Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 171848 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 148 PM EST WED DEC 17 2014 .SYNOPSIS... HIGH PRESSURE WILL GRADUALLY BUILD EAST INTO THE AREA THIS AFTERNOON AND TONIGHT RESULTING IN OVERALL DRIER WEATHER UNDER GUSTY NORTHWEST WINDS. THE HIGH WILL REMAIN ACROSS THE REGION THROUGH THE END OF THE WEEK BEFORE MOISTURE STARTS TO RETURN AHEAD OF A LOW PRESSURE SYSTEM APPROACHING FROM THE SOUTHWEST LATE FRIDAY NIGHT. THIS SYSTEM WILL BRING UNSETTLED WEATHER WITH A MIXED BAG OF PRECIPITATION POSSIBLE SATURDAY INTO SATURDAY NIGHT BEFORE DRIER WEATHER RETURNS ON SUNDAY. && .NEAR TERM /THROUGH TONIGHT/...
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AS OF 100 PM EST WEDNESDAY... STRONG DOWNSLOPE WARMING AND DRYING HAS DONE A GOOD JOB AT MITIGATING THE COLD AIR ADVECTION CLOUDINESS FROM YESTERDAYS FRONTAL PASSAGE. WITH THE EXCEPTION OF JUST THE WESTERN SLOPES OF THE WV MTNS...DECREASED CLOUD COVER AND INCREASED TEMPERATURES A FEW DEGREES. FOR THE REMAINDER OF THE AFTERNOON ANTICIPATING MOSTLY SUNNY SKIES. MODELS DO HINT AT SOME MOUNTAIN WAVE CIRRUS DEVELOPING MID AFTERNOON. AS OF 1PM...NOT SEEING MUCH. WITH THE NEXT GRID UPDATE WILL NIX POPS ON THE WESTERN SLOPES. MOISTURE HAS BECOME TOO SHALLOW AND CLOUD TOP TEMPERATURES HAVE BECOME TOO WARM TO SUPPORT PRECIP DEVELOPMENT. FOR TONIGHT...UPPER TROUGH PIVOTS BY TO THE NE OVERNIGHT ALLOWING WEAK HIGH PRESSURE TO GRADUALLY BUILD IN FROM THE WEST. HOWEVER FAST BUT ZONAL CONFLUENT FLOW ALOFT LIKELY TO BRING SOME SHEARED MID/HIGH CLOUDS IN AS EARLY AS THIS EVENING ESPCLY SOUTH BEFORE FADING SOMEWHAT OVERNIGHT PER GUIDANCE RH SECTIONS. OTRW STILL EXPECTING NW FLOW TO KEEP LOW CLOUDS BANKED UP AGAINST THE WESTERN SLOPES WITH PERHAPS ADDED FREEZING DRIZZLE IN SPOTS BUT GIVEN UNCERTAINTY WONT INCLUDE FOR NOW. LOW CLOUDS COULD AGAIN SPILL OUT TO THE BLUE RIDGE LATE WITH MAINLY PC ELSW FOR HIGH CLOUDS. COMBO OF ADDED MIXING AND CLOUDS SHOULD HOLD TEMPS UP...WITH UNIFORM UPPER 20S/LOW 30S ACROSS THE REGION WITH A FEW MID 20S VALLEYS PENDING CLOUDS.
