Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 010011 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 711 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 /00Z SUNDAY THROUGH THURSDAY/...
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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.
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&& .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...PM

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