Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 190927 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 427 AM EST FRI DEC 19 2014 .SYNOPSIS... HIGH PRESSURE OVER THE UPPER MIDWEST WILL GRADUALLY BUILD SOUTHEAST ACROSS THE AREA RESULTING IN OVERALL DRY WEATHER INTO TONIGHT. A WEAK AREA OF LOW PRESSURE WILL DEVELOP ALONG THE GULF COAST STATES LATE TONIGHT AND MOVE EAST OVER THE SOUTHEAST STATES ON SATURDAY. THIS SYSTEM WILL BRING A PERIOD OF LIGHT WINTRY PRECIPITATION TO MAINLY SOUTHERN AND WESTERN AREAS SATURDAY MORNING BEFORE TAPERING OFF SATURDAY AFTERNOON. && .NEAR TERM /THROUGH TONIGHT/... AS OF 218 AM EST FRIDAY... CLOUDS AGAIN THE MAIN CONCERN TODAY AS SHORTWAVE EXITS EARLY THIS MORNING AND WEAK SUBSIDENCE FILLS IN BEFORE THE NEXT WAVE APPROACHES FROM THE SW LATE TONIGHT. IR PICS SHOW A VARIETY OF MID DECK AS WELL AS HIGH END STRATO-CU PASSING ACROSS WITH LINGERING LOW CLOUDS PINNED ALONG THE NW SLOPES. GUIDANCE HANGS ON TO THIS SCENARIO INTO MID MORNING BEFORE SHOWING PERHAPS ENOUGH DRYING ALOFT TO AID CLEARING BY EARLY AFTERNOON AS BRIEF SHORTWAVE RIDGING BUILDS EAST. THIS SUPPORTS GOING WITH MORE SUN BY THIS AFTERNOON BEFORE HIGH/MID CLOUDS MAKE A RETURN OVER THE SW LATE. HIGH TEMPS REMAIN A BIT TRICKY GIVEN THE WIDE RANGE OF VALUES TO INIT THIS MORNING AND TIMING OF CLOUD EXODUS THIS AFTERNOON. OVERALL MOS A BIT COOLER THAN PREVIOUS SO LOWERED A DEGREE OR TWO IN SPOTS BUT NOT AS COOL AS THE MET TODAY PER MORE EXPECTED INSOLATION. MID LEVEL WAVE CURRENTLY HEADING NE OUT OF NEW MEXICO WILL GIVE RISE TO WEAK SURFACE LOW PRESSURE ALONG THE NORTHERN GULF LATE TONIGHT WITH PLENTY OF SHEARED MOISTURE ZIPPING NE INTO THE REGION OVERNIGHT. HOWEVER THE SYSTEM STILL LOOKS TO REMAIN WEAK GIVEN THE MAIN UPPER JET WELL TO THE SOUTH AND DAMPENING OF THE MID LEVEL SHORTWAVE AS IT GETS BOOTED EAST WITHOUT PHASING VIA A SEPARATE NORTHERN STREAM VORT. BEST MOISTURE TRANSPORT WITH THE WEAK SURFACE LOW WILL STAY SOUTH WITH PERHAPS A SECOND ZONE OF LIGHT PRECIP FARTHER NORTH DRIVEN BY THE COMBO OF THE WAVE ALOFT AND WEAK ISENTROPIC LIFT INTO SW SECTIONS LATE. MODELS CONTINUE TO ONLY SHOW VERY LIGHT QPF AND WOULDNT TAKE MUCH LIFT TO THE SOUTH TO TOTALLY CUT OFF MOISTURE INTO THE CWA PER LATEST EURO. HOWEVER WITH SOME SPOTTY QPF OF UP TO A TENTH OF AN INCH OFF THE NAM OVER THE NW NC MOUNTAINS...BROUGHT IN LOW LIKELYS THERE BY DAYBREAK WHILE SPREADING LOW CHANCES FARTHER NORTH ACROSS MOST OF THE MOUNTAINS/FOOTHILLS UNDER THE WAVE AXIS. FORECAST SOUNDINGS SHOW MOST OF THE REGION BELOW FREEZING ALOFT SO PTYPE MAINLY SNOW WITH PERHAPS THE WARMER BOUNDARY LAYER IN SPOTS CAUSING A BIT MORE RAIN TO INIT FOOTHILLS EAST. SOME SLEET ALSO POSSIBLE DURING THE CHANGE TO SNOW AT THE ONSET IN THESE SPOTS AS WELL SO INCLUDED MENTION. OVERALL SNOWFALL LOOKS TO BE LESS THAN A HALF INCH AT