Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 172117 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 417 PM EST WED DEC 17 2014 .SYNOPSIS... HIGH PRESSURE OVER THE UPPER MIDWEST WILL GRADUALLY BUILD EAST ACROSS THE AREA RESULTING IN OVERALL DRY WEATHER THROUGH FRIDAY. PERIODS OF MID/UPPER LEVEL CLOUDINESS WILL SKIRT THE FORECAST AREA PER MOISTURE FESTERING OVER TEXAS. AN AREA OF LOW PRESSURE WILL EVENTUALLY DEVELOP OVER TEXAS BY FRIDAY...MOVING NORTHEAST AND PROVIDING THE MID ATLANTIC REGION A WINTRY MIX OF PRECIPITATION FOR THE WEEKEND. && .NEAR TERM /THROUGH THURSDAY/... AS OF 400 PM EST WEDNESDAY... AREA OF ELONGATED LOW PRESSURE EXTENDED FROM THE GREAT LAKES INTO NEW ENGLAND WITH A RELATIVELY FLAT UPPER LEVEL RIDGE OVER THE SOUTHEAST. CONFLUENT FLOW BETWEEN THE TWO WAS RESULTING IN FAST WESTERLY FLOW ALOFT...MIXING TO THE SURFACE IN THE FORM OF GUSTY WESTERLY WINDS. THE WESTERLY FLOW AND STRONG SUBSIDENCE WAS RESULTING IN A LARGE AREA OF LOW LEVEL CLOUDINESS OVER THE OHIO VALLEY...THIS MOISTURE BUTTING UP AGAINST THE WESTERN SLOPES OF THE WV MTNS...OUR EXTREME NW CWA. ELSEWHERE...THE WESTERLY FLOW WAS RESULTING IN DOWNSLOPE DRYING...WITH LITTLE OR NO CLOUD COVER OVER THE REMAINDER OF THE CWA. SOME UPPER LEVEL CIRRUS WAS BEGINNING TO INCREASE ACROSS THE CWA FROM THE SOUTHWEST COURTESY OF AN UPPER LEVEL DISTURBANCE OVER TX/OK. FOR TONIGHT...LOOKING AT MAINLY CLEAR SKIES TO START WITH...TEMPERATURES QUICKLY FALLING AFTER SUNSET. READINGS MOST AREAS WILL PROBABLY DIP INTO THE 20S UNLESS THE UPPER LEVEL CIRRUS THICKENS AND NEGATES THE RADIATIONAL COOLING. THE LOW LEVEL CLOUDS IN THE OH VALLEY MAY ALSO SNEAK BACK INTO THE GREENBRIER AND NEW RIVER VALLEYS...SOME OF THE MODELS HINTING AT THIS POSSIBILITY. IF THIS OCCURS...THEN LIGHT FREEZING DRIZZLE OR RIME ICE WOULD BECOME POSSIBLE IN THE HIGHER ELEVATIONS. ATTM...HELD OFF ON BRINGING IT BACK INTO THE NEW RIVER VALLEY...BUT DID ADD SOME LOWER CLOUD TO THE FAR NORTHWESTERN CWA FROM BLUEFIELD TO LEWISBURG. BY THURSDAY...AREA OF MOISTURE ASSOCIATED WITH THE DISTURBANCE OVER TX/OK WILL GET CAUGHT UP IN THE FAST WESTERLY FLOW ALOFT...QUICKLY ZIPPING ACROSS THE OH/TN VALLEYS AND REACHING OUR FORECAST AREA DURING THE AFTERNOON/EVENING. THE CONFLUENT FLOW ALOFT HOWEVER...WILL SQUASH ANY CHANCE FOR ANY MEASURABLE PRECIP...ALTHOUGH CERTAINLY CAN`T RULE OUT SOME SPRINKLES OR FLURRIES...A TRACE EVENT. WITH MORE CLOUDS...TEMPERATURES WILL NOT GET NEARLY AS WARM AS THEY DID WEDNESDAY...TOPPING OUT IN THE 40S AS OPPOSED TO THE 50S...A CHANGE OF 10 DEGREES. && .SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY NIGHT/... AS OF 400 PM EST WEDNESDAY... WEAK SHORT WAVE WILL MOVE QUICKLY OFF EAST COAST. MUCH OF THE CLOUD COVER WILL CLEAR FOR THURSDAY NIGHT AND FRIDAY. EARLY FRIDAY NIGHT HIGH CLOUDS AHEAD OF THE NEXT SYSTEM WILL FILL IN FROM THE SOUTHWEST. MAV GUIDANCE USED FOR MAXIMUM AND MINIMUM TEMPERATURES THIS TIME FRAME. WATER VAPOR LOOP SHOWED A COMPACT BUT WELL DEFINED SHORT WAVE OVER SOUTHERN