Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 291842 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 240 PM EDT FRI APR 29 2016 .SYNOPSIS...THE STATIONARY FRONT LOCATED IN VICINITY OF THE VIRGINIA BORDER THE PAST 48 HOURS WILL SAG SOUTH SOUTHWEST THROUGH CENTRAL NORTH CAROLINA AS A BACK DOOR COLD FRONT TODAY...STALL NEAR THE SOUTH CAROLINA BORDER TONIGHT...THEN GRADUALLY LIFT BACK TO THE NORTH AS A WARM FRONT SATURDAY INTO SATURDAY NIGHT. && .NEAR TERM /THROUGH TONIGHT/... AS OF 1050 AM FRIDAY... LOW CLOUDS SLOWLY ERODING FROM THE SW THIS MORNING WITH THE CLEARING LINE AT 1430 EXTENDING FROM ROXBORO-RALEIGH-FAYETTEVILLE. CLOUDS WILL CONTINUE TO SLOWLY ERODE FROM THE WEST-SW....REACHING THE RZZ VICINITY AROUND 17Z-18Z. EROSION PROCESS WILL RESULT IN A WIDE VARIANCE IN MID AFTERNOON TEMPS ACROSS THE CWA. 19Z TEMPS SHOULD VARY FROM THE LOW/MID 80S OVER THE SOUTHERN PIEDMONT TO AROUND 70 OVER THE FAR NORTHERN COASTAL PLAIN. TONIGHT...NARROW RIDGE OF HIGH PRESSURE WILL SCOOT EAST. THIS WILL ALLOW A RETURN FLOW OF MOISTURE TO OCCUR OVER THE SOUTHERN AND WESTERN PIEDMONT. THIS WILL BE IN CONTRAST TO THE NE PIEDMONT/NORTHERN COASTAL PLAIN WHERE THE RETURN WILL NOT BECOME ESTABLISHED UNTIL AFTER DAYBREAK. AREAS OF MID-HIGH LEVEL CLOUDS WILL TRAVERSE EAST ACROSS THE REGION OVERNIGHT THOUGH NOT ENOUGH LIFT NOTED TO GENERATE PRECIPITATION. MIN TEMPS SHOULD VARY FROM THE MID 50S NE TO THE LOWER 60S SW. && .SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/... AS OF 340 AM FRIDAY... A HYBRID CAD EVENT IS LIKELY OVER THE PIEDMONT DAMMING REGION THIS WEEKEND. MODELS CAN NOT BE TRUSTED WITH THE HYBRID CAD... NOR PLACEMENT OF THE WARM FRONT. A ~1023-1025 MB SURFACE HIGH PRESSURE IS FORECAST TO BUILD SOUTHWARD INTO NORTH CAROLINA LATE FRIDAY NIGHT AND SATURDAY MORNING. THE PARENT HIGH IS ACTUALLY IN A FAVORABLE POSITION AND OF FAVORABLE STRENGTH TO ADEQUATELY DELIVER ENOUGH LOW LEVEL COOL STABLE AIR INTO OUR REGION TO SET UP A HYBRID PIEDMONT COLD AIR DAMMING (WARM SEASON) EVENT BEGINNING SATURDAY AND LASTING INTO SUNDAY. THE HIGH PRESSURE WILL SLOWLY MOVE EAST AND OFFSHORE OF THE NORTHERN MID- ATLANTIC COAST LATE SATURDAY... YET THE FOUNDATION OF CAD WILL BE IN PLACE OVER THE NW PIEDMONT... AND LIKELY EVENTUALLY LOCKED IN PLACE BY THE EXPECTED RAINFALL AND SUBSEQUENT DIABATIC PROCESSES. THE RESIDUAL COOL STABLE LOW LEVEL AIR MASS WILL PLAY HAVOC ON SENSIBLE WEATHER THIS WEEKEND. THIS DEVELOPS AS THE WARM AIR ADVECTION PATTERN ALOFT RAPIDLY TRANSPIRES AS THE NEXT POTENT SYSTEM THAT WILL BE APPROACHING FROM THE WEST THIS