Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 270229 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 1030 PM EDT SAT JUL 26 2014 .SYNOPSIS...A SURFACE TROUGH WILL DEVELOP OVER THE WESTERN PIEDMONT THIS WEEKEND...RESULTING IN A VERY WARM SOUTHWEST FLOW. A STRONG COLD FRONT WILL CROSS THE AREA ON MONDAY. && .NEAR TERM /THROUGH TONIGHT/... AS OF 1030 PM SATURDAY... MAIN ADJUSTMENT TO THE FORECAST OVERNIGHT WAS TO BEEF UP CLOUD COVERAGE OVER MOST OF THE PIEDMONT. THIS ALSO REQUIRED A SLIGHT ADJUSTMENT UPWARD IN OVERNIGHT TEMPS. ALSO...INDICATIONS THAT MOSTLY CLOUDY SKIES SUNDAY MORNING MAY INHIBIT INSOLATION UNTIL EARLY AFTERNOON. THIS MAY RESULT IN MAX TEMPS A COUPLE OF DEGREES COOLER THAN PREVIOUS FORECAST. INITIAL S/W RESPONSIBLE FOR CONVECTION ACROSS THE MID OH VALLEY THIS AFTERNOON TRACKING EAST INTO THE NORTHERN MID ATLANTIC. W-NW FLOW ALOFT HAS SPREAD CONVECTIVE DEBRIS CLOUDINESS INTO THE PIEDMONT THIS EVENING...THICKEST OVER THE NW PIEDMONT. WHILE EXPECT HIGH LEVEL CLOUDS TO THIN WITH TIME...OPAQUENESS MAY BE ENOUGH ACROSS THE PIEDMONT TO RESULT IN MIN TEMPS A COUPLE OF DEGREES WARMER THAN PREVIOUS FORECAST...ESPECIALLY IN THE TRIAD VICINITY. ALSO...ARRIVAL OF HIGH LEVEL CLOUDS WILL INHIBIT FOG FORMATION SO NOT EXPECTING MUCH IN FOG OVERNIGHT. && .SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/... AS OF 1030 PM SATURDAY... SUNDAY...BAND OF CONVECTION OCCURRING AT 02Z ACROSS THE LOWER OH VALLEY PROJECTED TO MOVE EAST-SE AND CROSS THE SW VA/NORTHERN NC MOUNTAINS SHORTLY AFTER DAYBREAK. BULK OF CONVECTION EXPECTED TO FIZZLE AS IT ADVANCES EAST PAST THE MOUNTAINS BUT ENOUGH RESIDUAL CLOUDINESS WILL OCCUR TO LIMIT INSOLATION FOR A GOOD PART OF THE MORNING...ESPECIALLY IN THE TRIAD...WITH PARTLY-MOSTLY CLOUDY SKIES PROBABLE IN THE TRIANGLE AREA FROM MID-LATE MORNING UNTIL MID AFTERNOON. IF THIS CLOUDINESS MATERIALIZES...THIS WILL HAVE AN EFFECT TEMPS. HAVE SHADED MAX TEMPS DOWN OF COUPLE OF DEGREES IN THE PIEDMONT AND NORTHERN COASTAL PLAIN. NOT AS CONFIDENT ABOUT THE SOUTHERN COUNTIES WHERE MORE SUN THAN CLOUDS EXPECTED. THUS MAX TEMPS IN THE UPPER 90S STILL APPEAR ON TRACK WITH HEAT INDICES 102- 104 DEGREES LIKELY. MAY SEE A STRAY THUNDERSTORM OR TWO SUNDAY MORNING OCCUR ALONG THE VA BORDER COUNTIES IN ASSOCIATION WITH THE WEAKENING THUNDERSTORM COMPLEX. SUBSIDENCE IN THE WAKE OF THE EXITING MCV MAY INHIBIT CONVECTIVE DEVELOPMENT IN THE AFTERNOON ACROSS THE REGION. -WSS SUNDAY NIGHT...THE PREFRONTAL SFC TROUGH IS PROGGED BY THE GFS AND NAM TO CROSS THE MOUNTAINS AROUND 06Z MONDAY THEN MOVE INTO OUR WESTERN ZONES BY 12Z MON. DESPITE THIS LOW LEVEL FORCING...THE MODELS HAVE LITTLE IF ANY QPF ACROSS MOST OF OUR CWA DURING