Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 020822 CCA AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 419 AM EDT SUN AUG 2 2015 .SYNOPSIS...AN AREA OF LOW PRESSURE OVER THE NORTHEAST GULF OF MEXICO THIS MORNING WILL TRACK SLOWLY NORTHEASTWARD ALONG A NEARLY STATIONARY FRONTAL ZONE OVER THE SOUTHEASTERN US THROUGH MON NIGHT...WHILE HIGH PRESSURE WILL REMAIN CENTERED FROM THE TN VALLEY TO THE CENTRAL APPALACHIANS. && .NEAR TERM /THROUGH TONIGHT/...
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AS OF 350 AM SUNDAY... THE LOW LEVEL FRONTAL ZONE...WHICH SEPARATED A DRIER AIR MASS OVER THE PIEDMONT FROM A SUBSTANTIALLY MORE MOIST OVER COASTAL AREAS...HAS NOCTURNALLY RETREATED INTO THE EASTERN SANDHILLS AND SOUTHERN-CENTRAL COASTAL PLAIN OF NC THIS MORNING. MEANWHILE...1016 MB SURFACE HIGH PRESSURE WAS SITUATED FROM THE TN VALLEY TO THE CENTRAL APPALACHIANS. THESE FEATURES ARE FORECAST TO MOVE LITTLE TODAY...THOUGH DIURNAL HEATING/MIXING WILL LIKELY HELP DRIVE THE FRONT...AND ASSOCIATED MOISTURE...LARGELY EAST OF THE RAH CWFA THROUGH MID-AFTERNOON...BEFORE RETREATING WEST ONCE AGAIN WITH NOCTURNAL COOLING BY THIS EVENING. ISOLATED SHOWERS AND STORMS WILL BE POSSIBLE INVOF WHAT WILL BECOME ESSENTIALLY A MERGED FRONT AND AN INLAND-RETREATING SEA BREEZE THIS AFTERNOON. THIS BOUNDARY WILL BRING A RELATIVE HIGHEST CHANCE OF A SHOWER OR STORM (STILL LESS THAN 20 PERCENT) TO THE NC COASTAL PLAIN BETWEEN 6-10 PM...WITH OTHERWISE DRY AND MOSTLY CLEAR CONDITIONS...WITH CONTINUED LOW RELATIVE HUMIDITY VALUES MAXIMIZED OVER THE PIEDMONT. GENERALLY PERSISTENT HIGHS IN THE LOWER TO MIDDLE 90S...THOUGH WITH A FEW 88- 89`S POSSIBLE OVER THE FAR NORTHERN PIEDMONT WHERE SLIGHT COOLING HAS OCCURRED IN ASSOCIATION WITH THE ARRIVAL INTO THE VIRGINIA/S OF A REINFORCING LOW LEVEL FRONTAL ZONE PER 00Z/2ND 850-925 MB DATA. FORECAST CONFIDENCE DECREASES LATER TONIGHT...AS A WEAK WAVE OF LOW PRESSURE OVER THE NORTHEASTERN GULF OF MEXICO TRACKS SLOWLY UP THE SOUTHEAST US COAST. MOIST SOUTHERLY FLOW AROUND THE LOW...DIRECTED INTO THE EASTERN CAROLINAS...WILL LIKELY RESULT IN THE NORTHWARD DEVELOPMENT/EXPANSION OF AN AREA OF LOW CLOUDS...AND EVEN A FEW SHOWERS INTO AT LEAST THE SOUTHERN COASTAL PLAIN. THE ASSOCIATED LOW CLOUDS MAY CREEP AS FAR WEST AS THE PIEDMONT PER THE 00Z/ECMWF... WHICH INITIALIZED MUCH BETTER WITH LOW LEVEL MOISTURE VALUES THAN THE DRIER/CLEARER GFS SOLUTIONS...THOUGH THE MOISTURE WOULD LIKELY BE TOO SHALLOW AND CAPPED TO SUPPORT ANY PRECIPITATION THERE. LOWS RANGING FROM THE LOWER 60S IN THE RESIDUALLY DRY/CONTINENTAL AIR MASS OVER THE PIEDMONT...PARTICULARLY THE WESTERN HALF...TO AROUND 70 DEGREES OR SO OVER THE COASTAL PLAIN.
