Area Forecast Discussion
Issued by NWS Blacksburg, VA

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337 FXUS61 KRNK 082351 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 651 PM EST MON FEB 8 2016 .SYNOPSIS...
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A STRONG CYCLONE IN THE UPPER LEVELS OF THE ATMOSPHERE WILL SINK SOUTH ACROSS THE GREAT LAKES AND INTO THE OHIO VALLEY THIS EVENING. THE AREA OF LOW PRESSURE WILL CUTOFF AND REMAIN NEARLY STATIONARY FOR THE NEXT THREE DAYS. THE COLDEST OF THE AIR WILL NOT ARRIVE UNTIL TUESDAY. WEAK UPPER LEVEL IMPULSES WILL MOVE ACROSS THE MOUNTAINS DURING THE WEEK RESULTING IN A PROLONGED SNOW SHOWER EVENT ESPECIALLY OVER THE MOUNTAINS THROUGH MIDWEEK.
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&& .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
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AS OF 615 PM EST MONDAY... FOCUS IS ON TRANSITION OF RAIN TO SNOW IN THE WEST...BUT OVERALL RADAR COVERAGE IS MORE SCATTERED THAN CATEGORICAL IN TERMS OF POPS. WILL FOLLOW CLOSE TO THE 22Z HRRR AND 18Z LOCAL WRF AS IT SLIDES A NARROW BAND OF SNOW ACROSS THE NEW RIVER VALLEY INTO THE SHENANDOAH VLY AND BLUE RIDGE NORTH OF CARROLL COUNTY VA THROUGH EVENING. THERE IS SOME GOOD REFLECTIVITY SIGNATURES AND WITH COLDER AIR ALOFT WE HAVE HAD SOME THUNDERSNOW REPORTS. SOME AREAS COULD SEE A GOOD 1-2 INCHES OF SNOW IN A 1 HOUR PERIOD AND AN SPS WILL COVER THIS THROUGH THE NEXT COUPLE OF HOURS. ONCE THIS MESOLOW ALONG THE FRONT OVER SW VA MOVES EAST EXPECT A DRIER PERIOD BUT UPSLOPE KICKS IN. PREVIOUS DISCUSSION FROM EARLY AFTERNOON... TODAY`S PRECIPITATION DID NOT START UNTIL LATE IN THE MORNING...WHICH ALLOWED TEMPERATURES TO PEAK IN THE UPPER 30S TO LOWERS 40S WEST OF THE BLUE RIDGE TO THE UPPER 40S TO LOWER 50S EAST. WARM AIR ADVECTION AHEAD OF A COLD FRONT BROUGHT SOME SNOW TO HIGHER ELEVATIONS AND WHITE RAIN TO THE VALLEYS THIS AFTERNOON. THIS PRECIPITATION LOWERED TEMPERATURES ACROSS THE MOUNTAINS DURING THE AFTERNOON BY 5F OR SO. BECAUSE THE WARM BOUNDARY IS SO SHALLOW...SNOW WAS ABLE TO MAKE IT TO THE GROUND EVEN...THOUGH TEMPERATURES WERE ABOVE FREEZING. THE FIRST COLD FRONT...LOCATED ACROSS THE OHIO AND TENNESSEE VALLEYS...WILL MOVE ACROSS THE MOUNTAINS EARLY THIS EVENING...THEN ACROSS THE PIEDMONT BY MIDNIGHT. THIS FRONT MAY BE A FEW HOURS SLOWER TO CLEAR THE AREA...AS A SURFACE REFLECTION DEVELOPS ALONG THE FRONT TRACKING ACROSS THE PIEDMONT THIS EVENING. PRECIPITATION WITH THE FRONT WILL REMAIN LIGHT WITH SNOW OR WHITE RAIN ACROSS THE MOUNTAINS AND A COLD RAIN IN THE EAST. A SECOND COLD FRONT WITH ARCTIC AIR WILL APPROACH THE AREA EARLY TUESDAY MORNING. PRECIPITATION AHEAD AND BEHIND THIS FRONT WILL BE ALL SNOW WITH ACCUMULATIONS PRIMARILY ALONG WESTERN SLOPES. WESTERN SLOPES OF GREENBRIER AND SUMMERS COUNTY COULD SEE 2-3 INCHES THIS AFTERNOON INTO TONIGHT. WESTERN SLOPES FROM THE BLUEFIELD-RICHLANDS AREA TO THE GRAYSON HIGHLANDS AND NORTHWEST