WEEKEND. THERE WILL BE PLENTY OF AVAILABLE DEEP MOISTURE TO SURGE BACK NORTHWARD ALONG AND THEN ATOP A NEARLY STATIONARY LOW LEVEL BOUNDARY... AS THE WESTERN ATLANTIC AND GULF ARE TAPPED. RAIN IS EXPECTED TO DEVELOP MOST LIKELY LATE SATURDAY MORNING INTO THE AFTERNOON FROM SOUTH TO NORTH. MODELS AND ENSEMBLES SHOW CONSIDERABLE SPREAD WITH TIMING OF ONSET... BUT THE EARLIER TIMING USUALLY WINS OUT IN THESE RESUMES. THE FAVORED HIGHER QPF WILL BE IN THE WEST... WITH LOWER POP/QPF SE. THE LATEST SEVERAL RUNS OF THE OPERATIONAL EC APPEAR TO BE FIT THE OVERALL PATTERN AND OUR THINKING BETTER THAN THE NAM AND GFS WITH THE TIMING OF ONSET OF RAIN AND THE EVENTUAL EVOLUTION OF THE CAD EVENT OVER THE REGION SATURDAY NIGHT INTO SUNDAY. ONCE THE RAIN DEVELOPS ON SATURDAY AFTERNOON... IT IS EXPECTED TO BECOME WIDESPREAD OVER THE PIEDMONT DAMMING REGION... ESPECIALLY THE WESTERN AND NORTHERN PIEDMONT... WITH THE RAIN BECOMING MORE AND MORE SPOTTY WITH TIME IN THE SE ZONES. THIS WILL OCCUR AS THE WARM FRONT TRIES TO COME NORTHWARD BUT WILL LIKELY A VERY DIFFICULT TIME GETTING INTO THE CAD REGION OF THE PIEDMONT SATURDAY NIGHT AND SUNDAY MORNING. AS THE STORM SYSTEM LIFTS WEST OF THE APPALACHIANS SUNDAY AND SUNDAY NIGHT THERE SHOULD CONTINUE TO BE ENOUGH ISENTROPIC LIFT TO KEEP THE RAIN/SHOWERS GOING ESPECIALLY OVER THE WESTERN TWO THIRDS OF OUR REGION. THIS WILL MOST LIKELY KEEP THE LOW LEVEL COOL POOL AND DAMMING IN PLACE INTO SUNDAY. FINALLY... AS THE MAIN STORM MOVES FROM THE CENTRAL APPALACHIANS TO VA/MD... THE TRAILING COLD FRONT WILL PUSH INTO THE REGION... THEN LIKELY STALL SUNDAY NIGHT AND MONDAY. SENSIBLE WEATHER SATURDAY INTO SUNDAY... COOL WITH PERIODS OF RAIN WEST AND NORTH. AREAS OF FOG AND DRIZZLE. HIGHS GENERALLY 60S... OR WELL BELOW CURRENT MOS STATISTICS. LOWS SATURDAY NIGHT HOLDING STEADY IN THE 60S. HIGHS SUNDAY NEAR 70. QPF AROUND 0.50 TO 1 INCH. LARGE TEMPERATURE SPREAD POTENTIAL FOR SUNDAY... FOR AREAS FROM THE SANDHILLS INTO THE CENTRAL COASTAL PLAIN... A CHANCE OF SHOWERS SATURDAY... SHOWERS LIKELY SATURDAY NIGHT AND SUNDAY. HIGHS IN THE LOWER TO MID 70S. LOWS IN THE 60S. HIGHS SUNDAY IN THE 70S TO LOWER 80S SC/NC BORDER AREA. && .LONG TERM /SUNDAY THROUGH FRIDAY/... AS OF 240 PM FRIDAY... SUNDAY...LOW AMPLITUDE MID LEVEL RIDGE SHIFTS OFFSHORE WITH INCREASINGLY SOUTHWEST RETURN FLOW ACROSS AREA. INSTABILITY WILL BE HIGH...WITH CAPE APPROACHING 2K JOULES...DUE TO STEEPENING MID LEVEL LAPSE RATES AND PWAT >1.5 INCHES...BUT SHEAR AND FORCING WILL BE VERY WEAK...HENCE EXPECT LESSER COVERAGE AND ORGANIZATION IN THE MAINLY DIURNALLY