Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 300659 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 257 AM EDT SAT AUG 30 2014 .SYNOPSIS...
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A WARM FRONT WILL RETREAT NORTHEASTWARD ACROSS CENTRAL AND EASTERN NC AND VA TODAY. HIGH PRESSURE WILL BUILD ALOFT OVER OUR REGION INTO MID-WEEK.
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&& .NEAR TERM /TONIGHT/... AS OF 1030 PM FRIDAY... TWO PRIMARY FORECAST CONCERNS FOR TONIGHT INVOLVE THE DEVELOPMENT OF LOW STRATUS AND FOG...AND SHOWERS. THE FORMER HAS A HIGHER PROBABILITY OF OCCURRENCE OWING TO A REGIME OF ABUNDANT LOW LEVEL MOISTURE - CHARACTERIZED BY SFC DEWPOINTS IN THE UPPER 60S TO MIDDLE 70S - THAT HAS POOLED INVOF THE FRONT STALLED OVER SE NC...AND WHICH HAS SINCE BECOME TRAPPED IN THE VERTICAL BY A SHALLOW INVERSION. LIGHT TO CALM SFC WIND AND ASSOCIATED COOLING OF THE BOUNDARY LAYER...IN BETWEEN PERCOLATING PATCHES OF 2-6 THOUSAND FT CLOUDINESS...SHOULD THEN SUPPORT THE DEVELOPMENT AND EXPANSION OF LOW CLOUDS AND FOG. THE HRRR SUGGESTS SOME FOG MAY BECOME DENSE IN PATCHES OVER THE SOUTHERN AND WESTERN PIEDMONT...WHERE SFC WINDS HAVE BEEN...AND WILL CONTINUE TO BE...RELATIVELY LIGHTER. THE PROBABILITY OF SHOWERS IS LESS CERTAIN. THERE IS A QPF SIGNAL FOR SHOWER DEVELOPMENT OVER THE NORTHERN PIEDMONT PER NEAR TERM GUIDANCE FROM BOTH THE HRRR AND RUC...BUT FORCING FOR ASCENT AND INSTABILITY TO DRIVE SUCH DEVELOPMENT...ARE EXPECTED TO BE VERY WEAK. THE FORCING FOR ASCENT WILL COME COURTESY OF WEAK AND SHALLOW ISENTROPIC UPGLIDE ATOP THE AFOREMENTIONED STALLED SFC FRONT TONIGHT...AND RECENT REGIONAL VWP WINDS CORROBORATE THIS IDEA WITH THEIR DEPICTION OF WEAK BUT VEERING WINDS IN THE LOWEST SEVERAL THOUSAND FT. WILL INTRODUCE JUST A SLIGHT CHANCE OF A SHOWER GENERALLY NORTH OF HIGHWAY 64 TO ACCOUNT FOR THIS POSSIBILITY. LOWS GENERALLY 69 TO 75. && .SHORT TERM /SATURDAY AND SATURDAY NIGHT/... AS OF 250 PM FRIDAY... CENTRAL NC WILL REMAIN UNDER THE INFLUENCE OF AN UPPER LEVEL RIDGE ON SATURDAY. THE LINGERING BACKDOOR FRONT IS EXPECTED TO WASH OUT DURING THE DAY AS THE SURFACE HIGH SHIFTS OFFSHORE AND A LIGHT SOUTHERLY RETURN FLOW DEVELOPS ACROSS THE REGION. ALL OF THIS WILL RESULT IN A TYPICAL SUMMERTIME PATTERN...WITH HIGHS RISING INTO THE LOWER 90S. WITH MARGINAL INSTABILITY EXPECTED TO DEVELOP (HIGHEST ACROSS THE SOUTHEAST)...ISOLATED DIURNAL CONVECTION WILL BE POSSIBLE...ALTHOUGH MANY AREA LIKELY REMAINING DRY. OVERNIGHT LOWS ARE EXPECTED TO BE IN THE UPPER 60S TO LOWER 70S. && .LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
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AS OF 257 AM SATURDAY... UPPER RIDGING WILL PREVAIL FOR WHAT APPEARS TO BE THE FIRST REAL "EXTEND" TIME THIS SUMMER OVER NC. THEREFORE... ANY SURFACE FRONTS APPROACHING FROM THE NORTH WILL HAVE A DIFFICULT TIME PUSHING THIS FAR SOUTH... LIKELY STALLING OVER VA OR NEAR THE VA/NC BORDER. WE WILL MAINTAIN A FORECAST THAT DEPICTS SLIGHTLY ABOVE CLIMATOLOGY FOR HIGHS/LOWS... AND VERY NEAR CLIMATOLOGY FOR PM THUNDERSTORM CHANCES (THE ONLY CHANCE OF RAINFALL IN THIS PATTERN) DURING SUMMER. EXPECT DAILY HIGHS GENERALLY 88-94 NW TO SANDHILLS WITH LOWS 68-73. THESE NUMBERS WILL BE 2-4 DEGREES ABOVE NORMAL. A DAILY CHANCE OF CONVECTION IN THE AFTERNOON AND EARLY EVENING SHOULD BE LOWEST TUE (15-20 PERCENT)... THEN PICK UP SLIGHTLY WED-FRI (30-40) PERCENT.
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&& .AVIATION /00Z SATURDAY THROUGH WEDNESDAY/... AS OF 819 PM FRIDAY... CONDITIONS HAVE IMPROVED TO VFR AT ALL TERMINALS THIS EVENING. IFR CONDITIONS WILL RETURN TO THE AREA OVERNIGHT... AS A FRONTAL BOUNDARY REMAINS ACROSS THE AREA... WITH HIGH LOW LEVEL MOISTURE AND LIGHT WIND. CONDITIONS WILL IMPROVE AFTER SUNRISE... AND RETURN TO VFR DURING THE DAY SATURDAY AS THE BOUNDARY DISSIPATES. OUTLOOK...A SUMMERTIME PATTERN WILL PERSIST THROUGH EARLY/MID NEXT WEEK...WITH ISOLATED TO SCATTERED AFTERNOON/EVENING CONVECTION AND A POTENTIAL FOR EARLY MORNING FOG/STRATUS. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...MWS/PWB NEAR TERM...MWS SHORT TERM...KRD LONG TERM...PWB AVIATION...SEC/KRD

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