Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 210926 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 426 AM EST SUN DEC 21 2014 .SYNOPSIS...
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HIGH PRESSURE OVER THE OHIO VALLEY WILL MOVE EAST TODAY AND WEDGE DOWN THE EAST SIDE OF THE APPALACHIANS TONIGHT. LOW PRESSURE WILL REMAIN ALONG THE CAROLINA COAST TODAY THROUGH MONDAY. A VERY STRONG COLD FRONT WILL MOVE THROUGH THE REGION ON WEDNESDAY...BRINGING RAIN AND GUSTY WINDS TO THE AREA.
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&& .NEAR TERM /THROUGH TONIGHT/...
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AS OF 330 AM EST SUNDAY... SURFACE HIGH PRESSURE OVER THE OHIO VALLEY MOVES EAST TODAY THEN WEDGES DOWN THE EAST SIDE OF THE APPALACHIANS TONIGHT. BY LATE TONIGHT LOW PRESSURE WILL DEVELOP ALONG THE SOUTHEAST COAST AND HELP RE-ENFORCE THE WEDGE. DEEP WESTERLY FLOW ON THE 00Z SOUNDINGS. ONCE WEAK SHORT WAVE CROSSING OUT OF THE TENNESSEE VALLEY CROSSES THE FORECAST AREA...WINDS DIMINISH WHICH WILL RESULT IN MOST LOW CLOUDS ERODING AND LIGHT PRECIPITATION WILL END. BUFKIT SHOWED THERE WILL BE SOME BREAKS IN THE CLOUD COVER AFTER NOON. CLOUDS FILL BACK IN FROM THE SOUTH TONIGHT. MODELS SIMILAR WITH TIMING OF ISENTROPIC LIFT AND UPSLOPE SOUTHEAST WINDS...BRINGING THE PROBABILITY OF PRECIPITATION INTO THE SOUTHERN COUNTY WARNING AREA AFTER MIDNIGHT...THEN SPREADING NORTH THROUGH 12Z/7AM MONDAY. STAYED CLOSE TO MAV GUIDANCE FOR TEMPERATURES THROUGH THE PERIOD.
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&& .SHORT TERM /MONDAY THROUGH WEDNESDAY NIGHT/...
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AS OF 330 AM EST SUNDAY... FOR MONDAY...AN UPPER LEVEL TROUGH APPROACHING FROM THE WEST WILL SUPPORT LOW PRESSURE DEEPENING OFF THE CAROLINA COAST...WHILE HIGH PRESSURE WILL BE WEDGED AGAINST THE EASTERN FACE OF THE APPALACHIANS. MOISTURE RADIATING INLAND FROM THE LOW WILL ALREADY BE SPREADING ACROSS OUR AREA BY SUNRISE...AND FORECAST TEMPERATURE PROFILES SUPPORT A MIXTURE OF SLEET AND FREEZING RAIN ACROSS THE MOUNTAINS THROUGHOUT THE DAY...AS RAIN FALLING FROM THE WARM AIR RIDING IN ALOFT FROM THE SOUTH FALLS THROUGH THE COLD AIR BEING DRAWN IN BY THE HIGH PRESSURE FROM THE NORTHEAST. EAST OF THE MOUNTAINS...SURFACE TEMPERATURES ARE EXPECTED TO BE WARM ENOUGH THAT ALL PRECIPITATION WILL REMAIN LIQUID. BEST CHANCES FOR PRECIPITATION WILL BE EAST OF THE BLUE RIDGE...CLOSER TO THE LOW PASSING ALONG THE COAST...WITH PRECIPITATION CHANCES DIMINISHING FURTHER WEST AS THE MOISTURE FIGHTS THE DRY AIR ALREADY IN PLACE. PRECIPITATION WILL BE MOST WIDESPREAD DURING THE MORNING AND AFTERNOON...AND WILL DECREASE BY EARLY EVENING AS THE COASTAL LOW BEGINS TO PUSH AWAY FROM THE AREA. STRONG NORTHEASTERLY FLOW AND WIDESPREAD PRECIPITATION