Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 081756 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 156 PM EDT TUE JUL 8 2014 .SYNOPSIS...
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BROAD HIGH PRESSURE WEAKENS AS A COLD FRONT MOVES TOWARD THE REGION FROM THE GREAT LAKES. THIS COLD FRONT SHOULD MOVE INTO THE MID-ATLANTIC WEDNESDAY...WEAKENING AS IT MOVES INTO NORTH CAROLINA THURSDAY. A TROUGH OF LOW PRESSURE THEN PERSISTS OVER THE REGION AT LEAST THROUGH FRIDAY.
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&& .NEAR TERM /THROUGH TONIGHT/... AS OF 910 AM TUESDAY... THE LATEST SURFACE ANALYSIS SHOWED BROAD HIGH PRESSURE MOSTLY OVER THE MID-ATLANTIC AND THE CAROLINAS WITH A WEAK SURFACE TROUGH AMONG THE BROAD RIDGE OVER THE CENTRAL PIEDMONT. THE SPC MESOANALYSIS SHOWED A NOTICEABLE MINIMUM OF PRECIPITABLE WATER VALUES OVER THE WESTERN PART OF THE STATE...SIMILAR TO WHAT WAS FORECAST BY THE MONDAY GUIDANCE. THE RAP FORECASTS THIS MINIMUM TO MOVE ACROSS CENTRAL NORTH CAROLINA DURING THE DAY...AND FOR THE MOST PART RAP SOUNDINGS ARE SIMILAR TO SOUNDINGS FORECAST BY THE GFS MONDAY... QUITE STABLE TO DEEP CONVECTION DURING THE DAY. TWO CAVEATS TO THIS ARE CURRENTLY...AND VERY LATE TODAY. CURRENTLY...PRECIPITABLE WATER VALUES ARE AT OR ABOVE 1.5 INCHES OVER A LARGE PART OF CENTRAL NORTH CAROLINA...AND RAP SOUNDINGS SHOW THE PRESENCE OF MID-LEVEL INSTABILITY THAT WANES BY 18Z AS THE LOWER MOISTURE VALUES MOVE EAST. THE LATEST VISIBLE IMAGERY SHOWED A NARROW BAND OF MID-LEVEL CLOUDS THAT DEVELOPED FROM NEAR ROXBORO TO WADESBORO...AND THE HRRR WRF ACTUALLY FORECASTS A SHOWER OR TWO DEVELOPING FROM THIS. WATER VAPOR IMAGERY WOULD SUGGEST ENOUGH SUBSIDENCE TO PRECLUDE A SHOWER... BUT THE DEVELOPMENT OF THE CLOUDS PLUS THE PRESENCE OF WEAK INSTABILITY MAKES IT WORTHY OF NOTE HERE. LATE TODAY...THE RAP FORECASTS LIFT MOVING INTO THE FAR NORTHWEST PIEDMONT TOWARD KINT BY 23Z. RAP SOUNDINGS ARE STILL FAIRLY STABLE AT THAT POINT...AND QPF ON THE RAP IS NIL THROUGH 00Z WEDNESDAY. PRECIPITABLE WATER VALUES INCREASE QUICKLY ON THE RAP...TO NEAR 1.5 INCHES JUST AFTER 00Z WEDNESDAY...AS K INDICES RISE TO NEAR 40. LIKE THE GFS FORECAST MONDAY...MODEST MID-LEVEL COOLING COUPLED WITH MOISTURE ADVECTION MAY BE ENOUGH FOR A SHOWER OR THUNDERSTORM TO MOVE INTO THE WEST AND NORTHWEST PIEDMONT THIS EVENING. MOS GUIDANCE POPS ARE A FEW PERCENTAGE POINTS LOWER THAN THAT GUIDANCE OF MONDAY...AND WRF ARW GUIDANCE SUGGESTS LITTLE PRECIPITATION INTO THE EVENING. STILL...THE MOISTURE ADVECTION AND SLIGHT COOLING ALOFT... COUPLED WITH A WEAKENING MID-LEVEL SHORTWAVE MOVING INTO THE WESTERN PIEDMONT THIS EVENING...IS ENOUGH TO AT LEAST CONTINUE THE SMALL CHANCES WEST AS CURRENTLY FORECAST THIS EVENING...AND MAY NEED TO EXPAND SLIGHTLY FARTHER EAST. THE 00Z GFS APPEARED TO SUFFER FROM SOME MINOR CONVECTIVE FEEDBACK WHILE THE ECMWF HAS BEEN VERY CONSISTENT IN SUGGESTING THE BEST THREAT FOR OVERNIGHT CONVECTION TO OUR NW. IT SHOULD ALSO BE NOTED THAT THE CONVECTIVE ALLOWING MODELS VERIFIED WAY OVERDONE ACROSS THE OH VALLEY INTO THE MID ATLANTIC AT 06Z. HIGHS TODAY IN THE LOWER TO MID 90S. WARM OVERNIGHT WITH LOWS NEAR 70 TO THE LOWER 70S. && .SHORT TERM /WEDNESDAY AND WEDNESDAY NIGHT/... AS OF 310 AM TUESDAY... MID LEVEL SHEAR AXIS ASSOCIATED WITH THE NORTHERN STREAM S/W AND ITS ATTENDANT SURFACE BOUNDARY WILL DRIFT SEWD INTO CENTRAL NC WEDNESDAY AFTERNOON-WEDNESDAY NIGHT. THIS SYSTEM WILL INTERACT WITH STRONG HEATING AND AVAILABLE MOISTURE (PRECIPITABLE WATER VALUES IN THE NEIGHBORHOOD OF 1.67-1.9 INCHES) TO INITIATE AND SUSTAIN SCATTERED CONVECTION...ESPECIALLY WEDNESDAY AFTERNOON-WEDNESDAY EVENING. SOME CONVECTIVE