THE OVERNIGHT HOURS...PERHAPS DUE IN PART TO A DRY WESTERLY FLOW PRECEDING IT AND LOW LEVEL NIGHT-TIME STABILITY. ANY CONVECTION THAT CAN GET GOING OVERNIGHT WOULD LIKELY BE ELEVATED...BUT STILL WORTH CLOSE WATCHING. FOR NOW WILL CONTINUE SLIGHT CHANCE POPS ACROSS THE ENTIRE CWA SUNDAY NIGHT. THE OTHER MAIN CONCERN FOR SUNDAY IS TEMPS AND HIGH HEAT INDICES. GUIDANCE CURRENTLY HAS TEMPS RANGING FROM AROUND 94 NW TO AROUND 98 SE. WITH DWPTS RANGING FROM THE MID 60S NW TO AROUND 70 SE...HEAT INDICES WILL LIKELY RANGE FROM 100-103 ACROSS OUR SOUTHERN COASTAL PLAIN ZONES. WHILE THIS IS BELOW HEAT ADVISORY CRITERIA...WE HAVE HAVE THIS HIGHLIGHTED IN OUR CURRENT HWO. LOWS SUNDAY NIGHT IN THE LOWER TO MID 70S. -NP MONDAY AND MONDAY NIGHT: THE UNSEASONABLY STRONG SHORTWAVE TROUGH/LOW TRAVERSING THE GREAT LAKES THIS WEEKEND WILL MOVE NE THROUGH NY AND ALONG THE U.S./CANADA BORDER THROUGH MONDAY NIGHT. ITS ASSOCIATED COLD FRONT WILL MOVE THROUGH THE AREA MONDAY AFT/EVE...RESULTING IN INCREASED CHANCES FOR SEVERE WEATHER. THE GFS AND ECMWF HAVE COME INTO BETTER AGREEMENT WITH THE TIMING AND LOCATION OF THE FRONT...HOWEVER THE CHANCES FOR CONVECTION HAVE DECREASED SOMEWHAT. THE BEST CHANCES ARE STILL MAINLY ALONG AND EAST OF I-95 FROM 18Z MONDAY THROUGH 06Z TUESDAY. IN THIS FAVORED REGION...MODELS ARE FORECASTING MUCAPE IN THE 1500-2500 J/KG RANGE...0-6 KM BULK SHEAR OF 40-50 KTS...LOW LEVEL LAPSE RATES OF 8- 8.5 DEG/KM...AND MID LEVEL LAPSE RATES OF 6.5-7 DEG/KM. LOW LEVEL SHEAR REMAINS WEAK. GIVEN THAT ENVIRONMENT...EXPECT CONVECTION... WHERE IT DEVELOPS...TO BE STRONG TO SEVERE...WITH THE MAIN THREATS BEING LARGE HAIL AND DAMAGING WINDS. THERE CONTINUES TO BE UNCERTAINTIES WITH RESPECT TO COVERAGE OF CONVECTION AND WHETHER THERE WILL BE MUCH OVER CENTRAL NC. SOME OF THE MODELS INDICATE THAT THE CONVECTION WILL FALL APART AS IT CROSSES THE APPALACHIANS... WITH SOME REDEVELOPMENT ALONG THE COAST LATE MONDAY AND/OR REMAIN NORTH OF THE NC/VA BORDER. THE GFS CONTINUES TO FORECAST THE BEST UPPER LEVEL FORCING WELL TO THE NORTH OF THE AREA. THUS...ALTHOUGH THE CHANCE FOR CONVECTION DEFINITELY EXISTS AND SHOULD IT DEVELOP ITS LIKELY THAT STORMS WILL BE STRONG/SEVERE...CONFIDENCE IS DECREASING WITH REGARD TO WHETHER STORMS WILL DEVELOP OVER THE AREA. ALSO...RESIDUAL CLOUDINESS AND OUTFLOW BOUNDARIES FROM CONVECTION SUNDAY/SUNDAY NIGHT (SHOULD IT OCCUR) MAY ALSO PLAY A ROLE IN LIMITING CONVECTION. HIGHS WILL BE MAINLY IN THE UPPER 80S NW TO MID 90S SE WITH OVERNIGHT LOWS...DEPENDING ON THE PROGRESSION OF THE FRONT...MAINLY IN THE LOW 60S NW TO UPPER 60S SE. -KC && .LONG TERM /TUESDAY THROUGH SATURDAY/... AS OF 235 PM SATURDAY... THE UPPER LEVEL TROUGH WILL