Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 300556 RRA AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 155 AM EDT THU JUL 20 2015 .SYNOPSIS...A COLD FRONT WILL APPROACH FROM THE WEST TODAY...THEN TRACK SOUTHEAST ACROSS THE CAROLINAS TONIGHT AND SETTLE SOUTH OF THE AREA ON FRIDAY. MEANWHILE...A WEAK LOW PRESSURE SYSTEM OFF THE SOUTHEAST COAST WILL TRACK NORTH NORTHEAST OFFSHORE THE CAROLINA COAST. && .NEAR TERM /THROUGH TONIGHT/... AS OF 1025 PM WEDNESDAY... CENTRAL NC REMAINS ON THE FAR NORTHEASTERN PERIPHERY OF AN UPPER LEVEL RIDGE ANCHORED OVER THE LOWER MIDWEST. AS A RESULT...LIGHT NW FLOW ALOFT AND A WEAK/ILL-DEFINED MSLP GRADIENT WILL PREVAIL THROUGH TONIGHT. A FEW ISOLATED SHOWERS HAVE DEVELOPED ACROSS THE WEST...AND COULD LINGER FOR THE NEXT SEVERAL HOURS. OVERNIGHT LOWS IN THE LOW TO MID 70S EXPECTED. && .SHORT TERM /THURSDAY AND THURSDAY NIGHT/... AS OF 315 PM WEDNESDAY... A DEEPENING UPPER LEVEL TROUGH OVER EASTERN CANADA WILL EXTEND SOUTHWARD THROUGH THE GREAT LAKES INTO THE OH VALLEY AND MID- ATLANTIC THU/THU NIGHT...RESULTING IN BROAD (ALBEIT WEAK) CYCLONIC FLOW ALOFT OVER THE CAROLINAS. PERHAPS MORE IMPORTANTLY...THIS WILL AID IN DRIVING A WEAK COLD FRONT ACROSS THE MOUNTAINS AND INTO THE CAROLINAS LATE THU/THU NIGHT. DIURNAL DESTABILIZATION IS EXPECTED TO BE LOW-END MODERATE (1000-1500 J/KG)...LIMITED BY WEAK MID-LEVEL LAPSE RATES. MOISTURE/INSTABILITY AND FORCING /CONVERGENCE/ ATTENDANT THE PRE-FRONTAL TROUGH IN ADDITION TO DPVA ATTENDANT A SMALL AMPLITUDE WAVE (OR WAVES) EMBEDDED WITHIN CYCLONIC FLOW ALOFT SHOULD BE SUFFICIENT FOR AT OR ABOVE CLIMATOLOGICAL CHANCES FOR CONVECTION (30-40%) BY LATE AFT/EVE...WITH THE HIGHEST CHANCES ALONG/EAST OF THE HWY 1 CORRIDOR...DIMINISHING IN INTENSITY AND COVERAGE FROM WEST-EAST LATE THU EVE AND EARLY THU NIGHT. EXPECT HIGHS THU AFT IN THE LOWER TO MID 90S AND LOWS FRI MORNING IN THE LOWS 70S. -VINCENT && .LONG TERM /FRIDAY THROUGH WEDNESDAY/... AS OF 320 PM WEDNESDAY... THE 12Z MODEL CYCLE...ESP THE GFS...IS CONTINUING A DRYING TREND FOR FRIDAY THROUGH MOST OF THE WEEKEND...THANKS TO A DEEPENING LONGWAVE TROUGH OVER THE EAST AND A DRIER WESTERLY FLOW OVER OUR AREA. THE DEPTH OF ITS TROUGH WOULD LIKELY BE SUCH THAT THE DEEPER MOISTURE TO OUR SOUTH INVOF OF THE OLD BOUNDARY WOULD REMAIN WELL TO OUR SOUTH. THE LATEST ECMWF ALSO TRENDED IN THIS DIRECTION...BUT KEEPS THE BOUNDARY AND DEEPER MOISTURE HELD UP JUST OFF THE CAROLINA COAST...WHICH