Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 181127 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 730 AM EDT THU SEP 18 2014 .SYNOPSIS...A WEAK SURFACE TROUGH WILL EXTEND NORTH-TO-SOUTH OVER THE FOOTHILLS AND WESTERN PIEDMONT TODAY THEN DISSIPATE ON FRIDAY. COOL CANADIAN HIGH PRESSURE CENTERED OVER THE GREAT LAKES TODAY WILL DRIFT EAST AND EXTEND INTO THE CAROLINAS FRIDAY AND SATURDAY. && .NEAR TERM /THROUGH TONIGHT/... AS OF 310 AM THURSDAY... TODAY...WATER VAPOR IMAGERY DEPICTS A WEAK MID LEVEL S/W EXITING THE TN VALLEY EARLY THIS MORNING. THIS FEATURE WILL PROGRESS EAST AND CROSS CENTRAL NC LATER THIS MORNING-EARLY AFTERNOON. NOT MUCH IN THE MANNER OF WEATHER ASSOCIATED WITH THIS FEATURE AT THIS TIME. SFC ANALYSIS DEPICTS A WEAK INVERTED SURFACE TROUGH OVER THE WESTERN PIEDMONT. MODEL GUIDANCE MAINTAINS THIS FEATURE IN VICINITY OF THE YADKIN RIVER VALLEY THROUGH TONIGHT. WEAK MOISTURE CONVERGENCE WAS OCCURRING IN VICINITY OF THIS TROUGH AS SFC DEWPOINTS WERE IN THE LOW-MID 60S. THIS POOLING HAS RESULTED IN THE FORMATION OF LOW STRATUS AND FOG EARLY THIS MORNING OVER OUR FAR WESTERN COUNTIES. THIS AREA OF LOW CLOUDS/FOG MAY EXPAND EAST...POSSIBLY AS FAR EAST AS THE TRIANGLE AREA BY DAYBREAK. LATER THIS MORNING...THE APPROACH OF THE MID LEVEL S/W MAY TRIGGER A FEW SHOWERS IN VICINITY OF THE SURFACE TROUGH...MAINLY OVER THE WESTERN-SOUTHERN PIEDMONT. DUE TO MARGINAL INSTABILITY AND WEAK LIFT...BELIEVE THAT COVERAGE WILL BE NO WORSE THAN 20 PERCENT. EARLY MORNING CLOUDINESS WILL GIVE WAY TO PARTLY-MOSTLY SUNNY SKIES WITH MORE SUN THAN CLOUDS ANTICIPATED EAST OF HIGHWAY 1. MAX TEMPS IN THE UPEPR 70S -LOWER 80S. TONIGHT...AVAILABLE LOW LEVEL MOISTURE IN THE WESTERN PIEDMONT...POOLING ALONG THE SFC TROUGH...MAY MAINTAIN A FEW SHOWERS THROUGH THE LATE EVENING HOURS. OTHERWISE AVAILABLE LOW LEVEL MOISTURE MAY CAUSE THE FORMATION OF FOG AND/OR LOW CLOUDS...ESPECIALLY OVER THE PIEDMONT. MIN TEMPS NEAR 60-LOWER 60S. && .SHORT TERM /FRIDAY AND FRIDAY NIGHT/... AS OF 310 AM THURSDAY... DRY AIR RIDGE WILL BUILD INTO AND EXTEND ACROSS CENTRAL NC THIS PERIOD. THE DRIEST AIR WILL ENCOMPASS THE NE PIEDMONT AND MOST OF THE COASTAL PLAIN. THE LOW LEVEL EASTERLY FLOW MAY CAUSE MOISTURE TO BANK UP AGAINST THE HIGHER TERRAIN OF WESTERN NC WHICH MAY SPILL INTO OUR FAR WESTERN COUNTIES. THE MOISTURE APPEARS TOO SHALLOW TO SUPPORT ANY SHOWER ACTIVITY PLUS LIFT IS MINIMAL THIS PERIOD. MAX TEMPS SIMILAR TO TODAY IN THE UPPER 70S TO THE LOWER 80S. MIN TEMPS FRIDAY NIGHT IN THE UPPER 50S TO THE LOWER 60S. && .LONG TERM /FRIDAY THROUGH WEDNESDAY/... AS OF 330 AM THURSDAY... A PORTION OF THE LONGWAVE TROUGH INITIALLY ALONG THE EAST COAST WILL BE LEFT BEHIND AND SUPPORT WEAK FRONTAL WAVE DEVELOPMENT 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 THIS WKND-EARLY NEXT WEEK. THE WESTERN RIDGE...IN PROGRESSIVE FLOW