Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 290745 AFDRAH AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE RALEIGH NC 345 AM EDT FRI APR 29 2016 .SYNOPSIS...
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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.
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&& .NEAR TERM /TODAY AND TONIGHT/...
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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
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&& .LONG TERM /SATURDAY THROUGH THURSDAY/... AS OF 340 PM THURSDAY... A BROAD UPPER LEVEL TROUGH WILL INITIALLY COVER THE LOWER 48 SATURDAY. THIS WILL TRANSITION TO AN AMPLIFIED RIDGE OVER THE WESTERN U.S. AND AN TROUGH OVER THE EASTERN U.S. FORECAST CONFIDENCE IS LOWER THAN NORMAL DUE TO THIS TRANSITION AS MODELS USUALLY HAVING DIFFICULTY RESOLVING WHICH PARTICULAR S/W WILL CAUSE AN ENHANCED CHANCE OF PRECIP TO A GIVEN REGION. SINCE WEDNESDAY...THE MODELS HAVE SPED UP THE RETURN FLOW OF MOISTURE INTO CENTRAL NC SATURDAY INTO SATURDAY NIGHT AS THE S/W RIDGE SCOOTS QUICKLY EAST SATURDAY MORNING. THIS LOW LEVEL WARM AIR ADVECTION COUPLED WITH A SERIES OF DISTURBANCES ALOFT WILL INCREASE RAIN CHANCES SW-NE ACROSS CENTRAL NC SATURDAY AFTERNOON INTO SATURDAY NIGHT. WHILE A SHORT-LIVED HYBRID/INSITU DAMMING EVENT MAY OCCUR SATURDAY AFTERNOON-SATURDAY EVENING... MODEL GUIDANCE NOW SUGGESTING THAT A WARM FRONT WILL LIFT ACROSS THE AREA SATURDAY NIGHT...PLACING CENTRAL NC SOLIDLY IN THE WARM SECTOR ON SUNDAY. THUS HAVE ADJUSTED MAX TEMPS UP SEVERAL DEGREES FROM EARLIER FORECAST AND BACKED SFC WINDS TO A SWLY DIRECTION. S/W IN THE NORTHERN STREAM WILL DRAG A WEAK COLD FRONT ACROSS CENTRAL NC LATE MONDAY AND MONDAY NIGHT...BRINGING ANOTHER THREAT FIR SCATTERED CONVECTION. NELY LOW LEVEL FLOW WILL ADVECT A COOLER AND MORE STABLE AIR MASS TUESDAY LEADING TO PLENTY OF CLOUD COVER AND COOLER DAYTIME TEMPS. -WSS AMPLIFYING RIDGE OVER THE WESTERN CONUS WILL ALLOW FOR A DIGGING TROUGH OVER THE EASTERN CONUS WITH A DEVELOPING UPPER LEVEL FEATURE TO OUR SOUTH. GFS SHOWS A SURFACE LOW PRESSURE SYSTEM DEVELOPING OVER PORTIONS OF NORTHERN FL ON TUE AFTERNOON. ECMWF SHOWS A MUCH STRONGER BUT MUCH SLOWER DEVELOPING DISTURBANCE OVER THE MS VALLEY. WITH THE CURRENT PATTERN AND SLOW MOVEMENT OF THE ECMWF... THE GFS SEEMS TO BE THE MORE REALISTIC SOLUTION AT THIS TIME ALTHOUGH CONFIDENCE IS LOW. THE LOW WILL LIKELY DEVELOP AND MOVE NORTHWARD ALONG THE COAST FOR WED NIGHT INTO THU. GUIDANCE SUGGESTS EASTERLY AND NORTHEASTERLY WINDS IN ASSOCIATION WITH THE LOW PRESSURE SYSTEM. THE WEATHER PATTERN ASSOCIATED WITH THIS LOW COULD BRING SOME ISENTROPIC UPGLIDE ALONG WITH INCREASE RAIN CHANCES FOR WED NIGHT AND INTO THU MORNING WITH POPS TAPERING OFF AS THE DISTURBANCE MOVES NORTHEASTWARD. TEMPS ARE CURRENTLY FORECASTED TO BE 5 TO 8 BELOW CLIMO ON WED WITH INCREASING CLOUD COVER AND MOISTURE ADVECTION OFF OF THE ATLANTIC. THE COLD AIR ADVECTION ASSOCIATED WITH THIS COULD BE LIGHT ENOUGH TO ALLOW FOR TEMPERATURES TO GET CLOSER TO CLIMO. CLOUD COVER COULD LIMIT THE CURRENT FORECAST LOWS... HOWEVER GFS SUGGESTS LOW LEVEL COLD AIR ADVECTION CONTINUING WED NIGHT. -JLB && .AVIATION /00Z FRIDAY THROUGH TUESDAY/... AS OF 815 PM THURSDAY... CLUSTERS OF SHOWERS AND STORMS OVER THE NORTHERN PIEDMONT AND NORTHERN COASTAL PLAIN WILL SLOWLY DIMINISH THROUGH 04Z/MIDNIGHT LOCAL TIME. IN VICINITY OF THE HEAVIER SHOWERS AND STORMS...EXPECT A BRIEF PERIOD OF MVFR CONDITIONS. AFTER 06Z...POCKETS OF MVFR/IFR CEILINGS AND FOG WILL DEVELOP...MAINLY IN VICINITY OF KRDU AND KRWI. ELSEWHERE...BRIEF INTERVALS OF MVFR/IFR FOG AND/OR CEILINGS WILL OCCUR BETWEEN 09Z-13Z. AFTER 14Z...EXPECT CLOUD BASES TO LIFT AND SCATTER BY MID-LATE MORNING 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. WARMER AIR WILL MAKE A RETURN SUNDAY AND MAINTAIN A THREAT OF SCATTERED CONVECTION ALONG WITH PERIODS OF MVFR CEILINGS SUNDAY AFTERNOON THROUGH TUESDAY. && .RAH WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...VINCENT NEAR TERM...VINCENT SHORT TERM...CBL LONG TERM...WSS/JLB AVIATION...WSS

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