Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 301731 CCA AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 130 PM 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 1100 AM THURSDAY... THE COLD FRONT IS CONTINUING ITS PROGRESSION EASTWARD...NOW LOCATED ROUGHLY FROM W-CNTRL PA SOUTHWEST ALONG THE APPALACHIANS. THE CURRENT FORECAST IS STILL ON TRACK...WITH THE FRONT EXPECTED TO MOVE ACROSS CENTRAL NC FROM LATE THIS AFTERNOON THROUGH THE EVENING. LATEST HRRR STILL ON TRACK WITH PREV ASSESSMENTS...SUGGESTING WIDELY SCATTERED PREFRONTAL SHOWERS AND PERHAPS A FEW TSTMS ARE POSSIBLE THIS AFTERNOON...AND AGAIN THIS EVENING AS THE FRONT PUSHES ACROSS. NO MAJOR CHANGES TO THE CURRENT FORECAST GRIDS...AND PREV DISC INCLUDED BELOW FOR REFERENCE. PREV NEAR TERM 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 NEAR 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. && .SHORT TERM /FRIDAY AND FRIDAY NIGHT/... 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. && .LONG TERM /SATURDAY THROUGH THURSDAY/... AS OF 1200 PM THURSDAY... AN UPPER LEVEL RIDGE IS EXPECTED TO PERSIST OVER THE WESTERN CONUS THROUGH THE EXTENDED PERIOD...WITH THE RIDGE UNDERGOING FURTHER AMPLIFYING OVER THE ROCKIES BY EARLY NEXT WEEK. DOWNSTREAM IN THE CAROLINAS AND MID-ATLANTIC...PERSISTING TROUGHING /CYCLONIC FLOW/ ALOFT WILL PREVAIL. THOUGH NUMEROUS SMALL AMPLITUDE DISTURBANCES /SHORTWAVES/ WILL NO DOUBT BE PRESENT IN THIS AMPLIFIED PATTERN... THE BULK OF NORTH CAROLINA IS EXPECTED TO REMAIN ALONG/WEST THE BASE OF THE UPPER LEVEL TROUGH AXIS...WHERE MOISTURE WILL BE LESS FAVORABLE FOR (OR PERHAPS INSUFFICIENT TO SUPPORT) DIURNAL CONVECTION...EXCEPT IN EASTERN/COASTAL PORTIONS OF THE CAROLINAS. WILL MAKE LITTLE CHANGE TO THE PREVIOUS FORECAST INDICATING HIGHS IN THE LOWER TO MID 90S...LOWS IN THE LOWER 70S...AND DIURNAL PRECIP CHANCES CONFINED PRIMARILY TO THE SE COASTAL PLAIN. IT SHOULD BE NOTED THAT A WESTWARD SHIFT IN THE UPPER LEVEL PATTERN (RIDGE/TROUGH AXES) OVER THE LOWER 48 WOULD RESULT IN INCREASED PRECIP CHANCES ACROSS PORTIONS OF CENTRAL NC...PARTICULARLY ALONG/EAST OF HWY 1... THOUGH NO SIGNIFICANT CHANGE IS APPARENT AT THIS TIME. -VINCENT && .AVIATION /18Z THURSDAY THROUGH TUESDAY/...
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AS OF 130 PM THURSDAY... ISOLATED PREFRONTAL SHOWERS AND A FEW TSTMS HAVE DEVELOPED ACROSS THE WESTERN PIEDMONT...AND MAY PRESENT A BRIEF AVIATION CONCERN THIS AFTERNOON SHOULD THEY PASS OVER ANY OF THE SITES. IMPACTS WOULD BE BRIEF PERIOD OF IFR CIGS/VSBY...AND WIND GUSTS AS HIGH AS 30KT. THE RISK FOR SUCH ACTIVITY WILL SHIFT EAST TOWARD OUR EASTERN TAF SITES LATER TODAY. OTHERWISE...THE COLD FRONT IS STILL ON TRACK TO MOVE ACROSS CENTRAL NC LATE THIS EVENING AND OVERNIGHT...SO THE RISK FOR THE AFOREMENTIONED ISOLATED SHOWERS/TSTMS WILL CONTINUE UNTIL THE FRONT MOVES THROUGH. LIGHT WINDS WILL SHIFT TO NORTHWESTERLY BEHIND THE FRONT AS IT SETTLES SOUTH AND EAST OF THE AREA OVERNIGHT. VFR CONDITIONS ARE EXPECTED BEHIND THE FRONT LATER TONIGHT AND THROUGH THE REST OF THE 24 HOUR TAF PERIOD. LOOKING AHEAD: THE COLD FRONT WILL STALL NEAR THE COAST DURING THE DAYTIME FRIDAY...WITH PREDOMINATELY VFR CONDITIONS EXPECTED THIS WEEKEND. ITS WORTH NOTING THAT ANY NORTHWARD SHIFT IN THE PATTERN MAY RESULT IN WORSE CONDITIONS THAN ARE CURRENTLY FORECAST.
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&& .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...22 NEAR TERM...RAH/22 SHORT TERM...22 LONG TERM...VINCENT AVIATION...RAH

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