Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 270717 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 315 AM 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 300 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. SHORTWAVE ENERGY EMBEDDED IN THE SOUTHWEST FLOW ALOFT AND SEASONABLY MOIST PWATS OF 1.5-1.6"(~80TH PERCENTILE) WILL SUPPORT SCATTERED CONVECTION AS HEATING WILL STEEPEN LOW-LEVEL LAPSE RATES DURING THE DAY. ADDITIONALLY...LEFT-OVER OUTFLOW BOUNDARY FROM WEAKENING CONVECTION CURRENTLY OVER THE WESTERN PIEDMONT MAY ALSO SERVE AS A FOCUS FOR CONVECTIVE INITIATION LATER TODAY. AS SUCH...POPS WILL BE MARGINALLY HIGHER THAN THE PAST FEW DAYS... AND PERHAPS MORE EQUITABLE RAIN CHANCES FOR THE CENTRAL PIEDMONT...WITH NEARBY UPPER RIDGE LIMITING RAIN/CONVECTIVE CHANCES IN THE EAST. WEAK/MARGINAL ML CAPE BETWEEN 500-800J/KG COUPLED WITH DEEP LAYER SHEAR OF 10-15KTS WILL FAVOR DISORGANIZED CONVECTION WITH LITTLE TO NO SEVERE THREAT. TEMPERATURES...WITH PWATS CREEPING UP TODAY...EXPECTED INCREASE IN CLOUD COVER AND SLIGHTLY BETTER RAIN CHANCES MAY KNOCK A DEGREE OR TWO OFF OF YESTERDAYS READINGS. HIGHS IN THE LOWER TO MID 80S NORTHWEST TO MID/UPPER 80S SOUTHEAST. LOWS IN THE MID TO 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 /06Z WEDNESDAY THROUGH SUNDAY/... AS OF 140 AM WEDNESDAY... CONVECTION ACROSS THE WESTERN PIEDMONT CONTINUES TO WEAKEN...AND SHOULD DIMINISH OVER THE NEXT HOUR OR TWO WITH NO FURTHER AVIATION IMPACTS AT KGSO...KINT OR KRDU. SOUTH-SOUTHEASTERLY RETURN FLOW AROUND BERMUDA HIGH PRESSURE OVER THE WESTERN ATLANTIC WILL MAINTAIN A MOIST LOW-LEVEL FEED OVER THE AREA...CREATING FAVORABLE CONDITIONS FOR THE DEVELOPMENT OF SUB-VFR STRATUS AT ALL TAF SITES BETWEEN 06 TO 14Z. BY 15 TO 16Z...ANY SUB-VFR CEILINGS SHOULD LIFT TO VFR. MAINLY DIURNAL ISOLATED TO SCATTERED SHOWERS AND STORMS ARE EXPECTED THIS AFTERNOON. BUT THIS PROBABILITY APPEARS TOO LOW TO MENTION IN THE TERMINAL FORECAST AT THIS TIME. BEYOND THE 00Z VALID TAF PERIOD...THE THREAT FOR RESTRICTIONS IN EARLY MORNING FOG/STRATUS WILL CONTINUE 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 INTO THE WEEKEND AS UPPER LEVEL RIDGE RETROGRADES WEST OVER THE AREA. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...CBL NEAR TERM...CBL SHORT TERM...CBL LONG TERM...BLS AVIATION...CBL

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