Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000
FXUS62 KRAH 260612
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
210 AM EDT SAT JUL 26 2014

.SYNOPSIS...A SURFACE TROUGH WILL DEVELOP OVER THE WESTERN PIEDMONT
THIS WEEKEND...RESULTING IN A VERY WARM SOUTHWEST FLOW. A STRONG
COLD FRONT WILL CROSS THE AREA ON MONDAY.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 210 AM SATURDAY...

SHEARED S/W TROUGH AXIS WILL TRAVERSE THE AREA THIS MORNING...
RESULTING IN SCATTERED TO OCCASIONALLY BROKEN  MID AND HIGH CLOUDS.
SUBSIDENCE WILL FOLLOW IN ITS WAKE...COINCIDENT WITH PEAK AFTERNOON
HEATING...WHICH SHOULD LARGELY SUPPRESS CONVECTIVE RAIN CHANCES
TODAY AS FORCING WILL OTHERWISE BE CONFINED TO VERY SHALLOW
CONVERGENCE ASSOCIATED WITH THE DEVELOPING PIEDMONT SFC TROUGH.

LOW-LEVEL THICKNESSES ARE PROGGED TO REBOUND 20M FROM YESTERDAY AND
DESPITE SOME MORNING CLOUDS FROM BOTH S/W MOVING THROUGH THE AREA
ALONG WITH SLOW LIFTING/DISSIPATION OF MORNING STRATUS ANTICIPATE WE
SHOULD REACH FULL SUN READINGS. HIGHS IN THE UPPER 80S/NEAR 90 NORTH
TO LOWER 90S SOUTH. LOWS TONIGHT UNDER CLEAR SKIES IN THE LOWER TO
MID 70S.

&&

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

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 /06Z SATURDAY THROUGH WEDNESDAY/...
AS OF 130 AM SATURDAY...

24-HR TAF PERIOD: RESIDUAL LOW-LEVEL MOISTURE AND LIGHT SELY WINDS
WILL RESULT IN STRATUS OVERNIGHT AND POCKETS OF FOG OVERNIGHT.
CEILINGS OF IFR TO MVFR ARE POSSIBLE WITH GUIDANCE SUGGESTING THE
BEST FOG POTENTIAL IN THE EAST...NEAR KFAY AND KRWI...WHERE SFC
DEWPOINTS HAVE REMAINED IN THE LOWER 70S.

PERHAPS SOME LINGERING MVFR STRATOCUMULUS COULD LINGER INTO THE LATE
MORNING BEFORE VFR CONDITIONS RETURN BY EARLY AFTERNOON WITH OVERALL
DRY CONDITIONS EXPECTED.

LOOKING AHEAD: A COLD FRONT WILL APPROACH FROM THE NW SUNDAY/EARLY
NEXT WORK WEEK... BRINGING THE POTENTIAL FOR SHOWERS/STORMS AND SUB-
VFR CONDITIONS LATE SUNDAY (IN THE NORTHWEST) INTO MONDAY...
PARTICULARLY MONDAY (ESPECIALLY EAST). VFR CONDITIONS ARE EXPECTED
TO RETURN BEHIND THE FRONT ON TUESDAY AND CONTINUE THROUGH AT LEAST
MID WEEK.

&&

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

&&

$$

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


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