Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 011113 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 713 AM EDT WED APR 1 2015 .SYNOPSIS...
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COOL HIGH PRESSURE WILL BUILD SOUTH ACROSS OUR REGION TODAY...THEN LINGER THROUGH THU. A WARM FRONT MOVE NORTH THROUGH THE REGION THU NIGHT...FOLLOWED BY THE PASSAGE OF A STRONG COLD FRONT FRI NIGHT AND EARLY SAT.
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&& .NEAR TERM /THROUGH TONIGHT/...
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AS OF 340 AM WEDNESDAY... OBSERVATIONAL DATA INDICATE THE SFC COLD FRONT HAD MOVED INTO THE SOUTHERN PIEDMONT/SANDHILLS/SOUTHERN COASTAL PLAIN AT 0730Z...AND THE FRONT WILL CONTINUE TO MOVE SOUTH AND OUT OF NC THROUGH 12Z. NORTH TO NE SFC WINDS WILL BE BRIEFLY GUSTY TO AROUND 15-20 KTS BOTH IN THE FEW HOUR WAKE OF THE FRONT...AND AGAIN AS THE MIXED LAYER DEEPENS WITH HEATING BETWEEN 12-15Z...MAINLY EAST OF 1-95. WHILE A FEW PATCHES OF ALTOCUMULUS IN THE VICINITY OF THE FRONT WILL DOT THE SKY THIS MORNING...IT WILL BE SHORT-LIVED AS THE PARENT S/W TROUGH ALOFT MOVES AWAY FROM THE MIDDLE ATLANTIC COAST. CLEARING AND HEIGHT RISES IN DEEP LAYER RIDGING ALOFT WILL FOLLOW...AND CAUSE A 1018 MB SFC HIGH OVER SOUTHERN OH TO STRENGTHEN A FEW MB AS IT BUILDS SOUTHEASTWARD ACROSS VA/NC TODAY. ASSOCIATED NE FLOW WILL RESULT IN COOLER (THAN TUE) TEMPERATURES...WITH DRY ADIABATIC MIXING NEAR H85 SUPPORTIVE OF HIGHS IN THE LOWER 60S NE TO LOWER 70S SW. SKIES WILL REMAIN CLEAR OR MOSTLY SO TONIGHT...WITH PERHAPS THE SOUTHERN FRINGE OF CIRRUS IN NW FLOW ALOFT GRAZING THE NORTHERN PIEDMONT THIS EVENING. H85-925 FLOW WILL BECOME SOUTHWESTERLY LATE TONIGHT AS THE CENTER OF THE ANTI-CYCLONE IN THAT LAYER DRIFTS OFF THE SC COAST...AND ASSOCIATED MOISTURE ADVECTION WILL CAUSE SOME STRATOCUMULUS TO DEVELOP AND CREEP TOWARD THE YADKIN BY DAYBREAK. BASED ON CURRENT AND PREVIOUS MODEL PROGS...IT IS UNLIKELY THAT THIS CLOUD COVER WILL ARRIVE SOON OR THICK ENOUGH TO HAVE A LARGE IMPACT ON OVERNIGHT TEMPERATURES. GIVEN THE RELATIVE CLEAR AND CONTINUED NEARBY PRESENCE OF THE AFOREMENTIONED SFC HIGH NEAR THE VA/NC COAST THAT GUIDANCE SUGGESTS WILL STRENGTHEN FURTHER BENEATH THE SUBSIDENT RIDGING ALOFT (TO NEAR 1028 MB)...GOOD TO EXCELLENT RADIATIONAL COOLING CONDITIONS ARE EXPECTED. PROJECTED LL THICKNESS VALUES AROUND 1345 METERS AT 12Z THU WILL SUPPORT MIDDLE 30S TO LOWER 40S...COOLEST EAST WHERE PATCHY FROST WILL BE POSSIBLE...NEARER THE CENTER OF THE SFC HIGH.
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&& .SHORT TERM /THURSDAY AND THURSDAY NIGHT/...
