From Daryl Stout@57:57/10 to All on Tue Dec 1 00:01:49 2020
Public Information Statement
National Weather Service Little Rock AR
600 AM CST Tue Dec 1 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 precipitation types.
Snow -- Snow forms in the clouds and remains as snow all the way to
the ground. It most commonly takes the form of snowflakes, which
are the familiar six-sided ice crystals. It may also fall in the
from of snow pellets or snow grains.
Snow flurries are normally seen as a few snowflakes falling, although visibilities can be reduced at times. In Arkansas, the term snow
flurries is used to indicate that no accumulation is expected.
Snow showers is a term not often used in Arkansas. Given this type
of precipitation, snow falls at varying rates, often changing
intensities over brief periods. Accumulation may occur, especially
during moderate to heavy snow showers.
Blowing snow refers to snow that is already on the ground and is
lifted into the air by the wind.
In Arkansas, heavier snows usually occur when cold air is already
in place over the state and a strong upper level low pressure
system moves out of the southwestern United States. The low serves
to pull moist air from the Gulf of Mexico northward into the cold
air. Light snow or snow flurries can also occur in the cold air that
follows the passage of an Arctic cold front.
Sleet -- Sleet consists of pellets of ice. In fact, for people who
have trouble with the difference between sleet and freezing rain, it
may be easier to associate sleet with its technical name, which is
ice pellets. For sleet to form, snow begins falling from the clouds
but then goes through a layer of above-freezing air thousands of
feet above the ground. This causes the snow to change to rain. Then,
the rain goes through a layer of below-freezing air, usually at least
two to three thousand feet thick, and the precipitation turns into
pellets of ice.
Sleet typically occurs in a fairly narrow band between an area of
rain to the south and snow to the north. This band usually
moves as the temperature profile changes, but may remain nearly
stationary if temperatures fail to fluctuate. This often results
in accumulations of sleet.
Freezing rain -- This weather phenomenon is sometimes called glaze,
because of the glaze of ice that builds up on surfaces near the ground. Freezing rain normally occurs when precipitation falls from the clouds
as snow, then goes through an above-freezing layer, which turns the precipitation to rain. Then, the rain reaches the ground where
temperatures are below freezing. The rain then freezes as it hits
exposed objects. In the worst cases, everything becomes coated with
a layer of ice.
In Arkansas, freezing rain commonly occurs as an Arctic high pressure
system begins to move away from the state. In this situation, cold
air is still lingering at the ground, but warmer southerly winds
from the Gulf of Mexico begin bringing moisture back over the top
of the cold air. Since the air at the ground has not warmed above
freezing, the rain that falls freezes on the ground and other objects. Freezing rain, and its cousin freezing drizzle, often develop during
the late night hours, creating icy conditions for morning rush hour.
Freezing Fog -- While this is not precipitation falling from the
clouds, it is another winter weather hazard. Freezing fog typically
develops on clear, calm nights when temperatures are below freezing.
Fog forms and freezes, usually on bridges, overpasses, and other
elevated roadways. The resulting thin layer of ice can create
quite a surprise for motorists due to the presence of clear skies
Frost -- Frost describes the formation of thin ice crystals on the
ground or other surfaces in the form of scales, needles, feathers,
or fans. Frost forms when water vapor in the air turns directly
to ice crystals on an object. The temperature of the object must be
below freezing for frost to occur. However, frost is sometimes seen
on the ground when official temperatures are reported to be above
freezing. This is because the official temperature is taken about
five feet above the ground, where the air can be a few degrees
warmer than the temperature at ground level.