NORTH CAROLINA HIGH COUNTY COULD HAVE 1-2 INCHES...POSSIBLE 3-4 INCHES ABOVE 4000 FT. FOR HEADLINES...WE WILL CONTINUE THE WINTER WEATHER ADVISORY FOR THE FIRST FRONT THROUGH 6PM THIS EVENING FOR OUR WESTERN COUNTIES. WE WILL ALLOW THIS ADVISORY TO EXPIRE. WE WILL THEN UPGRADE THE CURRENT WINTER STORM WATCH TO A WINTER STORM WARNING FOR WESTERN SLOPES OF GREENBRIER COUNTY SOUTH INTO SUMMERS AND MERCER COUNTY. OTHER COUNTIES IN THE WATCH WILL BE CHANGED TO A WINTER WEATHER ADVISORY FROM THE ALLEGHANY HIGHLANDS TO THE MOUNTAIN EMPIRE AND NORTHWEST NORTH CAROLINA HIGH COUNTY. AT THIS TIME...NO OTHER COUNTIES WILL HAVE HEADLINES TO INCLUDED THE NEW RIVER AND ROANOKE VALLEYS...WHO MAY SEE SOME SNOW TONIGHT INTO TUESDAY WITH ONLY LIGHT ACCUMULATIONS.
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&& .SHORT TERM /6 AM TUESDAY MORNING THROUGH THURSDAY NIGHT/... AS OF 330 PM EST MONDAY... DEEP UPPER LOW OVER THE OHIO VALLEY TUESDAY AND WEDNESDAY. SHORT WAVE OVER THE FORECAST AREA TUESDAY MORNING ALONG WITH MUCH COLDER TEMPERATURES ALOFT...IN THE RANGE OF -30 TO -36 WILL PROVIDE SOME LIFT AND RELATIVE INSTABILITY. THIS SHOULD EXTEND SNOW SHOWERS WELL EAST OF THE BLUE RIDGE ON TUESDAY...ESPECIALLY NORTH OF ROANOKE. 850 MB TEMPERATURES WILL CONTINUE TO DROP...REACHING -18 TO -20 BY 12Z/7AM THURSDAY. MODELS ARE SIMILAR IN OVERALL SYNOPTIC PATTERN BUT SUBTLE DIFFERENCES SHOW UP IN SPEED AND LOCATION OF SHORT WAVED EMBEDDED IN THE LARGE UPPER TROF. ENOUGH COLD AIR COMING IN THAT WESTERN SLOPE LOCATIONS AND AREAS WITH SNOW SHOWERS WILL HAVE STEADY OR EVEN SLIGHTLY FALLING TEMPERATURES DURING THE DAY WEDNESDAY. EXPECTING SNOW TO LIQUID RATIOS OF 25:1 BY WEDNESDAY NIGHT. ENOUGH DRY AIR AND DOWNSLOPING ON WEDNESDAY AND THURSDAY TO HAVE SOME CLEARING EAST OF THE BLUE RIDGE. && .LONG TERM /FRIDAY THROUGH MONDAY/... AS OF 250 PM EST MONDAY... EASTERN UPPER TROF GETS RE-ENFORCED FRIDAY NIGHT AND SATURDAY...THEN TROF AXIS MOVES OF THE COAST ON SUNDAY. BOTH THE ECMWF AND GFS BRING A CLIPPER ACROSS THE CENTRAL UNITED STATES MONDAY THEN INTO THE MID ATLANTIC REGION BY TUESDAY. WPC SUGGESTED THE TRACK OFF THE ECMWF MAY BE TOO FAR SOUTH. SOME 850 MB WARM AIR ADVECTION AND LOW LEVEL CONVERGENCE ALONG THE LEADING EDGE OF THE NEXT SURGE OF ARCTIC AIR. BEST LIFT LOOKS TO BE ON FRIDAY WITH SOME UPPER DIFFLUENCE. SNOW SHOULD BE MORE WIDESPREAD THAN JUST UPSLOPE. THEN GUSTY WINDS AND VERY LOW WIND CHILL VALUES ON FRIDAY NIGHT THROUGH SATURDAY NIGHT WITH NORTHWEST 850 MB WINDS APPROACHING 50 KNOTS. WIND CHILLS WILL AGAIN BE IN ADVISORY CRITERIA...BETWEEN -5 TO -19 IN THE MOUNTAINS ON SATURDAY NIGHT. A ROUGHLY 1045 MB SURFACE HIGH WILL BUILD INTO THE AREA FRIDAY NIGHT AND SATURDAY. THIS FEATURE WILL BE CENTERED OVER THE MID ATLANTIC REGION MONDAY MORNING. WINDS WILL DIMINISH ENOUGH WITH THE APPROACH OF THIS HIGH...AND WITH THE ASSOCIATED DRY AIR...TO END UPSLOPE SNOW SHOWERS IN THE MOUNTAINS SUNDAY. && .AVIATION /00Z TUESDAY THROUGH SATURDAY/...
