Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 201756 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 1256 PM EST SAT DEC 20 2014 .SYNOPSIS... WEAK LOW PRESSURE ACROSS THE SOUTHEAST STATES WILL PASS EAST AND OFFSHORE THIS AFTERNOON KEEPING MOST SIGNIFICANT PRECIPITATION TO THE SOUTH OF THE REGION. HIGH PRESSURE WILL SPILL BACK SOUTH INTO THE AREA TONIGHT THROUGH SUNDAY NIGHT AHEAD OF ANOTHER LOW PRESSURE SYSTEM THAT WILL SLIDE UP THE COAST ON MONDAY. A STRONG COLD FRONT APPROACHES FROM THE WEST TUESDAY INTO TUESDAY NIGHT BEFORE PASSING THROUGH THE REGION ON WEDNESDAY. && .NEAR TERM /THROUGH TONIGHT/... AS OF 940 AM EST SATURDAY... FLAVOR OF THE GOING FORECAST IS LOOKING GOOD SO JUST MINOR ADJUSTMENTS FOR LATEST OBSERVATIONS AND TRENDS. RETURNS ON RADAR CONTINUE TO RACE EASTWARD THIS MORNING AS AN UNINSPIRED AREA OF LOW PRESSURE CONTINUES TO SLIDE BY TO OUR SOUTH. WATER VAPOR IMAGERY SHOWS A LOT OF DRYING MOVING IN ALOFT SO THERE WILL BE NO DEEP MOISTURE TO WORK WITH ONCE WE GET INTO THIS AFTERNOON...BUT BUFKIT SOUNDINGS STILL SHOW DECENT MOISTURE IN THE LOW LEVELS FROM THE BLUE RIDGE WEST SO LIKELY TRANSITIONING INTO A SNIZZLE SCENARIO FOR THE MTNS. WE SHOULD BE JUST ABOUT DONE WITH MEASURABLE PCPN FOR TODAY SO NOT EXPECTING ANY ADDITIONAL ACCUMS OF SNOW. BEST RETURNS ON RADAR ARE CURRENTLY OVER THE PIEDMONT WHERE LOW LEVELS ARE STILL FAIRLY DRY SO PROBABLY MORE VIRGA THAN ANYTHING REACHING THE GROUND. .PREVIOUS AFD... LIGHT PRECIP EVENT TO UNFOLD THIS MORNING STILL LOOKS ON TRACK AS SURFACE LOW PRESSURE PASSES WELL TO THE SOUTH AND EAST OF THE REGION THROUGH THIS EVENING. THIS SHOULD KEEP THE MAJORITY OF THE BETTER LIFT AND DEEP MOISTURE OFF TO THE SE WITH ANY PRECIP OVER THE REGION PRIMARILY DRIVEN VIA WEAK UPPER DIFFLUENCE BETWEEN MID LEVEL WAVES. ONE SUCH SHORTWAVE BEING WITH THE LEAD SOUTHERNMOST IMPULSE LOOKS TO SLIDE ACROSS NW N CAROLINA THIS MORNING AND COINCIDE WITH WEAK SE FLOW UNDER THE LEFT FRONT OF THE PASSING SPEED MAX ALOFT. THIS SHOULD HELP DEVELOP AN AXIS OF LIGHT SNOW FROM THE NC MOUNTAINS ALONG THE I-77 CORRIDOR EARLY ON WITH SOME OF THIS SPREADING EAST BUT IN A DIMINISHING STATE GIVEN DAMPENING SUPPORT AND RESIDUAL DRY AIR. WITH THE LATEST MODELS ESPCLY SREF PRINTING OUT QPF OF AROUND A TENTH OF AN INCH OR SO...BUMPED UP POPS TO HIGHER CHANCE SW AND KEPT EXTENSION OF THE GOING CHANCE POPS ESPCLY SOUTH OF HIGHWAY 460 THIS MORNING. THIS MAY BRING A HALF/ONE INCH OF SNOW AT ELEVATION FROM I-77 AND POINTS WEST EARLY ON BUT WITHOUT ANY HEADLINES AS COULD EASILY END UP BEING SNOW SHOWERS/FLURRIES AT WORSE PER LATEST RADAR TRENDS. ELSW EXPECT LITTLE OR NO ACCUMULATION GIVEN THE VERY LIGHT PRECIP TYPE SCENARIO IF AT ALL AS SEEN OFF THE LATEST HRRR. HIGH TEMPS REMAIN TRICKY AFTER SUCH A COLD START WITH POTENTIAL TO SEE SOME BREAKS DEVELOP BLUE RIDGE AND ACROSS THE NORTH/WEST LATER ON. THUS TRENDED VALUES UP A DEGREE OR TWO NORTH WHILE DECREASING A CAT OR SO ESPCLY SE WHERE SOMEWHAT DEEPER MOISTURE WILL BE LAST TO EXIT. WEAK RIDGING TO THE NW DIPS BACK INTO THE AREA BEHIND THE DEPARTING WAVE OVERNIGHT ALLOWING DRYING