Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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FXUS62 KRAH 250744
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
343 AM EDT FRI JUL 25 2014

.SYNOPSIS...A COLD FRONT PUSHING SOUTHEAST THROUGH THE REGION EARLY
THIS MORNING WILL WEAKEN AND STALL NEAR THE SOUTH CAROLINA BORDER
LATER TODAY...AS WEAK HIGH PRESSURE BUILDS IN FROM THE NORTH. THIS
FRONT WILL DISSIPATE OVER THE WEEKEND AS SOUTHWEST FLOW RETURNS. A
STRONGER COLD FRONT WILL MOVE THROUGH THE REGION EARLY NEXT WEEK.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 255 AM FRIDAY...

WITH THE COLD FRONT HAVING PUSHED SOUTHWARD THROUGH MUCH OF NC...
ASIDE FROM VARIABLY CLOUDY SKIES TODAY... MUCH OF CENTRAL NC WILL
SEE IMPROVED WEATHER CONDITIONS... WITH THE EXCEPTION OF THE SE AND
FAR SRN CWA. LAST NIGHT`S WIDESPREAD CONVECTION HAS SHIFTED OFF THE
COAST... ALONG WITH A LEADING PROMINENT SHORTWAVE TROUGH SWINGING
THROUGH THE BASE OF A WEAKENING TROUGH COVERING THE ERN THIRD OF
NOAM. THE LOCATION OF THE COLD FRONT IS NOT EASY TO SPECIFY ON THE
LATEST SURFACE MAP AS IT APPEARS TO HAVE MERGED WITH THE PREFRONTAL
TROUGH... BUT IT LOOKS TO STRETCH FROM THE NC COASTAL AREA BACK
ACROSS SRN NC AND NRN GA/AL. SURFACE WINDS HAVE SHIFTED AROUND TO
LIGHT N OR NE AREAWIDE... AND THESE LIGHT SPEEDS COMBINED WITH
STABILIZING LOW LEVELS POST-FRONT AND PLENTY OF RESIDUAL LOW LEVEL
MOISTURE HAVE KEPT AREAS OF LOW CLOUDS OVER CENTRAL NC... CLOUDS
THAT WILL BE SLOW TO DISLODGE/DISPERSE DESPITE LIMITED CLOUDINESS
ABOVE. AS SUCH... EXPECT VARIABLY CLOUDY SKIES TODAY... WITH A BIT
LOWER HUMIDITY LEVELS ESPECIALLY NORTH OF 64. THE FRONT IS EXPECTED
TO REMAIN ACROSS SRN NC TODAY AS WEAK HIGH PRESSURE NOW CENTERED
OVER NRN OH BUILDS IN... AND WHILE PW WILL SLIP TO NEAR/BELOW NORMAL
VALUES OVER MOST OF CENTRAL NC... SOUTHERN SECTIONS SHOULD HOLD NEAR
2.0 INCHES. WITH ELEVATED DEW POINTS PERSISTING THERE ALONG WITH
WEAK DPVA AND LINGERING WEAK UPPER DIVERGENCE... THE RISK OF
SHOWERS/STORMS WILL CONTINUE ON OUR SOUTH... FOCUSED THROUGH THE
AFTERNOON AND EARLY EVENING. A STORM OR TWO COULD BECOME STRONG
GIVEN THAT DEEP LAYER SHEAR SHOULD STILL BE 25-30 KTS WITH MODELS
SHOWING MUCAPE OF 1000-2000 J/KG... ALTHOUGH THIS RISK WITH BE LOWER
IF THE THICKER LOW CLOUDS HANG ON LONGER AND INHIBIT INSOLATION.
ISOLATED SHOWERS ARE A GOOD BET OVER THE REST OF THE FORECAST AREA
THIS MORNING WITH A LOBE OF VORTICITY SWINGING THROUGH THE AREA...
BUT LATE MORNING THROUGH THE AFTERNOON SHOULD BE DRY OUTSIDE OF THE
AFOREMENTIONED SOUTHERN SECTIONS WITH 20-30 M HEIGHT RISES. HIGHS 84-
89... IN LINE WITH THICKNESSES THAT ARE PROJECTED TO BE 15-20 M
BELOW NORMAL. MOISTURE PERSISTING BENEATH THE SUBSIDENCE INVERSION
ALOFT SHOULD TRANSLATE TO PARTLY CLOUDY SKIES TONIGHT. HAVE HELD
ONTO LOWS IN THE 66-71 RANGE. -GIH

&&

.SHORT TERM /SATURDAY THROUGH SATURDAY NIGHT/...
AS OF 325 AM FRIDAY...