CALIFORNIA. MODELS TRACK THIS FEATURE ACROSS THE SOUTHERN PLAINS THEN INTO THE MID ATLANTIC REGION. SPEED AND TIMING OF THIS SYSTEM ON THE GFS AND ECMWF WERE STILL REASONABLE. THIS BRING THE BEST POSITIVE VORTICITY ADVECTION OVER THE FORECAST AREA ON SATURDAY AFTERNOON AND EVENING...SLIGHTLY SLOWER THAN ON PREVIOUS RUNS. BEST ISENTROPIC LIFT REMAINS JUST SOUTH OF THE FORECAST AREA...AND IS MAINLY ON SATURDAY. FRIDAY NIGHT AND SATURDAY THE SURFACE HIGH MOVES FROM THE GREAT LAKES TO NEW ENGLAND. ON SATURDAY THE SURFACE LOW WILL TRANSITION FROM THE FLORIDA PANHANDLE TO OFF THE SOUTH CAROLINA COAST. THIS WILL BRING WINDS AROUND TO THE EAST THEN NORTHEAST. PRECIPITATION ON SATURDAY WILL HELP ENHANCE AND MAINTAIN AN IN-SITU WEDGE. BUFKIT SOUNDINGS SUPPORT MIXED PRECIPITATION WITH DENDRITIC GROWTH THROUGH 21Z/4PM SATURDAY THEN MAINLY RAIN OR FREEZING RAIN AFTER THAT. ONLY SITE THAT WAS CLEARLY COLD ENOUGH FOR SNOW FOR FROM THE ONSET THROUGH THE DAY SATURDAY WAS NEAR HOT SPRINGS. NAM WAS WARMER WITH THE WARM LAYER ALOFT. LEANING TOWARD COOLER GFS FOR THE EXPECTED TEMPERATURE PROFILE. SURFACE TEMPERATURES ON SATURDAY AND SATURDAY NIGHT WILL HAVE A NON-DIURNAL PROFILE.&& .LONG TERM /SUNDAY THROUGH WEDNESDAY/... AS OF 250 PM EST WEDNESDAY... THIS PORTION OF THE FORECAST HAS THE POTENTIAL TO BE AN ACTIVE WEATHER PATTERN BASED UPON THE VARIOUS MODELS. HOWEVER...THESE SAME MODELS OFFER ENOUGH DIFFERENCES TO MAKE THE DETAILS OF THE SENSIBLE WEATHER ENOUGH OF CHALLENGE THAT CONFIDENCE IN THE SPECIFICS IS NOT HIGH. ON SUNDAY...THE CENTER OF SATURDAY/SATURDAY NIGHT SYSTEM WILL TO OUR EAST ALONG A BAROCLINIC ZONE THAT WILL BE ALONG THE EAST COAST FROM NORTH CAROLINA TO FLORIDA. WHAT REMAINS AS A QUESTION MARK IS WHETHER OR NOT ANOTHER WAVE ALONG THIS SAME BAROCLINIC ZONE WILL PROGRESS FROM GEORGIA NORTHEAST ALONG THE COAST AND DRAW MOISTURE BACK INTO AT LEAST THE EASTERN PORTIONS OF THE REGION. THEN...BY MONDAY...THIS SAME LOW MAY OR MAY NOT STRENGTHEN AND DEEPEN AS ANOTHER CLOSED COASTAL LOW OFF THE COAST OF NORTH CAROLINA. DEPENDING UPON HOW MUCH OR LITTLE THIS SYSTEM DEEPENS WILL CORRELATE TO HOW LONG ANY ASSOCIATED PRECIPITATION REMAINS OVER OUR REGION. THE PRECIPITATION TYPE ACROSS THE AREA IS ALSO A QUESTION. EACH MODEL HAS A DIFFERENT TAKE ON THE MAGNITUDE OF THE WARM NOSE OVER OUR REGION. THE ONLY CONSISTENT ELEMENT IS THE EXISTENCE OF A WARM NOSE. GIVEN THIS...WILL OFFER RAIN VERSUS FREEZING RAIN FORECAST DURING THE LATE SUNDAY NIGHT THROUGH MONDAY PORTION OF THE FORECAST. PRECIPITATION CHANCES THOUGH WILL BE ON THE LOW SIDE...MAINLY RANGING IN THE SLIGHT CHANCE CATEGORY. BY MONDAY NIGHT...GUIDANCE IS IN FAIRLY GOOD AGREEMENT OF BRINGING A CANADIAN LOW PRESSURE SYSTEM INTO THE NORTHERN MISSISSIPPI VALLEY. FROM THAT POINT...A DEEP LONGITUDINAL TROUGH DEVELOPS SOUTH TO THE GULF OF MEXICO BY TUESDAY AFTERNOON WITH INCREASING SOUTHERLY LOW LEVEL FLOW ACROSS OUR REGION...ACCOMPANIED BY AN INCREASING MOISTURE FETCH. BY TUESDAY NIGHT INTO EARLY WEDNESDAY...BOTH THE GFS AND