Subj : Public Information Statem
To : ALL USERS
From : DARYL STOUT
Date : Tue Nov 17 2015 05:30 pm
PUBLIC INFORMATION STATEMENT
NATIONAL WEATHER SERVICE LITTLE ROCK AR
600 AM CST TUE NOV 17 2015
...WINTER PRECIPITATION TYPES...
NOVEMBER 16TH THROUGH 20TH IS WINTER WEATHER AWARENESS WEEK
IN ARKANSAS. PEOPLE ARE ASKED TO TAKE SOME TIME TO PREPARE FOR
THE UPCOMING WINTER SEASON.
TODAYS 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. IN THIS TYPE OF
PRECIPITATION...THE SNOW FALLS AT VARYING INTENSITIES...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. THIS BAND USUALLY
MOVES...BUT AT TIMES MAY REMAIN NEARLY STATIONARY...RESULTING IN
ACCUMULATIONS OF SLEET.
IN ARKANSAS...SLEET MOST COMMONLY OCCURS IN A NARROW BAND BETWEEN
AN AREA OF RAIN TO THE SOUTH AND AN AREA OF SNOW TO THE NORTH.
FREEZING RAIN -- THIS WEATHER PHENOMENON IS SOMETIMES CALLED GLAZE...
BECAUSE OF THE GLAZE OF ICE IT PUTS ON SURFACES AT 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. IT CAN CREATE QUITE A SURPRISE FOR MOTORISTS...DUE
TO THE PRESENCE OF CLEAR SKIES OVERHEAD.
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.
$$
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