Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 032340 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 740 PM EDT MON AUG 3 2015 .SYNOPSIS... A STATIONARY FRONT WILL CONTINUE TO EXTEND THROUGH CENTRAL NORTH CAROLINA... FROM THE SANDHILLS THROUGH THE NORTHERN OUTER BANKS... THROUGH MIDWEEK. A COLD FRONT APPROACHING FROM THE NORTHWEST WILL STALL NEAR THE NORTH CAROLINA VIRGINIA BORDER EARLY WEDNESDAY. && .NEAR TERM /THROUGH TONIGHT/... AS OF 325 PM MONDAY... COASTAL SHOWERS HAVE THUS FAR HELD MAINLY SE OF THE FORECAST AREA... WITHIN THE ABOVE-NORMAL PW AND HIGHER SURFACE THETA-E AIR. ISOLATED SHOWERS FORMED CLOSED TO MIDDAY OVER THE FAR NRN PIEDMONT ALONG AN OLD OUTFLOW FROM LAST NIGHT`S OH VALLEY CONVECTION. THESE FAILED TO GATHER A LOT OF STEAM DUE TO THE DRY AIR... HOWEVER HAVE HELD ONTO ISOLATED POPS OVER THE FAR NE FOR A FEW MORE HOURS GIVEN THE STEEP LOW LEVEL LAPSE RATES AND 35-40 KTS OF EFFECTIVE DEEP LAYER SHEAR. ANY SHOWERS SHOULD BE GONE CLOSE TO SUNSET WITH THE LOSS OF HEATING. WILL ALSO MAINTAIN SMALL CHANCE POPS AS OUTFLOW FROM COLLAPSING COASTAL CONVECTION MAY YIELD SECONDARY SHALLOW SHOWERS/STORMS INTO THE FAR SE CWA. OTHERWISE... EXPECT DRY WEATHER WITH DECREASING CLOUDS BY MID EVENING. LOW LEVEL MOISTURE LATE TONIGHT SHOULD BE NEAR TO SLIGHTLY HIGHER THAN IT WAS EARLY THIS MORNING WITH WEAK MASS CONVERGENCE ALONG THE 925 MB INVERTED TROUGH... FAVORING ANOTHER ROUND OF PATCHY LOW STRATUS AND FOG OVERNIGHT... ESPECIALLY OVER THE EASTERN TWO THIRDS OF THE CWA. THIS IS SUPPORTED BY HIGH SREF PROBABILITIES OF LOW VSBYS OVERNIGHT. LOWS OF 68-73. -GIH && .SHORT TERM /TUESDAY AND TUESDAY NIGHT/... AS OF 350 PM MONDAY... THE SYNOPTIC FRONT NOW JUST NW OF THE OH VALLEY IS EXPECTED TO PROGRESS STEADILY TO THE ESE THROUGH TUE NIGHT... AS THE OLD FRONTAL ZONE OVER CENTRAL/ERN NC GETS NEW LIFE AS A PREFRONTAL PIEDMONT TROUGH... CAUSING AN INCREASE IN SURFACE DEWPOINTS ACROSS CENTRAL NC AND A RISING RISK OF LATE-DAY STORMS. THE LATEST MODEL RUNS CONTINUE TO DISAGREE ON THE DETAILS OF QPF. WHILE ALL FAVOR A CONTINUED HIGH COVERAGE OF CONVECTION OVER COASTAL NC ESPECIALLY SOUTH OF HATTERAS... THE NAM/SREF AND ECMWF SUPPORT SHOWERS/STORMS DEVELOPING JUST SOUTH OF THE FRONT... ACROSS SRN KY INTO SRN VA AND NW NC IN THE AFTERNOON. THE ECMWF SHOWS A QUICKLY DIMINISHING TREND AFTER 00Z... RESULTING IN DRY WEATHER FOR ALL BUT THE FAR NORTH AND FAR ERN