AGAIN...IS DRIER FOR CENTRAL NC COMPARED TO ITS 00Z RUN. OTHERWISE...TIMING OF FRIDAYS FRONT CONTINUES ITS EARLIER TREND AS WELL...WITH LATEST GUIDANCE PACKAGE SUGGESTING THAT THE FRONT...AND THE RISK OF RAIN...WILL BE TO OUR SOUTH AND EAST BY 12Z FRIDAY. LATEST GFS FORECAST SOUNDINGS SHOW PWATS FALLING BELOW ONE INCH BY 12Z FRIDAY AND REMAINING AT OR BELOW ONE INCH THROUGH AT LEAST SATURDAY...BEFORE SLIGHTLY REBOUNDING ON SUNDAY. HOWEVER... WITH SCANT FORCING MECHANISMS...LOOK FOR FAIR WEATHER RIGHT THROUGH THAT TIME FRAME. GIVEN THE DRIER AIRMASS AND DEPTH OF THE BOUNDARY LAYER...FORECAST SOUNDINGS SUGGEST TEMPS WILL ACTUALLY CLIMB SEVERAL DEGREES ABOVE NORMAL...PERHAPS EVEN MID 90S OVER THE WEEKEND...BUT WITH DRIER AIRMASS...HEAT INDICES SHOULDN`T BE MUCH HIGHER. EARLY NEXT WEEK...BACKING FLOW AHEAD OF THE NEXT SHORT WAVE DIVING INTO THE AFOREMENTIONED TROUGH WILL DRAW MOISTURE NORTHWARD...BUT STILL NOT ENOUGH TO WARRANT MORE THAN SLT CHANCE POPS MONDAY AND EARLY TUESDAY. POPS WILL NEED TO BE INCREASED TO AT LEAST CLIMO VALUES BY LATE TUESDAY AND/OR WEDNESDAY AS THE NEXT NEXT COLD FRONT APPROACHES. TEMPS EARLY NEXT WEEK REMAINING SEVERAL DEGREES ABOVE NORMAL...LOW-MID 90S. && .AVIATION /06Z THURSDAY THROUGH MONDAY/... AS OF 145 AM THURSDAY... A FEW ISOLATED AND MOSTLY LIGHT SHOWERS WILL CONTINUE TO PERCOLATE ALONG A WEAK SURFACE TROUGH OVER THE WESTERN PIEDMONT...BUT EVEN THOUGH THESE MAY DRIFT INTO THE VICINITY OF KGSO OR KINT..NO SIGNIFICANT IMPACTS ARE EXPECTED. ELSEWHERE...CLEAR SKIES CAUSE SOME VSBY RESTRICTIONS AND/OR STRATUS TO DEVELOP BY 09Z...WITH HIGHEST PROBABILITIES AT KFAY AND KRWI. A COLD FRONT WILL APPROACH FROM THE NORTHWEST TODAY AND CROSS THE AREA LATE THIS EVENING AND TONIGHT. INSTABILITY IS EXPECTED TO BE LIMITED WHEN THE FRONT ARRIVES...ESPECIALLY TONIGHT...AND ONLY SCATTERED SHOWERS AND A FEW ISOLATED STORMS ARE ANTICIPATED...FIRST AROUND KINT/KGSO AFTER 21Z AND KRDU/KRWI/KFAY AFTER 00-003Z. LIGHT WINDS WILL SHIFT TO NORTHWESTERLY BEHIND THE FRONT. LOOKING AHEAD: SFC FRONT WILL LIKELY STALL NEAR/ALONG THE SOUTHEAST COAST FRIDAY AND THROUGH THE WEEKEND. EXPECT PREDOMINATELY VFR CONDITIONS THROUGH EARLY NEXT WEEK...WITH THE BEST POTENTIAL FOR DIURNAL CONVECTION GENERALLY ALONG/ OFFSHORE THE CAROLINA COAST. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...22 NEAR TERM...VINCENT/RAH SHORT TERM...VINCENT LONG TERM...RAH AVIATION...CBL/22

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