Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 251036 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 635 AM EDT FRI JUL 25 2014 .SYNOPSIS...A COLD FRONT PUSHING SOUTHEAST THROUGH THE REGION EARLY THIS MORNING WILL WEAKEN AND STALL NEAR THE SOUTH CAROLINA BORDER LATER TODAY...AS WEAK HIGH PRESSURE BUILDS IN FROM THE NORTH. THIS FRONT WILL DISSIPATE OVER THE WEEKEND AS SOUTHWEST FLOW RETURNS. A STRONGER COLD FRONT WILL MOVE THROUGH THE REGION EARLY NEXT WEEK. && .NEAR TERM /THROUGH TONIGHT/... AS OF 255 AM FRIDAY... WITH THE COLD FRONT HAVING PUSHED SOUTHWARD THROUGH MUCH OF NC... ASIDE FROM VARIABLY CLOUDY SKIES TODAY... MUCH OF CENTRAL NC WILL SEE IMPROVED WEATHER CONDITIONS... WITH THE EXCEPTION OF THE SE AND FAR SRN CWA. LAST NIGHT`S WIDESPREAD CONVECTION HAS SHIFTED OFF THE COAST... ALONG WITH A LEADING PROMINENT SHORTWAVE TROUGH SWINGING THROUGH THE BASE OF A WEAKENING TROUGH COVERING THE ERN THIRD OF NOAM. THE LOCATION OF THE COLD FRONT IS NOT EASY TO SPECIFY ON THE LATEST SURFACE MAP AS IT APPEARS TO HAVE MERGED WITH THE PREFRONTAL TROUGH... BUT IT LOOKS TO STRETCH FROM THE NC COASTAL AREA BACK ACROSS SRN NC AND NRN GA/AL. SURFACE WINDS HAVE SHIFTED AROUND TO LIGHT N OR NE AREAWIDE... AND THESE LIGHT SPEEDS COMBINED WITH STABILIZING LOW LEVELS POST-FRONT AND PLENTY OF RESIDUAL LOW LEVEL MOISTURE HAVE KEPT AREAS OF LOW CLOUDS OVER CENTRAL NC... CLOUDS THAT WILL BE SLOW TO DISLODGE/DISPERSE DESPITE LIMITED CLOUDINESS ABOVE. AS SUCH... EXPECT VARIABLY CLOUDY SKIES TODAY... WITH A BIT LOWER HUMIDITY LEVELS ESPECIALLY NORTH OF 64. THE FRONT IS EXPECTED TO REMAIN ACROSS SRN NC TODAY AS WEAK HIGH PRESSURE NOW CENTERED OVER NRN OH BUILDS IN... AND WHILE PW WILL SLIP TO NEAR/BELOW NORMAL VALUES OVER MOST OF CENTRAL NC... SOUTHERN SECTIONS SHOULD HOLD NEAR 2.0 INCHES. WITH ELEVATED DEW POINTS PERSISTING THERE ALONG WITH WEAK DPVA AND LINGERING WEAK UPPER DIVERGENCE... THE RISK OF SHOWERS/STORMS WILL CONTINUE ON OUR SOUTH... FOCUSED THROUGH THE AFTERNOON AND EARLY EVENING. A STORM OR TWO COULD BECOME STRONG GIVEN THAT DEEP LAYER SHEAR SHOULD STILL BE 25-30 KTS WITH MODELS SHOWING MUCAPE OF 1000-2000 J/KG... ALTHOUGH THIS RISK WITH BE LOWER IF THE THICKER LOW CLOUDS HANG ON LONGER AND INHIBIT INSOLATION. ISOLATED SHOWERS ARE A GOOD BET OVER THE REST OF THE FORECAST AREA THIS MORNING WITH A LOBE OF VORTICITY SWINGING THROUGH THE AREA... BUT LATE MORNING THROUGH THE AFTERNOON SHOULD BE DRY OUTSIDE OF THE AFOREMENTIONED SOUTHERN SECTIONS WITH 20-30 M HEIGHT RISES. HIGHS 84- 89... IN LINE WITH THICKNESSES THAT ARE PROJECTED TO BE 15-20 M BELOW NORMAL. MOISTURE PERSISTING BENEATH THE SUBSIDENCE INVERSION ALOFT SHOULD TRANSLATE TO PARTLY CLOUDY SKIES TONIGHT. HAVE HELD ONTO LOWS IN THE 66-71 RANGE. -GIH && .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 TH 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 THROUGN 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 /12Z FRIDAY THROUGH TUESDAY/... AS OF 635 AM FRIDAY... PROBLEMATIC AVIATION CONDITIONS EARLY THIS MORNING... AS SCATTERED TO BROKEN CLOUDS BASED BETWEEN 600 AND 1400 FT AGL MEANDER ABOUT CENTRAL NC. THESE LOW CIGS ARE EXPECTED TO COME AND GO THROUGH MID MORNING... WITH MVFR/IFR CIGS DOMINATING. AFTER AROUND 14Z... MVFR CIGS ARE EXPECTED THROUGH THE MID-LATE MORNING AS THESE CLOUDS LIFT SLOWLY... WITH CIGS NOT REACHING VFR UNTIL CLOSE TO 18Z... AND EVEN AFTER THIS TIME AT FAY... CLOSE TO WHERE THE COLD FRONT IS EXPECTED TO HAVE PUSHED BY AFTERNOON. A FEW SHOWERS AND ISOLD STORMS WILL BE RESTRICTED TO NEAR FAY THIS AFTERNOON. VFR CIGS ARE EXPECTED TO PERSIST THEN FROM MID AFTERNOON THROUGH MIDNIGHT... BUT CIGS MAY DROP BACK DOWN TO MVFR LATE TONIGHT. ALSO... POCKETS OF IFR FOG ARE POSSIBLE 09Z-12Z SAT MORNING... ESPECIALLY AT RWI/FAY. AS THE FRONT SETTLES SOUTH OF ALL TAF SITES THIS MORNING... EXPECT A LIGHT BREEZE FROM THE NORTH TO DOMINATE THROUGH THE DAY. LOOKING BEYOND 12Z SAT MORNING... VFR CONDITIONS ARE LIKELY TO DOMINATE THROUGH THE WEEKEND WITH HIGH PRESSURE BUILDING IN... FOLLOWED BY A RESUMPTION OF SOUTHWEST FLOW AND PIEDMONT TROUGH LATE IN THE WEEKEND. A COLD FRONT WILL APPROACH FROM THE NW EARLY NEXT WORK WEEK... BRINGING THE POTENTIAL FOR SUB-VFR SHOWERS/STORMS... PARTICULARLY MONDAY. -GIH && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...HARTFIELD NEAR TERM...HARTFIELD SHORT TERM...HARTFIELD LONG TERM...MWS AVIATION...HARTFIELD

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