Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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FXUS62 KRAH 251930
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
330 PM EDT FRI JUL 25 2014

.SYNOPSIS...A STALLED FRONT WILL REMAIN NEAR OR JUST SOUTH OF THE
SOUTH CAROLINA BORDER THROUGH TONIGHT. A CLIMATOLOGICALLY MOIST AND
UNSTABLE AIRMASS WILL PREVAIL OVER THE WEEKEND. AN UNSEASONABLY DEEP
UPPER LEVEL TROUGH AND ATTENDANT COLD FRONT WILL APPROACH FROM THE
NORTHWEST SUNDAY NIGHT...THEN CROSS THE REGION ON MONDAY.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 300 PM FRIDAY...

OUTFLOW ASSOC/W CONVECTION THAT DEVELOPED ALONG THE COLD FRONT
TRACKING SOUTHWARD THROUGH VA/NC YESTERDAY EVENING SERVED TO 1)
STRENGTHEN THE FRONTAL ZONE AND 2) ACCELERATE THE FRONT SOUTHWARD.
AS A RESULT OF THE AFOREMENTIONED ACCELERATION...THE FRONT WAS
LOCATED WELL SOUTH OF CENTRAL NC THIS MORNING...EXTENDING ROUGHLY
WEST-EAST FROM ATLANTA-COLUMBIA-MYRTLE BEACH AT 14Z. WV IMAGERY AND
RAOB DATA INDICATED A DRY/SUBSIDENT AIRMASS OVER CENTRAL NC THIS
MORNING...IN THE WAKE OF PRONOUNCED SHORTWAVE ENERGY LOCATED
OFFSHORE THE MID-ATLANTIC COAST AT 14Z. ALTHOUGH SFC DEWPOINTS HAVE
FALLEN INTO THE MID/UPPER 60S IN MOST AREAS AND LOW-LEVEL MOISTURE
HAS CERTAINLY DECREASED IN COMPARISON TO YESTERDAY...SUFFICIENT LOW-
LEVEL MOISTURE STILL EXISTS FOR MARGINAL DIURNAL DESTABILIZATION
WITH MLCAPE PROGGED IN THE 250-1000 J/KG RANGE...LOWEST NEAR THE VA
BORDER AND HIGHEST NEAR THE SC BORDER. SHALLOW LOW-LEVEL CONVERGENCE
ALONG THE STALLED FRONT SHOULD REMAIN SOUTH OF CENTRAL NC TODAY...
AND WOULD BE MORE LIKELY TO SERVE AS A FOCUS FOR CONVECTIVE
DEVELOPMENT OVER CENTRAL/UPSTATE SC WHERE GREATER DESTABILIZATION IS
EXPECTED. CYCLONIC FLOW ALOFT WILL PERSIST OVER THE REGION TODAY...
AND SUBSIDENCE IN THE WAKE OF EXITING SHORTWAVE ENERGY SHOULD
EFFECTIVELY SUPPRESS DEVELOPMENT THROUGH THE AFTERNOON. ADDITIONAL
SHORTWAVE ENERGY (UPSTREAM IN IL/IN AT 14Z) WILL TRACK INTO THE
SOUTHERN MID-ATLANTIC LATE TONIGHT...HOWEVER...DPVA ASSOC/W THIS
FEATURE WILL OCCUR WELL INTO THE NOCTURNAL COOLING CYCLE...WITH
LITTLE OR NO INSTABILITY AND NO CHANCE FOR CONVECTION. LOWS IN THE
MID/UPPER 60S TONIGHT. -VINCENT

&&

.SHORT TERM /SATURDAY THROUGH MONDAY NIGHT/...
AS OF 300 PM FRIDAY...

