Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 271943 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 342 PM EDT SUN JUL 27 2014 .SYNOPSIS...A SURFACE TROUGH WILL PERSIST OVER THE CAROLINAS THROUGH TONIGHT. A STRONG COLD FRONT WILL CROSS THE AREA ON MONDAY... BRINGING NOTICEABLY COOLER AND LESS HUMID AIR INTO THE AREA. && .NEAR TERM /THROUGH TONIGHT/... AS OF 340 PM SUNDAY... AFTER A COOL START OWING TO ABUNDANT MULTI-LAYERED CLOUDS AND RAIN...TEMPERATURES HAVE CLIMBED QUICKLY DURING THE PAST FEW HOURS IN AN AREA OF CLEARING IN THE WAKE OF THE MORNING MCV...COINCIDENT WITH THE ARRIVAL OF THE LEADING EDGE OF HOT/22C 12Z-OBSERVED H85 TEMPS AT KBNA. THE CONFIGURATION OF THE WAA REGIME DEVELOPING FROM THE WESTERN CAROLINAS AND EARLIER RAIN-COOLED AIR WILL FAVOR THE STRENGTHENING OF A NW TO SE-ORIENTED OUTFLOW BOUNDARY/EFFECTIVE FRONT FROM THE TN VALLEY SOUTHEASTWARD ACROSS SOUTHERN VA/NORTHERN NC. THIS BOUNDARY WILL SERVE TO ENHANCE WHAT NEAR TERM GUIDANCE SUGGESTS WILL BE ALREADY STRONG LOW LEVEL SHEAR IN THE 250-400 MS/S2 RANGE CENTERED OVER SOUTHSIDE VA AND NORTH-CENTRAL NC...FROM JUST PRIOR TO SUNSET THROUGH MIDNIGHT. MID-LEVEL/DEEP LAYER WINDS WILL BE EQUALLY IMPRESSIVE...AS THE EXIT REGION OF AN UPSTREAM MID LEVEL JET AT THE BASE OF THE UPPER MID WEST UPPER LOW EMERGES EAST OF THE CENTRAL APPALACHIANS AND STRENGTHENS KGSO AND KRNK 12Z-OBSERVED MID LEVEL FLOW OF ALREADY RESPECTABLE 35-40 KTS...INTO THE 45-55 KT RANGE THIS EVENING. THE STRONGLY SHEARED ENVIRONMENT WILL SUPPORT A CONDITIONAL PROBABILITY OF SEVERE THUNDERSTORMS OVER CENTRAL NC...PARTICULARLY FROM LATE THIS AFTERNOON THROUGH MIDNIGHT. IT IS PROBABLE THAT SCATTERED STORMS WILL DEVELOP INVOF THE OUTFLOW BOUNDARY/EFFECTIVE FRONT FROM SOUTHWEST VA INTO THE NORTHERN NC PIEDMONT...ON THE SOUTHERN FRINGE OF AN MCV MOVING ESE INTO WEST- CENTRAL VA THIS AFTERNOON...AND AMIDST INCREASING LARGE SCALE LIFT AHEAD OF THE UPPER LOW APPROACHING FROM THE UPPER MIDWEST. THE LAST SEVERAL RUNS OF THE HRRR HAVE FINALLY PICKED UP ON THIS POTENTIAL. WILL ADVERTISE A CHANCE OF STORMS MAINLY OVER THE NORTHERN HALF OF THE FORECAST AREA (INVOF THE BOUNDARY) THROUGH THIS EVENING...WITH AN ASSOCIATED CONDITIONAL PROBABILITY OF A MULTI-FACETED SVR RISK OF DAMAGING WINDS...LARGE HAIL...AND EVEN AN ISOLATED TORNADO GIVEN THE EXPECTED STRONG LOW LEVEL SHEAR CENTERED OVER THE NE PIEDMONT AROUND 00Z. NWP GUIDANCE THEN SUGGESTS THAT STORMS OVER THE TN VALLEY THIS AFTERNOON WILL DEVELOP SOUTHEASTWARD AND SPREAD ACROSS THE CENTRAL APPALACHIANS LATE THIS EVENING...AND INTO CENTRAL NC AFTER LOW LEVEL SHEAR DIMINISHES - AND WHEN CINH SHOULD BE MAXIMIZED - DURING THE OVERNIGHT HOURS. ANY OVERNIGHT CONVECTION WOULD THEN POSE PRIMARILY A THREAT