Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 270803 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 400 AM EDT MON JUL 27 2015 .SYNOPSIS...SURFACE HIGH PRESSURE WILL RETREAT OFFSHORE TODAY. A COUPLE OF WEAK DISTURBANCES IN NORTHWEST FLOW ALOFT WILL THEN CROSS THE REGION THROUGH THE MIDDLE OF THE WEEK. && .NEAR TERM /THROUGH TONIGHT/... AS OF 400 AM MONDAY... WEAK HIGH PRESSURE RIDGE OVER THE AREA THIS MORNING WILL SHIFT OFFSHORE TODAY...WHILE A SERIES OF WEAK DISTURBANCES APPROACH IN NORTHWESTERLY FLOW ALOFT. DEEP MIXING TO JUST ABOVE 850MB AND RELATIVELY DRY BOUNDARY LAYER AIR WILL LIMIT THE POTENTIAL DEWPOINT RECOVERY TODAY...WHILE MID-LEVEL LAPSE RATES REMAIN WEAK AND THE STEEPER LAPSE RATES OVER THE OHIO VALLEY (6-6.5 C/KM OBSERVED AT KILN) STAY TO OUR NORTH. THUS...FORECAST INSTABILITY OVER CENTRAL NC IS WEAK TODAY...300-600 J/KG AT BEST PER NAM/GFS BUFR SOUNDINGS. A STRONG SPEED MAX CROSSING THE MOUNTAINS AND DIFFERENTIAL HEATING SHOULD TRIGGER SCATTERED CONVECTION IN THE MOUNTAINS..WHICH WILL HAVE THE PROPENSITY TO DRIFT SOUTHEAST INTO PIEDMONT THIS EVENING. WITH A LESS FAVORABLE ENVIRONMENT DOWNSTREAM...CONVECTION IS NOT EXPECTED TO MAKE IT FURTHER THAN THE TRIANGLE...IF IT MAKES IT THAT FAR...SO WILL KEEP A CHANCE POP FOR THE TRIAD AREA AND NORTHER PIEDMONT THROUGH LATE EVENING. HIGH CLOUDS POURING IN FROM THE NORTHWEST COULD PROVE TRICKY FOR HIGHS TODAY..BUT AT THE MOMENT THEY DO NOT APPEAR WIDESPREAD TO LIMIT FULL HEATING...WHICH SHOULD YIELD HIGHS IN THE 89-93 RANGE. && .SHORT TERM /TUESDAY AND TUESDAY NIGHT/... AS OF 400 AM MONDAY... NORTHWEST FLOW ALOFT CONTINUES ON TUESDAY...THOUGH HEIGHTS ALOFT ALSO START TO RISE SLIGHTLY IN RESPONSE TO AN EASTWARD SHIFT OF THE CENTRAL US RIDGE AXIS. CONTINUED MOISTENING IN THE LOW-LEVELS WILL SUPPORT BETTER INSTABILITY THAN TODAY DESPITE WEAK LAPSE RATES. THE MAIN TRIGGERS FOR CONVECTION WILL AGAIN BE TERRAIN INDUCED CIRCULATION AND THE FLOW OF WEAK DISTURBANCES ALOFT. WITH BETTER INSTABILITY FORECAST..HOWEVER...WIDELY SCATTERED CONVECTION SEEMS POSSIBLE ACROSS MOST OF CENTRAL NC WITH HIGHER CONFIDENCE IN THE WESTERN PIEDMONT. HIGHS MAY BE A DEGREE OR TWO COOLER ON TUESDAY GIVEN INCREASED CLOUD COVER...BUT STILL INT HE UPPER 80S AND LOWER 90S. THE COVERAGE OF STORMS WILL LESSEN TUESDAY EVENING WITH LOSS OF HEATING...BUT GUIDANCE SUGGESTS A FEW STORMS COULD CONTINUE TO PERCOLATE WELL INTO THE NIGHT...ESPECIALLY OVER THE SOUTHERN AND WESTERN PIEDMONT AREAS. LOWS MORE SOLIDLY IN THE LOWER 70S. && .LONG TERM /TUESDAY THROUGH SUNDAY/... AS OF 230 PM SUNDAY... THE LONG TERM PATTERN PROMINENTLY FEATURES A LOWER MS VALLEY RIDGE CENTERED