Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 300805 RRA AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 405 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/...
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AS OF 405 AM THURSDAY... A COLD FRONT...WHICH CURRENTLY STRETCHES FROM EASTERN CANADA THROUGH THE OHIO VALLEY TO THE MID-MISSISSIPPI VALLEY REGION...WILL APPROACH FROM THE NORTHWEST TODAY AS A SHORTWAVE TRAVERSES THE GREAT LAKES ON THE SOUTHERN PERIPHERY OF AN INTENSE VORTEX NEAT THE HUDSON. THE FRONT IS GENERALLY EXPECTED TO MOVE INTO THE WESTERN PIEDMONT BY LATE AFTERNOON...REACHING THE TRIANGLE AREA PRIOR TO MIDNIGHT AND THEN MOVE INTO THE COASTAL PLAIN EARLY FRIDAY MORNING. AHEAD OF THE FRONT...CENTRAL NC LIES IN A RELATIVE MIN IN PW...WITH AREAS NEAR 2 INCHES TO OUR NORTH AND SOUTH. STRONG HEATING AND 850MB TEMPS APPROACHING 20C WILL PUSH TEMPS IN TO THE LOW TO MID 90S TODAY...BUT INSTABILITY IS PROJECTED TO BE WEAK TODAY...AROUND 500-1000 J/KG WITH A SLIGHT UPTICK IMMEDIATELY AHEAD OF THE FRONT OWING TO A NARROW RIBBON OF PREFRONTAL MOISTURE CONVERGENCE. MOST OF THE CAMS AND LARGER SCALE NWP ARE IN GOOD AGREEMENT ON JUST A BAND OF SCATTERED CONVECTION REACHING THE TRIAD AROUND 20Z OR SO...THEN STRUGGLING TO MAINTAIN INTENSITY AND COVERAGE AS IT MOVES EAST IN TO A LESS SUPPORTIVE ENVIRONMENT AFTER SUNSET. SHEAR PARAMETERS WILL BE WEAK THROUGHOUT AND WIDESPREAD SEVERE WEATHER IS NOT ANTICIPATED. NOTICEABLY DRIER AIR BEHIND THE FRONT AND CLEARING WILL HELP ALLOW TEMPS TO FALL INTO THE UPPER 60S IN THE NORTHWEST PIEDMONT..BUT AREAS TO THE EAST SHOULD STILL SEE LOWS IN THE LOWER 70S AS THE FRONT SLOWLY PUSHES EAST AND PRECIP CHANCES DWINDLING TOWARD 12Z FRIDAY. NOTE...THE WEAK LOW OFF THE GEORGIA COAST ...NOTED BY NHC AS HAVING ONLY A 10 PERCENT CHANCE OF FURTHER DEVELOPMENT...WILL DRIFT NORTH TODAY AND BECOME ABSORBED BY THE FRONT OFF THE OBX LATER TONIGHT...WITH NO DIRECT SENSIBLE IMPACT INLAND.
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&& .SHORT TERM /FRIDAY AND FRIDAY NIGHT/...
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AS OF 405 AM THURSDAY... THE COLD FRONT WILL PUSH TOWARD THE COAST AND THEN STALL ON FRIDAY AS A BROAD UPPER TROUGH SLOWLY BEGINS TO DEVELOP OVER THE EASTERN US. THE NAM AND GFS ARE FAR ENOUGH EAST WITH THE FRONT AND MORE UNSTABLE AIRMASS TO BE COMPLETELY DRY ON FRIDAY AFTERNOON. THE ECMWF HANGS THE FRONT UP JUST A TOUCH FURTHER WEST AND DEVELOPS SOME QPF EAST OF I-95. WILL KEEP A SLIGHT CHANCE OF THE COASTAL PLAIN...BUT MOST OF THE AREA WILL BE DRY AND MUCH LESS HUMID AS DEWPOINTS HAVE THE POTENTIAL TO MIX OUT INTO THE UPPER 50S AND LOWER 60S BEHIND THE FRONT. ONLY A SMALL DROP IN THICKNESSES IS FORECAST...SO HIGHS WILL STILL BE AROUND NORMAL...89-94. LOWS FRIDAY NIGHT IN THE MID 60S TO AROUND 70.
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&& .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...22 SHORT TERM...22 LONG TERM...RAH AVIATION...CBL/22

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