DRIVEN CONVECTION. WILL LOWER POPS TO CHANCE CATEGORY AND RAISE HIGH TEMPERATURES A BIT...UPPER 70S NORTH TO LOWER 80S SOUTH...IN THE WARM ADVECTION REGIME. WARM AND MOIST REGIME LINGERS INTO MONDAY AS A BACKDOOR FRONT SLOWLY SAGS SOUTH INTO THE AREA. MONDAY MORNING MINS WILL BE MILD...RANGING FROM 60 TO 65. SOUTHWEST FLOW VEERS MORE WESTERLY...NUDGING THE DEEPER MOISTURE PLUME AHEAD OF THE FRONT TO THE COAST MONDAY AFTERNOON...WITH DRIER AIR MOVING IN TO PRODUCE DECREASING CHANCES OF CONVECTION AS THE DAY PROGRESSES. AIRMASS CHANGE WILL BE DELAYED UNTIL UNTIL TUESDAY...SO HIGHS MONDAY SHOULD BE A BIT WARMER THAN SUNDAY...BUT STILL MAINLY UPPER 70S TO LOWER 80S. THIS FRONTAL ZONE WILL BE LINGERING ACROSS EASTERN NORTH CAROLINA OR JUST OFFSHORE INTO MID WEEK. WILL HAVE THE POTENTIAL FOR SURFACE WAVE DEVELOPMENT WITH SUBSEQUENT MOVEMENT UP THE FRONTAL ZONE IN INCREASINGLY DEEP SOUTHWEST FLOW AS A FAIRLY DEEP UPPER TROF TRANSITIONS ACROSS THE EASTERN CONUS. THIS WILL PRODUCE A CHANCE OF CONVECTION ON TUESDAY AND WEDNESDAY. HIGHS BOTH DAYS WILL BE MOSTLY 70 TO 75 AFTER MORNING LOWS IN THE MID 50S. QUITE A SPREAD IN MODEL SOLUTIONS FOR THE LATE WEEK...WHETHER THE UPPER TROF ACTUALLY SHIFTS EAST OF THE AREA OR WHETHER IT CUTS OFF...WITH A MEANDERING UPPER LOW LEFT OVER THE EAST COAST INTO THE WEEKEND. REGARDLESS...WOULD EXPECT ONLY SLIGHT CHANCES FOR DIURNALLY DRIVEN CONVECTION AS WE WILL REMAIN COOL...MID 70S THURSDAY AND FRIDAY...AND DRY IN PREDOMINANTLY NORTHWEST FLOW. && .AVIATION /18Z FRIDAY THROUGH WEDNESDAY/... AS OF 145 PM FRIDAY... THE LAST VESTIGES OF LOW STRATUS OVER THE NORTHERN COASTAL PLAIN IN VICINITY OF KRWI AND KRZZ WILL LIFT/DISSIPATE PRIOR TO 20Z. OTHERWISE WEAK HIGH PRESSURE AT THE SURFACE WILL MAINTAIN VFR PARAMETERS THROUGH 04Z SATURDAY. OVERNIGHT/AFTER 05Z...WIDESPREAD IFR/LIFR CONDITIONS DUE TO LOW CEILINGS WILL DEVELOP. THE ADVERSE AVIATION CONDITIONS WILL PERSIST THROUGH SATURDAY NIGHT. AREAS OF LIGHT RAIN WILL DEVELOP OVER THE SOUTHERN PIEDMONT SATURDAY AFTERNOON...AND OVERSPREAD THE REMAINDER OF CENTRAL NC THROUGH SATURDAY NIGHT. SUB VFR CONDITIONS EXPECTED SUNDAY MORNING WITH SLOW IMPROVEMENT IN AVIATION CONDITIONS SUNDAY AFTERNOON THROUGH MONDAY. AN UNSETTLED WEATHER PATTERN IS EXPECTED TO RESULT IN VARIABLE AVIATION CONDITIONS THROUGH WEDNESDAY. IT IS HIGHLY PROBABLE THAT MVFR/IFR PARAMETERS WILL OCCUR DUE TO CEILINGS. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...VINCENT NEAR TERM...WSS SHORT TERM...BADGETT LONG TERM...MLM AVIATION...WSS

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