Area Forecast Discussion
Issued by NWS Blacksburg, VA

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000 FXUS61 KRNK 010949 AFDRNK AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BLACKSBURG VA 549 AM EDT SUN MAY 1 2016 .SYNOPSIS...
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A COOL AIR WEDGE THIS MORNING WILL GIVE WAY TO A WARM FRONT THIS AFTERNOON...THEN A COLD FRONT TONIGHT...BOTH OF WHICH WILL BRING SHOWERS AND THUNDERSTORMS TO THE AREA. THE FRONT WILL STALL TO OUR SOUTH MONDAY AS A WAVE OF LOW PRESSURE RIDES ALONG THE FRONT MONDAY INTO TUESDAY. FOR WEDNESDAY THROUGH FRIDAY...AN UPPER LOW WILL DRIFT SOUTHWARD INTO THE REGION FROM THE GREAT LAKES...KEEPING AN UNSETTLED AND UNSEASONABLY COOL PATTERN THROUGHOUT THE REGION.
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&& .NEAR TERM /THROUGH TONIGHT/...
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AS OF 500 AM EDT SUNDAY... COMPLICATED WEATHER PATTERN IN PLACE THROUGH THE NEXT 24 HOURS AS A VARIETY OF SYSTEMS IMPACT THE REGION. TO START...A STRONG MID- LEVEL DISTURBANCE WAS TRACKING FROM THE TN VALLEY NORTHEAST ACROSS THE REGION THIS MORNING. A STRONG WEDGE WAS IN PLACE AT THE SURFACE...EXTENDING AS FAR SOUTHWEST AS NORTHEAST GA. RAIN CONTINUING TO FALL INTO THE WEDGE SERVES TO ENHANCE IT FURTHER. BIG QUESTION TODAY IS WHEN WILL THE WEDGE BREAK. MOST MODELS...INCLUDING THE HRR...INSIST THAT IT WILL RAPIDLY RETREAT NORTHEAST BY MID- DAY...LEAVING THE AREA IN A MUCH MORE UNSTABLE AND WARMER AIR MASS BY AFTERNOON. THIS IS ALWAYS A BIG QUESTION IN THIS TYPE OF SYNOPTIC SETUP. HOWEVER...WE HAVE SEEN SIMILAR RECENT EVENTS OVER THE PAST COUPLE OF MONTHS...SO IT REMAINS A POSSIBILITY. ALOFT...SOME OF THE BEST FORCING PASSES NORTHEAST OF THE AREA BY MID-DAY. HOWEVER...THE AREA IS LEFT WITH SOUTHWEST FLOW ALOFT THANKS TO A PERSISTENT BROAD AREA OF LOW PRESSURE IN THE SOUTHWEST U.S. ADDITIONAL WEAK DISTURBANCES ARE EMBEDDED WITHIN THE UPPER FLOW...ONE WHICH WILL HELP PUSH A NEW COLD FRONT INTO THE REGION OVERNIGHT...WHICH WILL THEN STALL JUST TO OUR SOUTH BY MON. MANY QUESTIONS REGARDING DEGREE OF INSTABILITY AND FORCING FOR THE AFTERNOON. ECMWF/CANADIAN ARE VERY LACK LUSTER WITH INSTABILITY BY AFTERNOON...HOLDING THE WEDGE IN MUCH OF THE AFTERNOON...WHILE THE GFS IS ON THE OTHER END OF THE SPECTRUM SHOWING AN UNSTABLE AIR MASS SUPPORTIVE OF MORE WIDESPREAD AND STRONGER CONVECTION. SPC HAS PLACED MUCH OF THE CWA EXCEPT THE EXTREME E-NE PORTION IN A MARGINAL RISK TODAY...NOTING AS I HAVE QUESTIONS REGARDING THE DEGREE OF INSTABILITY AND FORCING. HAVE INCLUDED THUNDER ALL AREAS...ESPECIALLY IN THE AFTERNOON...WITH EVEN A FEW RUMBLES POSSIBLE THIS MORNING. BUT SEVERE FOR THIS AFTERNOON/EVENING IS A BIG UNCERTAINTY AT THIS POINT. MODEL MOISTURE/QPF FIELDS ARE EXTREMELY NOISY...MURKY...AND RATHER NON-DESCRIPT FOR THIS AFTERNOON/EVENING...MAKING IT VERY DIFFICULT TO PINPOINT SPECIFICALLY FAVORED AREAS. CATEGORICAL TO DEFINITE POPS ARE IN ORDER FOR THE MORNING...WITH HIGH CHANCE TO LIKELY POPS ARE IN ORDER FOR THE AFTERNOON TEMPERATURES TODAY ALSO AN UNCERTAINTY AND HINGENT ON WHEN/IF THE WEDGE BREAKS. AGAIN...THE GFS IS ON THE WARM END OF THE SPECTRUM SHOWING WIDESPREAD MID 70S ACROSS MUCH OF THE CWA BY 18Z. ECMWF IS ON THE COOL END OF THE SPECTRUM WITH HIGHS MAINLY IN THE 60S EAST OF THE ALLEGHANY FRONT. HAVE LEANED TOWARD THE COOLER ECMWF AS CONFIDENCE IN THE WEDGE COMPLETELY BREAKING IS NOT THAT HIGH AT THIS POINT. THIS IS AN INTENSE WEDGE...MORE SO THAN RECENT ONES. HOWEVER...DO FEEL THAT WHATEVER IS LEFT OF THE WEDGE IN EASTERN SECTIONS WILL FINALLY ERODE OVERNIGHT INTO MONDAY MORNING...ALLOWING TEMPERATURES TO CONTINUE TO MODERATE WITH MINIMAL COOLING OVERNIGHT. AREAS EAST OF THE BLUE RIDGE MAY SEE MIN TEMPS MONDAY MORNING CLOSE TO MAX TEMPS THIS AFTERNOON.