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&& .SHORT TERM /THURSDAY THROUGH SATURDAY/... AS OF 330 AM EST WEDNESDAY... EXPECT THURSDAY TO BEGIN WITH FAIR WEATHER EAST OF THE BLUE RIDGE... BUT CONDITIONS WILL BE OVERCAST WEST OF THE RIDGE THANKS TO NW UPSLOPE FLOW AND A SHALLOW LAYER OF MOISTURE TRAPPED UNDER THE SUBSIDENCE INVERSION...WHICH IS SHOWN NICELY BY BUFKIT MODEL SOUNDINGS. JUST AS THE LOW LEVEL MOISTURE IS ON THE WAY OUT WE TRANSITION TO SOME MID LEVEL CLOUDINESS. MODELS CONTINUE TO JUST WHEN THIS SHALLOW MOISTURE IS DISSIPATING...MID LEVEL MOISTURE WILL SPREAD OVER THE AREA AS A WEAK SHORT WAVE MOVES THROUGH THE REGION IN ZONAL UPPER FLOW. VARIATIONS ON THIS THEME FOR THURSDAY HAVE BEEN ADVERTISED BY GUIDANCE FOR THE PAST FEW RUNS. BELIEVE WE WILL LACK ENOUGH MOISTURE TO GENERATE ANYTHING MORE THAN A SPRINKLE OR FLURRY FOR THE RIDGES SO WILL CONTINUE TO CARRY POPS AT OR BELOW SLIGHT CHANCE THURSDAY AND THURSDAY NIGHT. FAIR CONDITIONS WITH INCREASING CLOUDS FOR FRIDAY AS HIGH PRESSURE SLIDES BY TO OUR NORTH AND STARTS WORKING ITS WAY DOWN THE EASTERN SEABOARD AS A WEAK WEDGE. OUR ATTENTION THEN TURNS TO THE DEVELOPING LOW PRESSURE SYSTEM WE HAVE BEEN FOLLOWING FOR THE PAST SEVERAL DAYS AS IT MOVES FROM THE GULF COAST THE MIDDLE ATLANTIC COAST THIS WEEKEND. OVERALL...THE LOW AMPLITUDE SPLIT FLOW UPPER PATTERN IS NOT VERY CONDUCIVE TO SUPPORTING A MAJOR LOW PRESSURE SYSTEM. A TRAILING NORTHERN STREAM SHORT WAVE MOVING OUT OF THE PACIFIC NORTHWEST IS NEVER ABLE TO CATCH AND PHASE WITH THE SOUTHERN STREAM SHORT WAVE...WHICH PREVENTS DEVELOPMENT OF A SIGNIFICANT UPPER TROF TO GENERATE A *MILLER A* TYPE COASTAL LOW. THE MOST LIKELY SCENARIO IS FOR THE LOW TO SCOOT BY TO OUR SOUTH AND DELIVER THE BULK OF ITS OVERRUNNING PRECIPITATION TO US SATURDAY/SATURDAY NIGHT. PRECIPITATION TYPE IS GOING TO BE A MAJOR CHALLENGE WITH THIS SYSTEM AS TEMPERATURES WILL BE MARGINAL OVER THE AREA AND THE LOW WILL NOT BE STRONG ENOUGH TO PULL DOWN SIGNIFICANTLY COLDER AIR TO THE NORTH. EXPECT THE MOST LIKELY SCENARIO EAST OF THE BLUE RIDGE TO BE FOR A MIX AT THE START SATURDAY MORNING...TO MAINLY RAIN AND POSSIBLY SOME FREEZING RAIN FOR THE PIEDMONT WITH THE WEAK HIGH PRESSURE WEDGE HOLDING SHALLOW COLD AIR NEAR THE SURFACE...BACK TO MIX SATURDAY NIGHT AS PRECIPITATION LESSENS. BLUE RIDGE WEST WILL SEE THINGS START AS SNOW...THEN GO TO A MIX...THEN BACK TO SNOW SATURDAY NIGHT WITH THINGS WINDING DOWN. THE BEST CHANCE OF A MOSTLY SNOW EVENT SEEMS TO BE THE FAR WESTERN SLOPES ON INTO THE ALLEGHANY HIGHLANDS WHERE A SLUSHY COUPLE OF INCHES IS POSSIBLE. MANY DETAILS HAVE YET TO EMERGE WITH THIS SYSTEM SO EXPECT PRECIPITATION TYPE AND POTENTIAL ACCUMULATIONS TO CHANGE AS WE GET CLOSER TO THE EVENT AND THINGS COME INTO FOCUS. && .LONG TERM /SATURDAY NIGHT THROUGH TUESDAY/... AS OF 230 PM EST TUESDAY... LATEST 00Z ECMWF SHOWS WEAK LOW PRESSURE SLIDING NE ALONG THE N CAROLINA COAST SATURDAY NIGHT WITH AN AXIS OF DEFORMATION PRECIP INLAND ACROSS MOST OF THE REGION ESPCLY BEFORE MIDNIGHT. HOWEVER ADDED QPF LOOKS RATHER LIGHT AND MAINLY EAST OF THE BLUE RIDGE AT THIS POINT WHERE LIKELY MORE LIQUID NATURE TO START THE EVENING. MAJORITY OF THE SIGNIFICANT PRECIP SHOULD BE EXITING TO EAST LATER SATURDAY NIGHT WITH PERHAPS MOST SEEING THINGS TAPER OFF AS A PERIOD OF LIGHT SNOW AS COLDER AIR FINALLY WRAPS IN. HOWEVER THIS