PARAMETERS SUGGEST SOME POTENTIAL FOR ORGANIZED CONVECTION IN THE FORM OF BROKEN CONVECTIVE SEGMENTS. IF THESE SEGMENTS WERE TO DEVELOP...COULD SEE A DAMAGING WIND THREAT WITH THE STRONGER CELLS. THIS THREAT APPEARS GREATEST ACROSS THE NORTHERN PIEDMONT INTO THE NORTHERN COASTAL PLAIN (GENERALLY NORTH OF I-40) WHERE BULK SHEAR VALUES APPROACH 30 KTS. DUE TO PRESENCE OF SHEAR AXIS AND SFC BOUNDARY...EXPECT SCATTERED CONVECTION TO PERSIST WELL INTO THE NIGHT THOUGH OVERALL COVERAGE AND INTENSITY WILL DIMINISH AS NEAR SURFACE AIR MASS UNDERGOES NOCTURNAL STABILIZATION. HIGH TEMPS WEDNESDAY DEPENDENT UPON AMOUNT OF INSOLATION AND CONVECTIVE COVERAGE. IF SUN LIMITED DUE TO EXTENSIVE CLOUD COVERAGE OR IF THE GFS IS CORRECT AND SCATTERED CONVECTION IS OCCURRING AT THE THE START OF THE DAY...THEN MAX TEMPS ACROSS THE NORTH COULD END UP BEING 5-6 DEGREES COOLER THAN FORECAST. DUE TO ANTICIPATED TIMING...BELIEVE THAT THE SOUTHERN HALF OF THE FORECAST AREA STANDS A GOOD SHOT OF SEEING TEMPS RETURNING TO THE MID 90S. MIN TEMPS WEDNESDAY NIGHT IN THE UPPER 60S TO AROUND 70 NORTH AND LOWER 70S SOUTH. && .LONG TERM /THURSDAY THROUGH MONDAY/... AS OF 310 AM TUESDAY... THURSDAY THROUGH FRIDAY: THURSDAY LOOKS TO BE THE MOST ACTIVE DAY OF THE FORECAST PERIOD AS AN APPROACHING MID LEVEL TROUGH WILL HELP TO SEND A WEAKENING COLD FRONT/SURFACE TROUGH SLOWLY ACROSS THE AREA. MODELS ARE IN GENERAL AGREEMENT IN SHOWING THE FRONT/SURFACE TROUGH LOCATED ACROSS CENTRAL NC DURING DURING PEAK HEATING THURSDAY. THE BEST MLCAPE AND MUCAPE IS EXPECTED TO BE LOCATED ACROSS THE SOUTHEASTERN HALF OF CENTRAL NC.... WHERE 800 TO 1200 J/KG MLCAPE IS EXPECTED... ALONG WITH UPWARDS OF 2000-2500 J/KG OF MUCAPE. THIS COMBINED WITH A MOIST AIR MASS CHARACTERIZED BY PW`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AS OF 155 PM TUESDAY... VFR CONDITIONS ARE EXPECTED THROUGHOUT MUCH OF THE 18Z VALID TAF PERIOD. AS MOISTURE INCREASES AGAIN OVER THE REGION FROM THE WEST...SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS SHOULD OCCUR PARTICULARLY TOWARD THE TRIAD VERY LATE THIS AFTERNOON INTO THE EVENING. WITH UNCERTAINTY IN THE LOCATION OF ANY THUNDER ONLY INCLUDED A TEMPO FOR SHOWERS IN THE TAFS FOR KINT AND KGSO FROM ABOUT 23Z TO 04Z. ISOLATED SHOWERS OR SPRINKLES ARE POSSIBLE OVERNIGHT THEN CHANCES FOR SHOWERS INCREASE DURING WEDNESDAY WITH AT LEAST TEMPO CONDITIONS ANTICIPATED AROUND THE TRIAD DURING THE MORNING. SREF MODEL PROBABILITY OF IFR CONDITIONS ARE LOW BUT PROBABILITIES OF MVFR CONDITIONS ESPECIALLY OVER THE NORTHWEST PIEDMONT INCREASE AFTER 12Z WEDNESDAY AND HAVE INCLUDED SUCH CEILINGS IN THE TEMPO CONDITIONS AT KINT AND KGSO WEDNESDAY MORNING. GUSTY SOUTHWEST WINDS SHOULD DIMINISH BUT REMAIN NOTICEABLE OUT OF THE SOUTH TO SOUTHWEST OVERNIGHT...WITH A FEW GUSTS DEVELOPING MAINLY TOWARD KFAY WEDNESDAY MORNING WHERE HEATING TO START THE DAY SHOULD BE A LITTLE BETTER RELATIVE TO THE REST OF CENTRAL NORTH CAROLINA. BEYOND THE 18Z VALID TAF PERIOD...AT LEAST SCATTERED SHOWERS AND THUNDERSTORMS...AND THEIR ASSOCIATED SUB-VFR CONDITIONS...CAN BE EXPECTED OVER CENTRAL NORTH CAROLINA AT LEAST INTO THE END OF THE WORK WEEK. A COLD FRONT WEAKENS AS IT APPROACHES THE STATE THURSDAY...BUT A SURFACE TROUGH THEN LINGERS AT LEAST THROUGH FRIDAY AND LIKELY INTO AT LEAST PART OF THE WEEKEND. COVERAGE OF PRECIPITATION OVER CENTRAL NORTH CAROLINA SHOULD BE GREATER THURSDAY AND FRIDAY AS COMPARED TO THE UPCOMING WEEKEND.
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&& .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...DJF NEAR TERM...WSS/DJF SHORT TERM...WSS LONG TERM...BSD AVIATION...DJF

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