EXPECT A LARGELY DRY DAY WITH INCREASED SUNSHINE. THE WEAKENING MID
LEVEL TROUGH AXIS WILL SHIFT OFF THE COAST WITH MODEST HEIGHT RISES
CONTINUING OVER NC. THE QUICKLY WEAKENING SURFACE FRONTAL ZONE NEAR
THE NC/SC BORDER WILL FALL APART AND BE OVERTAKEN BY INCREASING LOW
LEVEL SOUTHWEST FLOW AND DEVELOPMENT OF A WEAK PIEDMONT TROUGH. PW
IS EXPECTED TO BE AT OR UNDER 1.2 INCHES TO START THE DAY... BUT IS
FORECAST TO REBOUND TO AROUND 1.8 INCHES IN STRIP FROM CENTRAL VA
THROUGH CENTRAL NC BY LATE AFTERNOON... WHICH THEN DRIFTS TO ERN NC
SAT NIGHT. CORRESPONDINGLY THE MODELS DEPICT MODERATE INSTABILITY...
MUCAPE OF 1000-1500 J/KG ON THE GFS LATE IN THE DAY... WITH AROUND
1000 J/KG LINGERING IN THE FAR EAST OVERNIGHT. BUT THE MODELS
GENERATE LITTLE MORE THAN AN ISOLATED SHOWER OR STORM AS THE COLUMN
REMAINS WARM/STABLE AND DRY THROUGH THE 850-500 MB LAYER. WILL KEEP
THE FORECAST DRY... AS ANY CONVECTION WOULD BE EXTREMELY ISOLATED.
THICKNESSES REBOUND TO JUST 5-10 M BELOW NORMAL... WHICH WITH DECENT
SUNSHINE SUPPORTS HIGHS OF 89-93. LOWS 69-74... MILDER THAN TONIGHT
DUE TO THE RETURN OF HIGHER DEWPOINTS. -GIH

&&

.LONG TERM /SUNDAY THROUGH THURSDAY/...
AS OF 335 AM FRIDAY...

MEDIUM RANGE GUIDANCE IS IN EXCELLENT AGREEMENT REGARDING THE
DEVELOPMENT OF HIGH AMPLITUDE/UNSEASONABLY MERIDIONAL FLOW ACROSS
NOAM THROUGH MID-WEEK - INCLUDING A DEEP TROUGH CENTERED NEAR 80-85W
AND ASSOCIATED 3 STANDARD DEVIATION NEGATIVE HEIGHT ANOMALY CENTERED
OVER THE LOWER OH VALLEY - WITH SLIGHT RETROGRESSION AND RELAXATION
OF THE FLOW BY TH END OF THE PERIOD.

SUN AND SUN NIGHT: HOT...WITH PROJECTED H85 TEMPERATURES AROUND 22-
23 C OVER THE CAROLINAS AS THE MID LEVEL RIDGE OVER THE DESERT SW
AND PLAINS BUILDS BRIEFLY EAST IN ADVANCE OF THE AMPLIFYING TROUGH
ALOFT.  THE FOCUS FOR CONVECTION WILL BE DIRECTED FROM THE LOWER OH
VALLEY EAST ACROSS THE VIRGINIAS...WHERE THE AMPLIFYING TROUGH ALOFT
WILL MAXIMIZE HEIGHT FALLS ALOFT/RIGHT JET ENTRANCE REGION
DIVERGENCE. SOME OF THIS ACTIVITY MAY DEVELOP SOUTHWARD INTO THE
NORTHERN AND WESTERN PIEDMONT LATE IN THE DAY AND ESPECIALLY DURING
THE EVENING HOURS...AS BOTH LARGER SCALE FORCING AND OUTFLOW FROM
UPSTREAM CONVECTION SPREADS SSE. FORECAST GUIDANCE SUGGESTS THE HOT
AND DEEP DRY ADIABATICALLY-MIXED BOUNDARY LAYER WILL BE TOPPED BY
STEEP (7 C/KM) LAPSE RATES ALL THE WAY THROUGH THE MID LEVELS. THE
RESULT WILL BE MODERATE TO STRONG INSTABILITY AMIDST 30-35 KTS OF
MID LEVEL FLOW...SUPPORTIVE OF MOSTLY MULTI-CELLULAR ORGANIZATION...
WITH PERHAPS A FEW SUPERCELLS NEAR AND JUST NORTH OF THE VA BORDER.
LARGE HAIL...AND DAMAGING WIND GUSTS AIDED BY SUB-CLOUD ACCELERATION
OWING SFC DEWPOINT DEPRESSIONS OF 25-30 C KM...WILL POSE A SVR
THREAT. THIS THREAT SHOULD BE MAXIMIZED INVOF THE VA BORDER...BEFORE
INSTABILITY WANES AFTER SUNSET...AND SOUTHBOUND OUTFLOWS UNDERCUT
STORMS WITH MEAN WIND-DRIVEN ENE STORM MOTIONS. WARM OVERNIGHT...
WITH LOWS GENERALLY 73 TO 78 DEGREES.

