[BNAWX] Public Information Statement

[EMWIN Server]

NOUS44 KOHX 181517
PNSOHX
TNZ005>011-022>034-056>066-075-077>080-093>095-190600-
PUBLIC INFORMATION STATEMENT
NATIONAL WEATHER SERVICE NASHVILLE TN
920 AM CST THU NOV 18 2004

...WINTER PRECIPITATION TYPES...

WE END WINTER WEATHER AWARENESS WEEK WITH TODAYS TOPIC...WHICH 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 MOST COMMONLY SEEN AS A FEW SNOWFLAKES FALLING...
ALTHOUGH VISIBILITIES CAN BE REDUCED AT TIMES. IN THE MID SOUTH...THE
TERM SNOW FLURRIES IS USED TO INDICATE THAT NO ACCUMULATION IS
EXPECTED.

SNOW SHOWERS IS A TERM NOT OFTEN USED IN THE MID SOUTH. 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 MOST COMMONLY REFERS TO SNOW THAT IS ALREADY ON THE
GROUND AND IS LIFTED INTO THE AIR BY THE WIND.

IN THE MID SOUTH...HEAVIER SNOWS MOST COMMONLY 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 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 THE MID SOUTH...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 MOST COMMONLY 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 THE MID SOUTH...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.

$$

PLEASE VISIT OUR WEB SITE AT   WWW.SRH.NOAA.GOV/OHX

END/ORCHANIAN



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