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Public Information Statement
National Weather Service Little Rock AR
600 AM CST Wed Nov 29 2023
...Winter Weather Awareness Week in Arkansas...
November 27th through December 1st is Winter Weather Awareness
Week in Arkansas. The purpose of this week is to remind people
what winter weather can bring, and how to deal with
hazardous winter conditions. Now is the time to prepare
for the upcoming winter season.
Today's topic is winter watches, warnings, and advisories.
A watch indicates that conditions are favorable for a winter storm
to develop over all or part of a forecast area, but the occurrence,
location, or timing is still uncertain. Watches are generally
issued when there is a 50 percent or greater chance of a winter
storm.
In Arkansas, watches are usually issued 12 to 24 hours in
advance of the anticipated weather. However, they can be issued as
much as 48 hours in advance. The term Winter Storm Watch is always
used no matter what types of wintry precipitation are expected.
A warning indicates that winter storm conditions are occurring,
imminent, or have a very high probability of occurring. Warnings
are generally issued when there is an 80 percent or greater chance
of a winter storm.
Warnings are issued for conditions posing a threat to life or
property. In Arkansas, warnings are usually issued for weather that
is expected to occur within the next 12 hours. However, they can be
issued as much as 36 hours in advance.
Blizzards, heavy snow, and significant ice /sleet and freezing rain/
are often preceded by watches and warnings.
A blizzard is defined as sustained winds or frequent gusts of 35 mph
or higher, and considerable falling or blowing snow causing visibility
to be frequently less than one quarter mile. A blizzard is an extremely
rare in Arkansas.
In the Little Rock County Warning Area /47 of 75 counties in Arkansas/,
snow is considered heavy when there are three inches or more in an event
across southern, central, and eastern sections of the state, and four
inches or more in the north and west (including the Ozark and Ouachita
Mountains). This is a slight adjustment from the previous heavy snow
criteria, and was made in 2023 as part of a nationwide effort to
improve decision support services, collaboration between forecast
offices, and communication to customers and partners. Non-meteorological
discontinuities were removed to facilitate consistent hazard messaging
and headlines.
The underlying basis of the new heavy snow criteria is a climatological
dataset used by the Winter Storm Severity Index (WSSI). This is a tool
that enhances communication regarding an event's expected severity.
The WSSI provides winter storm impact information out to 72 hours.
Ice is considered significant when freezing rain accruals are at least
one quarter inch thick. Heavy sleet covers the ground to a depth of one
half inch or more.
An advisory is issued for similar conditions to a warning, except
that conditions are expected to be less serious. In other words,
snow or ice is expected, but amounts will be less than required for
a warning. Still, conditions will cause significant inconvenience.
When an advisory is posted, look for less than four inches of snow,
under a quarter inch of freezing rain, and sleet less than a half
inch.
Freeze Warnings are normally issued for the first few freezes in the
fall and for late season freezes in the spring. In far south Arkansas
where freezes are more uncommon, Freeze Warnings may be issued at any
time during the winter.
Frost Advisories are issued for the first few frosts in the fall and
for late season frosts in the spring.
Wind Chill Warnings are relatively new. In the counties for which the
National Weather Service in Little Rock makes the forecast, warnings
will be issued for wind chills of 15 below zero or lower when winds
average 10 mph or more, and conditions are expected to persist for an
hour or more.
Wind Chill Advisories are issued for wind chills of zero degrees or
lower when winds average 10 mph or more, and conditions are expected
to persist for three hours or more.
Freezing fog Advisories are issued when fog is present with temperatures
below freezing, and the fog is expected to cause a thin layer of ice to
develop on bridges, overpasses, and other elevated roadways.
There is a short fuse warning /30 to 60 minute valid time/ that was
introduced recently. A Snow Squall Warning will be issued when a brief
period of intense snowfall /moderate to heavy in intensity/ is expected,
accompanied by gusty winds resulting in reduced visibility /a quarter
mile or less/. Ideally, road temperatures would be sub-freezing. It is
thought this type of warning will seldom be disseminated.
&&
For more information about Watches, Warnings, and Advisories:
https://www.weather.gov/lzk/lzkwwa.htm
For the latest Winter Storm Severity Index (WSSI):
https://www.wpc.ncep.noaa.gov/wwd/wssi/wssi.php?id=LZK
$$
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