watch products:
Winter Storm Watch - Conditions are favorable for either
heavy snow, heavy sleet, damaging ice accumulations, or a
combination of these factors, to develop within the next 48
hours. For the GSP CWFA, heavy snow is defined as 3 inches
accumulating across the foothills and piedmont and 4 inches across the NC mountians in a 12-hour period, or 4 inches across the foothills and piedmont and 5 inches across the NC mountains in a 24-hour
period. Damaging ice accumulations typically result from freezing
rain accumulating 1/4 inch or more on exposed surface. It
has been locally determined that 1/2 inch of sleet is considered
"heavy" for Watch and Warning purposes.
Wind Chill Watch - Conditions are favorable for wind
chill temperatures to fall to 20 below zero in the mountains,
or 15 below zero in the foothills and piedmont, within the
next 48 hours.
Blizzard Watch - Conditions are favorable for a blizzard
to develop within the next 48 hours. A blizzard is falling
or blowing snow accompanied by frequent wind gusts to 35 mph
or greater, with visibility less than 1/4 mile for three hours
Watches should be updated at least every 12 hours
until a Warning or Advisory is issued, or the Watch is cancelled.
WFO GSP will issue winter weather Warnings when there is an
80% or greater chance
of a hazardous winter weather
event meeting or exceeding local Warning criteria
WFO GSP will use CAEWSWGSP to issue
the following types of Warning products:
- 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.
Ice Storm Warning
- Ice accumulation of 1/4 inch or more.
Winter Storm Warning
- Heavy winter weather event producing either:
a. Heavy 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. Warnings are based on the average value (rounded up to the nearest inch) of the forecast snowfall range.
b. Heavy sleet accumulating ½ inch or more.
c. A heavy mixed precipitation event in which snow, sleet, and/or ice reach Warning criteria, or an event containing both winter weather and wind hazards in which weather or wind Warning criteria are met.
Wind Chill Warning - Wind chill temperatures reaching
or exceeding minus 20 in the mountains, or minus 15 outside
of the mountains.
WFO GSP can also issue Winter Warning products
for events where objective Warning criteria are not met if
a significant public impact is expected, e.g. early season
or holiday travel snow or ice storms. Winter Weather Warnings
must be updated at least once every 6 to 8 hours until the
event ends, or the Warning is cancelled.
WFO GSP will issue Winter Weather Advisories to provide advance
notice of hazardous winter weather which could lead to life-threatening
situations if caution is not exercised.
WFO GSP will use CAEWSWGSP to issue
the following types of Advisory products:
Freezing Rain Advisory - Light ice accumulations
(from freezing rain or freezing drizzle) totaling from a
trace to less than 1/4 inch. In practice, a Freezing Rain
Advisory should be issued anytime freezing rain is occurring,
or there is high confidence it will occur, and any glazing
of sidewalks, roadways, or bridges is expected.
Winter Weather Advisory - Hazardous winter weather event producing either:
a. Light snow accumulations of at least one inch, but less than Warning criteria. Since snowfall amounts of ½ inch are rounded to an inch for reporting purposes, snow advisories are appropriate for expected amounts of ½ inch or greater across the foothills and piedmont and 2 inches across the mountains. Advisories can also be issued for “impact events” where a dusting of snow on very cold road surfaces can lead to numerous accidents.
b. Light sleet accumulations of less than ½ inch.
c. Widespread or localized blowing snow reducing visibilities to ¼ mile or less with winds less than 35 mph.
d. Light snow and blowing snow where sustained winds, or frequent gusts, of 25 to 34 mph are accompanied by falling and blowing snow, occasionally reducing visibility to ¼ mile or less for three hours or more.
e. Winter weather events with multiple precipitation types in which at least one precipitation element meets or exceeds Advisory criteria. Or, a winter weather event Advisory-level event plus Advisory criteria wind speeds.
Wind Chill Advisory - Wind chill temperatures reaching
or exceeding minus 5 in the mountains, or zero outside of
WFO GSP will use CAENPWGSP to issue
the following type of Advisory product:
Freezing Fog Advisory - Issued for fog that freezes
upon contact with exposed objects to form a coating of rime
Advisories should be updated at least once every 6 to 8
hours until the event ends, or is cancelled.
Nowcasts and Special Weather Statements
The Short-Term Forecast
(CAENOWGSP) is the primary
vehicle for conveying the evolution of imminent or occurring
winter weather over the next six hours. NOW's are event-driven
and should be updated every 1 to 3 hours when weather conditions
When short-fuse weather conditions require wider dissemination
and more immediate attention, a Special Weather Statement
(CAESPSGSP) can be issued. For example, this might be useful
when mesoscale bands with intense snowfall rates are expected
to set up over a certain location.
Public Information Statements
The Public Information Statement (CAEPNSGSP) is the
primary public product used to summarize the latest winter
precipitation, high wind, or wind chill observations for the
public and the media.