Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 280214 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 1015 PM EDT SUN JUL 27 2014 .SYNOPSIS...A STRONG COLD FRONT WILL CROSS THE AREA ON MONDAY... BRINGING NOTICEABLY COOLER AND LESS HUMID AIR INTO THE AREA. HIGH PRESSURE BUILDS OVER MUCH OF THE REGION FOR TUESDAY INTO WEDNESDAY. && .NEAR TERM /THROUGH TONIGHT/... AS OF 815 PM SUNDAY... A S/W ROUNDING THE BASE OF THE L/W TROUGH OVER THE LOWER OH AND TN VALLEY WILL CONTINUE TO PUSH E-SE THROUGH THE OVERNIGHT. THIS FEATURE WILL INTERACT WITH THE MOIST AND SLIGHT-MODERATELY UNSTABLE AIR MASS OVER CENTRAL NC TO SUPPORT THE DEVELOPMENT OF SCATTERED THUNDERSTORMS...SOME OF WHICH MAY BE STRONG TO SEVERE OWING TO EFFECTIVE BULK SHEAR IN THE NEIGHBORHOOD OF 45-50KTS. MOST OF THE SEVERE STORM PARAMETERS FAVOR THE WESTERN PIEDMONT...MAINLY SOUTH OF THE TRIAD TOWARD THE CLT METRO AREA. AS THE NEAR SURFACE AIR MASS IS BEGINNING TO STABILIZE WITH LOSS OF HEATING...TORNADIC THREAT IS BECOMING LESS OF A CONCERN. HOWEVER...LARGE HAIL AND DAMAGING WINDS REMAIN A VIABLE THREAT...POSSIBLY INTO THE WEE HOURS OF MONDAY MORNING IF STORMS ORGANIZE/STRENGTHEN ONCE THEY CROSS THE HIGHER TERRAIN OF WESTERN NC. IF STORMS DO ORGANIZE...WILL NEED TO INCREASE POPS OVERNIGHT ACROSS THE EASTERN PIEDMONT INTO THE SANDHILLS AND COASTAL PLAIN. BEHIND THE CONVECTIVE STORMS...MAY SEE PATCHES/AREAS OF FOG DEVELOP...MAINLY OVER THE WESTERN PIEDMONT BY DAYBREAK MONDAY. MIN TEMPS IN THE LOW-MID 70S. && .SHORT TERM /MONDAY AND MONDAY NIGHT/...
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AS OF 325 PM SUNDAY... NWP GUIDANCE CONTINUES TO SUGGEST DESTABILIZATION WILL BE LIMITED AND CONFINED TO THE SANDHILLS ANTO THE STATE. GUIDANCE POPS ARE LOW IN GENERAL...AND THE CONVECTIVE ALLOWING MODELS HAVE NOT BEEN HELPFUL OVERALL IN THEIR FORECASTS OF SHOWER AND THUNDERSTORM DEVELOPMENT IN AND NEAR CENTRAL NORTH CAROLINA. A FEW SHOWERS HAVE DEVELOPED JUST WEST AND SOUTHWEST OF THE TRIAD...AND AHEAD OF THE COMPLEX OF STORMS...THINK THERE IS ENOUGH SHEAR AND INSTABILITY...AND SIMPLE DYNAMICS FROM THE ONGOING STORMS...SIMILAR TO THE LATEST TREND OF RAP FORECASTS...TO ALLOW FOR SOME CONTINUED PROGRESSION OF ACTIVITY INTO AND THROUGH CENTRAL NORTH CAROLINA. TAFS WILL LIKELY INCLUDE A MENTION OF THUNDER AND GUSTY WINDS...SHOWERS AND LESSER GUSTS CURRENTLY TOWARD KRWI. CONFIDENCE IS ONLY MODEST...AND ND 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.
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&& .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 /02Z MONDAY THROUGH FRIDAY/...
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AS OF 1015 PM SUNDAY... GOOD INSTABILITY REMAINED LATE IN THE EVENING EAST OF THE MOUNTAINS INTO CENTRAL NORTH CAROLINA...WHILE A COMPLEX OF SHOWERS AND THUNDERSTORMS MOVED SOUTHEAST ACROSS THE WESTERN PART OF THE STATE. BASED ON THE LATEST SPC MESOANALYSIS...THE LEADING COMPLEX OF SHOWERS AND STORMS TENDED TO HEAD TOWARD THE BETTER MID-LEVEL INSTABILITY/LAPSE RATES TOWARD UPSTATE SOUTH CAROLINA...AND JUST WEST OF CENTRAL NORTH CAROLINA. SOME PARAMETERS STILL FAVOR THE POTENTIAL FOR DEEP CONVECTION UPSTREAM TO MAKE IT INTO CENTRAL NORTH CAROLINA...AND THE LATEST GUIDANCE VARIES FROM DRY CONDITIONS OVER THE AREA ON THE RAP MODEL...A STARK CHANGE FROM AFTERNOON RUNS...TO STILL A FEW SHOWERS AND ISOLATED STORMS INTO THE OVERNIGHT. BASED ON THE GUIDANCE TRENDS AND THE KGSO 00Z UPPER-AIR SOUNDING...UPDATED TAFS TO BE A LITTLE MORE OPTIMISTIC IN CONDITIONS...BUT LEFT STILL THE POTENTIAL FOR A FEW SHOWERS WITH A GUSTY WIND GIVEN CONTINUED INSTABILITY...SURFACE WINDS REMAINING GUSTY ESPECIALLY FROM THE TRIANGLE WEST...AND ONLY MODEST CONFIDENCE IN EVOLVING CONDITIONS. AVIATION INTERESTS SHOULD KEEP ABREAST OF THE LATEST OBSERVATIONAL AND RADAR TRENDS INTO THE OVERNIGHT HOURS. LATE TONIGHT INTO MONDAY...OVERALL DRIER AIR MOVES INTO CENTRAL NORTH CAROLINA. WITH MIXING MONDAY...WINDS SHOULD BECOME 250-290 AND WITH MODEST GUSTS TO AT OR SLIGHTLY ABOVE 20KT. A SHOWER OR THUNDERSTORM IS POSSIBLE TOWARD KFAY AND KRWI MONDAY AFTERNOON BUT CONFIDENCE IN THEIR DEVELOPMENT AND LOCATION IS TOO LOW TO INCLUDE IN THE 00Z TAF. BEYOND THE 00Z VALID TAF PERIOD...VFR CONDITIONS SHOULD PREVAIL FOR MUCH OF THE REST OF THE WORK WEEK...WITH INCREASING CHANCES FOR SHOWERS AND THUNDERSTORMS FROM FRIDAY INTO THE WEEKEND.
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&& .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...MWS/DJF NEAR TERM...WSS SHORT TERM...MWS LONG TERM...BLS AVIATION...DJF

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