Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 170739 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 340 AM EDT WED SEP 17 2014 .SYNOPSIS...A COLD FRONT WILL TRACK SOUTHEAST THROUGH THE CAROLINAS THIS MORNING. COOL HIGH PRESSURE WILL BUILD INTO THE REGION FROM THE NORTH THIS AFTERNOON AND PERSIST THROUGH THE REMAINDER OF THE WEEK. && .NEAR TERM /THROUGH TONIGHT/... AS OF 340 AM WEDNESDAY... TODAY...SURFACE COLD FRONT CURRENTLY DRIFTING SOUTH ACROSS CENTRAL NC (AT 07Z FRONT WAS FAIRLY ALIGNED WITH HIGHWAY 64) AND SHOULD BE DRAPED ACROSS THE SANDHILLS AND SOUTHERN COASTAL PLAIN THIS MORNING...DRIFTING INTO NORTHERN SC-SE NC THIS AFTERNOON. A MID- UPPER LEVEL VORTICITY MAXIMUM CROSSING SC EARLY THIS MORNING WILL MAINTAIN A THREAT FOR SHOWERS AND AN ISOLATED STORM FOR THE FAR SOUTHERN SECTIONS OF OUR FORECAST AREA THROUGH 12Z. LATER THIS MORNING...THE COOL MOIST STABLE AIR MASS BEHIND THE FRONT SHOULD RESULT IN A WEAK DAMMING EVENT. AS IS TYPICAL WITH THIS SET- UP...SHOULD SEE WIDESPREAD LOW CLOUDS AND PATCHES OF LIGHT RAIN OR DRIZZLE AS A SERIES OF UPPER LEVEL DISTURBANCES PASS OVERHEAD. THE EXTENSIVE CLOUDS AND SPOTTY LIGHT PRECIP SHOULD HOLD TEMPS IN THE LOW-MID 70S ACROSS THE PIEDMONT. GFS APPEARS TOO OPTIMISTIC IN ITS DEPICTION OF SCATTERING THE LOW CLOUDS INTO A SCATTER-BROKEN STRATOCU DECK THIS AFTERNOON. IF THE GFS IS MORE CORRECT...THEN EXPECT SCATTERED SHOWERS RATHER THAN LIGHT RAIN ACROSS THE PIEDMONT ALONG WITH WARMER TEMPS. CURRENTLY...PLAN TO HAVE MAX TEMPS RANGE FROM THE LOWER 70S NW TO THE LOWER 80S FAR SOUTH-SE. SLIGHT TO MODERATE INSTABILITY ACROSS THE SANDHILLS AND SOUTHERN COASTAL PLAIN SUGGEST A THREAT FOR SCATTERED CONVECTION THIS AFTERNOON. GFS DEPICTS BULK SHEAR OF 30KTS...SUGGESTING SOME ORGANIZATION TO THE CONVECTION...MAINLY IN THE FORM OF A BROKEN LINE. MAY SEE A STRONG WIND GUSTS WITH CELLS THAT HAVE SUSTAINED UPDRAFTS DUE TO PRECIP LOADING BUT MAJORITY OF SHOWERS AND STORMS WILL BE BELOW SEVERE LIMITS. FORCING THAT NOT ALL THAT IMPRESSIVE SO PLAN TO CAP POPS AT 30-40 PERCENT. TONIGHT...EXPECT WEAK CAD AIR MASS TO PERSIST OVER MOST OF THE PIEDMONT WITH PATCHES OF DRIZZLE OR FOG AND LOW CLOUDS. BULK OF CONVECTION IN THE SE WILL DIMINISH WITH LOSS OF HEATING AND LACK OF SUPPORT ALOFT. MAY SEE A SLIGHT UPSURGE IN LIGHT PRECIP TOWARD MORNING AS MOST OF THE MODELS DEPICT A MINOR S/W APPROACHING FROM THE WEST. MIN TEMPS GENERALLY 