BEST BY MORNING...THUS NO HEADLINES GIVEN LIGHT AMOUNTS AND POTENTIAL FOR JUST MORE CLOUDS THAN SIGNIFICANT QPF AT THIS POINT. OTRW BECOMING CLOUDY ALL SECTIONS WITH LOWS IN THE 20S TO LOW 30S...MAINLY THIS EVENING...THEN STEADYING OR RISING LATE AS CLOUDS THICKEN. && .SHORT TERM /SATURDAY THROUGH MONDAY NIGHT/... AS OF 330 AM EST FRIDAY... WEATHER FORECAST MODELS OVER THE PAST FEW RUNS ARE SETTLING ON A MODEST UPPER LEVEL TROUGH PASSING ACROSS THE AREA ON SATURDAY...WITH A WEAK LOW PRESSURE SYSTEM MOVING NORTHEAST ALONG THE ATLANTIC COAST. THIS WILL BRING LIGHT SNOW ACROSS THE AREA DURING THE MORNING AND AFTERNOON...WITH SPOTTY ACCUMULATIONS...MOSTLY LESS THAN AN INCH...CONFINED TO THE HIGHER RIDGES...PARTICULARLY ALONG THE BLUE RIDGE PARKWAY SOUTH OF ROANOKE INTO THE MOUNTAIN EMPIRE. ENERGY ASSOCIATED WITH THE UPPER TROUGH WILL EXIT TO THE EAST DURING THE AFTERNOON...LEAVING ONLY LIGHT SNOW SHOWERS ALONG THE WESTERN RIDGES DURING THE EVENING. OTHERWISE...WILL BE LOOKING AT DRY WEATHER THROUGH SATURDAY NIGHT...AS ANOTHER ROUND OF HIGH PRESSURE PASSES ACROSS EASTERN CANADA...AND BUILDS SOUTHWARD ACROSS NEW ENGLAND AND THE MID ATLANTIC TO WEDGE AGAINST THE EASTERN FACE OF THE APPALACHIANS. YET ANOTHER TROUGH WILL APPROACH FROM THE WEST ON SUNDAY... SUPPORTING DEVELOPMENT OF LOW PRESSURE ALONG THE CENTRAL GULF COAST. SOUTHERLY FLOW OFF THE SURFACE WILL PUSH WARM GULF AIR ALONG THE CENTRAL APPALACHIANS TO OVERRUN THE COLD NORTHEASTERLY WIND FLOW ASSOCIATED WITH THE HIGH PRESSURE WEDGE. AS SUCH...EXPECT TO SEE A WINTRY MIX DEVELOP SUNDAY NIGHT AS PRECIPITATION ENTERS OUR AREA. FORECAST MODEL SOUNDINGS INDICATE THAT THE COLD AIR ASSOCIATED WITH THE WEDGE IS DEEP ENOUGH TO CAUSE MUCH OF THE PRECIPITATION ACROSS THE MOUNTAINS TO FALL AS A MIXTURE OF SLEET AND RAIN NORTH OF HIGHWAY 460...WITH TEMPERATURES TOWARD THE INTERSTATE 64 CORRIDOR BECOMING COLD ENOUGH THAT SNOW WILL BECOME MORE OF A POSSIBILITY. STILL A LITTLE EARLY TO DISCUSS ACCUMULATIONS...BUT AS OF THIS MORNING...IT IS LOOKING MORE LIKE AN ADVISORY CRITERIA EVENT RATHER THAN A WARNING EVENT...ALTHOUGH THIS CAN EASILY CHANGE OVER THE NEXT DAY OR TWO. TEMPERATURES WILL WARM ENOUGH BY EARLY MONDAY AFTERNOON TO ALLOW PRECIPITATION TO CHANGE MAINLY TO RAIN...POSSIBLY WITH A FEW POCKETS OF SLEET OR FREEZING RAIN REMAINING THROUGH THE DAY. THE MAIN ENERGY ASSOCIATED WITH THE SYSTEM WILL PASS EAST DURING MONDAY EVENING...LEAVING ONLY PATCHES OF LIGHT PRECIPITATION TO PASS ACROSS THE AREA OVERNIGHT. && .LONG TERM /TUESDAY THROUGH THURSDAY/... AS OF 230 PM EST THURSDAY... A DEEP LONGITUDINAL TROUGH DEVELOPS SOUTH TO THE GULF OF MEXICO ON TUESDAY WITH INCREASING SOUTHERLY LOW LEVEL FLOW ACROSS OUR REGION...ACCOMPANIED BY INCREASING MOISTURE ADVECTION. TEMPERATURES WILL TREND MILDER FOR HIGHS TUESDAY FROM THE MID 40S TO THE LOWER 