WILL STRICTLY LIMIT HEATING THROUGH THE DAY...AND HAVE UNDERCUT MODEL GUIDANCE FOR TEMPERATURES...HOLDING HIGHS IN THE 30S AND LOW 40S MOST LOCATIONS. FOR TUESDAY...THE HIGH PRESSURE WEDGE WILL ONLY SLIGHTLY WEAKEN... BUT WILL DO SO SUFFICIENTLY TO SUPPORT WARMER TEMPERATURES...MAKING FOR RAIN ACROSS THE REGION...PERHAPS WITH A RESIDUAL AND ISOLATED POCKET OF LIGHT FREEZING RAIN IN THE MOUNTAINS. RAIN CHANCES WILL BEGIN TO INCREASE DURING THE EVENING AS A DEEP UPPER LEVEL TROUGH APPROACHES FROM THE SOUTHERN PLAINS...SUPPORTING DEVELOPMENT OF A LOW PRESSURE SYSTEM ALONG THE GULF COAST. THE LOW WILL LIFT NORTH INTO THE TENNESSEE VALLEY OVERNIGHT...RESULTING IN WIDESPREAD RAIN REACHING THE CENTRAL APPALACHIANS BEFORE SUNRISE WEDNESDAY. AS THE LOW LIFTS TOWARD THE GREAT LAKES ON CHRISTMAS EVE...IT WILL CONTINUE TO DEEPEN. WITH IT...THE LOW WILL DRAG A COLD FRONT EASTWARD...WHICH WILL ENTER OUR WESTERN MOST COUNTIES BY AROUND SUNSET. STRONG LOW LEVEL WINDS ASSOCIATED WITH THE LOW MAY REACH TO THE SURFACE AT TIMES...AND MAY RESULT IN SPORADIC TREE DAMAGE AND POWER OUTAGES. ALSO...WITH PRECIPITABLE WATER VALUES REACHING THE BALLPARK OF 1.2 INCHES...MAY SEE LOCALLY HEAVY RAIN AS THE COLD FRONT BEGINS TO PASS ACROSS THE AREA. THE COLD FRONT WILL PASS RAPIDLY EAST LATE CHRISTMAS EVE EVENING... AND MAY SEE A BRIEF SHOT OF STRONG WINDS IN THE WAKE OF THE FRONT...ESPECIALLY ALONG THE HIGHER RIDGES. PRECIPITATION WILL RAPIDLY DIMINISH HOWEVER AS DRIER AIR WORKS IN FROM THE WEST...RESULTING IN ONLY RESIDUAL UPSLOPE SHOWERS THAT WILL CHANGE OVER TO SNOW BY SUNRISE CHRISTMAS DAY.
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&& .LONG TERM /THURSDAY THROUGH SATURDAY/...
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AS OF 300 PM EST SATURDAY... WEST TO NORTHWEST UPPER FLOW WILL CONTINUE INTO THURSDAY WITH MOUNTAIN RAIN AND SNOW SHOWERS. HIGHS CHRISTMAS DAY WILL VARY FROM AROUND 30 DEGREES IN THE NORTHWEST MOUNTAINS TO AROUND 50 DEGREES IN PIEDMONT. WINDS WILL BE QUITE STRONG ON THURSDAY AS A 50 TO 55 KNOT 850MB JET PIVOTS ACROSS THE REGION. AT THIS TIME...LOOKS LIKE VALUES SHOULD REMAIN BELOW WIND ADVISORY LEVELS. AS HIGH PRESSURE SLIDES OFF THE COAST...DRY WEATHER IS EXPECTED CHRISTMAS NIGHT/THURSDAY NIGHT WITH LOW TEMPERATURES GENERALLY IN THE UPPER 20S AND LOWER 30S. THE UPPER FLOW SHIFTS TO THE SOUTHWEST FRIDAY INTO FRIDAY NIGHT AS TROF CURVES OUT IN THE CENTRAL US WITH SFC LOW PRESSURE DEVELOPING OVER THE MIDWEST WITH A FRONTAL BOUNDARY TRAILING SOUTH. HIGHS ON FRIDAY WILL VARY FROM THE LOWER 40S IN THE MOUNTAINS TO THE MID 50S IN THE PIEDMONT. MOISTURE SLOWLY RETURN FRIDAY NIGHT INTO SATURDAY AS FRONTAL BOUNDARY APPROACHES. LOWS FRIDAY NIGHT DROP INTO THE LOWER AND MID 30S IN MOST LOCATIONS. A COLD FRONT MOVES ACROSS OUR REGION SATURDAY INTO SATURDAY NIGHT.
