Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 280840 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 440 AM EDT THU APR 28 2016 .SYNOPSIS...A FRONTAL ZONE WILL REMAIN STALLED TO THE NORTH AND NORTHEAST OF CENTRAL NORTH CAROLINA TODAY THROUGH FRIDAY. THE FRONT MAY SHIFT SOUTHWARD INTO NORTHEAST PORTIONS OF THE STATE AS A BACK DOOR COLD FRONT FRIDAY NIGHT INTO SATURDAY BEFORE LIFTING NORTH ALONG THE MID-ATLANTIC COAST AS A WARM FRONT SATURDAY NIGHT INTO SUNDAY. && .NEAR TERM /TODAY AND TONIGHT/... AS OF 330 AM THURSDAY... ELEVATED CONVECTION HAS PERSISTED THROUGH 08Z IN ASSOC/W LOW-LEVEL WARM ADVECTION ATOP A WEST-EAST ORIENTED (ROUGHLY) OUTFLOW BOUNDARY INVOF THE HWY 64 CORRIDOR...AIDED BY DIFFLUENT FLOW ALOFT AS A SHORTWAVE RIDGE FLATTENS/PROGRESSES OFFSHORE THE CAROLINA COAST THIS MORNING AND AN UPPER LEVEL LOW TRACKS FROM THE MIDWEST TO THE UPPER GREAT LAKES. THROUGH 12Z...EXPECT ONGOING ACTIVITY TO DECREASE IN COVERAGE/INTENSITY VIA CONVECTIVE OVERTURNING /STABILIZATION/ AND SHIFT CLOSER TO THE VA BORDER ATTENDANT THE STRONGEST FORCING (LOW- LEVEL WARM ADVECTION/FGEN INVOF THE SFC-925 MB FRONT IN SOUTHERN VA. DPVA IN THE FORM OF A N-S ORIENTED SHEAR AXIS IS EXPECTED TO PROGRESS ACROSS THE REGION LATER THIS MORNING AS THE SHORTWAVE RIDGE ALOFT FLATTENS/SHIFTS OFFSHORE. EXTRAPOLATION OF CURRENT TRENDS IN WV IMAGERY (AND FCST SOUNDINGS) INDICATE PRONOUNCED DRYING ALOFT WILL OCCUR BY EARLY AFTERNOON...RESULTING IN A CLEARING TREND OVER MUCH OF THE AREA...EXCEPT PERHAPS IN THE NORTHERN PIEDMONT/NE COASTAL PLAIN IN CLOSER VICINITY TO THE STALLED FRONTAL ZONE. MODERATE DIURNAL DESTABILIZATION IS EXPECTED THIS AFTERNOON... THOUGH GUIDANCE DIFFERS MARKEDLY IN THE MAGNITUDE. AT THE SAME TIME...DEEP LAYER SHEAR WILL INCREASE TO 30-40 KT (HIGHEST NORTH) AS WESTERLY FLOW ALOFT SUPPLANTS SHORTWAVE RIDGING OVER THE REGION. AS A RESULT...A POTENTIAL FOR ISOLD SEVERE THUNDERSTORMS WILL NO DOUBT EXIST OVER THE AREA THIS AFT/EVE. HOWEVER...SPECIFICS REMAIN DIFFICULT TO ASCERTAIN GIVEN A COMPLEX MESOSCALE PATTERN... CONSIDERABLE DRYING ALOFT BY EARLY AFTERNOON...AND DISAGREEMENT AMONG GUIDANCE WITH REGARD TO WHETHER OR NOT SMALL AMPLITUDE WAVE(S) /DPVA/ WILL TRAVERSE THE REGION IN NEWLY ESTABLISHED WESTERLY FLOW ALOFT MID/LATE THIS AFTERNOON. THE 00Z NAM IS CERTAINLY THE MOST AGGRESSIVE MODEL WITH REGARD TO DESTABILIZATION/SHEAR...WITH MLCAPE VALUES UP TO 2500 J/KG AND SUPERCELL COMPOSITE VALUES AS HIGH AS 7- 15 FROM THE TRIANGLE SOUTH AND EAST. THE 00Z GFS INDICATES MLCAPE VALUES CLOSER TO 1000-1500 J/KG AND SCP VALUES NO HIGHER THAN 2-3. BASED ON PREVIOUS EXPERIENCE IN SIMILAR PATTERNS...I.E. WHERE THERE IS CONSIDERABLE UNCERTAINTY IN BOTH THE TIMING/MAGNITUDE OF FORCING AND MAGNITUDE OF DESTABILIZATION...THE SEVERE POTENTIAL IS TYPICALLY MARGINAL/ISOLD IN NATURE. IF ORGANIZED CONVECTION DEVELOPS AROUND PEAK