50S. BY TUESDAY NIGHT INTO WEDNESDAY...BOTH GFS AND ECWMF DEEPEN THE UPPER LOW AND ASSOCIATED TROUGH AND NEGATIVELY TILT THE FEATURE SO THAT THE TROUGH AXIS SHIFTS TO OFF THE NORTH CAROLINA COAST... COINCIDENT TO THE POSITION OF THE ASSOCIATED SURFACE OCCLUDED FRONT...WITH THE TRIPLE POINT PASSING SOMEWHERE NEAR OR JUST SOUTH OF OUR REGION. AT THIS TIME...SPC DOES NOT HAVE ANY THUNDERSTORMS IN ITS DAY 4-8 CONVECTIVE OUTLOOK. IT LOOKS LIKE...THERE IS THE POTENTIAL FOR OUR REGION TO HAVE ACTIVE WEATHER LATE TUESDAY NIGHT INTO WEDNESDAY WITH PLENTY OF SHOWERS...PERHAPS VERY GUSTY WINDS AND A FEW THUNDERSTORMS. COLD AIR PUSHES INTO THE REGION TUESDAY NIGHT INTO WEDNESDAY MORNING...ALLOWING FOR SOME RAIN AND SNOW SHOWERS. IF ENOUGH COLD AIR ARRIVES QUICKLY...THERE COULD BE SOME ACCUMULATING SNOW IN THE WESTERN MOUNTAINS. KEPT THE HIGHEST POPS OF RAIN AND SNOW SHOWERS IN THE WEST AS THE LOW CENTER MARCHES NORTHEAST PUSHES A COLD FRONT TO THE COAST. IN THE WAKE OF THE COLD FRONT A COOLING TRENDS WILL CONTINUE WEDNESDAY INTO THURSDAY...WITH WEST TO NORTHWEST FLOW ALOFT. UPPER FLOW SHIFTS TO THE SOUTHWEST AS TROF CURVES OUT IN THE CENTRAL US WITH SFC INFLECTION OF LOW PRESSURE DEVELOPS OVER THE TENNESSEE VALLEY BY FRIDAY MORNING. && .AVIATION /09Z FRIDAY THROUGH TUESDAY/... AS OF 1045 PM EST THURSDAY... NOT MUCH CHANGE TO THE AVIATION FORECAST...THOUGH CONFIDENCE IS LESS THAT BLF WILL DROP BELOW 1KFT PER UPSTREAM OBS. STILL WILL HAVE A TEMPO GROUP TOWARD 12Z FOR BLF DROPPING TO 9H FEET FOR A COUPLE HOURS. OTHERWISE BECOMING MVFR AT BLF/LWB OVERNIGHT THEN BACK TO VFR BY MIDDAY FRIDAY...WHILE REST OF THE TAF SITES STAY VFR. COULD SEE SOME SCT SUB 3KFT CLOUDS ACROSS BCB BUT CONFIDENCE HIGH THAT THREAT OF BKN IS NOT GOING TO HAPPEN. CLOUDS AHEAD OF THE NEXT SYSTEM WILL BE INCREASING OVERNIGHT FRIDAY SO EXPECT MAINLY CIRROSTRATUS IN THE LATE EVENING ACROSS THE REGION. EXTENDED DISCUSSION... THE SAT SYSTEM NOW HAS TRENDED WEAKER AND WILL SHIFT MOST OF THE PRECIP ACROSS THE CAROLINAS...THOUGH STILL WILL SEE SOME WINTRY MIX BUMP UP INTO THE SE WV/SW VA CORRIDOR INTO THE NC MTNS...THOUGH TRENDS ARE SHOWING LESS. EXPECT SUB VFR THOUGH AT TIMES SATURDAY INTO SAT NIGHT. ON THE HEELS OF THIS SYSTEM WILL BE ANOTHER SYSTEM TO POTENTIALLY IMPACT MAINLY THE EASTERN PORTION OF THE REGION SUNDAY NIGHT INTO MONDAY...WITH YET ANOTHER SYSTEM SLATED FOR LATE TUESDAY INTO WEDNESDAY. THESE SYSTEMS ARE EXPECTED TO BRING A PERIOD MAINLY RAIN BUT COULD BE SOME WINTRY WX AS WELL ESPECIALLY IN THE MOUNTAINS. EXPECT POTENTIAL LOW LEVEL WIND SHEAR AS WELL AND POOR FLYING WEATHER MONDAY. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...NONE. NC...NONE. WV...NONE. && $$ SYNOPSIS...JH/RCS NEAR TERM...JH SHORT TERM...NF LONG TERM...KK AVIATION...JH/RCS/WP

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