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&& .SHORT TERM /MONDAY THROUGH WEDNESDAY/...
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AS OF 530 AM EDT SUNDAY... THE COLD FRONT SHOULD PUSH EASTWARD OVER THE MID ATLANTIC ON MONDAY...AND BRING ANOTHER ROUND OF SHOWERS AND THUNDERSTORMS. SPC HIGHLIGHTS THE CWA FOR A MARGINAL RISK OF SEVERE WEATHER...AND THE MODEL SOUNDINGS APPEAR FAVORABLE FOR CONVECTIVE DEVELOPMENT. HIGHS FOR MONDAY REACH THE LOWER 70S TO THE LOWER 80S...WHICH WILL ALLOW CAPE VALUES TO EXCEED 1000 J/KG BY THE AFTERNOON IN THE PIEDMONT. IF ANY STRONGER STORMS MATERIALIZE AHEAD OF THE COLD FRONT...LARGE HAIL AND DAMAGING WINDS WOULD BE THE MAIN THREATS. THIS FRONT IS PROJECTED TO WEAKEN AND STALL DURING MONDAY NIGHT INTO TUESDAY...BUT HOW FAR SOUTH IT CAN REACH BEFORE IT BECOMES STATIONARY REMAINS A LITTLE QUESTIONABLE. REGARDLESS...IT WILL KEEP SCATTERED SHOWERS IN THE FORECAST THROUGHOUT THIS TIME. SEVERAL MORE WAVES OF LOW PRESSURE RIDE NORTHWARD ALONG THE STALLED FRONTAL BOUNDARY DURING TUESDAY AND WEDNESDAY. WHILE THE CHANCE OF SHOWERS SHOULD LINGER THROUGH THESE TWO DAYS...THE THREAT OF THUNDERSTORMS APPEARS LIMITED TO MAINLY NORTHWEST NORTH CAROLINA ON TUESDAY AFTERNOON DUE TO LINGERING INSTABILITY AND THE PROXIMITY OF THE STALLED FRONT. HIGH TEMPERATURES ON TUESDAY SHOULD DIP FIVE TO TEN DEGREES LOWER THAN ON MONDAY. THE CHANCE OF THUNDERSTORMS DIMINISHES ON TUESDAY NIGHT...AS THE WAVES OF LOW PRESSURE SUCCESSFULLY PUSH THE FRONTAL BOUNDARY TOWARD THE COAST BY WEDNESDAY. THAT SITUATION SHOULD KEEP JUST A CHANCE OF SHOWERS THROUGH WEDNESDAY...WITH HIGHS NEARLY THE SAME COMPARED TO TUESDAY.
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&& .LONG TERM /WEDNESDAY NIGHT THROUGH SATURDAY/...