REMAIN OVER...TO JUST WEST OF THE REGION THROUGH THE PERIOD. AT THE SURFACE...HIGH PRESSURE WILL BUILD INTO THE AREA BEHIND THE FRONT...BRINGING COOLER AND DRIER AIR INTO CENTRAL NC THROUGH THE END OF THE WEEK. THIS WILL RESULT IN BELOW NORMAL TEMPERATURES...WITH HIGHS IN THE LOW TO MID 80S THROUGH THE WEEK AND LOWS FROM THE UPPER 50S TO MID 60S TUE/WED NIGHTS AND LOW TO MID 60S THU/FRI NIGHTS. WITH THE SUBSIDENCE IN THE WEST/NORTHWEST FLOW ALOFT AND SIGNIFICANTLY DRIER AIR ADVECTING INTO THE MID/UPPER LEVELS...EXPECT MUCH OF THE WEEK TO REMAIN DRY...WITH SOME SLIGHT CHANCES IN THE NW FRI/SAT AS THE UPPER LEVEL TROUGH SHIFTS WEST AND THE PIEDMONT TROUGH TRIES TO DEVELOP OVER THE AREA ONCE AGAIN. && .AVIATION /00Z SUNDAY THROUGH THURSDAY/... AS OF 740 PM SATURDAY... MAINLY VFR CONDITIONS ARE EXPECTED TO CONTINUE FOR THE 24 HOUR TAF PERIOD. UPSTREAM CONVECTION CURRENTLY OVER THE OHIO VALLEY MOVING INTO THE CENTRAL APPALACHIANS AND CONVECTION FURTHER UPSTREAM/WEST ACROSS THE MIDWEST WILL HELP TO SPREAD SOME MID AND HIGH CLOUD COVER INTO THE AREA OVERNIGHT (NO CONVECTION OUTSIDE OF A POSSIBLY ROUGE SHOWER ACROSS THE NORTH/NORTHWEST NEAR DAYBREAK). THIS COMBINED WITH A WEST TO SOUTHWESTERLY LOW LEVEL FLOW SHOULD LEAD TO LESS OF A CHANCE FOR SOME SUB-VFR CONDITIONS TONIGHT. LOCATIONS ACROSS THE EASTERN HALF OF THE AREA MAY STILL SEE SOME MVFR VISBYS NEAR DAYBREAK THOUGH... WITH FOG PRONE KRWI POSSIBLY SEE VISBYS RANGE FROM LIFR TO VFR OVERNIGHT. CONFIDENCE IN SUB-VFR CONDITIONS IS LOW THOUGH... SO WILL JUST INCLUDED A TEMPO MENTION OF SUB-VFR CONDITIONS AT THE EASTERN TAF SITES FOR THE PRE-DAWN HOURS OF SUNDAY. DURING THE DAY SUNDAY...LOOK FOR MOSTLY VFR CONDITIONS TO CONTINUE. LATER IN THE DAY (MID MORNING ONWARD)...A BRIEF SHOWER OR TSTM WITH LOCAL IFR CONDITIONS WILL BE POSSIBLE MAINLY ACROSS THE NORTHERN HALF OF CENTRAL NC...AHEAD OF AN APPROACHING PREFRONTAL TROUGH. GIVEN THE TIME FRAME AND LOW CONFIDENCE WILL LEAVE OUT ANY MENTION OF CONVECTION AND SUB-VFR CONDITIONS DURING THE DAY SUNDAY. HOWEVER... WE EXPECTED SOUTHWESTERLY WINDS TO STRENGTHEN DURING THE AFTERNOON ON SUNDAY... WITH POSSIBLY SOME GUSTS TO 20 MPH.... POSSIBLY EVEN 25 MPH. BEYOND THE 24 HOUR TAF PERIOD...A COLD FRONT WILL MOVE ACROSS CENTRAL NC ON MONDAY...BRINGING THE CHANCE FOR SHOWERS AND TSTMS AND ASSOC REDUCED FLIGHT CONDITIONS MONDAY MORNING/MONDAY AFTERNOON ...ESP ALONG AND EAST OF A LINE FROM KRDU TO KFAY. VFR CONDITIONS ARE EXPECTED TO RETURN BEHIND THE FRONT FOR THE MIDWEEK PERIOD. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...WSS NEAR TERM...WSS SHORT TERM...WSS/NP/KC LONG TERM...KC AVIATION...BSD/NP

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