60-65. && .SHORT TERM /THURSDAY AND THURSDAY NIGHT/... AS OF 340 AM WEDNESDAY... THURSDAY...MINOR S/W PROJECTED TO PASS ACROSS THE FORECAST AREA IN THE MORNING. WEAK SUBSIDENCE IN ITS WAKE IN THE AFTERNOON AND ADVECTION OF DRIER AIR WILL BEGIN EROSION OF RESIDUAL CAD AIR MASS IN THE PIEDMONT. HOWEVER...MODELS TYPICALLY ARE TOO AGGRESSIVE WITH THIS TRANSITION. FAVOR A SLOWER IMPROVEMENT TREND THAN ADVERTISED BY THE MODELS. THIS LEADS TO MAX TEMPS ON THE COOL SIDE OF GUIDANCE. IF EROSION IS EVEN SLOWER THAN EXPECTED...MAX TEMPS MAY BE AS MUCH A 3- 4 DEGREES TOO WARM IN THE PIEDMONT. CONVECTION THURSDAY AFTERNOON APPEARS LIMITED TO THE FAR EAST-SE SECTIONS. JUST WEAK INSTABILITY AND SHEAR PROJECTED SO EXPECT MAINLY ISOLATED SHOWERS IN THE COASTAL PLAIN/SANDHILLS. MAX TEMPS MID-UPPER 70S NORTH TO AROUND 80 SOUTH. THURSDAY NIGHT...EXPECT GRADUAL IMPROVEMENT IN SKY CONDITIONS. THIS MAY LEAD TO SOME PATCHY FOG BUT INTRUSION OF DRIER AIR NEAR THE SURFACE MAY LIMIT/INHIBIT FOG FORMATION. BEST CHANCE FOR FOG WILL LIKELY BE THE SE HALF. MIN TEMPS IN THE UPPER 50S NW TO THE LOWER 60S SE. && .LONG TERM /FRIDAY THROUGH TUESDAY/... AS OF 340 AM WEDNESDAY... A PORTION OF THE LONGWAVE TROUGH INITIALLY ALONG THE EAST COAST WILL BE LEFT BEHIND...OFFSHORE THE SE US COAST THIS WKND...BUT THE OTHERWISE DEAMPLIFYING/LIFTING TROUGH WILL YIELD TO RISING HEIGHTS ALOFT OVER THE CAROLINAS...AS A FLAT MID LEVEL RIDGE RIDGE NOSES EASTWARD FROM THE SOUTHERN PLAINS AND LOWER MS VALLEY. THE RE- ESTABLISHMENT AND AMPLIFICATION OF A WESTERN NOAM RIDGE WILL THEN RESULT IN DOWNSTREAM TROUGH AMPLIFICATION FROM SOUTH-CENTRAL CANADA TO THE EAST-CENTRAL US DAYS 5-7. BENEATH THE RISING HEIGHTS ALOFT...A CANADIAN-SOURCE SFC HIGH (AROUND 1030 MB) WILL BUILD FROM CENTRAL CANADA TO THE CANADIAN MARITIMES AND RIDGE SOUTH/SOUTHWESTWARD THROUGH THE EASTERN STATES THROUGH THE FIRST HALF OF THE WEEKEND...BEFORE YIELDING - AMIDST FALLING HEIGHTS DOWNSTREAM OF THE AFOREMENTIONED REDEVELOPING TROUGH ALOFT HEADED FOR THE EAST-CENTRAL US - TO APPALACHIAN-LEE SFC TROUGH DEVELOPMENT SUN...AND A PASSING COLD FRONT MON-MON NIGHT. THOUGH THE CANADIAN RIDGING WILL RESULT IN A RELATIVELY PROLONGED PERIOD OF EAST TO NORTHEAST LOW LEVEL FLOW THROUGH EARLY THIS WEEKEND...THE LATEST GUIDANCE SUGGESTS THE BRUNT OF THE ASSOCIATED COOLER AND DRIER AIR WILL HOLD OVER THE NORTHERN MIDDLE ATLANTIC AND NORTHEAST STATES. IN ADDITION...THE