Area Forecast Discussion
Issued by NWS Blacksburg, VA

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FXUS61 KRNK 282109
AFDRNK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
409 PM EST SAT FEB 28 2015

.SYNOPSIS...
HIGH PRESSURE TO OUR NORTH WILL MOVE EAST TONIGHT AND SLIDE OFFSHORE
SUNDAY. THIS WILL RESULT IN A WINTRY MIXTURE LATE TONIGHT INTO
SUNDAY. A COLD FRONT WILL PASS THROUGH THE AREA SUNDAY NIGHT INTO
MONDAY.

&&

.NEAR TERM /THROUGH SUNDAY/...
AS OF 408 PM EST SATURDAY...

A 1044 MB ARCTIC SURFACE HIGH PRESSURE CENTERED OVER PENNSYLVANIA
THIS AFTERNOON WILL WEDGE SOUTH INTO OUR REGION TONIGHT INTO SUNDAY.
THE HIGH CENTER WILL SLOWLY SLIDE SOUTHEAST OVERNIGHT INTO SUNDAY
NIGHT. THIS WILL RESULT IN AN EASTERLY FLOW OF LOW LEVEL MOISTURE AS
A WEAK UPPER SHORTWAVE PIVOT NORTHEAST ACROSS THE REGION. POSTED A
WINTER WEATHER ADVISORY FOR LATE TONIGHT INTO SUNDAY FOR A WINTRY
MIXTURE OF SNOW...SLEET AND FREEZING RAIN. STARTED THE EARLIEST IN
THE SOUTHWEST WHERE LIFT DEVELOPS FIRST AND SPREAD MOISTURE
NORTHEAST OVERNIGHT INTO SUNDAY. INITIALLY SHAPED POPS TOWARDS A
BLEND OF THE HIRESW-ARW...SREF AND NAM...THEN GFS SOLUTION. HARD TO
TELL ONSET WITH MOISTURE RUNNING INTO RESIDUAL COLD/DRY AIR IN PLACE
ACROSS REGION. USED A TOP DOWN APPROACH FOR PYTPES DURING THE
PERIOD. A LIGHT WINTRY MIX WILL DEVELOP IN THE NORTHWEST MOUNTAINS
OF NORTH CAROLINA TONIGHT AND SPREADING UP ALONG THE SOUTHERN BLUE
RIDGE AND POINTS EAST SUNDAY MORNING. MOSTLY CLOUDY OVERNIGHT WITH
LOWS TEMPERATURES FROM AROUND 20 DEGREES IN THE NORTHWEST
MOUNTAINS TO THE MID 20S...STEADYING OR SLOWLY RISING LATE WITHIN
THE SURFACE- 85H WEAK WARM ADVECTION REGIME. GOOD ISENTROPIC LIFT
CONTINUES SUNDAY AS WARM SOUTHWESTERLY WINDS RUN OVER THE TOP OF
THE COLD AIR WEDGE. SNOW AND SLEET ACCUMULATIONS ACROSS THE NORTH
AROUND AN INCH ESPECIALLY IN THE GREENBRIER VALLEY AND ALLEGHANY
HIGHLANDS OF VIRGINIA. ICING WILL RANGE FROM A TRACE/COATING TO UP
TO TWO TENTH OF AN INCH OF ICE EAST OF THE BLUE RIDGE POSSIBLE.
THE WARM AIR WILL RESULT IN A TRANSITION TO RAIN BY SUNDAY
AFTERNOON. WITH THE VERY COLD ANTECEDENT CONDITIONS AND A SNOW
PACK TO REINFORCE THE COLD AIR...THE COLD WEDGE WILL HAVE A HARD
TIME ERODING. TEMPERATURES WILL SLOWLY RISE THROUGH SUNDAY AND
CONTINUE RISING INTO SUNDAY EVENING.

&&

.SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY NIGHT/...
AS OF 405 PM EST SATURDAY...

