Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 251456 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 1056 AM EDT FRI JUL 25 2014 .SYNOPSIS...
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A STALLED FRONT WILL REMAIN NEAR OR JUST SOUTH OF THE SOUTH CAROLINA BORDER THROUGH TONIGHT. A CLIMATOLOGICALLY MOIST AND UNSTABLE AIRMASS WILL PREVAIL OVER THE WEEKEND. AN UNSEASONABLY DEEP UPPER LEVEL TROUGH AND ATTENDANT COLD FRONT WILL APPROACH FROM THE NORTHWEST SUNDAY NIGHT...THEN CROSS THE REGION ON MONDAY.
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&& .NEAR TERM /THROUGH TONIGHT/...
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AS OF 1045 AM FRIDAY... OUTFLOW ASSOC/W CONVECTION THAT DEVELOPED ALONG THE COLD FRONT TRACKING SOUTHWARD THROUGH VA/NC YESTERDAY EVENING SERVED TO 1) STRENGTHEN THE FRONTAL ZONE AND 2) ACCELERATE THE FRONT SOUTHWARD. AS A RESULT OF THE AFOREMENTIONED ACCELERATION...THE FRONT WAS LOCATED WELL SOUTH OF CENTRAL NC THIS MORNING...EXTENDING ROUGHLY WEST-EAST FROM ATLANTA-COLUMBIA-MYRTLE BEACH AT 14Z. WV IMAGERY AND RAOB DATA INDICATED A DRY/SUBSIDENT AIRMASS OVER CENTRAL NC THIS MORNING...IN THE WAKE OF PRONOUNCED SHORTWAVE ENERGY LOCATED OFFSHORE THE MID-ATLANTIC COAST AT 14Z. ALTHOUGH SFC DEWPOINTS HAVE FALLEN INTO THE MID/UPPER 60S IN MOST AREAS AND LOW-LEVEL MOISTURE HAS CERTAINLY DECREASED IN COMPARISON TO YESTERDAY...SUFFICIENT LOW- LEVEL MOISTURE STILL EXISTS FOR MARGINAL DIURNAL DESTABILIZATION WITH MLCAPE PROGGED IN THE 250-1000 J/KG RANGE...LOWEST NEAR THE VA BORDER AND HIGHEST NEAR THE SC BORDER. SHALLOW LOW-LEVEL CONVERGENCE ALONG THE STALLED FRONT SHOULD REMAIN SOUTH OF CENTRAL NC TODAY... AND WOULD BE MORE LIKELY TO SERVE AS A FOCUS FOR CONVECTIVE DEVELOPMENT OVER CENTRAL/UPSTATE SC WHERE GREATER DESTABILIZATION IS EXPECTED. CYCLONIC FLOW ALOFT WILL PERSIST OVER THE REGION TODAY...AND SUBSIDENCE IN THE WAKE OF EXITING SHORTWAVE ENERGY SHOULD EFFECTIVELY SUPPRESS DEVELOPMENT THROUGH AT LEAST MID AFTERNOON. ADDITIONAL SHORTWAVE ENERGY (UPSTREAM IN IL/IN AT 14Z) IS EXPECTED TO TRACK INTO THE SOUTHERN MID-ATLANTIC LATE THIS EVENING. DPVA ASSOC/W THIS FEATURE SHOULD OCCUR AT LEAST SEVERAL HRS AFTER PEAK HEATING (~03Z)...WITH NOCTURNAL COOLING FURTHER STABILIZING AN ALREADY MARGINAL THERMODYNAMIC ENVIRONMENT. GIVEN LIMITED FORCING FOR ASCENT...A DRY MID/UPPER LEVEL AIRMASS AND VERY MARGINAL DESTABILIZATION...EXPECT A VERY LOW PROBABILITY FOR CONVECTIVE DEVELOPMENT TODAY...PERHAPS A SLIGHT CHANCE (10-20%) IN THE FAR SOUTHERN TIER OF COUNTIES IN THE WFO RAH CWA (I.E. ANSON EAST TO SAMPSON) DURING THE MID/LATE AFTERNOON. EXPECT HIGHS IN THE MID/UPPER 80S AND LOWS IN THE MID/UPPER 60S. -VINCENT