ALOFT...WILL BUILD EAST ACROSS THE MID-LATITUDES OF THE CENTRAL AND EASTERN STATES MID TO LATE NEXT WEEK. BENEATH THE CONTINUED RISING HEIGHTS ALOFT SAT...A CANADIAN 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. ANOTHER STRONG CANADIAN HIGH WILL EXPAND AND STRENGTHEN ACROSS MUCH OF THE CENTRAL AND EASTERN CONUS IN THE WAKE OF THE PASSING COLD FRONT...WHICH GUIDANCE SUGGESTS WILL CLEAR ALL BUT PERHAPS SOUTHERN FL BY MID NEXT WEEK. WITH THE BRUNT OF THE COOLER AND DRIER AIR ASSOCIATED WITH THE LEAD HIGH LIKELY TO HOLD OVER THE NORTHERN MIDDLE ATLANTIC AND NORTHEAST STATES THIS WKND...CENTRAL NC TEMPERATURES ARE APT TO WARM TO ABOVE AVG...IN THE LOWER TO MIDDLE 80S - WARMEST SUNDAY. ANY SIGNIFICANT LOW-MID LEVEL CLOUD COVER ATTENDING THE OFFSHORE FRONTAL WAVE IS FORECAST AT THIS TIME TO HOLD ALONG COASTAL AREAS...WITH MORE OF A NORTHWESTERLY FLOW COMPONENT OVER CENTRAL NC...INTO THE OFFSHORE LOW/FRONTAL ZONE. FRONTAL PASSAGE TIMING HAS SPED FOR MON...SUCH THAT A FEW LINGERING SHOWERS FROM UPSTREAM CONVECTION MAY DRIFT INTO THE NW PIEDMONT SUN NIGHT...AND LEAVE MAINLY THE FAR SOUTHEAST CWFA IN THE WARM SECTOR THROUGH EARLY AFTERNOON...WITH EARLIER/UNFAVORABLE DIURNAL FRONTAL TIMING ACROSS THE REMAINDER OF THE AREA. SHOWER CHANCES WILL BE RELATIVELY LOW...THROUGHOUT THIS PERIOD...HOWEVER...AS GULF MOISTURE RETURN WILL BE LIMITED. COOLER TUE-WED...WITH HIGHS IN THE 70S IN THE POST-FRONTAL CANADIAN HIGH...WITH SFC DEWPOINTS IN THE 40S-50S. && .AVIATION /12Z THURSDAY THROUGH MONDAY/... AS OF 730 AM THURSDAY... AVIATION CONDITIONS ACROSS CENTRAL NC THIS MORNING VARY FROM VFR IN THE COASTAL PLAIN AND SANDHILLS TO MVFR/IFR DUE TO VISIBILITY RESTRICTIONS CAUSED BY FOG IN THE PIEDMONT. THE AREAS OF FOG AND PATCHY LOW CLOUDS WILL LIFT/DISSIPATE BY 13-14Z. A WEAK SURFACE TROUGH OVER THE WESTERN PIEDMONT AND FOOTHILLS WILL SERVE AS A FOCUS FOR MOISTURE POOLING. THIS FEATURE COUPLED WITH HEATING AND THE PASSAGE OF A WEAK MID LEVEL TROUGH MAY TRIGGER A FEW SHOWERS LATE THIS MORNING INTO THE AFTERNOON. DUE TO EXPECTED SPARSE COVERAGE...WILL OMIT FROM MENTIONING IN THE TRIAD TERMINALS AT THIS TIME. OTHERWISE...EXPECT VFR CONDITIONS WITH CLOUD BASES GENERALLY BET3500-5000FT. LATE TONIGHT INTO EARLY FRIDAY...MAY SEE POCKETS OF LOW CLOUDS AND/OR FOG WITH ASSOCIATED MVFR/IFR CONDITIONS. THE PROBABILITY OF THIS OCCURRING AT ANY PARTICULAR TAF SITE IS LESS THAN 30 PERCENT SO WILL OMIT FROM THE TERMINAL FORECAST AT THIS TIME. EXPECT VFR CONDITIONS FOR MOST OF FRIDAY THROUGH SUNDAY WITH JUST BRIEF INSTANCES OF EARLY MORNING FOG. AN APPROACHING SURFACE FRONT LATE SUNDAY INTO MONDAY MAY BRING A BRIEF PERIOD OF ADVERSE AVIATION CONDITIONS ON MONDAY. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...WSS NEAR TERM...WSS SHORT TERM...WSS LONG TERM...MWS AVIATION...WSS

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