National Weather Service National Headquarters

• Home
• Site Map
• News
• Organization
• Search for: NWS All NOAA 

000
FXUS61 KRNK 010338
AFDRNK

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BLACKSBURG VA
1038 PM EST SAT FEB 28 2015

.SYNOPSIS...
HIGH PRESSURE TO OUR NORTH WILL MAINTAIN COLD AIR OVER THE AREA
THROUGH SUNDAY. MEANWHILE...AN UPPER LEVEL DISTURBANCE AND
ASSOCIATED AREA OF SURFACE LOW PRESSURE WILL MOVE FROM THE MID-MS
VALLEY TONIGHT INTO WESTERN PENNSYLVANIA BY SUNDAY. MOIST AIR
FLOWING NORTH AHEAD OF THIS DISTURBANCE WILL INTERACT WITH THE
COLD AIR RESULTING IN A WINTRY MIX OF PRECIPITATION ACROSS THE
MID ATLANTIC STATES SUNDAY.

&&

.NEAR TERM /THROUGH SUNDAY/...
AS OF 1000 PM EST SATURDAY...

FORECAST REMAINS ON TRACK...ALTHOUGH THINK IT WILL BE CLOSER TO
DAYBREAK BEFORE WE SEE MUCH IN THE WAY OF ACCUMULATING
PRECIPITATION. ONSET IS STILL FORECAST IN THE 3-5 AM TIME FRAME
AND THIS STILL LOOKS OK.

WARM AIR IS BEGINNING TO FLOW NORTH IN RESPONSE TO APPROACHING
SHORT WAVE FROM THE MID MS VALLEY. AREA TO FOCUS...HOWEVER...IS
NOT JUST THE RADAR RETURNS OVER THE MS VALLEY...BUT THE
PRECIPITATION THAT IS BEGINNING TO BLOSSOM OVER GEORGIA AND SOUTH
CAROLINA. MODELS ADVECT THIS MOISTURE RAPIDLY NORTHWARD AFTER
MIDNIGHT...ENTERING OUR SOUTHERN CWA...NC COUNTIES...AROUND
5AM...THEN EXPANDING NORTH INTO VIRGINIA AND WEST VIRGINIA BETWEEN
5-9AM.

THE EVENING RNK SOUNDING WAS STILL WELL BELOW FREEZING...
SUPPORTING A P-TYPE OF SNOW. MODEL SOUNDINGS DO FORECAST THIS TO
CHANGE BY 12Z/7AM WITH TEMPERATURES WARMING ABOVE 0 DEG C BETWEEN
3-7KFT AGL. THIS WARM NOSE WILL THEN MELT ANY SNOW
FLAKES...RESULTING IN EITHER SLEET OR FREEZING RAIN AT THE
SURFACE.

COLD AIR WITHIN THE FIRST 1-2KFT AGL WILL LIKELY REMAIN IN PLACE
THROUGH MUCH OF THE DAY SUNDAY...REINFORCED BY A 1040 MB ARCTIC
SURFACE HIGH PRESSURE CENTERED OVER NEW ENGLAND. THIS HIGH IS
FORECAST TO GRADUALLY RETREAT...MOVE OFF THE NEW ENGLAND
COAST...DURING THE DAY SUNDAY...SO THE COLD AIR SHOULD SLOWLY BUT
SURELY MODIFY WITH TIME. IT MAY TAKE MOST OF THE DAY SUNDAY
HOWEVER TO COMPLETELY RID THE SUBFREEZING TEMPERATURES...ESP THE
FOOTHILLS JUST EAST OF THE BLUE RIDGE...AND WITHIN THE ROANOKE AND
SHENANDOAH VALLEYS. THE HIGHER ELEVATIONS WILL MOST LIKELY WARM
THE SOONEST PER THE WARMER AIR WORKING ITS WAY FROM TOP DOWN.

WINTER WEATHER ADVISORIES HAVE BEEN POSTED FOR THE ENTIRE CWA...
STARTING THE EARLIEST IN THE SOUTHWEST WHERE LIFT DEVELOPS FIRST
AND SPREADS MOISTURE NORTHEAST OVERNIGHT INTO SUNDAY. INITIALLY
SHAPED POPS TOWARDS A BLEND OF THE HIRESW-ARW...SREF AND
NAM...THEN GFS SOLUTION. HARD TO TELL EXACT ONSET TIME WITH
MOISTURE RUNNING INTO RESIDUAL COLD/DRY AIR WHICH COULD DELAY
START TIME DUE TO PRECIP EVAPORATING BEFORE REACHING THE GROUND.
IF THERE IS A DELAY...IT SHOULD ONLY BE AN HOUR OR TWO FROM
CURRENT ONSET TIMES ALREADY DISCUSSED.

