Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 031952 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 350 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/...
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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
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&& .SHORT TERM /TUESDAY AND TUESDAY NIGHT/...
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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
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&& .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 /18Z MONDAY THROUGH SATURDAY/... AS OF 145 PM MONDAY... VFR CONDITIONS LIKELY TO DOMINATE AT LEAST THROUGH THIS EVENING. THIS MORNING`S PATCHY SUB-VFR CIGS LIFTED AND MIXED OUT BY 15Z... NOW REPLACED BY MOSTLY SCATTERED VFR CUMULUS. ISOLATED SHOWERS/STORMS HAVE PERSISTED WELL SE OF FAY... WHILE IN THE LAST FEW HOURS... SCATTERED SHOWERS HAVE DEVELOPED NEAR THE VA/NC STATE LINE WELL NORTH OF RDU. THIS LOOSELY-ORGANIZED BAND OF SHOWERS MAY LENGTHEN AND EXPAND SOUTHWESTWARD TO AFFECT GSO AND/OR RDU WITH BRIEF MVFR VSBYS/CIGS FOR A PERIOD OF LESS THAN AN HOUR THIS AFTERNOON 18Z-22Z... AS IT DRIFTS TOWARD THE ESE. SIMILARLY... THE SHOWERS AND STORMS NOW OVER THE COASTAL CAROLINAS ARE EXPECTED TO EXPAND TO THE NW THROUGH EARLY EVENING... POTENTIALLY BRINGING BRIEF MVFR CONDITIONS TO FAY. BUT IN ALL CASES... VFR CONDITIONS WILL BE THE RULE FOR MUCH OF THE NEXT 9 HOURS... WITH ANY SHOWERS/STORMS LIKELY TO BE CIRCUMNAVIGABLE. LATER THIS EVENING INTO THE OVERNIGHT... SHOWER/STORM CHANCES WILL DIMINISH (ALTHOUGH AN ISOLATED SHOWER MAY LINGER OVERNIGHT NEAR FAY)... BUT PATCHES OF SUB- VFR CIGS/VSBYS ARE PROBABLE AT FAY AND RWI... WITH A LOWER CHANCE AT RDU... AND ARE UNLIKELY AT INT/GSO. THE MOST LIKELY TIME FOR IFR/LIFR CIGS/VSBYS WITH FOG/STRATUS WILL BE 07Z-12Z... WITH IMPROVEMENT TO VFR LIKELY TO OCCUR 12Z-14Z. LOOKING BEYOND 18Z TUE... VFR CONDITIONS LIKELY INTO TUE EVENING AT ALL SITES... ALTHOUGH LATE DAY SHOWER/STORM CHANCES WILL BE HIGHER AT FAY/RWI AND PERHAPS RDU FROM 19Z TO 02Z. THERE IS A GOOD CHANCE OF ANOTHER ROUND OF IFR VSBYS/CIGS AT ALL SITES BUT MAINLY RDU/RWI/FAY LATE TUE NIGHT INTO WED MORNING. CONFIDENCE IN THE FORECAST DETAILS DROPS TO LOWER THAN USUAL FROM TUE NIGHT ONWARD... AS A COLD FRONT DROPS INTO THE REGION FROM THE NW AND STAYS STALLED ACROSS VA AND NC THROUGH LATE WEEK... WAVERING NORTH AND SOUTH AS WEAK DISTURBANCES ALOFT TRACK ACROSS THE REGION. A STRONGER WAVE APPROACHING FROM THE WNW WED NIGHT MAY BRING THE BEST COVERAGE OF SUB-VFR SHOWERS/STORMS THU INTO EARLY FRI. -GIH && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...HARTFIELD NEAR TERM...HARTFIELD SHORT TERM...HARTFIELD LONG TERM...KRD AVIATION...HARTFIELD

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