NEAR AR/OK ON TUESDAY THAT SHIFTS WEST TO THE FOUR CORNERS REGION BY SUNDAY. HEIGHTS INITIALLY RISE A BIT FROM TUESDAY INTO THURSDAY ACROSS THE MID ATLANTIC BEFORE AN EASTERN U.S. TROUGH DEVELOPS INTO THE WEEKEND. AT THE SURFACE...WEAK HIGH PRESSURE WILL EXTEND INTO THE REGION EARLY IN THE PERIOD WITH WEAK TROUGHING EXTENDING ALONG THE COAST. A COLD FRONT WILL APPROACH THE REGION FROM THE WEST ON THURSDAY AND THEN MOVE INTO AND STALL NEAR OR JUST SOUTH OF OUR REGION ON FRIDAY INTO THE WEEKEND. GUIDANCE SUGGESTS THAT A WEAK WAVE OR TWO OF LOW PRESSURE MAY DEVELOP ALONG THE FRONT DURING THE WEEKEND. THE EVENTUAL LOCATION OF THE FRONT AND ITS EVOLUTION WILL HAVE A BIG IMPACT ON THE SENSIBLE WEATHER IN CENTRAL NC. RISING HEIGHTS AND A WARMING ATMOSPHERE WILL LEAD TO HOTTER AND MORE HUMID CONDITIONS IN CENTRAL NC FROM TUESDAY INTO THURSDAY. A TYPICAL SUMMERTIME CHANCE OF A MAINLY AFTERNOON OR EVENING THUNDERSTORM IS EXPECTED ON TUESDAY AND PERHAPS A SLIGHTLY REDUCED CHANCE ON WEDNESDAY. HIGHS WILL CLIMB FROM THE UPPER 80S TO NEAR 90 ON TUESDAY TO THE LOWER TO MID 90S BY THURSDAY. THE CHANCES OF THUNDERSTORMS INCREASES ON THURSDAY INTO THE WEEKEND AS THE COLD FRONT APPROACHES AND LIKELY STALLS NEAR OUR REGION OVER THE WEEKEND. SLIGHTLY COOLER CONDITIONS ARE EXPECTED WITH LOWER HEIGHTS AND INCREASED CLOUD COVER. HIGHS WILL RANGE AROUND 90 ON FRIDAY AND IN THE MID 80S TO AROUND 90 OVER THE WEEKEND. -BLAES && .AVIATION /06Z MONDAY THROUGH FRIDAY/... AS OF 145 AM MONDAY... HIGH CLOUDS HAVE AT LEAST TEMPORARILY CLEARED OUT ACROSS CENTRAL NC ...THOUGH MORE HIGH CLOUDS UPSTREAM WILL APPROACH TODAY. THIS PERIOD OF CLEARING MAY PROMOTE A BETTER CHANCE OF MVFR VSBYS AND/OR PATCHY LOW CLOUDS BETWEEN 09Z AND 12Z ACROSS THE COASTAL PLAIN...BUT CONFIDENCE REMAINS LOW GIVEN THE LACK OF SUPPORT FROM MODEL GUIDANCE. IF ANY SUB-VFR CONDITIONS DEVELOP...IT WILL BE MOST LIKELY FROM KRWI TO KFAY. MOST OF TODAY WILL BE VFR FOR ALL OF CENTRAL NC...WITH A CHANCE OF A LATE AFTERNOON STORM AROUND KGSO/KINT AND A MUCH LESSER CHANCE OF STORMS MAKING IT ALL THE EAST EAST TO KRDU. OUTLOOK...INCREASING MOISTURE WILL LEAD TO BETTER CHANCE OF EARLY MORNING (09-13Z) STRATUS/FOG FROM TUESDAY ONWARD. MEANWHILE... AFTERNOON STORMS WILL ALSO BE POSSIBLE...ESPECIALLY AS A COUPLE DISTURBANCES CROSS THE AREA IN NORTHWESTERLY FLOW ALOFT. A COLD FRONT WILL APPROACH THE AREA LATE IN THE WEEK AND MAY BRING A BETTER CHANCE OF CONVECTION AND ADVERSE AVIATION CONDITIONS. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...22 NEAR TERM...22 SHORT TERM...22 LONG TERM...BLAES AVIATION...22

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