ALOFT TO TAKE SHAPE UNDER WEAK SUBSIDENCE. HOWEVER JUST HOW MUCH LOW LEVEL MOISTURE REMAINS TRAPPED IN QUESTION AND PARTLY DEPENDENT ON THE DEGREE OF MOISTENING TODAY WITH THE CURRENT EVENT. GFS REMAINS RATHER DRY WITH WEAK NW FLOW THROUGH THE COLUMN...WHILE THE NAM WETTER UNDER A LIGHT LOW LEVEL EAST/SE COMPONENT THAT KEEPS QUITE A BIT OF BOUNDARY LAYER MOISTURE ACROSS THE REGION. THIS COULD POSE A FREEZING DRIZZLE ISSUE ESPCLY BLUE RIDGE WITH LOTS OF FREEZING FOG/LOW CLOUDS AROUND BUT QUITE IFFY. THUS WILL GO WITH MORE CLOUDS AND SOME FREEZING FOG OVERNIGHT WHILE LEAVING OUT ANY -FZDZ MENTION FOR NOW DESPITE DECENT DEPTH TO MOISTURE UNDER THE INVERSION OFF THE NAM. LOW TEMPS ALSO REFLECT MOISTURE DIFFERENCES WITH THE MAV MOS WELL INTO THE 20S MOST SPOTS WHILE THE MET MOS A GOOD 5-10 DEGREES WARMER DUE TO CLOUDS. FOR NOW...TWEAKED DOWN IN THE VALLEYS AND BLUE RIDGE WHILE LEAVING THINGS A BIT WARMER WEST-SW WHERE LEFTOVER CLOUDS MORE OF A GOOD BET IN THE WAKE OF TODAYS POSSIBLE PRECIP. && .SHORT TERM /SUNDAY THROUGH MONDAY/... AS OF 430 AM EST SATURDAY... WILL START SUNDAY OFF WITH LOW PRESSURE DEVELOPING ALONG THE SOUTHEAST COAST. HIGH PRESSURE OVER EASTERN CANADA WILL CONTINUE TO BUILD SOUTHWARD ACROSS NEW ENGLAND AND THE MID ATLANTIC...BECOMING INCREASINGLY WEDGED AGAINST THE EASTERN FACE OF THE APPALACHIANS. WILL SEE WINDS SHIFT MORE EAST NORTHEASTERLY BY EVENING...WITH THE UPSLOPE FLOW ALONG THE BLUE RIDGE SUPPORTING POCKETS OF LIGHT RAIN OR DRIZZLE...MAINLY OVER THE NORTH CAROLINA HIGHLANDS BY SUNSET. THE LOW WILL PASS ALONG THE CAROLINA COAST SUNDAY NIGHT...RESULTING IN INCREASING PRECIPITATION CHANCES APPROACHING DAWN ON MONDAY. AS TEMPERATURES COOL THROUGH THE NIGHT...EXPECT TO SEE LIGHT RAIN/ DRIZZLE CHANGE OVER TO A MIXTURE OF RAIN AND FREEZING DRIZZLE OR SLEET ACROSS THE AREA...WITH MORE MIXED PRECIPITATION NORTH OF HIGHWAY 460. FORECAST SOUNDINGS INDICATE THAT MOISTURE REMAINS SHALLOW HOWEVER...SO EXPECT VERY LITTLE ICE ACCUMULATION...IF ANY. 20/00Z MODELS HAVE TRENDED SLIGHTLY WEAKER WITH THIS LOW...WITH SOME MODELS INDICATING MOISTURE HAVING A HARD TIME MAKING IT INTO SOUTHEAST WEST VIRGINIA/FAR WESTERN VIRGINIA...REMAINING MORE CONFINED TO THE PIEDMONT AND BLUE RIDGE. PRECIPITATION AMOUNTS ARE ALSO LOWER...GENERALLY A FEW HUNDREDTHS OF AN INCH ACROSS THE WESTERN RIDGES...TO A TENTH OR TWO ACROSS THE PIEDMONT. MODEST DAYTIME WARMING ON MONDAY WILL CAUSE ANY MIXED PRECIPITATION TO CHANGE OVER TO LIQUID MOST AREAS...ALTHOUGH A FEW POCKETS OF SLEET OR LIGHT FREEZING RAIN MAY LINGER IN THE COLDER AIR ALONG AND NORTH OF THE INTERSTATE 64 CORRIDOR THROUGH THE DAY. THE BRUNT OF THE ENERGY WILL PASS EAST DURING EARLY AFTERNOON...LEAVING ONLY SPOTTY PRECIPITATION THROUGH THE REMAINDER OF THE DAY. BEGINNING MONDAY NIGHT...WILL SEE A GRADUAL WARMING TREND TAKE SHAPE AS A DEEP LOW PRESSURE SYSTEM DEVELOPS OVER THE SOUTHERN PLAINS. THE HIGH PRESSURE WEDGE WILL REMAIN IN PLACE THROUGH THE NIGHT...HOWEVER TEMPERATURES ARE EXPECTED TO REMAIN WARM ENOUGH MOST LOCATIONS FOR PRECIPITATION TO REMAIN LIQUID. LOW PRESSURE WILL PUSH NORTH TOWARD