Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 271732 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 132 PM EDT WED MAY 27 2015 .SYNOPSIS...BERMUDA HIGH PRESSURE CENTERED OVER THE WESTERN ATLANTIC WILL PREVAIL THROUGH THE WEEKEND. && .NEAR TERM /THROUGH TONIGHT/... AS OF 1020 AM WEDNESDAY... STRONG MID/UPPER LEVEL RIDGE OFF THE EASTERN SEABOARD MAY WEAKEN A BIT WHILE DRIFTING EVER SO SLIGHTLY EASTWARD. MEANWHILE...BERMUDA HIGH PRESSURE OVER THE WESTERN ATLANTIC WILL KEEP A WARM HUMID AIRMASS IN PLACE. SOME SHOWER ACTIVITY HAS DEVELOPED IN EASTERN SC AND SOUTHEASTERN NC AND IS TRACKING TO THE NORTHEAST. THIS IS LIKELY IN RESPONSE TO A WEAK DISTURBANCE WITHIN THE SOUTHEASTERLY FLOW ALOFT. THESE WEAK DISTURANCES WILL BE THE MAIN TRIGGERS FOR ANY CONVECTION INTO THE AFTERNOON AS WELL. HOWEVER...A LEFT-OVER OUTFLOW BOUNDARY FROM CONVECTION OVERNIGHT ACROSS THE WESTERN PIEDMONT MAY ALSO SERVE AS A FOCUS FOR CONVECTIVE INITIATION LATER TODAY. IN ADDITION...AN AREA OF STRATUS ACROSS THE NORTHEAST PIEDMONT AND SANDHILLS HAS BEEN SLOW TO BURN OFF THIS MORNING. SO DIFFERENTIAL HEATING ALONG THE BOUNDARIES OF THIS AREA OF CLOUD COVER COULD ALSO SERVE AS A TRIGGER. ALL OF THIS WILL LEAD TO SCATTERED AFTERNOON STORMS...WITH SLIGHTLY HIGHER COVERAGE THAN PREVIOUS DAYS. WEAK/MARGINAL ML CAPE BETWEEN 500-1000 J/KG COUPLED WITH DEEP LAYER SHEAR OF 10-15 KTS WILL FAVOR DISORGANIZED CONVECTION WITH LITTLE TO NO SEVERE THREAT. MOISTURE WILL BE SLIGHTLY HIGHER TODAY AND GIVEN THE BETTER CLOUD COVER AND SLIGHTLY HIGHER PRECIP CHANCES...HIGH TEMPS SHOULD BE A COUPLE OF DEGREES LOWER THAN YESTERDAY. HIGHS ARE EXPECTED TO BE IN THE LOW/MID 80S ACROSS THE NORTHWEST AND MID/UPPER 80S ACROSS THE SOUTHEAST. PRECIP SHOULD DIMINISH AFTER SUNSET...BUT PLENTY OF CLOUDS AND MOISTURE WILL BE AROUND OVERNIGHT...KEEPING TEMPS FROM FALLING MUCH. THEREFORE...OVERNIGHT LOWS ARE EXPECTED TO BE IN THE MID/UPPER 60S. && .SHORT TERM /THURSDAY AND THURSDAY NIGHT/... AS OF 300 AM WEDNESDAY... MID AND UPPER-LEVEL FLOW BECOMES INCREASINGLY MORE WESTERLY ON THURSDAY AS THE SHORTWAVE TROUGH OVER THE LOWER GREAT LAKES PROGRESSES EASTWARD INTO SOUTHERN NEW ENGLAND THROUGHOUT THE DAY. IN RESPONSE...MODELS HINT AT WEAK LEE-SIDE TROUGHINESS DEVELOPMENT ACROSS THE WESTERN PIEDMONT...WHILE DRIFTING THE LINGERING VORTICITY SHEAR AXIS EASTWARD INTO THE COASTAL PLAIN. WITH CONTINUED SEASONABLY MOIST AIR IN PLACE...THESE TWO FEATURES ALONG WITH DIURNAL DESTABILIZATION WILL SERVE AS A FOCUS FOR SCATTERED CONVECTION THURSDAY AFTERNOON/EARLY EVENING. PERSISTENCE TEMPERATURE FORECAST WILL BE FOLLOWED. HIGHS 83 TO 88. LOWS IN THE MID TO UPPER 60S. && .LONG TERM /FRIDAY THROUGH TUESDAY/... AS OF 315 AM WEDNESDAY... THE UPPER LEVEL RIDGE AXIS ALONG THE EAST COAST WILL RETROGRADE WESTWARD ON FRIDAY AS SURFACE HIGH PRESSURE ALSO EDGES BACK ACROSS THE AREA. DRIER AIR WITHIN THE RIDGE SHOULD LEAD TO A SIGNIFICANT REDUCTION IN INSTABILITY ACROSS THE EAST...WITH