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&& .AVIATION /09Z SUNDAY THROUGH THURSDAY/... AS OF 1100 PM EST SATURDAY... LOW LEVEL MOISTURE WILL REMAIN IN PLACE OVER THE MID ATLANTIC OVERNIGHT. MVFR WILL PERSIST AND POTENTIALLY BECOME IFR VCNTY OF THE MTNS WHERE RIDGES MAY BE OBCSD ATTMS. RESIDUAL BOUNDARY LAYER MOISTURE MAY ALSO LEAD TO SOME VERY LIGHT PRECIP...MIXED DRIZZLE/FLURRIES WITH THE POTENTIAL FOR RIME ICING. CONFIDENCE IS LOWER FOR THE EVENTUAL CLEARING OF FOG AND LOW CEILINGS ON SUNDAY...AS HIGH PRESSURE REMAINS WEDGED AGAINST THE EASTERN SIDE OF THE BLUE RIDGE. SOME OF THE GUIDANCE APPEARS TOO OPTIMISTIC AND DOES NOT ACCOUNT FOR THE REMAINING LAYER OF MOISTURE NEAR THE SURFACE...AS THEY PORTRAY SKIES CLEARING BY 18Z AT ALL TAF SITES. ALTHOUGH CONDITIONS SHOULD EVENTUALLY IMPROVE TO VFR SUNDAY AFTERNOON AT LYH/ROA/DAN...MVFR CEILINGS WERE LEFT AT BCB/LWB/BLF FOR THIS UPDATE AS IT MAY TAKE UNTIL MID/LATE AFTERNOON OR AFTER 18Z/1PM FOR THE LOW CLOUDS TO FINALLY SCATTER. EXTENDED DISCUSSION... A LOW PRESSURE SYSTEM ALONG THE GULF COAST WILL TRACK NORTHWARD ALONG THE EAST COAST DURING SUNDAY NIGHT INTO MONDAY...AND BRING PRIMARILY RAIN AND MVFR/IFR CONDITIONS OVER THE MID ATLANTIC. HOWEVER...THERE IS A POTENTIAL FOR PATCHY AREAS OF FREEZING RAIN ACROSS THE ALLEGHANY HIGHLANDS OF VIRGINIA AND SOUTHEAST WEST VIRGINIA...WHERE TEMPERATURES MAY STRUGGLE TO GET ABOVE FREEZING DURING EARLY MONDAY MORNING. LWB MAY BE IMPACTED...BUT THERE IS LOW CONFIDENCE DUE TO THE UNCERTAINTY OF THE THERMAL PROFILE IN THE MODEL SOUNDINGS. WARM AIR ADVECTION DURING MONDAY AND TUESDAY SHOULD END THE THREAT OF FROZEN PRECIPITATION...BUT PERIODS OF RAIN AND MVFR/IFR CONDITIONS COULD LINGER THROUGHOUT THIS TIME. A STRONG COLD FRONT WILL APPROACH FROM THE WEST BY TUESDAY NIGHT INTO WEDNESDAY. POOR FLYING WEATHER DUE TO MORE RAIN SHOWERS SHOULD ACCOMPANY THE FRONT...AND A STRONG LOW LEVEL JET MAY POSE A LOW LEVEL WIND SHEAR THREAT. GUSTY NORTHWEST WINDS AND A CONSIDERABLE TEMPERATURE DROP ARE EXPECTED BEHIND THE COLD FRONT ON WEDNESDAY NIGHT. UPSLOPE SNOW SHOWERS ARE POSSIBLE ALONG THE WESTERN SLOPES JUST IN TIME FOR CHRISTMAS DAY...WHILE VFR CONDITIONS SHOULD RETURN TO MOST LOCATIONS EAST OF THE BLUE RIDGE. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...NONE. NC...NONE. WV...NONE. && $$ SYNOPSIS...AMS NEAR TERM...AMS SHORT TERM...NF LONG TERM...KK AVIATION...PM/PW

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