• Winter Weather 2020 (D)

    From Daryl Stout@57:57/10 to All on Wed Dec 2 00:04:24 2020

    Public Information Statement
    National Weather Service Little Rock AR
    600 AM CST Wed Dec 2 2020

    November 30th through December 4th 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 is four inches or more in an event.
    This can be lowered to two to four inches if snow is expected to cause significant travel impacts.

    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/ available
    starting this winter. 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.

    Another new item is 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.

    &&

    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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