THE GREAT LAKES TUESDAY AND TUESDAY NIGHT...RESULTING IN INCREASING RAIN CHANCES DURING THE PERIOD. PRECIPITABLE WATER VALUES WILL INCREASE SIGNIFICANTLY... ESPECIALLY TUESDAY NIGHT...RISING TO THE 1.1 TO 1.4 INCH RANGE... WHICH IS SIGNIFICANTLY HIGHER THAN NORMAL FOR LATE DECEMBER. AS SUCH...HAVE WENT WILL HIGHER PRECIPITATION CHANCES FOR TUESDAY NIGHT...WITH A COLD FRONT APPROACHING FROM THE WEST. MAY ALSO SEE GUSTY WINDS TUESDAY NIGHT ACROSS THE MOUNTAINS AS A 50KT TO 60KT LOW LEVEL JET ENTERS THE AREA. && .LONG TERM /MONDAY NIGHT THROUGH FRIDAY/... AS OF 400 AM EST SATURDAY... MODEL CONSENSUS OF GFS AND ECMWF IS THAT A SYNOPTIC UPPER TROUGH OVER THE MISSISSIPPI VALLEY WILL EJECT A NEGATIVELY TILTED THROUGH THE SOUTHEAST U. S. EARLY WEDNESDAY. WITH THE POSITION OF THE ASSOCIATED SURFACE OCCLUDED FRONT AND THE TRIPLE POINT PASSING SOMEWHERE NEAR OR JUST SOUTH OF OUR REGION...THERE IS THE POTENTIAL FOR OUR REGION TO HAVE ACTIVE WEATHER WEDNESDAY WITH PLENTY OF SHOWERS...PERHAPS VERY GUSTY WINDS AND A FEW THUNDERSTORMS. LOOKS LIKE THE AXIS OF BETTER INSTABILITY MAY BE A LITTLE FURTHER SOUTH ON THE 12Z MODEL RUN. A COLD FRONT WILL MOVE EAST ACROSS OUR REGION WEDNESDAY INTO WEDNESDAY NIGHT. HIGHS ON WEDNESDAY WILL WARM INTO THE LOWER 40S IN THE WEST TO THE LOWER 50S IN THE EAST. RAIN AND SNOW SHOWERS WILL CHANGEOVER TO SNOW SHOWERS AND SNOW FLURRIES IN THE WEST WEDNESDAY NIGHT. LOW TEMPERATURES WEDNESDAY NIGHT WILL DROP INTO THE MID 20S IN THE MOUNTAINS TO THE LOWER 30S IN THE PIEDMONT. WEST TO NORTHWEST UPPER FLOW WILL CONTINUE INTO THURSDAY WITH HIGHS FROM THE UPPER 20S IN THE MOUNTAINS TO AROUND 50 IN PIEDMONT. WINDS WILL BE QUITE STRONG ON THURSDAY AS A 50 TO 55 KNOT 850MB JET PIVOTS ACROSS THE REGION. THE UPPER FLOW SHIFTS TO THE SOUTHWEST THURSDAY NIGHT INTO FRIDAY AS TROF CURVES OUT IN THE CENTRAL US WITH SFC INFLECTION OF LOW PRESSURE DEVELOPING OVER THE TENNESSEE VALLEY BY FRIDAY MORNING. MOISTURE SLOWLY RETURN FRIDAY NIGHT INTO SATURDAY AS THE HIGH CENTER SLIDE OFF THE COAST. && .AVIATION /18Z SATURDAY THROUGH THURSDAY/... AS OF 1255 PM EST SATURDAY... A WEAK LOW PRESSURE PASSING TO THE SOUTH WILL DEPART OFF THE EAST COAST THIS EVENING...BUT LOW LEVEL MOISTURE WILL REMAIN IN PLACE OVER THE MID ATLANTIC. MVFR CEILINGS SHOULD PERSIST AT BCB/LWB/BLF BEFORE LIKELY FALLING TO IFR TONIGHT. MEANWHILE...CEILINGS AT LYH/ROA/DAN SHOULD STAY VFR DURING THE AFTERNOON...BEFORE DIPPING DOWN TO MVFR TONIGHT. MODEL GUIDANCE HAS TURNED MORE CONFIDENT IN FOG FORMATION BY EARLY SUNDAY MORNING DUE TO LIGHT WINDS AND RESIDUAL BOUNDARY LAYER MOISTURE...WITH IFR/LIFR VISIBILITIES FOR BCB/LWB/BLF...AND MVFR VISIBILITIES FOR LYH/ROA/DAN. PATCHY FREEZING FOG IS ALSO A POSSIBILITY IN THE MOUNTAINS OVERNIGHT. 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 BY MIDDAY SUNDAY AT LYH/ROA/DAN...MVFR CEILINGS WERE LEFT AT BCB/LWB/BLF FOR THIS UPDATE AS IT MAY TAKE UNTIL AFTER 18Z 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...JH NEAR TERM...JH/MBS SHORT TERM...AMS/NF LONG TERM...KK AVIATION...PW

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