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&& .SHORT TERM /MONDAY AND MONDAY NIGHT/... AS OF 415 AM SUNDAY... MODEL SPREAD REMAINS RELATIVELY LARGE WITH THE TRACK AND SPEED OF THE WAVE OF LOW PRESSURE FORECAST TO RIPPLE NORTHEAST ALONG THE FRONT OVER THE EASTERN CAROLINAS MON AND MON NIGHT. GIVEN THE POORLY- ANALYZED MOISTURE FIELDS IN THE GFS NOTED IN THE NEAR TERM...WILL WEIGHT THE FORECAST TOWARD THE SLIGHTLY MORE WESTWARD TRACK AND ASSOCIATED CLOUDIER AND WETTER CONDITIONS OVER THE COASTAL PLAIN INDICATED BY THE 00Z/2ND ECMWF AND GEM. SUCH A SOLUTION WOULD RESULT IN LESS HOT TEMPERATURES OVER THE COASTAL PLAIN...IN THE UPPER 80S TO AROUND 90 DEGREES...TO LOWER 90S ACROSS THE REMAINDER OF CENTRAL NC. IF THE DAY PROVES DRIER AND MOSTLY SUNNY AREA-WIDE...PERSISTENCE HIGH TEMPERATURES IN THE LOWER TO MIDDLE 90S WOULD AGAIN OCCUR. ANY LINGERING RAIN CHANCE SHOULD END OVER THE FAR EASTERN NC COASTAL PLAIN BY MIDNIGHT...AS THE LOW LIFTS NE AND AWAY FROM THE NC OUTER BANKS. && .LONG TERM /TUESDAY THROUGH SATURDAY/... AS OF 245 AM SUNDAY... THURSDAY AND WEDNESDAY: LOW PRESSURE OVER CANADA WILL LIFT NORTHWARD AND UPPER LEVEL PATTERN OVER CENTRAL NC WILL BE VERY ZONAL WITH A GRADUAL SHIFT TO WEST SOUTHWESTERLY FLOW BY WEDNESDAY. WITH THE JET LIFTING NORTHWARD DURING THIS PERIOD AND MOST OF THE UPSTREAM SHORTWAVE ACTIVITY REMAINING WELL TO THE NORTHWEST...EXPECT GENERALLY DRY CONDITIONS DURING THIS PERIOD WITH THE OCCASIONAL DIURNAL SHOWER POPPING UP ON SURFACE BOUNDARIES SUCH AS THE SEA BREEZE. SOUTHWESTERLY SURFACE FLOW WILL KEEP TEMPERATURES UP WITH HIGHS IN THE MID 90S AND LOWS IN THE LOW TO MIDDLE 70S. THURSDAY THROUGH SATURDAY: THE FORECAST BECOMES MUCH MORE LOW CONFIDENCE BY THE END OF THE WEEK BUT THERE ARE A FEW THINGS WE DO KNOW FOR SURE. NUMBER ONE IS THAT MOISTURE WILL BE INCREASING SIGNIFICANTLY OVER THE AREA. NUMBER TWO IS THAT SEVERAL SHORTWAVE IMPULSES UPSTREAM WILL MAKE THEIR WAY INTO THE AREA OR AT LEAST SKIRT CLOSE ENOUGH TO THE ARE TO AFFECT OUR WEATHER HERE IN CENTRAL NC. THREE IS THAT ALTHOUGH MOISTURE IS INCREASING...INSTABILITY AND SHEAR ARE NOT INCREASING ALL THAT MUCH...THEREFORE WHILE WE CAN EXPECT INCREASE CONVECTIVE ACTIVITY BEGINNING ON THURSDAY THROUGH THE WEEKEND...THE LIKELIHOOD OF SEVERE WEATHER IS STILL FAIRLY SMALL. TOUGHER TO DETERMINE WILL BE THE TIMING OR EXACT LOCATIONS OF CONVECTIVE ACTIVITY LATE IN THE WEEK. MODELS HAVE NOT BEEN CONSISTENT AT ALL WITH TIMING THE LAST SEVERAL DAYS AND CONTINUE TO FLUCTUATE. CURRENTLY...MODELS ARE PREDICTING THE FIRST SHORTWAVE TO MOVE THROUGH ON THURSDAY. THERE WILL BE A GAP BETWEEN THE FIRST AND SECOND SHORTWAVE WHICH IS DUE TO ARRIVE FRIDAY EVENING WHICH MAY LINGER OVER THE AREA FOR A WHILE BEFORE POTENTIALLY DEVELOPING A FULL ON SURFACE LOW ON SATURDAY AS IT SLIDES OFF OF THE EAST COAST. INCREASED CLOUD COVER AND CONVECTIVE ACTIVITY WILL BRING TEMPERATURES DOWN INTO THE MID 80S TO LOWER 90S DURING THIS PERIOD BUT WITH THE INCREASED MOISTURE...RELATIVE HUMIDITIES WILL INCREASE. LOWS DURING THE PERIOD UPPER 60S TO LOWER 70S. && .AVIATION /06Z SUNDAY THROUGH WEDNESDAY/...
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AS OF 255 AM SUNDAY... GENERALLY A PERSISTENCE FORECAST WILL BE FOLLOWED GIVEN VERY LITTLE CHANGE IN THE PATTERN AND NEARBY AIR MASSES FROM THE PREVIOUS 24 HOURS. AS SUCH...RWI WILL LIKELY EXPERIENCE A PERIOD OF IFR-MVFR VISIBILITY RESTRICTIONS BETWEEN 09-12Z...AND FAY AS WELL SINCE SURFACE DEWPOINTS HAVE BEEN RUNNING A FEW DEGREES HIGHER VERSUS THIS TIME LAST NIGHT...OWING TO THE SLIGHT NOCTURNAL RETREAT OF A FRONTAL ZONE AND ASSOCIATED MARITIME TROPICAL AIR INTO SOUTHEASTERN NC. OTHERWISE...MAINLY CLEAR SKIES ARE EXPECTED UNDER THE INFLUENCE OF AN UNSEASONABLY DRY AIR MASS CENTERED OVER THE CENTRAL APPALACHIANS. WHILE A STRAY SHOWER OR STORM WILL BE POSSIBLE OVER EASTERN NC...INCLUDING AT FAY AND RWI...THIS PROBABILITY IS TOO LOW TO INCLUDE ANY MENTION IN THE TAFS. OUTLOOK: A BRIEF PERIOD IFR-MVFR CONDITIONS...AND SHOWERS...WILL BE POSSIBLE LATE TONIGHT-EARLY MON AT FAY...AS AN AREA OF LOW PRESSURE TRACKS UP THE SOUTHEAST US COAST. SOME OF THESE LOW CLOUDS MAY EXPAND AS FAR WEST AS PIEDMONT SITES...PARTICULARLY RDU BY DAYBREAK. A LINGERING SHOWER OR STORM WILL CONTINUE OVER SOUTHEASTERN NC AS THE LOW TRACKS ONLY SLOWLY NORTHEASTWARD THROUGH MON NIGHT.
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&& .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...26 NEAR TERM...26 SHORT TERM...26 LONG TERM...ELLIS AVIATION...26

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