Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 021934 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 333 PM EDT WED SEP 2 2015 .SYNOPSIS...A DISTURBANCE WILL DROP SOUTHEAST THROUGH THE AREA TONIGHT THROUGH EARLY THURSDAY...BUT OTHERWISE DEEP HIGH PRESSURE WILL HOLD OVER THE REGION THROUGH FRIDAY. A COLD FRONT WILL MOVE SOUTHWARD THROUGH THE AREA LATE FRIDAY INTO SATURDAY. && .NEAR TERM /THROUGH TONIGHT/... AS OF 252 PM WEDNESDAY... ISOLATED CONVECTION HAS BEGUN OVER THE FAR NRN CWA... ROUGHLY A COUPLE OF HOURS AHEAD OF THE TIMING SUGGESTED BY THE SPC SSEO / NSSL WRF / 3KM NAM CONUS NEST... AND JUST ABOUT AN HOUR AHEAD OF THE NCAR WRF ENSEMBLE. THE NCAR AND NSSL WRF ALONG WITH THE HRRR/NAM/GFS INDICATE GREATEST COVERAGE OF STORMS OVER THE NE CWA LATE THIS AFTERNOON THROUGH EARLY EVENING... REASONABLE CONSIDERING THAT THE BEST DPVA WILL BE LOCATED HERE... ALONG WITH STRONG HEATING AND HIGH INCOMING LOW-LEVEL LAPSE RATES OVER 8.5 C/KM. EFFECTIVE DEEP-LAYER SHEAR REMAINS MARGINAL AT AROUND 25 KTS... BUT MIXED-PHASE CAPE IS MAXIMIZED HERE AT 400 J/KG AND WITH OBSERVED DOWNDRAFT CAPE AOA 1000 J/KG... LOCALIZED ENHANCED WIND GUSTS ARE POSSIBLE IN/NEAR ANY STORMS ESPECIALLY NORTH OF A LINE FROM RDU TO WILSON. THIS IS ALSO SUPPORTED BY THE NCAR WRF ENSEMBLE NEIGHBORHOOD PROBABILITIES OF STRONG SURFACE WIND GUSTS VERY LATE AFTERNOON INTO EARLY EVENING. FOLLOWING THE TIMING OF THESE CONVECTION-ALLOWING MODELS... AND THEIR TRENDS WHICH ARE FOR GRADUAL WEAKENING AND DECREASING COVERAGE AS CONVECTION HEADS TO THE SSE OVER CENTRAL NC THROUGH THE EVENING... WILL MAINTAIN POPS FROM EARLIER FORECAST UPDATE WITH ONLY MINOR TEMPORAL CHANGES. WILL START WITH 25-45% COVERAGE (BEST NE) THROUGH EARLY EVENING... WITH ACTIVITY DROPPING TO THE SSE THROUGH EARLY TO MID EVENING WHILE STEADILY WEAKENING AND DECREASING IN COVERAGE BEFORE DISSIPATING AROUND OR SOON AFTER 06Z WITH LOSS OF HEATING / FALLING CAPE AND THE DEPARTURE OF THE POTENT MID LEVEL WAVE NOW DROPPING THROUGH ERN WV. THERE SHOULD BE AN INITIAL PARTIAL CLEARING BEHIND THE BROKEN/DIFFUSE CONVECTIVE BAND... BUT SCATTERED MID CLOUDS AS WELL AS HIGH THIN CLOUDS SPREADING OFF LOWER MISS VALLEY AND GULF CONVECTION WILL KEEP SKIES PARTLY CLOUDY OVERNIGHT... LIMITING THE FOG THREAT DESPITE THE LIGHT WINDS. LOWS 67-72. -GIH && .SHORT TERM /THURSDAY AND THURSDAY NIGHT/...
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AS OF 333 PM WEDNESDAY... THE MID LEVEL VORTICITY MAX SHOULD BE SHIFTING OFF THE NRN NC COAST THU MORNING... ALBEIT WITH A WEAK TRAILING SHEAR AXIS EXTENDING BACK ACROSS THE NRN CWA. THIS TRAILING VORTICITY WILL SINK SLOWLY SOUTHWARD THROUGH THE DAY BUT REMAIN EXTENDED ACROSS THE SRN CWA LATE THU THROUGH THU NIGHT. PW VALUES WILL HAVE FALLEN WITH A SLIGHTLY MORE STABLE AND SUBSIDING COLUMN BEHIND THE CORE OF THE EXITING WAVE... SO EXPECT ANY SHOWER/STORM COVERAGE TO BE FAIRLY SMALL GIVEN THE WEAK WIND FIELD... LACK OF STRONG FORCING FOR ASCENT... AND LIMITED CAPE. WILL RETAIN AN ISOLATED POP JUST ACROSS THE SOUTH AND SE NEAR THE SHEAR AXIS AND WHERE LOW LEVEL DEWPOINTS WILL LIKELY BE HIGHER. ANOTHER MUCH WEAKER WAVE WILL PUSH INTO THE REGION FROM THE SW LATE THU INTO THU NIGHT... BUT THIS APPEAR TO CONTRIBUTE VERY LITTLE DYNAMIC FORCING... AND WITH LACK OF HEATING AFTER SUNSET... COVERAGE SHOULD BE ISOLATED AT BEST WITH THIS SECOND WAVE. WILL KEEP A MENTION OF ISOLATED STORMS IN THE NE CWA THROUGH THE EVENING... THEN TREND POPS DOWN BELOW 15% OVERNIGHT. THIS PATTERN CORRELATES WITH THE LOCATION OF THE SREF`S HIGHER CHANCES OF MEASURABLE PRECIP. WITH GOOD MIXING AND CONTINUED ABOVE NORMAL THICKNESSES... EXPECT STEAMY HIGHS OF 90-95. LOWS 67-72 UNDER PARTLY CLOUDY SKIES. -GIH