ACTIVE WEATHER PATTERN TO CONTINUE THROUGH THE PERIOD AS A PARTIALLY
SPLIT/ZONAL FLOW SETS UP ACROSS THE REGION.  THIS PERIOD BEGINS WITH
AN ARCTIC HIGH SPREADING INTO THE REGION FROM THE OHIO VALLEY...WITH
THE ASSOCIATED FRONTAL BOUNDARY STALLING ACROSS THE GULF
COASTAL/SOUTHEAST STATES GIVEN THE ZONAL FLOW ALOFT ACROSS THAT
REGION AND A BROAD UPPER RIDGE DEVELOPING IN THE CENTRAL GULF. ANY
UPSLOPE -SHSN ASSOCIATED WITH THE ARCTIC FRONT SHOULD END EARLY
MONDAY. OVERALL MONDAY SHOULD BE A SEASONABLY COLD DAY WITH PERIODS
OF MID/HIGH CLOUDS ALL AREAS AND LOW CLOUDS EARLY IN THE
WEST/MOUNTAINS.

BY MONDAY NIGHT/EARLY TUESDAY...THE ARCTIC HIGH HAS MOVED EAST
TOWARD THE COAST SETTING UP IN YET ANOTHER FAVORABLE WEDGE
POSITION...SUPPORTED EVEN MORE SO ALOFT WITH THE UPPER RIDGE IN THE
GULF SHIFTING SLIGHTLY EASTWARD AND RIDGING NORTHWARD INTO THE OHIO
VALLEY. MEANWHILE...A DEEP AND FAIRLY PROGRESSIVE TROUGH IS
DEVELOPING IN THE CENTRAL U.S. WITH YET ANOTHER SURGE OF ARCTIC AIR
SPREADING SOUTHWARD THROUGH THE PLAINS. OVERRUNNING/ISENTROPIC WARM
FRONTAL LIFT BEGINS EARLY IN THE DAY TUESDAY ON TOP OF THE RESIDUAL
ARCTIC AIR. THIS WILL LEAD TO WINTER PRECIPITATION AT THE ONSET
ACROSS MUCH OF THE CWA...WITH THE GREATEST THREAT IN THE MOUNTAINS
AND WESTERN AREAS. ACCUMULATING SNOW IS POSSIBLE DURING THIS TIME
FRAME...AT LEAST ON THE ORDER OF A FEW INCHES IN THE WESTERN
COUNTIES. A VERY STRONG LLJ MOVING INTO THE REGION LATE IN THE
DAY/EVENING SHOULD ERODE THE WEDGE FAIRLY QUICKLY...BUT NOT QUITE AS
QUICK AS THE MODELS WOULD SHOW. THUS...THE PRECIPITATION SHOULD
CHANGE TO RAIN DURING THE AFTERNOON. BY TUE NIGHT...THE INITIAL
FRONT IS ON THE WESTERN DOORSTEP AND SHOULD MOVE TOWARD THE PIEDMONT
BY DAYBREAK. THIS COULD CHANGE PRECIPITATION BACK TO OR MIX WITH SNOW
ACROSS THE MOUNTAINS...BUT CURRENT THINKING IS THAT THE COLD AIR
WILL LAG FAR ENOUGH BEHIND THAT THE WINTER WEATHER THREAT WILL BE
LOW AT THIS POINT OUTSIDE THE MOUNTAINS. THIS IS FURTHER SUPPORTED
BY THE FACT THAT UPPER TROUGHING LAGS BACK TO THE WEST AND THE COLD
AIR IS SURGING SOUTHWARD RATHER THAN EASTWARD AT THIS POINT. IN
ADDITION...A WAVE IS EXPECTED TO DEVELOP ALONG THE FRONT IN THE MID-
SOUTH...FURTHER DELAYING THE PUSH OF THE ARCTIC AIR INTO OUR CWA.

IN SUMMARY...THERE ARE SEVERAL CONCERNS DURING THIS PERIOD.
FIRST...SNOW SHOWERS BEHIND THE FIRST ARCTIC FRONT EARLY MONDAY WITH
POSSIBLE 1-3 INCH ACCUMULATIONS ACROSS THE ALLEGHANYS. SECOND...THE
NEXT THREAT OF WINTER WEATHER EARLY TUESDAY WITH ADDITIONAL SNOW
ACCUMULATIONS POSSIBLE IN THE WEST AND NORTH BEFORE THE
PRECIPITATION CHANGES TO RAIN. THIRD...SNOW MELT DURING THIS PERIOD
OF THE FORECAST WILL BE MINIMAL AS THE MAJORITY OF THE TIME FRAME
TEMPERATURES WILL BE IN THE 30S OR BELOW FREEZING AND TOTAL QPF
THROUGH TUESDAY NIGHT SHOULD BE LESS THAN 1/2 INCH LIQUID
EQUIVALENT. FINALLY...THERE WILL BE SOME CONCERN FOR STRONG
SOUTHEAST WINDS TUESDAY EVENING/EARLY WEDNESDAY MORNING IN FAR SW
VA/SE WV AS THE LOW-LEVEL JET TRAVERSES THE AREA AND THE WEDGE
ERODES ACROSS THAT REGION FIRST.