ECWMF CONTINUE TO DEEPEN THE UPPER LOW AND ASSOCIATED TROUGH AND NEGATIVELY TILT THE FEATURE SO THAT THE TROUGH AXIS SHIFTS TO OFF THE COAST OF THE CAROLINAS...COINCIDENT TO THE POSITION OF THE ASSOCIATED SURFACE OCCLUDED FRONT....WITH THE TRIPLE POINT PASSING SOMEWHERE NEAR OR JUST SOUTH OF OUR REGION. THIS PAINTS A PICTURE OF VERY ACTIVE WEATHER ACROSS OUR REGION LATE TUESDAY NIGHT INTO WEDNESDAY WITH PLENTY OF SHOWERS...VERY GUSTY...IF NOT DAMAGING... WINDS...AND IF THE TRIPLE POINT PROGNOSTIC IS ACCURATE...SEVERE WEATHER...OR AT LEAST A RUMBLE OR TWO OF THUNDER...OVER OR VERY CLOSE TO OUR REGION OF THE COUNTRY. HOWEVER...THIS SCENARIO STILL IS DAY 6 INTO DAY 7 OF THE FORECAST...AND THERE IS PLENTY OF TIME FOR CHANGES IN THE OPERATIONAL MODELS TO TREND TOWARD A LESS AGGRESSIVE SYSTEM. GIVEN THIS...WILL OFFER A FORECAST LATE MONDAY NIGHT INTO TUESDAY THAT OFFERS INCREASING CHANCES OF LIGHT RAIN OR FREEZING RAIN ...WITH LIGHT TO MODERATE RAIN ON TUESDAY...WITH MODERATE RAIN SHOWERS TUESDAY NIGHT INTO EARLY WEDNESDAY ALONG WITH GUSTY WINDS. TIMING OF THE PUSH OF COLDER AIR INTO THE REGION AS WELL AS THE MAGNITUDE OF THAT COLDER AIR VARIES BETWEEN THE GFS AND ECWMF. HOWEVER...THE FORECAST WILL ALLOW FOR THE POTENTIAL FOR COLD ENOUGH AIR TO REACH WESTERN...HIGHER PARTS OF THE AREA LATE TUESDAY NIGHT INTO WEDNESDAY FOR ACCUMULATING SNOW SHOWERS. TEMPERATURES DURING THIS PORTION OF THE FORECAST WILL TREND MILDER THROUGH AT LEAST TUESDAY. WEDNESDAY MAY BE A BIT MILDER IN THE EAST...AND SLIGHTLY COOLER IN THE WEST AS COMPARED TO TUESDAY. ALL DAYS OF THIS PORTION OF THE FORECAST ARE EXPECTED TO BE ABOVE NORMAL FOR THIS TIME OF YEAR. && .AVIATION /21Z WEDNESDAY THROUGH MONDAY/... AS OF 130 PM EST WEDNESDAY... STRONG WESTERLY FLOW WILL RESULT IN GUSTY SURFACE WINDS THIS AFTERNOON...GUSTS DIMINISHING TOWARD SUNSET. LOW CLOUDS FROM THIS MORNING HAVE DISSIPATED EAST OF THE MOUNTAINS...BUT REMAIN ON THE WEST SIDE FROM THE OHIO VALLEY SOUTHWARD INTO EASTERN TENNESSEE. KBLF/KLWB ARE NEAR THE TRANSITION BETWEEN THE LOW CLOUDS TO THE WEST AND ESSENTIALLY NO LOW CLOUDINESS TO THE EAST. THIS WILL LIKELY REMAIN THE CASE THROUGH THE 24 HR TAF PERIOD...WITH MVFR AND OCNL IFR CONDITIONS WEST OF KLWB/KBLF...AND VFR FOR KROA/KLYH/KDAN. EXTENDED DISCUSSION... THURSDAY AND FRIDAY LOOK RELATIVELY BENIGN...THOUGH LOWER MVFR CIGS WILL LINGER IN THE WEST THURSDAY. THE FRI NIGHT-SAT SYSTEM NOW HAS TRENDED WEAKER BUT WILL STILL NEED TO BE WATCHED AS IT WILL LIKELY BRING A PERIOD OF SUB VFR WINTRY WEATHER ESPECIALLY FROM THE BLUE RIDGE WEST SAT. AVIATION INTERESTS WILL NEED TO MONITOR THIS SITUATION AS LATER FORECASTS BECOME AVAILABLE. THIS WILL LIKELY HAVE AN IMPACT ON AIR TRAVEL OVER THE WEEKEND...FROM THE SOUTHERN APPALACHIANS AND CAROLINAS NORTH TO THE MID ATLANTIC. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...NONE. NC...NONE. WV...NONE. && $$ SYNOPSIS...PM NEAR TERM...PM SHORT TERM...AMS LONG TERM...DS AVIATION...PM

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