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&& .LONG TERM /FRIDAY THROUGH WEDNESDAY/... AS OF 315 PM WEDNESDAY... THE MAIN PLAYER IN THE WEATHER PATTERN FOR THE LONG TERM WILL BE A 1026 MB SURFACE HIGH PRESSURE SYSTEM OVER NEW ENGLAND THAT WILL PUSH A BACKDOOR COLD FRONT THROUGH THE AREA ON FRIDAY NIGHT AND SET UP A WEDGE FRONT THAT IN PATTERN WILL BE REMINISCENT OF A COLD AIR DAMMING SCENARIO BUT WITHOUT THE ISENTROPIC LIFT THAT WE USUALLY SEE CONTRIBUTING TO MORE STRATIFORM RAIN ACROSS THE TRIAD. THE FEATURE THROUGH WILL CAUSE LOW CLOUDS TO SPREAD ACROSS MUCH OF THE AREA ON SATURDAY AND BRING IN MUCH COOLER HIGH TEMPERATURES (LOW TO MID 80S). AS THE WEEKEND CONTINUES...A VERY WEAK LOW OFF OF THE FLORIDA COAST WILL ATTEMPT TO HELP FORM AN INVERTED TROUGH ALONG THE CAROLINA COAST BUT THE STRENGTH OF THIS FEATURE REMAINS UNCERTAIN AT THIS TIME. CURRENT MODEL RUNS SUGGEST THAT THIS FEATURE MAY REMAIN FAIRLY WEAK BUT IT WILL CERTAINLY CAUSE AN UPTICK IN POPS ACROSS EASTERN PORTIONS OF THE CWA...PARTICULARLY SUNDAY AND MONDAY AFTERNOONS DURING PEAK HEATING WITH PSEUDO WEDGE FRONT BOUNDARY HELPING TO INITIATE CONVECTION. THE EXACT LOCATION OF THIS BOUNDARY IS TO BE DETERMINED AND THUS THE AFTERNOON FORECAST REMAINS FAIRLY LOW CONFIDENCE BUT GENERAL TRENDS SUGGEST THAT RAIN WILL BE MORE LIKELY FURTHER EAST. ON TUESDAY THE SURFACE HIGH BREAKS DOWN AND TEMPERATURES WILL START A SLOW WARMING TREND INTO THE MID TO UPPER 80S BY MID WEEK. THE MAIN THREAT FOR PRECIPITATION WILL BE WITH A FEW SHORTWAVES ALONG THE SOUTH CAROLINA COAST WHICH MAY PROVIDE SOME FORCING FOR DIURNAL SHOWERS OR STORMS BOTH DAYS. && .AVIATION /18Z WEDNESDAY THROUGH MONDAY/... AS OF 145 PM WEDNESDAY... HIGH CONFIDENCE IN VFR CONDITIONS HOLDING THROUGH MID AFTERNOON THU... ALTHOUGH THERE WILL BE ONE BRIEF PERIOD OF EXCEPTION. THE PASSAGE OF AN UPPER LEVEL DISTURBANCE FROM NW TO SE THROUGH THE REGION LATE TODAY THROUGH THIS EVENING WILL BRING SCATTERED STORMS... MOST LIKELY TO AFFECT RWI AND PERHAPS RDU... WITH INT/GSO SEEING A SLIGHTLY LOWER CHANCE OF STORMS AND FAY SEEING THE LEAST CHANCE. THE PRIMARY WINDOW OF STORM POTENTIAL WILL BE 21Z-01Z AT INT/GSO/RDU/RWI. A SHORT PERIOD OF GUSTY WINDS AND MVFR TO IFR CONDITIONS CAN BE EXPECTED IN AND NEAR ANY STORMS... ALTHOUGH COVERAGE WILL BE SMALL AND DURATION LESS THAN AN HOUR AT ANY GIVEN LOCATION. OTHERWISE... ANY CIGS ARE LIKELY TO BE ABOVE 6K FT AGL. LIGHT AND VARIABLE SURFACE WINDS WILL BECOME PREDOMINANTLY FROM THE NE OR NORTH TONIGHT BUT REMAIN LIGHT THROUGH THU. LOOKING BEYOND 18Z THU... VFR CONDITIONS LIKELY TO HOLD. THE CHANCE OF SHOWERS AND STORMS INCREASES LATE FRI INTO FRI NIGHT IN ASSOCIATION WITH A COLD FRONT PASSAGE... FOLLOWED BY A LOWER CHANCE SAT AFTERNOON. SUB-VFR LOW CLOUDS AND FOG POSSIBLE LATE FRI NIGHT / EARLY SAT MORNING... AND AGAIN LATE SAT NIGHT / EARLY SUN MORNING WITH A LOW LEVEL FLOW FROM THE EAST OR NE BEHIND THE FRONT DRAWING ATLANTIC MOISTURE INTO THE AREA. -GIH && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...HARTFIELD NEAR TERM...HARTFIELD SHORT TERM...HARTFIELD LONG TERM...ELLIS AVIATION...HARTFIELD

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