SAT/SAT NIGHT: THE MEAN TROUGH AXIS OVER THE EASTERN US WILL SHIFT
OFFSHORE ON SAT...WITH CYCLONIC FLOW ALOFT SHIFTING INTO THE
ATLANTIC AND AN INCREASINGLY NW FLOW ALOFT OVER THE CAROLINAS. WITH
STRONG INSOLATION AND LINGERING LOW-LEVEL MOISTURE...DIURNAL
DESTABILIZATION WILL BE BETTER THAN TODAY WITH MLCAPE VALUES PROGGED
AT 500-1500 J/KG. SUBSIDENCE ON THE WESTERN PERIPHERY OF THE
OFFSHORE TROUGH SHOULD SUPPRESS CONVECTIVE DEVELOPMENT FOR MOST (IF
NOT ALL) OF THE DAY SAT...WITH FORCING OTHERWISE CONFINED TO VERY
SHALLOW CONVERGENCE ASSOC/W A PIEDMONT SFC TROUGH. UNLESS POTENT
SHORTWAVE ENERGY PROGRESSES INTO THE REGION IN NW FLOW ALOFT DURING
THE EVENING HOURS (DOES NOT APPEAR LIKELY AT THIS TIME)...ANTICIPATE
LITTLE CHANCE FOR TOWERING CU TO SURVIVE WITHIN AN OTHERWISE DRY/
HOSTILE AIRMASS. HIGHS IN THE LOWER 90S...LOWS IN THE LOWER TO MID
70S. -VINCENT

SUN/SUN NIGHT: A SHORTWAVE TROUGH MOVING OUT OF CANADA AND ACROSS
THE GREAT LAKES SUNDAY WILL BEGIN THE AMPLIFICATION OF THE LONGWAVE
PATTERN FOR NEXT WEEK.  EXPECT CONVECTION CONVECTION TO BE ONGOING
OVER THE CENTRAL APPALACHIANS EARLY SUNDAY....WHICH SHOULD CONTINUE
EAST INTO VA AND MAY BLEED SOUTH ALONG OUTFLOW INTO THE NORTHERN
PORTIONS OF THE CWA. THE 12Z GFS BACKED OFF SIGNIFICANTLY ON THE
COVERAGE OF CONVECTION OVER VA...SO CHANCE POPS ACROSS THE NORTHERN
PIEDMONT AND COASTAL PLAIN ARE STILL A LITTLE UNCERTAIN.  THE BIGGER
STORY ON SUNDAY WILL BE THE HEAT AND HUMIDITY...AS DEEP MIXING AND
850MB TEMPS IN EXCESS OF 21C WILL LEAD TO HIGHS IN THE MID AND UPPER
90S.  THE GFS EVEN SUGGESTS 100 IN A FEW SPOTS.  MIXING WILL DROP
DEWPOINTS A BIT...ESPECIALLY WEST OF THE PIEDMONT TROUGH...BUT TO
THE EAST DEWPOINTS ARE FORECAST TO REMAIN IN THE UPPER 60S TO AROUND
70.  THE RESULTING HEAT INDEX VALUES ARE IN THE 100-105 RANGE FOR A
FEW HOURS AND MAY NECESSITATE A HEAT ADVISORY.  A SOUTHWEST WIND
WILL CONTINUE OVERNIGHT SUNDAY NIGHT AND LOWS WILL BE MUGGY IN THE
MID TO EVEN UPPER 70S.

MON/MON NIGHT: A STRONG COLD FRONT APPROACHING FROM THE NORTHWEST
WILL CROSS THE CWA ON MONDAY AS ADDITIONAL SHORTWAVE ENERGY DIVES
THROUGH THE BACKSIDE OF THE UPPER TROUGH.  UNSEASONABLY STRONG 40-
60M HEIGHT FALLS OVERSPREADING WHAT IS EXPECTED TO BE A MOIST AND
MODERATELY UNSTABLE AIRMASS WILL AID IN THE DEVELOPMENT OF STORMS
ALONG AND AHEAD OF THE FRONT.  BASED ON 40-50KT OF 0-6KM BULK SHEAR
ASSOCIATED WITH THE DEEP PUSH OF THE STRONG WESTERLIES AND
LONG...THERE IS GOOD CONFIDENCE THAT SUPERCELLS WITH A LARGE HAIL
AND DAMAGING WIND THREAT WILL BE POSSIBLE.  THE BIGGEST QUESTION
WILL BE EXACTLY WHERE THE LEE TROUGH SETS UP AND HOW MUCH DEWPOINTS
MIX OUT AS WEST-SOUTHWESTERLY LOW-LEVEL FLOW STRENGTHENS.  EAST OF
THE TROUGH...MOST LIKELY FROM US HWY 1 EAST...MODERATE INSTABILITY
IS EXPECTED WITH FAIRLY STEEP MID-LEVEL LAPSE RATES OF -6C/KM TO
MAYBE EVEN -7C/KM.  FORECAST SOUNDINGS ALSO SHOW RATHER DRY MID-
LEVEL AIR...THOUGH THE FORCING AND INSTABILITY SHOULD BE ABLE TO
OVERCOME THIS...AND THE DRY AIR WILL LIKELY ENHANCE DAMAGING WIND
THREAT.  AT THE MOMENT...CONFIDENCE IS STRONG THAT SEVERE WEATHER
WILL BE POSSIBLE...BUT THE UNCERTAINTY LIES HOW FAR EAST STORMS WILL
DEVELOP AND THE OVERALL COVERAGE.  HIGHS MONDAY WILL BE IN THE LOW
TO MID 90S. -BLS