GIVEN THE TENDENCY OF WEDGING MUCH OF THIS PERIOD...HAVE LEANED
TOWARD THE COLDEST GUIDANCE FOR MAX/MIN TEMPS.

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
AS OF 405 PM EST SATURDAY...

WILL START WEDNESDAY OFF WITH A SOUTHWESTERLY LOW LEVEL JET PASSING
ACROSS THE AREA...WITH WINDS STILL IN THE 50KT TO 60KT RANGE JUST
OFF THE SURFACE. NOTING THE POSSIBILITY OF A LOCALIZED DAMAGING WIND
THREAT AS ANY OF THE MORE INTENSE SHOWERS WILL BE CAPABLE OF
BRINGING THESE STRONGER WINDS DOWN TO THE SURFACE DURING THE
MORNING. WIND SPEEDS ALOFT WILL DIMINISH SIGNIFICANTLY BY NOON.

ATTENTION THEN TURNS MORE TO THE POTENTIAL FOR HEAVY RAIN DEVELOPING
WITH THE ARRIVAL OF A STRONG COLD FRONT WEDNESDAY AFTERNOON.
PRECIPITABLE WATER VALUES ACROSS THE AREA JUST AHEAD OF THE COLD
FRONT ARE EXPECTED TO RANGE ANYWHERE FROM 1.0 TO 1.3 INCHES...WHICH
IS SIGNIFICANTLY ABOVE NORMAL FOR EARLY MARCH...MAKING FOR PLENTY OF
AVAILABLE MOISTURE. WILL ALSO CLOSELY MONITOR HOW MUCH SNOWPACK
REMAINS IN THE COMING DAYS IN ADDITION TO ITS WATER EQUIVALENCY.
THIS IS MAINLY FOR THE INTERSTATE 64 CORRIDOR...WHICH HAS RECEIVED
ROUNDS OF HEAVY SNOW WITHIN THE PAST FEW WEEKS. A THIRD FACTOR TO
CONSIDER IS HOW FROZEN THE GROUND IS ACROSS THE REGION...AS FROZEN
GROUND RAISES THE POTENTIAL FOR MOST/ALL OF THE RAIN TO TRANSLATE
DIRECTLY INTO RUNOFF.

AS OF NOW...LOOKING LIKE WE WILL SEE ONE ROUND OF POTENTIALLY HEAVY
RAIN OCCUR WEDNESDAY AFTERNOON ALONG THE COLD FRONT AS IT MOVES
ACROSS THE AREA. THE FRONT WILL BRING WITH IT A NORTHWESTERLY WIND
SHIFT THAT WILL ACTUALLY LEAD TO A BRIEF PERIOD OF DOWNSLOPING AND
REDUCED RAINFALL FOR THE MOUNTAINS. HOWEVER...MODELS ARE IN GOOD
AGREEMENT THAT A STRONG WAVE WILL DEVELOP ALONG THE COLD FRONT
WEDNESDAY EVENING OVER THE COASTAL PLAIN OF THE CAROLINAS...
SLOWING/STALLING THE PASSAGE OF THE FRONT. THIS WILL KEEP ROUNDS OF
HEAVY RAIN PASSING ACROSS THE AREA INTO LATE EVENING. THE PASSAGE OF
THE COLD FRONT WILL BRING WITH IT ANOTHER SHOT OF ARCTIC AIR THAT
WILL END OUR SPRING-LIKE WEATHER FOR THE TIME BEING. AS SUCH...
EXPECT RAIN TO CHANGE TO SNOW ACROSS THE MOUNTAINS WEDNESDAY
NIGHT...WITH SNOW SHOWERS EXTENDING INTO THE PIEDMONT EARLY
THURSDAY. MODELS ARE VERY AGGRESSIVE IN WORKING THE COLDER AIR INTO
THE REGION...BUT PREFER TO BE MORE CONSERVATIVE AT THIS POINT UNTIL
WE GET CLOSER IN TIME TO THE EVENT.