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AS OF 355 AM WEDNESDAY... RETURN FLOW WILL DEVELOP AS THE PRECEDING SFC HIGH DRIFTS TOWARD BERMUDA...AND AS THE MSL PRESSURE GRADIENT TIGHTENS DOWNSTREAM OF A COLD FRONT APPROACHING FROM THE WEST - FROM THE LOWER GREAT LAKES TO THE CENTRAL PLAINS. WARMING SOUTHERLY FLOW WILL CONSEQUENTLY RESULT IN A RETURN OF TEMPERATURES IN THE 70S AREA-WIDE...EXCEPT PERHAPS OVER THE NW PIEDMONT WHERE STRATOCUMULUS CENTERED AROUND H85 (REFERENCED IN THE NEAR TERM DISCUSSION) MAY RESULT IN MOSTLY CLOUDY CONDITIONS BY AFTERNOON. THE WAA REGIME MAY ALSO SUPPORT THE MAINTENANCE OF A SHOWER OR TWO...FROM UPSTREAM TN VALLEY CONVECTION...ACROSS THE APPALACHIANS AND INTO THE WESTERN PIEDMONT DURING THE LATE AFTERNOON AND EVENING HOURS...BUT WEAK INSTABILITY AT BEST OVER CENTRAL NC SUGGESTS ANY SUCH ACTIVITY WILL BE DISSIPATING AS IT APPROACHES. THE PASSAGE OF A WARM FRONT AND ASSOCIATED THETA-E ADVECTION/ ISENTROPIC UPGLIDE THU NIGHT WILL CAUSE CLOUDS/STRATUS TO DEVELOP THROUGHOUT CENTRAL NC OVERNIGHT...WITH MILD AND BREEZY AT TIMES CONDITIONS...AND LOWS IN THE UPPER 50S TO LOWER 60S. BUFR SOUNDINGS DEPICT THE RELATIVE DEEPEST SATURATION - IN THE LOWEST 5-6 THOUSAND FT AND ENTIRELY ABOVE FREEZING - OVER THE WESTERN PIEDMONT...WHERE PATCHY LIGHT SHOWERS OR DRIZZLE WILL BE POSSIBLE AND IS SUPPORTED BY A SMATTERING OF A HUNDREDTH OR TWO OF QPF PER THE 00Z MODELS.
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&& .LONG TERM /FRIDAY THROUGH TUESDAY/... AS OF 345 AM WEDNESDAY... AN UPPER LEVEL DISTURBANCE CROSSING THE REGIN LATE THURSDAY WILL MOVE OFF TO THE NORTHEAST FRIDAY MORNING...SUGGESTING A PERIOD OF SUBSIDENCE IN ITS WAKE EARLY ON FRIDAY. 1000-850MB THICKNESSES ARE PROGGED TO REACH 1390M FRIDAY AFTERNOON WITH A BREEZY SOUTHWEST FLOW THAT MAY RESULT IN GUSTS TO 35-40MPH IF MIXING IS A DEEP AS GFS BUFR SOUNDINGS SHOW. SOME WEAK INSTABILITY IS EXPECTED WITH TEMPS CLIMBING INTO THE UPPER 70S/LOWER80S AND DEWPOINTS IN THE LOWER 60S OVER THE COASTAL PLAIN. HOWEVER...THERE IS NO OBVIOUS FORCING MECHANISM FOR CONVECTION...SO WILL KEEP JUST A SLIGHT CHANCE IN FOR THE EASTERN CWA FRIDAY AFTERNOON. BETTER FORCING FOR PRECIP IS EXPECTED FRIDAY NIGHT AND EARLY SATURDAY WITH THE ARRIVAL OF A FAIRLY POTENT SHORTWAVE AND THE ASSOCIATED DCVA AND COLD FRONT DIVING THROUGH THE MIDWEST. MODELS CONTINUE TREND SLOWER WITH THE FRONT AS A WAVE OF LOW PRESSURE MOVES ALONG FRONT AND THROUGH THE OHIO VALLEY FRIDAY NIGHT. THERE IS STILL A SURPRISING AMOUNT OF MODEL DISCREPANCY REGARDING THE STRENGTHEN AND TRACK OF THE SURFACE LOW...SO CONFIDENCE IN THE TIMING OF THE