&&

.LONG TERM /TUESDAY THROUGH FRIDAY/...
AS OF 300 PM FRIDAY...

IN THE WAKE OF THE THE FRONT ON MONDAY MEDIUM RANGE ENSEMBLES AND
DETERMINISTIC MODELS SHOW AN UNSEASONABLY DEEP UPPER TROUGH
DEVELOPING OVER THE EASTERN US BY MID WEEK WITH AN UPPER LOW
CENTERED JUST SOUTH OF THE HUDSON BAY.  MOST OF THE WEEK APPEARS TO
BE STABLE WITH HIGH PRESSURE SETTLING ACROSS THE MID-ATLANTIC STATES
AND DEWPOINTS IN THE UPPER 50S AND LOWER 60S. LOW-LEVEL THICKNESSES
ARE PROGGED TO DIP BELOW 1390M...WHICH SUGGESTS HIGHS IN THE LOW/MID
90S AND LOWS IN THE LOW/MID 60S... POSSIBLY TOUCHING THE UPPER 50S
IN THE COOLEST SPOTS. MORE UNCERTAINTY ARISES LATER IN THE WEEK WITH
MODELS SHOWING SOME DEGREE OF FLOW SEPARATION WHERE AN UPPER LOW
CUTS OFF AND DRIFTS SOUTH.  WHETHER OR NOT THIS OCCURS REMAINS TO BE
SEEN...SO AT THIS POINT WILL JUST HAVE A SLIGHT CHANCE POP BY FRIDAY
AS MOISTURE STARTS TO INCREASE BACK ACROSS THE AREA.

&&

.AVIATION /18Z FRIDAY THROUGH WEDNESDAY/...
AS OF 200 PM FRIDAY...

24-HR TAF PERIOD: VFR CONDITIONS WILL PREVAIL THROUGH THE MAJORITY
OF THE TAF PERIOD IN ASSOC/W A DRY AND SUBSIDENT AIRMASS IN THE WAKE
OF THE RECENT COLD FRONTAL PASSAGE...WITH LIGHT/VARIABLE WINDS
THROUGH TONIGHT. THE ONLY EXCEPTION TO THE ABOVE WILL BE A POTENTIAL
FOR REDUCED VISBYS IN FOG OR LOW CEILINGS WITH STRATUS DURING THE
PRE-DAWN HOURS SATURDAY MORNING (08-13Z)...AND A LOW CHANCE FOR AN
ISOLD SHOWER OR STORM AT THE FAY TERMINAL LATE THIS AFTERNOON.

LOOKING AHEAD: EXPECT A CHANCE FOR AFTERNOON SHOWERS/STORMS OVER THE
WEEKEND INTO EARLY NEXT WEEK...ESPECIALLY ON MONDAY WHEN THE
ENVIRONMENT WOULD SUPPORT SEVERE THUNDERSTORMS DURING THE AFTERNOON
AND EVENING HOURS. -VINCENT

&&

.RAH WATCHES/WARNINGS/ADVISORIES...
NONE.

&&

$$

SYNOPSIS...VINCENT
NEAR TERM...VINCENT
SHORT TERM...VINCENT/BLS
LONG TERM...BLS
AVIATION...VINCENT


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