CWA... HOWEVER THE NAM LEANS WETTER WITH APPARENT SOUTHEAST- MOVING OUTFLOW CONTINUING TO SUPPORT CONVECTION INTO THE NIGHT OVER CENTRAL NC. THE NSSL WRF IS SIMILAR IN THAT IT GENERATES ISOLATED TO SCATTERED CELLS OVER THE PIEDMONT LATE TUE... HOWEVER THE COVERAGE IS QUITE SPARSE. AND THE GFS STAYS LARGELY DRY OUTSIDE OF COASTAL NC. TOUGH CALL ON WHICH IS CORRECT... BUT I`M INCLINED TO THINK THAT THE NAM HAS THE MOST VALIDITY... AS THE MODELS SOMETIMES HAVE A DIFFICULT TIME DEALING WITH SUBSTANTIAL OUTFLOWS EMANATING FROM ORGANIZED CONVECTIVE COMPLEXES. WILL HAVE CHANCE POPS IN THE SE ONLY FOR MUCH OF TUE... THEN REDUCE POPS TO ISOLATED BUT EXPAND THEM ACROSS CENTRAL NC BY EVENING... CONTINUING OVERNIGHT... AS THERE MAY BE SUFFICIENT INSTABILITY AND STEEP LAPSE RATES IN THE COLUMN LINGERING AFTER NIGHTFALL. BUT CONFIDENCE IS NOT HIGH. ACCORDINGLY... THE RISK OF ANY STORMS BECOMING SEVERE IS ALSO HARD TO DETERMINE... BUT GIVEN THE UPTICK IN SURFACE DEWPOINTS... THE POTENTIAL CERTAINLY EXISTS FOR MODERATE INSTABILITY AND 30+ KTS OF EFFECTIVE DEEP LAYER SHEAR THAT WOULD SUPPORT A FEW STRONG TO SEVERE CELLS ACROSS THE NRN CWA. THICKNESSES AND GUIDANCE INDICATE HIGHS OF 90-94. LOWS 69-74. -GIH && .LONG TERM /WEDNESDAY THROUGH MONDAY/... AS OF 305 PM MONDAY... OVERALL THE SYNOPTIC PATTERN THROUGHOUT THE LONG TERM PERIOD WILL FEATURE RIDGING OVER THE SOUTHWEST CONUS AND TROUGHING (WITH VARYING STRENGTHS) OVER THE EAST. GIVEN THIS UPPER LEVEL FLOW PATTERN... MUCH OF OUR WEATHER WILL BE DICTATED BY NUMEROUS SHORTWAVES (WHICH ARE IMPOSSIBLE TO ACCURATELY PREDICT THIS FAR OUT). BESIDES SEVERAL WEAKER DISTURBANCES DURING THE MIDDLE PART OF THE WEEK TRIGGERING WIDELY SCATTERED SHOWERS/STORMS...THE FIRST SIGNIFICANT SHORT WAVE IS PROGGED TO CROSS THE REGION LATE THURSDAY INTO FRIDAY. THE GFS AND ECMWF DIFFER QUITE SIGNIFICANTLY...WITH THE GFS MUCH WEAKER AND DISORGANIZED...WHILE THE ECMWF SPINS UP QUITE A STRONG LOW THAT CROSSES VIRGINIA BEFORE EXITING OFF OF THE DELMARVA COAST. GIVEN THAT THE ECMWF IS MORE SIMILAR TO THE NAM (AT LEAST THROUGH 84 HOURS)...WILL FOLLOW ITS SOLUTION MORE CLOSELY. THIS WOULD RESULT IN PRECIP CHANCES RAMPING UP LATE THURSDAY INTO FRIDAY WITH THE APPROACH OF THE DEEPER SHORT WAVE/SURFACE FRONT BEFORE DECREASING LATE FRIDAY NIGHT AS THE NEXT KICKER WAVE PUSHES THE FRONT EAST. THE GFS DOES SHOW THIS OVERALL PATTERN (SHORT WAVE(S)/SURFACE FRONT)...BUT