OF DAMAGING WIND AND LARGE HAIL MAINLY OVER THE NW PIEDMONT...BEFORE STORMS WEAKEN AS THEY MOVE SOUTHEAST INTO THE REMAINDER OF CENTRAL NC. THOUGH THERE REMAINS OPPOSING SIGNALS FOR STORM DEVELOPMENT/MAINTENANCE (IE. STRONG AND INCREASING FORCING FOR ASCENT DOWNSTREAM OF THE DEEP UPPER LOW VERSUS STRONG CINH (NEAR 200 J/KG)...THE OVERWHELMING SIGNAL FROM NWP GUIDANCE IS FOR THE CINH TO WIN OUT AND CAUSE STORMS TO DIMINISH INVOF HWY 64 BY LATE THIS EVENING...SENDING ONLY A SURGING OUTFLOW BOUNDARY AND ASSOCIATED NW WIND GUSTS OF 25-35 KTS (STRONGEST NORTH) SOUTH THROUGH THE REMAINDER OF THE CENTRAL NC OVERNIGHT. REGARDLESS...IT WILL BE MUGGY AND QUITE MILD OVERNIGHT...WITH LOWS GENERALLY IN THE MIDDLE 70S. && .SHORT TERM /MONDAY AND MONDAY NIGHT/... AS OF 325 PM SUNDAY... NWP GUIDANCE CONTINUES TO SUGGEST DESTABILIZATION WILL BE LIMITED AND CONFINED TO THE SANDHILLS AND COASTAL PLAIN...GIVEN THE FASTER TREND NOTED IN NWP GUIDANCE WITH THE PASSAGE OF THE COLD FRONT THROUGH ALL BUT THE SOUTHEASTERN THIRD OF THE FORECAST AREA BY 18Z MON. INDEED...WESTERLY DOWNSLOPE FLOW WILL VEER THE SFC FLOW/LIMIT CONVERGENCE AND AUGMENT DRY ADVECTION BEHIND THE FRONT (AND LIKELY CAUSE THE FRONT TO ACCELERATE/MERGE WITH THE PRECEDING LEE TROUGH)...AND CONSEQUENTLY CAUSE SFC DEWPOINTS TO MIX INTO THE LOWER 60S (AND EVEN SOME UPPER 50S POSSIBLE) OVER THE PIEDMONT - YIELDING LITTLE BOUYANCY. TO THE EAST...IN THE PRE-FRONTAL AIR MASS OVER THE SANDHILLS AND SOUTHERN AND CENTRAL COASTAL PLAIN...A RESERVOIR OF UPPER 60S TO LOWER 70S SFC DEWPOINTS WILL REMAIN UNTIL THE FRONT CROSSES THOSE AREAS DURING THE MID-AFTERNOON HOURS. MORE FAVORABLE DIURNAL FRONTAL TIMING THERE WILL ALLOW FOR STRONG DIURNAL HEATING/DESTABILIZATION/STEEPENING OF LOW LEVEL LAPSE RATES... BENEATH A LINGERING PLUME OF STEEP MID LEVEL LAPSE RATES IN EXCESS OF 7 C/KM. THESE EXPECTED STEEP LOW-MID LEVEL LAPSE RATES AMIDST UNSEASONABLY STRONG MID LEVEL FLOW IN THE 40-50 KT RANGE - AND ASSOCIATED LONG AND STRAIGHT FORECAST HODOGRAPHS AT KFAY AT TIME OF FROPA AROUND 21Z - WILL SUPPORT A CONDITIONAL RISK OF DAMAGING WIND GUSTS AND LARGE HAIL LIKELY FROM SPLITTING SUPERCELLS...PROVIDED STORMS INDEED DEVELOP. THIS RISK WILL BE GREATEST ROUGHLY FROM GOLDSBORO TO FAYETTEVILLE TO LAURINBURG AND ESPECIALLY POINTS EAST...TO COASTAL AREAS. LOW LEVEL THICKNESS VALUES AROUND 1425 METERS SUPPORT HIGH TEMPERATURES IN THE MID-UPPER 80S NW TO LOWER-MID 90S SE. COOLER MON NIGHT...WITH LOWS RANGING FROM LOWER 60W NW TO MID-UPPER 60 SE. && .LONG TERM /TUESDAY THROUGH SUNDAY/... AS OF 315 PM SUNDAY... STRONGLY BLOCKED FLOW AROUND THE NORTHERN HEMISPHERE WILL LEAD TO A RELATIVELY UNCHANGED WEATHER PATTERN FROM TUESDAY THROUGH THE END OF NEXT WEEK. THE