Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000
FXUS62 KRAH 291021
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
620 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 /12Z FRIDAY THROUGH TUESDAY/...
AS OF 620 AM FRIDAY...

AREAS OF MVFR/IFR FOG AND/OR CEILINGS WILL EXIST THROUGH 14-17Z.
AFTER 17Z...EXPECT CIGS TO LIFT OUT IN ALL BUT THE KRDU/KRWI AREAS
WHERE THE PROCESS WILL BE SLOWER. IN GENERAL... VFR CIGS EXPECTED
LATER TODAY AT ALL TAF SITES.

THE VFR CONDITIONS WILL BE SHORT IN DURATION AS A QUICK RETURN FLOW
OF MOISTURE WILL ADVANCE OVER THE PIEDMONT TONIGHT AND SATURDAY
MORNING. THIS WILL LEAD TO MVFR CIGS THEN IFR TO LIFR CIGS AGAIN
BETWEEN 09Z-12Z/SAT. AREAS OF LIGHT RAIN MAY DEVELOP... ESPECIALLY
IN THE WESTERN AREAS SATURDAY AFTERNOON.

ADVERSE AVIATION CONDITIONS EXPECTED TO BE WIDESPREAD ACROSS CENTRAL
NC SATURDAY NIGHT THROUGH 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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