FOR PTYPES...USED A TOP DOWN APPROACH...WHICH SUPPORTS SNOW/SLEET
AT THE ONSET...THEN TRANSITIONING TO FREEZING RAIN. TEMPERATURES
WILL BE NON-DIURNAL...COLDEST AT THE ONSET OF PRECIPITATION...THEN
HOLDING STEADY FOR MUCH OF SUNDAY MORNING...BEFORE INCHING UPWARD
SUNDAY AFTERNOON. THE KEY TO THE WARM UP IS GETTING THE ARCTIC
HIGH TO RETREAT ENOUGH TO ALLOW WINDS AT THE SURFACE TO BECOME
SOUTHERLY. THIS WILL MOST LIKELY NOT TAKE PLACE UNTIL SUNDAY
AFTERNOON. THE ONLY EXCEPTION WILL BE THE WEST SIDE OF THE
APPALACHIAN DIVIDE WHERE WARMER AIR WILL BE MOVING UP THROUGH THE
TENNESSEE VALLEY PERMITTING TEMPERATURES TO CLIMB ABOVE FREEZING
ALOT EARLIER. PLACES LIKE BLUEFIELD...TAZEWELL...RICHLANDS...MARION...
AND THE HIGHER TERRAIN WEST OF BOONE AND WEST JEFFERSON WILL
EXPERIENCE THE TEMPS GETTING ABOVE 32 DEG F B4 ANYONE ELSE.

ISENTROPIC LIFT IS PROGGED TO BE THE GREATEST SUNDAY MORNING
WITH MODELS SUGGESTING THAT 80 PERCENT OF THE QPF WILL FALL
WITHING THE 12Z/7AM-18Z/1PM TIME FRAME...WITH AMOUNTS OF A TENTH
/0.10/ TO A QUARTER OF AN INCH /0.25/ LIQUID EQUIVALENT.
ATTM...MOST OF THIS HAS BEEN CONVERTED INTO SNOW/SLEET ACROSS THE
NORTHERN CWA WHERE WE ARE FORECASTING 1-2 INCHES FROZEN
PRECIPITATION...AND MOSTLY FREEZING RAIN ACROSS THE CENTRAL AND
SOUTHERN CWA WHERE WE ARE FORECASTING 1-2 TENTHS OF AN INCH OF
ICE AND ONLY TRACE TO HALF INCH AMOUNTS...OF SLEET/SNOW. WEST OF
THE APPALACHIAN DIVIDE...A LOT OF THIS MAY FALL AS JUST PLAIN OL
RAIN.

WARMER AIR WILL EVENTUALLY ARRIVE SUNDAY AFTERNOON...POSSIBLY AS
LATE AS SUNDAY EVENING IN OUR FOOTHILL COUNTIES FROM ROA/LYH
NORTHWARD WITH THE THERMOMETER NUDGING ABOVE 32 DEG F. IT WILL BE
A SLOW PROCESS...ESP SINCE WE HAVE ALL THIS SNOW ON THE GROUND
HELPING TO MAINTAIN THE VERY COLD ANTECEDENT CONDITIONS.

&&

.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 /04Z SUNDAY THROUGH THURSDAY/...
AS OF 700 PM EST SATURDAY...

BACKED OFF ON TIMING OF ONSET OF LOW CLOUD THIS EVENING. THE
AIRMASS HAS BEEN TOO DRY TO SUPPORT MUCH IN THE WAY OF LOW LEVEL
CLOUDINESS...THE MODELS TOO PESSIMISTIC WITH THE LOW CIGS. WILL
ADVERTISE VFR CONDITIONS THROUGH MIDNIGHT BEFORE INTRODUING
ANYTHING BLOW VFR.

AREA OF MOISTURE TO WATCH DURING THE OVERNIGHT IS THE
PRECIPITATION OVER GEORGIA AND SOUTH CAROLINA. MODELS ADVECT THIS
MOISTURE NORTHWARD WITH TIME...REACHING THE CENTRAL APPALACHAINS
JUST BEFORE DAYBREAK SUNDAY. AS THE MOISTURE ENCOUNTERS THE COLD
AIR OVER THE MID ATLANTIC...EXPECT A WINTRY MIX WITH SNOW/SLEET AT
THE ONSET...CHANGING TO FREEZING RAIN SUNDAY MORNING. VERY LITTLE
SNOW/SLEET ACCUMULATION IS EXPECTED...HOWEVER...UPWARDS OF 2
TENTHS OF AN INCH OF ICE ACCRETION IS EXPECTED FROM THE FREEZING
RAIN. TEMPERATURES WILL START OFF BELOW FREEZING IN THE
MORNING...THEN CREEP ABOVE FREEZING DURING THE AFTERNOON SUNDAY.
WARMING TEMPERATURES WILL ALSO SIGNAL DECREASE IN VSBY DUE TO
DEVELOPMENT OF FOG AND LOWERING CIGS DUE TO THE DEVELOPMENT OF LOW
LEVEL STRATUS. WIDESPREAD IFR IS ANTICIPATED SUNDAY.

STILL NO MORE THAN MEDIUM CONFIDENCE ON CEILINGS...VISIBILITIES
AND WINDS DURING THE PERIOD. MODELS HAVE NOT DONE A VERY GOOD JOB
WITH THE CLOUD FORECAST...SO USING PAST EXPERIENCE WITH SIMILAR
PATTERN RECOGNITION TO FORECAST CLOUD LAYERS AND P-TYPE. IN THIS
SITUATION THINK INTRODUCTION OF LOW CLOUD WILL HOLD OFF UNTIL JUST
PRIOR TO PRECIP ONSET.

.EXTENDED FORECAST...
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...PM
NEAR TERM...KK/PM
SHORT TERM...RAB
LONG TERM...NF
AVIATION...PM