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&& .SHORT TERM /SATURDAY THROUGH SATURDAY NIGHT/... AS OF 325 AM FRIDAY... EXPECT A LARGELY DRY DAY WITH INCREASED SUNSHINE. THE WEAKENING MID LEVEL TROUGH AXIS WILL SHIFT OFF THE COAST WITH MODEST HEIGHT RISES CONTINUING OVER NC. THE QUICKLY WEAKENING SURFACE FRONTAL ZONE NEAR THE NC/SC BORDER WILL FALL APART AND BE OVERTAKEN BY INCREASING LOW LEVEL SOUTHWEST FLOW AND DEVELOPMENT OF A WEAK PIEDMONT TROUGH. PW IS EXPECTED TO BE AT OR UNDER 1.2 INCHES TO START THE DAY... BUT IS FORECAST TO REBOUND TO AROUND 1.8 INCHES IN STRIP FROM CENTRAL VA THROUGH CENTRAL NC BY LATE AFTERNOON... WHICH THEN DRIFTS TO ERN NC SAT NIGHT. CORRESPONDINGLY THE MODELS DEPICT MODERATE INSTABILITY... MUCAPE OF 1000-1500 J/KG ON THE GFS LATE IN THE DAY... WITH AROUND 1000 J/KG LINGERING IN THE FAR EAST OVERNIGHT. BUT THE MODELS GENERATE LITTLE MORE THAN AN ISOLATED SHOWER OR STORM AS THE COLUMN REMAINS WARM/STABLE AND DRY THROUGH THE 850-500 MB LAYER. WILL KEEP THE FORECAST DRY... AS ANY CONVECTION WOULD BE EXTREMELY ISOLATED. THICKNESSES REBOUND TO JUST 5-10 M BELOW NORMAL... WHICH WITH DECENT SUNSHINE SUPPORTS HIGHS OF 89-93. LOWS 69-74... MILDER THAN TONIGHT DUE TO THE RETURN OF HIGHER DEWPOINTS. -GIH && .LONG TERM /SUNDAY THROUGH THURSDAY/... AS OF 335 AM FRIDAY... MEDIUM RANGE GUIDANCE IS IN EXCELLENT AGREEMENT REGARDING THE DEVELOPMENT OF HIGH AMPLITUDE/UNSEASONABLY MERIDIONAL FLOW ACROSS NOAM THROUGH MID-WEEK - INCLUDING A DEEP TROUGH CENTERED NEAR 80-85W AND ASSOCIATED 3 STANDARD DEVIATION NEGATIVE HEIGHT ANOMALY CENTERED OVER THE LOWER OH VALLEY - WITH SLIGHT RETROGRESSION AND RELAXATION OF THE FLOW BY THE END OF THE PERIOD. SUN AND SUN NIGHT: HOT...WITH PROJECTED H85 TEMPERATURES AROUND 22- 23 C OVER THE CAROLINAS AS THE MID LEVEL RIDGE OVER THE DESERT SW AND PLAINS BUILDS BRIEFLY EAST IN ADVANCE OF THE AMPLIFYING TROUGH ALOFT. THE FOCUS FOR CONVECTION WILL BE DIRECTED FROM THE LOWER OH VALLEY EAST ACROSS THE VIRGINIAS...WHERE THE AMPLIFYING TROUGH ALOFT WILL MAXIMIZE HEIGHT FALLS ALOFT/RIGHT JET ENTRANCE REGION DIVERGENCE. SOME OF THIS ACTIVITY MAY DEVELOP SOUTHWARD INTO THE NORTHERN AND WESTERN PIEDMONT LATE IN THE DAY AND ESPECIALLY DURING THE EVENING HOURS...AS BOTH LARGER SCALE FORCING AND OUTFLOW FROM UPSTREAM CONVECTION SPREADS SSE. FORECAST GUIDANCE SUGGESTS THE HOT AND DEEP DRY ADIABATICALLY-MIXED BOUNDARY LAYER WILL BE TOPPED BY STEEP (7 C/KM) LAPSE RATES ALL THE WAY THROUGH THE MID LEVELS. THE RESULT WILL BE MODERATE TO STRONG INSTABILITY AMIDST 30-35 KTS OF MID LEVEL FLOW...SUPPORTIVE OF MOSTLY MULTI-CELLULAR ORGANIZATION... WITH PERHAPS A FEW SUPERCELLS NEAR AND JUST NORTH OF THE VA BORDER. LARGE HAIL...AND DAMAGING WIND GUSTS AIDED BY SUB-CLOUD ACCELERATION