Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 290748 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 345 AM 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 /TODAY AND TONIGHT/... AS OF 345 AM FRIDAY... AS OF 06Z...WINDS HAVE SHIFTED TO THE NORTH OVER MUCH OF CENTRAL NC...EXCEPT IN THE THE SW PIEDMONT. AT A GLANCE...IT WOULD APPEAR THAT THE FRONTAL ZONE STALLED NEAR THE VIRGINIA BORDER FOR THE PAST 36-48 HRS HAS FINALLY PROGRESSED SOUTHWARD THROUGH MUCH OF CENTRAL NC. ALTHOUGH THE STATIONARY BOUNDARY HAS INDEED BEGUN TO MOVE SOUTH OF THE VA/NC BORDER AS A BACK DOOR COLD FRONT EARLY THIS MORNING... CLOSER INSPECTION OF OBSERVATIONAL DATA (THETA-E/WETBULB TEMPS IN PARTICULAR) REVEAL THAT THE TRUE FRONT /CHANGE IN AIRMASS/ HAS ONLY JUST BEGUN TO SAG SOUTH OF THE VA BORDER...EXTENDING (ROUGHLY) WNW- ESE FROM ROXBORO-LOUISBURG-TARBORO. SOUTH OF THE ACTUAL FRONT...A CONVECTIVELY MODIFIED WARM SECTOR CHARACTERIZED BY FOG/LOW STRATUS...TEMPS IN THE LOW/MID 60S AND A LIGHT NORTHERLY BREEZE EXTENDED SOUTHWARD THROUGH THE REMAINDER OF CENTRAL NC... EXCEPT IN THE FAR SW PIEDMONT WHERE CONVECTION FAILED TO DEVELOP OVER THE PAST 36-48 HRS AND A PRISTINE WARM SECTOR PERSISTS. IN THE UPPER LEVELS...SEVERAL SMALL AMPLITUDE SHORTWAVES WERE NOTED WITHIN UNIDIRECTIONAL /WESTERLY/ FLOW ALOFT OVER THE REGION. CHALLENGING FORECAST. 00Z MODEL GUIDANCE IS HAVING DIFFICULTY IN CAPTURING THE EXTENT OF FOG/STRATUS PRESENT AT 06Z THIS MORNING...AND THOUGH FCST SOUNDINGS EVENTUALLY SHOW FOG/STRATUS DEVELOPING BETWEEN 09-12Z...ANALYSIS OF REGIONAL OBSERVATIONAL DATA SUGGESTS THAT GUIDANCE IS ALSO UNDER-REPRESENTING THE SOUTHERN EXTENT OF THE BACK DOOR COLD FRONT /COOLER AIRMASS/ PROGRESSING INTO CENTRAL NC FROM THE N/NE THIS MORNING. FCSTING THE EVOLUTION OF THE BACKDOOR FRONT WILL BE FURTHER COMPLICATED BY THE PRESENCE OF SMALL AMPLITUDE WAVES IN WESTERLY FLOW ALOFT...THE PRECISE TIMING/ EVOLUTION OF WHICH WILL DETERMINE THE ORIENTATION/MAGNITUDE OF THE MSLP PATTERN/GRADIENT. WITH THE ABOVE IN MIND...CURRENT THINKING IS THAT GUIDANCE MAY BE TOO QUICK TO MIX OUT LOW-LEVEL CLOUD COVER THIS MORNING...AND THAT CONDITIONS THIS AFTERNOON MAY BE COOLER AND CLOUDIER THAN PREVIOUSLY EXPECTED...ESP IN THE TRIANGLE...NORTHERN PIEDMONT AND NE COASTAL PLAIN. WILL INDICATE MOSTLY CLOUDY/OVERCAST SKIES BECOMING PARTLY CLOUDY DURING THE AFTERNOON (EARLIEST SW AND LATEST NE) WITH HIGHS RANGING FROM ~70F FAR NE...TO LOW/MID 70S IN THE TRIANGLE...AND MID/UPPER 70S TO LOWER 80S IN THE SW PIEDMONT. ANTICIPATE NO POTENTIAL FOR PRECIP AS A DRIER/MORE STABLE LOW-LEVEL AIRMASS ADVECTS INTO THE AREA FROM THE NW. -VINCENT && .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 /MONDAY THROUGH THURSDAY/... AS OF 345 AM FRIDAY... ANOTHER WAVE OR SEVERAL WAVES ARE FAVORED TO DEVELOP OVER THE SE STATES EARLY TO MID WEEK AS THE UPPER LEVEL TROUGH BECOMES ESTABLISHED OVER THE REGION. THE FRONT MENTIONED ABOVE WILL SETTLE JUST TO OUR SOUTH AND EAST AND BECOME QUASI-STATIONARY MONDAY- WEDNESDAY. THERE IS PLENTY OF SPREAD WITH THE ENSEMBLES AS TO TIMING OF KEY RAIN PRODUCERS... SO WE WILL SIMPLY BROADBRUSH GOOD CHANCES OF RAIN. WE WILL ALSO ADVERTISE COOLER THAN NORMAL READINGS DUE TO THE TROUGH ALOFT... PREVALENT NE LOW LEVEL FLOW... CONSIDERABLE CLOUDINESS... AND SEVERAL SIGNIFICANT RAIN CHANCES. LOWS GENERALLY IN THE 50S TO LOWER 60S SE. HIGHS IN THE MID 60S TO MID 70S... EXCEPT 75-80 SE MONDAY. && .AVIATION /06Z FRIDAY THROUGH TUESDAY/... AS OF 140 AM FRIDAY... AREAS OF MVFR/IFR FOG AND/OR CEILINGS WILL OCCUR THROUGH 15-17Z. AFTER 17Z...EXPECT CLOUD BASES TO LIFT AND SCATTER AS DRIER AIR INFILTRATES THE REGION...RESULTING IN VFR CONDITIONS. THE OPTIMAL AVIATION CONDITIONS WILL BE SHORT IN DURATION AS A QUICK RETURN FLOW OF MOISTURE WILL ADVANCE OVER THE PIEDMONT SATURDAY MORNING. THIS WILL LEAD TO THICKENING LOWER CLOUD DECK AND SPOTS OF LIGHT RAIN DEVELOPING SATURDAY AFTERNOON. ADVERSE AVIATION CONDITIONS EXPECTED TO BE WIDESPREAD ACROSS CENTRAL NC SATURDAY NIGHT THROUGH EARLY SUNDAY DUE TO LOW CLOUDS AND WIDESPREAD RAIN. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...VINCENT NEAR TERM...VINCENT SHORT TERM...BADGETT LONG TERM...BADGETT AVIATION...BADGETT

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