Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 290137 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 937 PM EDT SUN JUL 28 2014 .SYNOPSIS...
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CANADIAN HIGH PRESSURE WILL EXPAND ACROSS THE CAROLINAS AND MIDDLE ATLANTIC THROUGH MID-WEEK... BRINGING UNSEASONABLY DRY AND COOL CONDITIONS FOR LATE JULY.
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&& .NEAR TERM /THROUGH TONIGHT/...
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AS OF 937 PM MONDAY... CONVECTION HAD GENERALLY SLIPPED OFF THE SE COAST OF NC THIS EVENING AS THE COLD FRONT PUSHED INTO THE COASTAL AREA. THE FRONT AT MID- EVENING WAS LOCATED OVER SAMPSON COUNTY... DRIFTING SE. DEW POINTS DROPPED 10-15 DEGREES JUST BEHIND THE FRONT OVER HARNETT... MOORE... CUMBERLAND... AND SCOTLAND COUNTIES. BEHIND THE FRONT TODAY... GRADIENT WINDS GUSTED TO 36 MPH AT GREENSBORO... WHICH IS A RARITY FOR JULY... ESPECIALLY THE LAST WEEK OF JULY WHEN THE HOTTEST WEATHER IS TYPICALLY RECORDED. MINIMUM RELATIVE HUMIDITY ALSO FELL INTO THE LOWER 30S... AGAIN A RARE FEAT IN LATE JULY IN NC. THE LATEST DATA INDICATED MOSTLY CLEAR TO PARTLY CLOUDY SKIES ACROSS OUR REGION. THE LATEST GREENSBORO AND BLACKSBURG RAOBS INDICATED A DEVELOPING MID LEVEL INVERSION WHICH HAD TRAPPED SOME MOISTURE IN THE H7 LEVEL. THIS WAS APPARENT IN THE SURFACE OBSERVATIONS JUST BEHIND THE FRONT WHERE SOME OBSERVATIONS REPORTED A BROKEN CEILING WITH BASES OF 7-10K FEET. THE OVERNIGHT WILL CONTINUE TO FEATURE CAA WITH A GRADUAL DIMINISH IN THE NW BREEZE. THE MID LEVEL INVERSION WILL CONTINUE TO TRAP JUST ENOUGH MOISTURE TO KEEP SKIES PARTLY CLOUDY IN THE SE... BUT SHOULD BECOME CLEAR OR MOSTLY CLEAR ACROSS MOST OF THE PIEDMONT IN THE LEE OF THE APPALACHIANS. LOWS 58-65... WITH SOME MID 50S NORTHERN PIEDMONT IF THE WINDS CAN GO CALM AROUND SUNRISE. RECORD LOWS ARE 55 AT BOTH GSO AND RDU... BOTH RECORDED IN 1946.
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&& .SHORT TERM /TUESDAY AND TUESDAY NIGHT/... AS OF 255 PM MONDAY... BENEATH AND WEST OF CYCLONIC FLOW ALOFT WITHIN A MID-UPPER TROUGH AXIS NEAR 85W...CANADIAN HIGH PRESSURE WILL EXTEND SOUTHEASTWARD INTO THE MIDDLE ATLANTIC AND CAROLINAS TUE AND TUE NIGHT. COOLER AIR CHARACTERIZED BY H85 TEMPERATURES AROUND 13C...WHICH WAS ALREADY ON THE DOORSTEP OF THE RAH CWFA/AT KRNK AND KBNA AT 12Z MON...WILL HAVE FULLY OVERSPREAD CENTRAL NC THIS PERIOD - SUPPORTIVE OF HIGH TEMPERATURES IN THE LOWER TO MIDDLE 80S. WITH DEWPOINTS EXPECTED IN THE 50S BASED ON UPSTREAM OBSERVATIONS OVER THE OH VALLEY...THE COMBINATION OF LOW RH AND MILD TEMPERATURES WILL FEEL FAR FROM LATE JULY. LOW LEVEL THICKNESS VALUES OF AROUND 1380 METERS OR