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AS OF 645 PM EST MONDAY... NARROW BAND OF HEAVIER SNOW WILL MOVE ACROSS BCB/ROA BETWEEN 00Z-01Z...AND ALSO LWB. THERE WILL BE SOME IFR OR LOWER VSBYS WITH THIS BUT SHORT LIVED. OVERALL LOOK FOR MVFR CIGS/VSBYS AT MOST TAF SITES THROUGH THIS PERIOD...EXCEPTION BEING BLF WHERE UPSLOPE WILL PROVIDE SOME IFR CIGS. A STRONGER UPPER VORT MOVING ACROSS SW VA TOWARD 12Z EXPECTED TO BRING AN ENHANCEMENT IN SNOW SHOWERS AT BLF/LWB REACHING BCB BY 13Z. HOW FAR EAST THIS GETS IS DEBATABLE BUT WILL LEAVE ROA/LYH/DAN VFR ONCE NW FLOW KICKS IN. THIS ENHANCEMENT OF SNOW SHOWERS 12-16Z WILL LIKELY RESULT IN IFR AT TIMES BLF WITH MVFR AT LWB/BCB...BUT CANNOT RULE OUT IFR WITH THIS. EXTENDED DISCUSSION... SUB-VFR SHOULD BECOME MORE CONFINED TO THE MOUNTAINS AND WESTERN SLOPES TUESDAY NIGHT INTO MIDWEEK WITH PROLONGED MVFR/IFR CONDITIONS AT KBLF/KLWB IN SNOW SHOWERS THROUGH AT LEAST WEDNESDAY NIGHT AS ARCTIC AIR ARRIVES. POTENTIAL ALSO FOR PERIODS OF MVFR AT KBCB/KROA AS IMPULSES ROTATE ACROSS THE MOUNTAINS AND BANDS OF SNOW DEVELOP DURING THE OVERNIGHT HOURS. ACCUMULATING SNOW IS LIKELY IN THE MOUNTAINS WEST OF THE BLUE RIDGE. FLURRIES MAY ALSO OCCUR AS FAR EAST AS THE PIEDMONT WHERE INTERVALS OF VFR TO MVFR CIGS COULD ALSO OCCUR. CONDITIONS SHOULD BRIEFLY RETURN TO MAINLY VFR THURSDAY/THURSDAY NIGHT AS WEAK HIGH PRESSURE BUILDS IN AND MOISTURE DECREASES. ANOTHER SYSTEM MOVING ACROSS THE SOUTH MAY BRING SUB VFR CONDITIONS WITH WINTRY PRECIP FRIDAY INTO FRIDAY NIGHT. ANOTHER ARCTIC FRONT CROSSES BY SAT MORNING WITH GUSTY WINDS AND UPSLOPE SNOW SHOWERS WITH SUB VFR IN THE MTNS.
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&& .RNK WATCHES/WARNINGS/ADVISORIES...
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VA...WINTER WEATHER ADVISORY UNTIL 7 AM EST THURSDAY FOR VAZ007- 009>012-015-019-020. NC...WINTER WEATHER ADVISORY UNTIL 7 AM EST THURSDAY FOR NCZ001-018. WV...WINTER WEATHER ADVISORY UNTIL 7 AM EST THURSDAY FOR WVZ042>044- 507. WINTER STORM WARNING UNTIL 7 AM EST THURSDAY FOR WVZ043-508.
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&& $$ SYNOPSIS...RCS NEAR TERM...RCS/WP SHORT TERM...AMS LONG TERM...AMS AVIATION...RCS/WP

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