PRECIPITATION WILL GRADUALLY WIND DOWN DURING THURSDAY AFTERNOON AS
THE WAVE EXITS THE AREA...AND HIGH PRESSURE BUILDS IN FROM THE WEST.
HIGH PRESSURE WILL PASS ACROSS THE AREA ON FRIDAY...RESULTING IN
LIGHT WINDS AND MOSTLY CLEAR SKIES...IN ADDITION TO AFTERNOON
TEMPERATURES IN THE 30S WEST AND THE 40S EAST.

&&

.AVIATION /21Z SATURDAY THROUGH THURSDAY/...
AS OF 1235 PM EST SATURDAY...

AS HIGH PRESSURE IN PENNSYLVANIA WEDGES SOUTH INTO OUR
REGION...EASTERLY FLOW EXPECTED THIS AFTERNOON INTO TONIGHT.
VFR CONDITIONS WILL LOWER TO MVFR THIS EVENING INTO TONIGHT.
MID AND HIGH CLOUDS WILL INCREASE ABOVE THE TRAPPED LOW LEVEL
MOISTURE IN ADVANCE OF AN APPROACHING COLD FRONT.

THE LOW LEVEL WIND FLOW WILL CONTINUE TO VEER SOUTHEASTERLY
ACROSS THE MOUNTAINS AND EASTERLY ACROSS THE PIEDMONT AS THE
CENTER OF HIGH PRESSURE SHIFTS OFF THE NEW ENGLAND COAST.
PRECIPITATION WILL BEGIN TO MOVE INTO THE AREA LATE
TONIGHT...STARTING OFF AS BRIEF SNOW/SLEET FOR MANY LOCATIONS BUT
GRADUALLY CHANGING OVER TO FREEZING RAIN AS WARM AIR ALOFT BUILDS
NORTHWARD ALONG THE APPALACHIAN CHAIN.

A WINTRY MIXTURE WILL TRANSITION TO FREEZING RAIN AND RAIN
ON SUNDAY. AS TEMPERATURES WARM ABOVE FREEZING FROM SOUTH TO
NORTH DURING AFTERNOON SUNDAY...CAUSING ALL FREEZING
PRECIPITATION TO CHANGE OVER TO RAIN. MVFR/ IFR CEILINGS AND
REDUCTIONS IN VISIBILITY DUE TO PRECIPITATION ARE EXPECTED
AREAWIDE.

MEDIUM CONFIDENCE ON CEILINGS...VISIBILITIES AND WINDS
DURING THE PERIOD.


A SHARP COLD FRONT WILL CROSS THE AREA MONDAY AFTERNOON WITH
NORTHWEST WINDS INCREASING.

ON THE HEELS OF THE SUNDAY/MONDAY SYSTEM WILL BE YET ANOTHER
POTENTIALLY POTENT SYSTEM THAT MAY IMPACT ALL OR PARTS OF THE
REGION TUESDAY INTO WEDNESDAY WITH SUB-VFR DEVELOPING IN MOST
LOCATIONS LATER TUESDAY INTO WEDNESDAY.

&&

.RNK WATCHES/WARNINGS/ADVISORIES...
VA...WINTER WEATHER ADVISORY FROM 4 AM TO 7 PM EST SUNDAY FOR
     VAZ010>014-016>020-022>024-032>035-043>047-058-059.
     WINTER WEATHER ADVISORY FROM 3 AM TO 5 PM EST SUNDAY FOR
     VAZ007-009-015.
NC...WINTER WEATHER ADVISORY FROM 4 AM TO 7 PM EST SUNDAY FOR
     NCZ003>006-019-020.
     WINTER WEATHER ADVISORY FROM 3 AM TO 5 PM EST SUNDAY FOR
     NCZ001-002-018.
WV...WINTER WEATHER ADVISORY FROM 4 AM TO 7 PM EST SUNDAY FOR
     WVZ042>044-507-508.

&&

$$
SYNOPSIS...KK
NEAR TERM...KK
SHORT TERM...RAB
LONG TERM...NF
AVIATION...JH/KK


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