FRONT IS STILL BELOW AVERAGE....BUT IN GENERAL THE FRONT SHOULD NOT ARRIVE UNTIL AFTER MIDNIGHT. DESPITE STRONG WESTERLIES AND DEEP LAYER SHEAR OF UP TO 40KT...WEAK LAPSE RATES AND POOR DIURNAL TIMING SHOULD LIMIT THE FRONTAL CONVECTION TO TO MAINLY SHOWERS. WILL INDICATE LIKELY POPS LATE FRIDAY NIGHT AND EARLY SATURDAY..WITH CLEARING CONDITIONS BY MIDDAY ON SATURDAY. TEMPS WILL BE WARM AHEAD OF THE FRONT AND MAY HOLD IN THE 60S FOR MUCH OF THE AREA FRIDAY NIGHT...WITH HIGHS ON SATURDAY KNOCKED BACK TO NEAR NORMAL BEHIND THE FRONT. MODIFIED HIGH PRESSURE WILL BUILD OVERHEAD SATURDAY NIGHT...WHEN 1000-850 MB THICKNESSES DROP TO 1320M. THIS SUGGESTS LOWS IN THE MID 30S FOR MANY LOCATIONS AND A GOOD CHANCE AT SOME FROST. A WARM UP WILL THEN ENSUE ON SUNDAY AS THE HIGH MOVES OFFSHORE. MOST OF EARLY NEXT SHOULD BE DRY AS A SHORTWAVE CROSS THE GREAT LAKES AND WE REMAIN JUST TO THE EAST OF THE BEST MOISTURE RETURN/INSTABILITY ASSOCIATED WITH THE WARM SECTOR WEST OF THE MOUNTAINS. HIGHS WILL BE MOSTLY NEAR NORMAL. && .AVIATION /12Z WEDNESDAY THROUGH SUNDAY/...
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AS OF 710 AM WEDNESDAY... VFR. A COLD FRONT HAS MOVED SOUTH OF OUR REGION THIS MORNING. ASSOCIATED POST-FRONTAL NNE WINDS WILL EXPERIENCE A BRIEF PERIOD OF HIGHER SUSTAINED SPEEDS AND GUSTS THROUGH AROUND 15Z-16Z...AS THE BRUNT OF HIGH PRESSURE RIDGING SOUTH FROM VA BUILDS IN. OTHERWISE... SKIES WILL BE MAINLY CLEAR...WITH JUST SOME PASSING CIRRUS THROUGH TONIGHT...THE DENSEST OF WHICH SHOULD CROSS SOUTHERN NC THIS MORNING. STRATOCUMULUS AROUND 5000 FT WILL APPROACH INT AND GSO FROM THE WEST AND SOUTHWEST BY THE END OF THE 12Z TAF PERIOD. OUTLOOK: THE PASSAGE OF A WARM FRONT WILL RESULT IN A LIKELY PROBABILITY OF MVFR-IFR CEILINGS AND A SLIGHT CHANCE OF SHOWERS THU NIGHT THROUGH EARLY FRI...WITH THE RELATIVELY HIGHEST PROBABILITY OF OCCURRENCE AND LOWEST CEILINGS AT INT AND GSO. THE DEVELOPMENT OF A 50 KT LOW LEVEL JET - AROUND 2000 FT - THU NIGHT MAY SUPPORT LOW LEVEL WIND SHEAR CONDITIONS AT THAT TIME...ALTHOUGH SOME OF THIS MOMENTUM MAY MIX TO THE SURFACE AND RESULT IN BREEZY SOUTHWESTERLY SURFACE WINDS AS OPPOSED TO LOW LEVEL WIND SHEAR. WARM AND WINDY FRI...WITH SUSTAINED SW WINDS NEAR 20 KTS AND GUSTS AROUND 30 KTS OR SO...FOLLOWED BY SUB-VFR CONDITIONS AND WIDESPREAD SHOWERS IN ASSOCIATION WITH A PASSING COLD FRONT...FRI NIGHT AND EARLY SAT.
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&& .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...RAH NEAR TERM...RAH SHORT TERM...RAH LONG TERM...22 AVIATION...RAH

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