HEATING INVOF MDT INSTABILITY...KINEMATIC PROFILES WOULD SUPPORT EQUALLY FAVORED LEFT/RIGHT SPLITTING SUPERCELLS...THOUGH THE MESOSCALE ENVIRONMENT IN PLACE SUGGESTS RIGHT SPLITS WOULD BE MORE LIKELY TO PRODUCE MARGINALLY SVR HAIL/WIND THAN LEFT SPLITS...SINCE LEFT MOVERS WOULD RAPIDLY TRACK N/NNE INTO A LESS FAVORABLE THERMO ENVIRONMENT. EXPECT PRECIP CHANCES TO DECREASE FROM WEST-EAST THIS TONIGHT AS SHORTWAVE ENERGY TRACKS THROUGH THE NORTHERN MID-ATLANTIC AND A DRIER/COOLER AIRMASS ADVECTS INTO THE AREA. -VINCENT && .SHORT TERM /FRIDAY THROUGH SATURDAY/... AS OF 310 AM THURSDAY... FRIDAY AND SATURDAY ARE BOTH SETTING UP TO BE DRIER AS THE MAIN LOW PRESSURE WILL MOVE EAST INTO THE ATLANTIC LEAVING BEHIND A WEAK RIDGE OF HIGH PRESSURE OVER CENTRAL AND EASTERN NC. IT WILL TURN COOLER ESPECIALLY FROM THE NORTH FRIDAY NIGHT AND SATURDAY AS A HIGH PRESSURE WILL PUSH FROM THE GREAT LAKES TO NEW ENGLAND... AND BRIEFLY EXTEND INTO OUR REGION FROM THE NORTH. HIGHS FRIDAY WILL BEGIN TO SHOW THE COOLING ARRIVING FROM THE NORTH WITH 70S EXPECTED ALONG THE NC/VA BORDER RANGING INTO THE LOWER TO MID 80S ALONG THE NC/SC BORDER COUNTIES. THERE MAY BE AN ISOLATED SHOWER IN THE AFTERNOON OVER THE COASTAL PLAIN. FRIDAY NIGHT AND SATURDAY... IT SHOULD BEGIN MOSTLY CLEAR TO PARTLY CLOUDY... THEN EXPECT INCREASING CLOUDINESS SATURDAY. SOME OF THE ENSEMBLES INDICATE A CHANCE OF LIGHT RAIN LATE IN THE DAY ESPECIALLY IN THE SOUTH. WE WILL NOT BIT ON THAT JUST YET. LOWS GENERALLY IN THE 50S EXPECTED. HIGHS SATURDAY IN THE 70S. SATURDAY NIGHT AND SUNDAY NOW LOOK TO BE WET WITH PERIODS OF RAIN... BEGINNING SATURDAY NIGHT AND CONTINUING ON SUNDAY. MODELS OFTEN SCOUR OUT CAD TOO QUICKLY... EVEN IN THE SPRING (WARM SEASON). THIS LOOKS TO BE A GREAT CASE OF THAT OVER OUR PIEDMONT DAMMING REGION SUNDAY. A PERIOD OF WAA RAINS ARE EXPECTED TO SPREAD NORTH ACROSS OUR REGION WITH AN AMPLE SUPPLY OF WESTERN ATLANTIC THEN GULF MOISTURE THAT WILL LIFT UP AND OVER THE DEVELOPING FRONT/THEN COOL STABLE DOME SATURDAY NIGHT AND SUNDAY. THERE ARE SOME DIFFERENCES IN THE MODELS AND USING THE ENSEMBLE APPROACH ALONG WITH PATTERN RECOGNITION... THE MAIN PARENT LOW PRESSURE IS EXPECTED TO LIFT NE FROM THE MID-MISSISSIPPI VALLEY INTO THE OHIO VALLEY SUNDAY INTO SUNDAY NIGHT... WITH THE TRAILING COLD FRONT TO ARRIVE IN OUR REGION EARLY NEXT WEEK. OUT AHEAD OF THE STORM SYSTEM SUNDAY... A WARM FRONT IS FORECAST TO LIFT BACK INTO THE COASTAL PLAIN AND SANDHILLS SUNDAY. HOWEVER... IN-SITU/HYBRID CAD WILL LEAD TO INCREASING STABILITY AND THE DIABATIC PROCESS SHOULD THE RAIN BECOME WIDESPREAD AS CURRENTLY EXPECTED WILL LEAD TO MUCH COOLER HIGHS IN THE 60S NORTH TO LOWER 70S SOUTH. CURRENT INDICATIONS ARE BETWEEN 0.25 TO 0.75 FOR THE QPF. THERE MAY BE A RATHER LARGE TEMPERATURE GRADIENT AND RAINFALL GRADIENT FROM SE TO NW FROM CLINTON TO WINSTON-SALEM BY LATE SUNDAY