PENDING LATER TIMING AND MODEL TRENDS WITH NORTHWARD EXTENT AND THE DEGREE OF COVERAGE OF THE PRECIP SATURDAY EVENING. BY SUNDAY...THERE IS BETTER AGREEMENT WITH THE MODELS THAT THE AREA WILL BE ON THE BACKSIDE OF THE SYSTEM WITH ENOUGH COLD AIR ACROSS THE REGION WITH A STIFF NORTHWEST WIND TRAJECTORY FOR UPSLOPE SNOW SHOWERS IN THE WEST TO CONCLUDE THE EVENT. BY THE TIME WE GET TO SUNDAY...MODEL GUIDANCE IS IN FAIRLY GOOD AGREEMENT THAT THE SYSTEM WILL BE LIFTING OUT OF THE REGION...AND SUB FREEZING AIR WILL HAVE WRAPPED IN BEHIND THE SYSTEM AT THE LOWER LEVELS. ANY LINGERING PRECIPITATION HAS A GREATER CHANCE TO BE SNOW OR RAIN WITHOUT THE PRESENCE OF A WARM NOSE ALOFT. BY SUNDAY AFTERNOON INTO SUNDAY NIGHT...LINGERING UPSLOPE SNOW SHOWERS ACROSS THE PREFERRED AREA OF SOUTHEAST WEST VIRGINIA AND NEIGHBORING PARTS OF SOUTHWEST VIRGINIA WILL GRADUALLY ERODE AS DRIER AIR WORKS ITS WAY INTO THE REGION AND THE LOW LEVEL FLOW GRADUALLY BACKS WEST TO SOUTHWEST. MONDAY INTO MONDAY NIGHT...HIGH PRESSURE BUILDS INTO THE THE REGION WITH LIGHT WINDS...LIMITED CLOUD COVER AND NO PRECIPITATION EXPECTED. TUESDAY WILL BE ANOTHER DAY WITH CONSIDERABLE UNCERTAINTY. THE GFS IS QUICK TO BRING THE COLD FRONT TOWARDS THE REGION IN ASSOCIATION WITH AN UPPER TROUGH PUSHING THROUGH THE GREAT LAKE REGION. THIS SYSTEM IS KEPT DISTINCT FROM A DISTURBANCE OFF THE COAST OF THE CAROLINAS THAT HAS LITTLE OR NO INTERACTION WITH THE GREAT LAKES TROUGH THROUGH AT LEAST THE END OF OUR FORECAST PERIOD. FOLLOWING THIS SOLUTION YIELD LIMITED COVERAGE OF RAIN OR SNOW REACHING THE WESTERN PARTS OF THE AREA THROUGH THE END OF THE DAY TUESDAY. THE ECMWF SOLUTION ALSO HAS THE TWO SYSTEMS DISTINCT THROUGH TUESDAY...BUT FOR A DIFFERENT REASON. THIS SOLUTIONS IS FARTHER WEST WITH THE COASTAL SYSTEM...AND WRAPS MOISTURE...AND A WARM NOSE...INTO OUR AREA DURING THE COURSE OF THE DAY TUESDAY. THE GREAT LAKES SYSTEM IS NOT AS PROGRESSIVE...AND HAS THE TIME TO ELONGATE MORE SOUTH INTO THE MISSISSIPPI RIVER VALLEY. IF THE ECMWF IS ON TRACK...THE AREA WILL HAVE A GENEROUS COVERAGE OF A WINTRY MIX MOVING INTO THE REGION FROM SOUTHEAST TO NORTHWEST ON TUESDAY. OUR FORECAST AT THIS POINT WILL RESEMBLE MORE THAT OF THE GFS. TEMPERATURES DURING THE FORECAST PERIOD WILL BE TRICKY. WHILE WE ARE EXPECTING A GENERAL TREND TOWARDS MILDER TEMPERATURES EACH DAY PAST TUESDAY...HOW MUCH...AND WHERE ANY SUBSTANTIAL ACCUMULATIONS OF SNOW ARE DEPOSITED WILL PLAY A FACTOR IN BOTH THE HIGHS AND THE LOWS. AT THIS POINT...AM LEANING ON THE LOW SIDE OF GUIDANCE...WITH SOME ALLOTMENT TOWARDS EVEN MORE COOLER WHERE...AT LEAST NOW...THE BEST CHANCE OF SNOW IS EXPECTED. AT THIS POINT...WILL NOT TOUCH THE FOG POTENTIAL ONCE WE START TO GET INTO THE RETURN FLOW SIDE OF THE SURFACE HIGH. ALTHOUGH...AS MILDER AIR STARTS ADVECTING ACROSS ANY REMAINING SNOWPACK...THE DEW POINT OF THAT AIR WILL LIKELY BE MILDER THAN THE TEMPERATURE OF THE SNOW IT WILL BE MOVING ACROSS. && .AVIATION /19Z WEDNESDAY THROUGH MONDAY/...
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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.
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&& .RNK WATCHES/WARNINGS/ADVISORIES... VA...NONE. NC...NONE. WV...NONE. && $$ SYNOPSIS...JH/PM NEAR TERM...JH/PM SHORT TERM...MBS LONG TERM...DS/JH AVIATION...PM

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