SO AT 12Z WED FAVORS LOWS IN THE UPPER 50S TO AROUND 60 DEGREES ON AVG. && .LONG TERM /WEDNESDAY THROUGH MONDAY/... AS OF 300 PM MONDAY... WEDNESDAY AND WEDNESDAY NIGHT... A STABLE LONGWAVE PATTERN WILL KEEP THE EAST/WEST COAST UPEPR TROUGH/RIDGE SETUP IN PLACE FOR THE REMAINDER OF THIS WEEK AND POTENTIALLY INTO NEXT WEEK. THE UNSEASONABLY DEEP TROUGH OVER THE EASTERN CONUS WILL LEAD TO THICKNESSES AS MUCH AS 20-25 DEGREES BELOW NORMAL WEDNESDAY...WITH ONLY A SLOW MODERATION THROUGH THE END OF THE WEEK. PW FALLS WELL BELOW ONE INCH WEDNESDAY...ABOUT 50 PERCENT OF NORMAL...WITH DEWPOINTS WILL INTO THE 50S ACROSS THE PIEDMONT. THE ECMWF PRODUCES A LITTLE QPF OVER THE SOUTHERN COASTAL PLAIN AS A SPEED MAX ON THE BACK SIDE OF THE UPEPR TROUGH NOSES ACROSS THE SOUTHERN APPALACHIANS. HOWEVER... PW FALLS WELL BELOW ONE INCH WEDNESDAY...ABOUT 50 PERCENT OF NORMAL...WITH DEWPOINTS WELL INTO THE 50S. THIS RESULTS IN ONLY A SHALLOW LAYER OF INSTABILITY AND LIKELY JUST A DECENT CU FIELD OVER THE COASTAL PLAIN. HIGHS 82-86. LOWS WEDNESDAY NIGHT IN THE LOW TO MID 60S. THURSDAY THROUGH MONDAY... MODELS SHOW SOME ADDITIONAL ENERGY DIVING INTO THE BACKSIDE OF THE TROUGH ON THURSDAY...WHILE THE TROUGH AXIS SHIFTS SLIGHTLY WESTWARD AND HEIGHTS BUILD OVER THE WESTERN ATLANTIC. THIS SHOULD LEAD INCREASING PRECIP CHANCES...MAINLY DIURNAL...AS 1) PW BEGINS TO INCREASE BACK TOWARD NORMAL...2)AN INVERTED COASTAL TROUGH POTENTIALLY SHIFTS WESTWARD AND INLAND...AND 3) AN UPPER JET BECOMES POSITIONED ALONG THE SPINE OF THE APPALACHIANS. GIVEN THAT FORCING SHOULD MAINLY COME FROM AFTERNOON DIFFERENTIAL HEATING AND/OR THE SEABREEZE...CHANCE POPS AROUND CLIMATOLOGY SEEM MOST REASONABLE THROUGH THE WEEKEND. THERE IS ALSO THE POTENTIAL FOR WEAK COLD AIR DAMMING AS THE UPPER LEVEL FLOW BECOMES MORE CONFLUENT OVER NEW ENGLAND AND A WEAK RIDGE OF HIGH PRESSURE EXTENDS THROUGH THE MID-ATLANTIC STATES. NOT SURPRISINGLY...FORECAST SOUNDINGS SHOW NOW SIGN OF LOW CLOUDS AT THIS POINT...AND ITS HARD TO TELL HOW MUCH IMPACT THERE WOULD BE. GIVEN THIS AND A GENERAL INCREASE IN CLOUD COVER...HIGHS WILL REMAIN ONE OR TWO CATEGORIES BELOW NORMAL. && .AVIATION /00Z TUESDAY THROUGH SATURDAY/... AS OF 700 PM MONDAY... DRY AIRMASS IN PLACE UNDER HIGH PRESSURE BUILDING INTO THE AREA WILL PRODUCE VFR CONDITIONS...ONLY PATCHY AFTERNOON CUMULUS EXPECTED... THROUGH THURSDAY. A COASTAL SURFACE TROF AND A STRONG UPPER SHORT WAVE DIGGING INTO THE PREDOMINANT TROF OVER THE EASTERN CONUS WILL PRODUCE A CHANCE OF SHOWERS BY FRIDAY INTO SATURDAY. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...32 NEAR TERM...32 SHORT TERM...MWS LONG TERM...BLS AVIATION...MLM

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