ONLY THE WESTERN PIEDMONT FORECAST TO SEE ANY CAPE VALUES APPROACHING 1000 J/KG. WITH MOISTURE AND INSTABILITY CONFINED TO THE WEST...MUCH OF THE CWA WILL BE FREE OF CONVECTION AND JUST ISOLATED TO WIDELY SCATTERED STORMS OVER THE WESTERN PIEDMONT. COVERAGE WILL BE EVEN LESS ON SATURDAY WITH THE UPPER RIDGE AXIS OVERHEAD...THOUGH MODELS HINT AT SOME ACTIVITY ALONG THE SEABREEZE AS IT MAKES A MODEST PUSH INLAND. LITTLE CHANGE IN THE AIRMASS AND EVEN A LITTLE WARMING ALOFT SUGGESTS HIGHS CONTINUING IN THE MID AND UPPER 80S FOR THE MOST PART. LOWS IN THE MID 60S. FROM SUNDAY ONWARD...PRECIP CHANCES ARE EXPECTED TO INCREASE RATHER DRAMATICALLY FROM NORTH TO SOUTH AS THE UPPER RIDGE AGAIN SHOWS SIGNS OF WEAKENING IN RESPONSE TO A NORTHERN STREAM SHORTWAVE CROSSING THE NORTHERN TIER OF THE US AND A COLD FRONT MOVES INTO THE OHIO VALLEY/MID-ATLANTIC REGION. HOWEVER...THE DETERMINISTIC GFS AND ECMWF RUNS DIFFER IN THE SOUTHWARD PUSH OF THE FRONT...WITH THE GFS INDICATING THE FRONT WILL SETTLE SOUTH OVER NC BY MONDAY AND THE ECMWF SUGGESTING THE FRONT WILL STALL TO OUR NORTH AS ANOTHER COUPLE SHORTWAVES RIDE ALONG THE FRONTAL ZONE...ONLY TO THEN BE FOLLOWED BY A BAGGING CUTOFF LOW SOMEWHERE OVER THE GULF COAST STATED BY MIDWEEK. NOT A LOT OF CONFIDENCE IN THE DETAILS...BUT WILL TEND TO FAVOR THE ECMWF...WHICH IS THE SOMEWHAT LESS ACTIVE SOLUTION WITH THE FRONT STALLING TO OUR NORTH. IN EITHER SCENARIO... MONDAY THROUGH WEDNESDAY COULD BE AN ACTIVE PERIOD WITH ABOVE NORMAL POPS AND TEMPS A BIT CLOSER TO NORMAL. && .AVIATION /18Z WEDNESDAY THROUGH MONDAY/... AS OF 130 PM WEDNESDAY... MOST OF CENTRAL NC HAS RETURNED TO VFR CONDITIONS...ALTHOUGH A FEW LINGERING MVFR CIGS REMAIN. SCATTERED SHOWERS/STORMS ACROSS THE AREA (BEST COVERAGE CURRENTLY ACROSS THE SOUTH AND EAST) WILL FILL IN ACROSS THE REGION THROUGH THE AFTERNOON HOURS. CONDITIONS ARE EXPECTED TO REMAIN LARGELY VFR THROUGH AT LEAST THE LATE EVENING HOURS...ALTHOUGH BRIEF SUB-VFR CONDITIONS WILL BE POSSIBLE IN ANY OF THE HEAVIER STORMS. HAVE INCLUDED A MENTION OF THUNDER AT KRDU...KFAY AND KRWI WHERE COVERAGE LOOKS TO BE THE GREATEST. HOWEVER...CANNOT RULE OUT THUNDER AT ANY TAF SITE. CONVECTIVE ACTIVITY IS EXPECTED TO DIMINISH AFTER SUNSET. ANOTHER ROUND OF LOW STRATUS/FOG WILL BE LIKELY AREAWIDE TOWARDS THE PRE-DAWN HOURS OF THURSDAY. ANY SUB-VFR CONDITIONS THAT DO DEVELOP SHOULD LIFT/DISSIPATE BY 15-16Z ON THURSDAY. OUTLOOK...THE THREAT FOR RESTRICTIONS IN EARLY MORNING FOG/STRATUS WILL CONTINUE INTO THE WEEKEND AS BERMUDA HIGH PRESSURE HOLDS OVER THE AREA. ISOLATED TO SCATTERED MAINLY AFTERNOON AND EVENING THUNDERSTORMS ARE EXPECTED AGAIN ON THURSDAY. RAIN CHANCES WILL BEGIN TO DECREASE SOME INTO THE WEEKEND AS THE UPPER LEVEL RIDGE RETROGRADES WEST OVER THE AREA. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...CBL NEAR TERM...KRD/CBL SHORT TERM...CBL LONG TERM...BLS AVIATION...KRD/CBL

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