Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 291919 RRA AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 318 PM EDT WED JUL 29 2015 .SYNOPSIS...A COLD FRONT WILL APPROACH THE MOUNTAINS FROM THE WEST ON THURSDAY...THEN TRACK SOUTHEAST ACROSS THE CAROLINAS THURSDAY NIGHT INTO FRIDAY. MEANWHILE...A WEAK LOW PRESSURE SYSTEM OFF THE SOUTHEAST COAST WILL TRACK NORTH NORTHEAST OFFSHORE THE CAROLINA COAST. && .NEAR TERM /THROUGH TONIGHT/... AS OF 300 PM WEDNESDAY... OVERVIEW: CENTRAL NC REMAINS ON THE FAR NORTHEASTERN PERIPHERY OF AN UPPER LEVEL RIDGE ANCHORED OVER THE LOWER MIDWEST. AS A RESULT... LIGHT NW FLOW ALOFT AND A WEAK/ILL-DEFINED MSLP GRADIENT WILL PREVAIL THROUGH TONIGHT. CONVECTION: DIURNAL DESTABILIZATION WILL BE RATHER LIMITED THIS AFTERNOON DUE TO WEAK MID-LEVEL LAPSE RATES...MORNING CLOUD COVER/SHOWERS...AND THE PRESENCE OF A DRY LOW-LEVEL AIRMASS (H85 DWPTS ~14C) ALONG/EAST OF HWY 1. 18Z SPC MESOANALYSIS DATA INDICATED MARGINAL MLCAPE VALUES RANGING FROM 250-750 J/KG...HIGHEST IN THE WESTERN PIEDMONT WHERE LOW-LEVEL MOISTURE IS GREATER (H85 DWPTS ~16C). SEVERAL SMALL AMPLITUDE WAVES WERE NOTED WELL UPSTREAM OVER THE OH VALLEY THIS AFTERNOON...THE WESTERN-MOST OF WHICH MAY TRACK SOUTHEAST INTO SOUTHERN WV BY ~12Z THU. IN ADDITION TO POOR DIURNAL TIMING...FORCING ASSOC/W THIS FEATURE SHOULD REMAIN N/NNW OF CENTRAL NC THROUGH SUNRISE THU. IN THE ABSENCE OF ADDITIONAL/SUBTLE SMALL AMPLITUDE WAVES EMBEDDED WITHIN LIGHT NW FLOW ALOFT IN CLOSER VICINITY TO CENTRAL NC (NONE APPEAR TO BE PRESENT)...UPPER LEVEL FORCING WILL BE ABSENT OVER THE REGION THROUGH TONIGHT. LOW-LEVEL FORCING WILL BE SIMILARLY ABSENT...CONFINED TO WEAK/SHALLOW CONVERGENCE ASSOC/W SUBTLE LEE TROUGHING...DIFFERENTIAL HEATING... AND THE SEABREEZE. WITH THE ABOVE IN MIND...EXPECT SHOWER ACTIVITY TO BE ISOLD /SPARSE/ AND LARGELY CONFINED TO THE WESTERN PIEDMONT THROUGH THIS EVENING...WITH DRY CONDITIONS IN THE COASTAL PLAIN. THOUGH THERMODYNAMICS/FORCING APPEAR MARGINAL AT BEST...A FEW LIGHTNING STRIKES CANNOT BE RULED OUT IN THE WESTERN PIEDMONT BETWEEN 21-02Z. THEREAFTER...EXPECT DRY CONDITIONS EVERYWHERE. TEMPS: EXPECT HIGHS RANGING FROM THE UPPER 80S TO LOWER/MID 90S... COOLEST N/NW WHERE CLOUD COVER /MOISTURE/ IS GREATER AND WARMEST EAST/SOUTH WHERE LESS CLOUD COVER /MOISTURE/ IS PRESENT. LOWS TONIGHT IN THE LOWER 70S. -VINCENT && .SHORT TERM /THURSDAY AND THURSDAY NIGHT/... AS OF 315 PM WEDNESDAY... A DEEPENING UPPER LEVEL TROUGH OVER EASTERN CANADA WILL EXTEND SOUTHWARD THROUGH THE GREAT LAKES INTO THE OH VALLEY AND MID- ATLANTIC THU/THU NIGHT...RESULTING IN BROAD (ALBEIT WEAK) CYCLONIC FLOW ALOFT OVER THE CAROLINAS. PERHAPS MORE IMPORTANTLY...THIS WILL AID IN DRIVING A WEAK COLD FRONT ACROSS THE MOUNTAINS AND INTO THE CAROLINAS LATE THU/THU NIGHT. DIURNAL DESTABILIZATION IS EXPECTED TO BE LOW-END MODERATE (1000-1500 J/KG)...LIMITED BY WEAK MID-LEVEL LAPSE RATES. MOISTURE/INSTABILITY AND FORCING /CONVERGENCE/ ATTENDANT THE PRE-FRONTAL TROUGH IN ADDITION TO DPVA ATTENDANT A SMALL AMPLITUDE WAVE (OR WAVES) EMBEDDED WITHIN CYCLONIC FLOW ALOFT SHOULD BE SUFFICIENT FOR AT OR ABOVE CLIMATOLOGICAL CHANCES FOR CONVECTION (30-40%) BY LATE AFT/EVE...WITH THE HIGHEST CHANCES ALONG/EAST OF THE HWY 1 CORRIDOR...DIMINISHING IN INTENSITY AND COVERAGE FROM WEST-EAST LATE THU EVE AND EARLY THU NIGHT. EXPECT HIGHS THU AFT IN THE LOWER TO MID 90S AND LOWS FRI MORNING IN THE LOWS 70S. -VINCENT && .LONG TERM /FRIDAY THROUGH TUESDAY/... AS OF 410 AM WEDNESDAY... FORECAST RATIONALE REMAINS GENERALLY UNCHANGED FROM PREVIOUS DAYS. THE MODELS REMAIN IN GOOD AGREEMENT REGARDING THE PERSISTENCE OF AN EASTERN CONUS TROUGH FORECAST TO DEVELOP DURING THE NEAR AND SHORT TERM...COINCIDENT WITH THE RETROGRESSION OF A SUB-TROPICAL RIDGE FROM THE SOUTHERN PLAINS AND MID-MS VALLEY WEST TO THE FOUR CORNERS REGION. MEANWHILE IN THE LOW LEVELS...THE MODELS AGREE THAT A COLD FRONT RELATED TO A POTENT UPPER LOW OVER SOUTHERN MANITOBA THIS MORNING WILL BE INVOF THE I-95 CORRIDOR FRI MORNING...THEN DRIFT SOUTHEAST THROUGH THE COASTAL PLAIN THROUGH THE MIDDAY-AFTERNOON HOURS. THIS GRADUALLY DIFFUSING BOUNDARY WILL BE THE FOCUS FOR SHOWERS AND STORMS CENTERED OVER THE EASTERN CAROLINAS FRI-SUN...WHILE A DRIER AIR MASS BOTH AT THE SURFACE AND ALOFT SETTLES ACROSS THE WESTERN... AND MUCH OF THE CENTRAL PART...OF NC. AS THE PREVIOUS SHIFT NOTED...ANY NORTHWESTWARD SHIFT IN THE FRONTAL POSITION AND ASSOCIATED AXIS OF TROPICAL MOISTURE --CHARACTERIZED BY PRECIPITABLE WATER VALUES AOA TWO INCHES-- WOULD RESULT IN A WETTER WEEKEND FOR PARTICULARLY EAST-CENTRAL NC. THOUGH MODEL SPREAD INCREASES BY THE EARLY-MIDDLE OF NEXT WEEK...THE MODELS TO VARYING DEGREES HAVE HINTED THAT THE TROPICAL MOISTURE MAY GET DRAWN NORTH/INCORPORATED INTO THE LONGWAVE TROUGH BY LATE SUN-MON...AT WHICH TIME THE PROBABILITY OF SHOWERS AND STORMS ARE MORE LIKELY TO INCREASE THROUGHOUT CENTRAL NC. && .AVIATION /18Z WEDNESDAY THROUGH MONDAY/... AS OF 200 PM WEDNESDAY... 24-HR TAF PERIOD: ASIDE FROM A POTENTIAL FOR ISOLD CONVECTION AT THE INT/GSO TERMINALS LATE THIS AFTERNOON/EVENING AND A POTENTIAL FOR EARLY MORNING STRATUS/FOG AT THE FAY/RWI TERMINALS...VFR CONDITIONS WILL PREVAIL THROUGH THE TAF PERIOD ALONG WITH LIGHT AND VARIABLE WINDS. LOOKING AHEAD: EXPECT AN INCREASED POTENTIAL FOR SHOWERS AND STORMS (CHANCES INCREASING WEST-EAST) LATE THU AFT/EVE AS A COLD FRONT APPROACHES THE MOUNTAINS FROM THE WEST AND INTO THU NIGHT (ESP AT EASTERN TERMINALS) AS THE FRONT TRACKS SLOWLY THROUGH THE CAROLINAS. EXPECT VFR CONDITIONS TO PREVAIL FRIDAY THROUGH EARLY NEXT WEEK... WITH THE BEST POTENTIAL FOR DIURNAL CONVECTION GENERALLY ALONG/ OFFSHORE THE CAROLINA COAST. -VINCENT && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...VINCENT NEAR TERM...VINCENT SHORT TERM...VINCENT LONG TERM...26 AVIATION...VINCENT

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