OWING SFC DEWPOINT DEPRESSIONS OF 25-30 C KM...WILL POSE A SVR THREAT. THIS THREAT SHOULD BE MAXIMIZED INVOF THE VA BORDER...BEFORE INSTABILITY WANES AFTER SUNSET...AND SOUTHBOUND OUTFLOWS UNDERCUT STORMS WITH MEAN WIND-DRIVEN ENE STORM MOTIONS. WARM OVERNIGHT... WITH LOWS GENERALLY 73 TO 78 DEGREES. MON AND MON NIGHT: LOW PREDICTABILITY ASSOCIATED WITH MESOSCALE INFLUENCES (IE. OUTFLOW AND CLOUD COVER) FROM EARLIER CONVECTION SUN NIGHT...AS WELL AS THE LIKELIHOOD OF STRONG WESTERLY/DOWNSLOPE H85 FLOW...COMPLICATE THE FORECAST FOR MON...DESPITE AN OTHERWISE STRONG SYNOPTIC SIGNAL FOR UPWARD VERTICAL MOTION OVER NC. THE DOWNSLOPE FLOW WILL LIKELY MIX OUT BL MOISTURE AND VEER THE LOW LEVEL FLOW WEST OF A LEE/PRE-FRONTAL SFC TROUGH INVOF US HWY 1...SUCH THAT ONLY A SLIGHT CHANCE POP IS WARRANTED THERE. BL MOISTURE AND CONVERGENCE WILL BE MORE PLENTIFUL TO THE EAST...WHERE POP WILL GRADUATE INTO THE LIKELY RANGE INVOF AND EAST OF I-95. CONTINUED STEEP LOW-MID LEVEL LAPSE RATES AMIDST STRENGTHENING MID LEVEL FLOW INTO THE 40-50 KT RANGE WILL SUPPORT A GOOD CHANCE OF SVR STORMS...INCLUDING SUPERCELLS...CAPABLE OF PRODUCING LARGE HAIL AND DAMAGING WIND GUSTS. TORNADO PROBABILITIES WILL BE ONLY MARGINAL OWING TO LIMITED SRH (GENERALLY BELOW 150 M2/S2)...AND BL/LCL HEIGHTS AROUND 5 K FT. DRY AND COOLER CONDITIONS WILL PREVAIL THROUGH MID-WEEK...AS POST- FRONTAL HIGH PRESSURE BUILDS INTO THE CENTRAL APPALACHIANS AND PRECIPITABLE WATER VALUES FALL BELOW AN INCH OVER CENTRAL NC. HIGHS AND LOWS ONLY IN THE LOWER TO MIDDLE 80S AND MID-UPPER 50S TO LOWER- MID 60S...RESPECTIVELY...TUE-WED...BEFORE AIR MASS MODIFICATION THROUGH THE END OF THE WEEK. && .AVIATION /18Z FRIDAY THROUGH WEDNESDAY/...
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AS OF 1045 AM FRIDAY... 24-HR TAF PERIOD: VFR CONDITIONS WILL PREVAIL THROUGH THE MAJORITY OF THE TAF PERIOD IN ASSOC/W A DRY AND SUBSIDENT AIRMASS IN THE WAKE OF THE RECENT COLD FRONTAL PASSAGE...WITH LIGHT/VARIABLE WINDS THROUGH TONIGHT. THE ONLY EXCEPTION TO THE ABOVE WILL BE A POTENTIAL FOR REDUCED VISBYS IN FOG OR LOW CEILINGS WITH STRATUS DURING THE PRE-DAWN HOURS SATURDAY MORNING (08-13Z)...AND A LOW CHANCE FOR AN ISOLD SHOWER OR STORM AT THE FAY TERMINAL LATE THIS AFTERNOON. LOOKING AHEAD: EXPECT A CHANCE FOR AFTERNOON SHOWERS/STORMS OVER THE WEEKEND INTO EARLY NEXT WEEK...ESPECIALLY ON MONDAY WHEN THE ENVIRONMENT WOULD SUPPORT SEVERE THUNDERSTORMS DURING THE AFTERNOON AND EVENING HOURS. -VINCENT
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&& .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...VINCENT NEAR TERM...VINCENT SHORT TERM...HARTFIELD LONG TERM...MWS AVIATION...VINCENT

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