TROUGH/RIDGE PATTERN OVER THE CONUS WILL AMPLIFY WITH AN UNSEASONABLY DEEP UPPER TROUGH OVER THE EASTERN US. IN THE WAKE OF MONDAY`S SYSTEM...PW DROPS BELOW ONE INCH AND THE MEAN TROUGH AXIS SETS UP NEARLY OVERHEAD. DEWPOINTS ARE PROGGED TO DROP WELL INTO THE 50S IN THE PIEDMONT...WITH THICKNESSES SUGGESTING TEMPS 5-10 DEGREES BELOW NORMAL IN THE LOW TO MID 80S. THUS... PRECIP CHANCES LOOK VERY SMALL THROUGH THURSDAY. HEADING INTO NEXT WEEKEND...MODELS SHOW ANOTHER SHORTWAVE REINFORCING THE UPPER TROUGH OVER THE EASTERN CONUS...THOUGH ALSO SHIFTING THE TROUGH AXIS WESTWARD TOWARD THE MIDWEST STATES. WITH AN FRONTAL ZONE/INVERTED TROUGH LINGERING NEAR THE COAST OR SLOWLY DRIFTING INLAND....MOISTURE RETURN AND A MORE FAVORABLE POSITION FOR INFLUENCE FROM DISTURBANCES ROUNDING THE BASE OF THE TROUGH SHOULD SLOWLY INCREASE CHANCES FOR PRECIP...WITH INCREASING CLOUD COVER THROUGH THE WEEKEND. HIGHS LOOK TO REMAIN A GOOD 5-10 DEGREES BELOW NORMAL. && .AVIATION /18Z SUNDAY THROUGH FRIDAY/... AS OF 205 PM SUNDAY... SCATTERED SHOWERS AND STORMS...WHOSE PROBABILITY OF OCCURRENCE AT ANY PARTICULAR TERMINAL IS ONLY AROUND 20 PERCENT...MAY FORM IN-SITU OVER CENTRAL NC THIS AFTERNOON...IN ASSOCIATION WITH LIFT AHEAD OF A MID LEVEL DISTURBANCE MOVING INTO SOUTH-CENTRAL VA...AND IN THE VICINITY OF AN OUTFLOW BOUNDARY FROM NEAR KMTV TO KRDU TO KCTZ. IN ADDITION...A BRIEF PERIOD OF MVFR CEILINGS WILL BE POSSIBLE ON THE COOL SIDE OF THE OUTFLOW BOUNDARY (AT KRWI) THROUGH 20Z. ANOTHER CLUSTER OF SHOWERS AND STORMS...THE ONE CURRENTLY DEVELOPING OVER EASTERN KY...IS FORECAST TO SPREAD SOUTHEASTWARD AND INTO CENTRAL NC...LIKELY IN A GRADUALLY WEAKENING STATE...BETWEEN 02-08Z. THE RELATIVE BEST CHANCE OF STORMS WILL BE AT TRIAD TERMINALS...WITH PROGRESSIVELY LOWER PROBABILITIES TOWARD KRDU/KRWI AND ESPECIALLY KFAY. DESPITE THE PROBABLE WEAKENING OF THE STORMS AS THEY MOVE INTO CENTRAL NC...A WELL-ORGANIZED OUTFLOW BOUNDARY AND ASSOCIATED NORTHWESTERLY WIND GUSTS OF 25-35 KTS (STRONGEST AT KRDU/KRWI) MAY SURGE ALL THE WAY SOUTH THROUGH CENTRAL NC OVERNIGHT. A BREEZY WSW WIND EARLY MONDAY WILL VEER TO WEST OR WNW WITH THE PASSAGE OF A PRONOUNCED COLD FRONT MONDAY AFTERNOON. THE FRONT IS FORECAST TO BE A DRY ONE FOR MOST OF CENTRAL NC...WITH AROUND A 30 PERCENT CHANCE OF A STORM AT KRWI AND KFAY...AND HIGHER PROBABILITIES TOWARD COASTAL AREAS. PREDOMINATELY VFR CONDITIONS ARE OTHERWISE EXPECTED THROUGHOUT THE FORECAST PERIOD...AS CANADIAN HIGH PRESSURE BECOMES CENTERED OVER THE TN VALLEY AND CENTRAL APPALACHIANS THROUGH MID-WEEK. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...MWS NEAR TERM...MWS SHORT TERM...MWS LONG TERM...BLS AVIATION...MWS

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