IF THE WARM FRONT CAN SURGE INTO THE SE ZONES (PER SOME OF THE MODELS INCLUDING THE LATEST EC). SUNDAY NIGHT INTO MONDAY SHOULD REMAIN RATHER UNSETTLED WITH A CHANCE OF SHOWERS AS THE MAIN COLD FRONT SHOULD BE SLOW TO MOVE INTO THE REGION. THEN WHEN THE FRONT DOES MOVE THROUGH... IT MOSTLY LIKELY WILL STALL OVER THE SOUTHERN AND EASTERN ZONES INTO TUESDAY. FOR THOSE THAT NEED RAINFALL AND COOLER TEMPERATURES... THIS LOOKS TO BE A GREAT SHOT AT BOTH. && .LONG TERM /FRIDAY THROUGH TUESDAY/... AS OF 300 PM WEDNESDAY... A BROAD UPPER LEVEL TROUGH WILL COVER THE COUNTRY AT THE BEGINNING OF THE PERIOD. A SERIES OF S/WS IN THE CYCLONIC FLOW WILL CAUSE BOUTS OF UNSETTLED WEATHER TO CENTRAL NC. THE FIRST MINOR S/W WILL CROSS NEAR OR NORTH OF OUR REGION FRIDAY AFTERNOON-EVENING. THE COOL POOL ALOFT ASSOCIATED WITH THIS FEATURE COUPLED WITH AFTERNOON HEATING AND RESIDUAL MOISTURE SHOULD TRIGGER A FEW SHOWERS/ISOLATED T-STORMS...PRIMARILY OVER OUR NE PIEDMONT/NORTHERN COASTAL PLAIN COUNTIES LATE FRIDAY-FRIDAY EVENING. WEAK HIGH PRESSURE WILL EXTEND ACROSS THE REGION SATURDAY BUT QUICKLY SCOOT EAST BY SATURDAY EVENING. THE RETURN FLOW ON THE BACKSIDE OF THE HIGH IN CONJUNCTION WITH AN APPROACHING S/W TRAVERSING THE DEEP SOUTH/TN VALLEY SHOULD ENHANCE LOW LEVEL MOISTURE RETURN...LEADING TO AREAS OF RAIN BREAKING OUT OVER OUR REGION BY SUNDAY. THE SFC PRESSURE PATTERN SUPPORTS THE POTENTIAL FOR A HYBRID/INSITU COLD AIR DAMMING EVENT...SUGGESTING TEMPS WELL BE LOW NORMAL IF THE RAIN DEVELOPS. EARLY NEXT WEEK...MODELS ADVERTISING A PATTERN AMPLIFICATION WITH A WESTERN U.S. RIDGE AND EASTERN US.S TROUGH. DISTURBANCES IN THE AMPLIFYING FLOW WILL CONTINUE TO BRING PERIODS OF UNSETTLED WEATHER THROUGH MID WEEK. TEMPERATURES ON AVERAGE WILL BE A LITTLE SHY OF NORMAL EARLY NEXT WEEK. && .AVIATION /06Z THURSDAY THROUGH MONDAY/... AS OF 200 AM THURSDAY... 24-HOUR TAF PERIOD: ASIDE FROM LOCALIZED AREAS OF IFR/LIFR CEILINGS AFFECTING THE RDU/RWI TERMINALS THROUGH ~12-13Z THIS MORNING...AND A POTENTIAL FOR A BRIEF PERIOD OF CONVECTION AT NORTHERN TERMINALS AS A SHEAR AXIS PROGRESSES ACROSS CENTRAL NC BETWEEN 12-18Z...VFR CONDITIONS WILL OTHERWISE PREVAIL THROUGH EARLY AFTERNOON. SCATTERED CONVECTION WILL BE POSSIBLE AT ALL TERMINALS MID/LATE AFTERNOON INTO THIS EVENING...THOUGH CONFIDENCE IN TIMING/LOCATION IS LOWER THAN AVERAGE EXCEPT TO SAY THAT NORTHERN TERMINALS ARE MORE LIKELY TO BE AFFECTED. LOOKING AHEAD: VFR CONDITIONS ARE EXPECTED ON FRIDAY...FOLLOWED BY A POTENTIAL FOR SUB-VFR CEILINGS ATTENDANT A BACKDOOR COLD FRONT PROGRESSING S/SW INTO THE AREA FRI NIGHT/SATURDAY AND ANOTHER ROUND OF SCATTERED CONVECTION SAT NIGHT/SUNDAY. -VINCENT && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...VINCENT NEAR TERM...VINCENT SHORT TERM...BADGETT LONG TERM...BADGETT AVIATION...VINCENT

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