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AS OF 545 AM EDT SUNDAY... AS THE COLD FRONT FINALLY GAINS ENOUGH ENERGY TO LIFT OFFSHORE ON WEDNESDAY NIGHT...A DEEP UPPER LEVEL TROUGH WILL MIGRATE FROM THE HUDSON BAY IN CANADA TOWARD THE GREAT LAKES. THE TROUGH SHOULD REACH THE APPALACHIAN MOUNTAINS BY THURSDAY...AND EVENTUALLY CUT OFF OVERHEAD. MEANWHILE...ANOTHER CLOSED UPPER LEVEL LOW WILL ALSO CUT OFF OVER THE ROCKY MOUNTAINS. IN BETWEEN THESE TWO LOWS...A STRONG UPPER LEVEL RIDGE WILL RESIDE OVER THE PLAINS. THIS ATMOSPHERIC PATTERN CREATES ANOTHER OMEGA BLOCK OVER THE UNITED STATES SIMILAR TO WHAT WAS WITNESSED BACK IN MID APRIL...WHICH BOTH THE LATEST ECMWF AND GFS MODELS DEPICT IN REASONABLY GOOD AGREEMENT. UNLIKE THE LAST OMEGA BLOCK WHERE THE MID ATLANTIC ENJOYED UNSEASONABLY WARM AND DRY CONDITIONS UNDER THE UPPER LEVEL RIDGE...JUST THE OPPOSITE WILL OCCUR DUE TO BEING UNDER THE UPPER LEVEL LOW...WITH COOL AND WET CONDITIONS EXPECTED THROUGH THE END OF THIS WORK WEEK. HIGHS WILL ONLY REACH THE 50S AND 60S BY THURSDAY AND FRIDAY. ON SATURDAY...THE OMEGA BLOCK GRADUALLY WEAKENS...WHILE UPPER LEVEL RIDGING SLOWLY BEGINS OVERHEAD. IT APPEARS THAT WARMER AND DRIER CONDITIONS COULD ARRIVE TOWARD THE END OF THIS WEEKEND.
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&& .AVIATION /09Z SUNDAY THROUGH THURSDAY/... AS OF 200 AM EDT SUNDAY... A STRONG COOL WEDGE WILL PERSIST THROUGH THE REMAINDER OF THE NIGHT...AND KEEP CEILINGS AT LIFR/IFR WITH VISIBILITIES AT MVFR. ALTHOUGH THERE COULD BE MOMENTS WHERE THE CEILINGS AND VISIBILITIES TEMPORARILY IMPROVE...THE OVERALL TREND SUGGESTS A DETERIORATION OF FLYING CONDITIONS. PERIODS OF RAIN AND FOG SHOULD ALSO CONTINUE...AS MOISTURE KEEPS INCREASING AHEAD OF AN APPROACHING LOW PRESSURE SYSTEM FROM THE SOUTHERN PLAINS. MODEL SOUNDINGS SHOW AN INTENSIFYING LOW LEVEL JET AHEAD OF THIS SYSTEM THAT COULD BRING LOW LEVEL WIND SHEAR FOR ALL SITES DURING EARLY SUNDAY MORNING. NOT MUCH CHANGE WILL TAKE PLACE AS THE MORNING PROGRESSES...WITH PERIODS OF RAIN AND LIFR/IFR CEILINGS ONGOING. BY SUNDAY AFTERNOON...CEILINGS EVENTUALLY IMPROVE TO MVFR/IFR ONCE THE COOL WEDGE BEGINS TO ERODE...ALTHOUGH KLYH MAY BE LAST TO BREAK OUT OF THE WEDGE. SCATTERED SHOWERS AND THUNDERSTORMS COULD DEVELOP WEST OF THE WEDGE BOUNDARY...AND THE POTENTIAL EXISTS FOR SCATTERED STRONG TO SEVERE STORMS IF ENOUGH SUNSHINE DESTABILIZES THE ATMOSPHERE. HOWEVER...CONFIDENCE IS TOO LOW TO PINPOINT WHICH SITES WILL SEE THUNDER AT THIS MOMENT TO ADVERTISE IT IN THE TAFS. THE THREAT OF SHOWERS AND THUNDERSTORMS SHOULD CEASE AFTER SUNSET. EXTENDED AVIATION DISCUSSION... THE AFOREMENTIONED LOW PRESSURE SYSTEM SHOULD CROSS OVER THE MID ATLANTIC DURING SUNDAY NIGHT...BUT THE BOUNDARY WILL STALL OVERHEAD BY MONDAY. MORE WAVES OF LOW PRESSURE WILL MOVE ALONG THE STALLED BOUNDARY FROM TUESDAY THROUGH THURSDAY...WHICH SHOULD HELP PUSH THE BOUNDARY OFFSHORE. A DEEP UPPER LEVEL TROUGH IS PROJECTED TO DIVE SOUTHWARD OVER THE APPALACHIAN MOUNTAINS BY WEDNESDAY INTO THURSDAY. OVERALL...FLYING CONDITIONS APPEAR RATHER POOR THROUGH MOST OF THIS WEEK DUE TO THE LIKELIHOOD OF LOW CLOUDS...PERIODS OF RAIN...AND PATCHY FOG. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...NONE. NC...NONE. WV...NONE. && $$ SYNOPSIS...RAB NEAR TERM...RAB SHORT TERM...PW LONG TERM...PW AVIATION...PW

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