JUST IS NOT AS DEEP/ORGANIZED WITH THE SYSTEM...THUS THE PRECIP IS MORE SCATTERED IN NATURE. BY THE WEEKEND...BOTH MODELS ARE THEN IN FAIRLY GOOD AGREEMENT WITH THE FRONT BEING PUSHED TO OUR EAST...AND BECOMING NEARLY STATIONARY THERE. THIS SHOULD RESULT IN A MOSTLY DRY FORECAST...WITH ONLY SOME ISOLATED DIURNAL TYPE ACTIVITY...MOSTLY ACROSS THE EAST IN CLOSER PROXIMITY TO THE BOUNDARY. TEMPS WILL BE RATHER WARM TO START THE PERIOD (HIGHS IN THE MID/UPPER 90S...LOWS IN THE LOW/MID 70S)...BUT BY THE WEEKEND THEY SHOULD FALL SOME BEHIND THE FRONT (HIGHS IN THE MID/UPPER 80S...LOWS IN THE MID/UPPER 60S). && .AVIATION /00Z WEDNESDAY THROUGH SATURDAY/... AS OF 740 PM MONDAY... WHILE VFR CONDITIONS ACROSS CENTRAL NC ARE LIKELY TO PERSIST THROUGH MUCH OF THE TAF PERIOD...A PERIOD OF MVFR/POSSIBLY IFR CONDITIONS IS POSSIBLE IN EARLY MORNING STRATUS AND FOG ACROSS THE COASTAL PLAIN AND EASTERN PIEDMONT ON TUESDAY MORNING. AN ISOLATED THUNDERSTORM IS POSSIBLE THIS EVENING BUT THE COVERAGE SHOULD BE EXTREMELY LIMITED AND GENERALLY CONFINED TO LOCATIONS SOUTH AND EAST OF U.S. ROUTE 1. PERSISTENCE AND VARIOUS SETS OF GUIDANCE SUGGEST AREAS OF STRATUS AND/OR FOG ARE POSSIBLE ON TUESDAY MORNING...MOST LIKELY IMPACTING THE KFAY AND KRWI TERMINALS WITH A SMALLER THREAT AT KRDU. THESE CONDITIONS SHOULD BE FOCUSED TO A PERIOD OF BETWEEN 09 AND 13Z IN MOST LOCATIONS WITH RESIDUAL RESTRICTIONS CLEARED BY 15Z. VFR CONDITIONS SHOULD PREAIL OVERNIGHT AT KINT AND KGSO. WITH HEATING...SCT CUMULUS IS LIKELY TO DEVELOP TOWARD MIDDAY WITH BASES OF BETWEEN 4-6KFT. LIGHT MAINLY SOUTH TO SOUTHWEST WINDS ARE EXPECTED THROUGH THE PERIOD...ALTHOUGH AN HOUR OR TWO OF SLIGHTLY STRONGER AND GUSTY SOUTHERLY WINDS IS POSSIBLE NEAR AND BEHIND A NORTHWARD MOVING BOUNDARY THAT CROSSES THE KRDU/KRWI/KFAY TERMINALS. LOOKING BEYOND 00Z WED... ADVERSE AVIATION CONDITIONS ON WED AND THU ARE LIKELY TO BE ASSOCIATED WITH SOME EARLY MORNING FOG AND STRATUS ALONG WITH SCT MAINLY AFTN AND EVENING THUNDERSTORMS ON WED AND A BETTER CHANCE OF STORMS ON THU AND THU NIGHT. A LINGERING COLD FRONT WILL LIKELY BRING A CONTINUED THREAT OF SCT MAINLY AFTN AND EVENING SHOWERS AND STORMS TO THE AREA ON FRI AND SAT. -BLAES && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...HARTFIELD NEAR TERM...HARTFIELD SHORT TERM...HARTFIELD LONG TERM...KRD AVIATION...BLAES

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