Area Forecast Discussion
Issued by NWS Blacksburg, VA

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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

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