ORIENTATION OF THE LOW LEVEL RIDGE AXIS SHOULD ALSO DIRECT MARITIME MOISTURE/CLOUDS AROUND THE RIDGE...TO THE SOUTH OF CENTRAL NC. AS SUCH...SKIES ARE APT TO BE PARTLY TO MOSTLY SUNNY OVER CENTRAL NC...WITH TEMPERATURES ABOUT A CATEGORY WARMER THAN EARLIER ANTICIPATED...IN THE MIDDLE 70S TO AROUND 80 DEGREES FRI-SAT. WARMER YET AHEAD OF THE APPROACHING FRONT SUN-MON - LIKELY LOWER TO PERHAPS MIDDLE 80S...WITH JUST A SLIGHT CHANCE OF SHOWERS ATTENDING THE FRONT LATE MON...GIVEN A LIMITED GULF MOISTURE FEED. COOLER TUE...AND THOUGH THERE REMAINS SOME POTENTIAL FOR LINGERING LIGHT RAIN (ESPECIALLY EAST) PER THE 12Z EC...THE 00Z EC HAS TRENDED TOWARD THE MORE CONSISTENT AND FAVORED EC ENSEMBLE MEAN WITH A "CLEANER" FRONTAL PASSAGE AND DRIER SOLUTION FOR TUE. && .AVIATION /06Z TUESDAY THROUGH SUNDAY/... AS OF 155 AM WEDNESDAY... VFR CONDITIONS REPORTED ACROSS MUCH OF CENTRAL NC AT 05Z WITH SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS MOVING EAST-SE ALONG THE NC-SC BORDER. THESE SHOWERS AND STORMS WERE AHEAD OF A SURFACE COLD FRONT THAT WAS DRIFTING SOUTH ACROSS THE NORTHERN PIEDMONT AT 05Z. THIS WEATHER FEATURE SHOULD BE CLOSE TO THE SC BORDER BY DAYBREAK THEN DRIFT FARTHER SOUTH LATER TODAY. LOW LEVEL NORTH- NORTHEAST FLOW BEHIND THE FRONT WILL MAINTAIN A COOL MOIST STABLE AIR MASS. THIS WILL RESULT IN WIDESPREAD IFR/LIFR CEILINGS ACROSS MUCH OF THE PIEDMONT INCLUDING KINT/KGSO AND KRDU...ALONG WITH PATCHES OF LIGHT RAIN OR DRIZZLE. THE LOW CEILINGS SHOULD DEVELOP BETWEEN 08Z-12Z AND PERSIST ALL DAY AND INTO TONIGHT. MVFR CEILINGS ARE EXPECTED IN THE VICINITY OF KRWI. NEAR KFAY...A BRIEF PERIOD OF MVFR/IFR CEILINGS THIS MORNING MAY LIFT INTO THE HIGH END MVFR-LOW END VFR BY AFTERNOON WITH A THREAT FOR SCATTERED SHOWERS...MAINLY TO THE EAST AND SOUTH. THE ADVERSE AVIATION WEATHER CONDITIONS WILL PERSIST ACROSS MUCH OF CENTRAL NC TONIGHT INTO THURSDAY MORNING WITH LOW CEILINGS AND MVFR/IFR VISIBILITY DUE TO DRIZZLE OR FOG. A GRADUAL IMPROVEMENT IN AVIATION CONDITIONS EXPECTED BY THURSDAY AFTERNOON AS DRIER AIR BEGINS TO ARRIVE INTO THE LOWER LEVELS OF THE ATMOSPHERE. VFR CONDITIONS ARE EXPECTED TO OCCUR THURSDAY NIGHT THROUGH SUNDAY AS HIGH PRESSURE GAINS GREATER INFLUENCE ON OUR WEATHER. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...VINCENT NEAR TERM...WSS SHORT TERM...WSS LONG TERM...MWS AVIATION...WSS

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