MON AND MON NIGHT: LOW PREDICTABILITY ASSOCIATED WITH MESOSCALE
INFLUENCES (IE. OUTFLOW AND CLOUD COVER) FROM EARLIER CONVECTION SUN
NIGHT...AS WELL AS THE LIKELIHOOD OF STRONG WESTERLY/DOWNSLOPE H85
FLOW...COMPLICATE THE FORECAST FOR MON...DESPITE AN OTHERWISE STRONG
SYNOPTIC SIGNAL FOR UPWARD VERTICAL MOTION OVER NC. THE DOWNSLOPE
FLOW WILL LIKELY MIX OUT BL MOISTURE AND VEER THE LOW LEVEL FLOW
WEST OF A LEE/PRE-FRONTAL SFC TROUGH INVOF US HWY 1...SUCH THAT ONLY
A SLIGHT CHANCE POP IS WARRANTED THERE. BL MOISTURE AND CONVERGENCE
WILL BE MORE PLENTIFUL TO THE EAST...WHERE POP WILL GRADUATE INTO
THE LIKELY RANGE INVOF AND EAST OF I-95. CONTINUED STEEP LOW-MID
LEVEL LAPSE RATES AMIDST STRENGTHENING MID LEVEL FLOW INTO THE 40-50
KT RANGE WILL SUPPORT A GOOD CHANCE OF SVR STORMS...INCLUDING
SUPERCELLS...CAPABLE OF PRODUCING LARGE HAIL AND DAMAGING WIND
GUSTS. TORNADO PROBABILITIES WILL BE ONLY MARGINAL OWING TO LIMITED
SRH (GENERALLY BELOW 150 M2/S2)...AND BL/LCL HEIGHTS AROUND 5 K FT.

DRY AND COOLER CONDITIONS WILL PREVAIL THROUGN MID-WEEK...AS POST-
FRONTAL HIGH PRESSURE BUILDS INTO THE CENTRAL APPALACHIANS AND
PRECIPITABLE WATER VALUES FALL BELOW AN INCH OVER CENTRAL NC. HIGHS
AND LOWS ONLY IN THE LOWER TO MIDDLE 80S AND MID-UPPER 50S TO LOWER-
MID 60S...RESPECTIVELY...TUE-WED...BEFORE AIR MASS MODIFICATION
THROUGH THE END OF THE WEEK.

&&

.AVIATION /06Z FRIDAY THROUGH TUESDAY/...
AS OF 125 AM FRIDAY...

PROBLEMATIC AVIATION CONDITIONS EARLY THIS MORNING... AS SCATTERED
TO BROKEN CLOUDS BASED BETWEEN 600 AND 1400 FT AGL MEANDER ABOUT
CENTRAL NC. WITH THESE LOW CIGS EXPECTED TO COME AND GO THROUGH
DAYBREAK... THE TIMING OF MVFR/IFR CIGS IS MADE DIFFICULT. EXPECT
CIGS TO VARY BETWEEN VFR AND MVFR/IFR THROUGH DAYBREAK AT ALL SITES
AS THESE CLOUDS DRIFT OVER THE REGION... WITH MVFR/IFR DOMINATING.
MVFR CIGS ARE EXPECTED THROUGH THE MORNING AS THESE CLOUDS LIFT
SLOWLY... WITH CIGS NOT REACHING VFR UNTIL CLOSE TO 18Z... AND EVEN
AFTER THIS TIME AT FAY... CLOSE TO WHERE THE COLD FRONT IS EXPECTED
TO HAVE PUSHED BY AFTERNOON. A FEW SHOWERS AND ISOLD STORMS WILL BE
RESTRICTED TO NEAR FAY THIS AFTERNOON. VFR CIGS ARE EXPECTED TO
PERSIST THEN FROM MID AFTERNOON THROUGH THE END OF THE TAF PERIOD.
AS THE FRONT SETTLES SOUTH OF ALL TAF SITES THIS MORNING... EXPECT A
LIGHT BREEZE FROM THE NORTH TO DOMINATE THROUGH THE DAY.

LOOKING BEYOND 06Z EARLY SAT MORNING... EXPECT CONTINUED VFR CIGS
THROUGH DAYBREAK SAT... ALTHOUGH POCKETS OF IFR FOG ARE POSSIBLE 09Z-
13Z SAT MORNING... ESPECIALLY AT RWI/FAY. OTHERWISE... VFR
CONDITIONS ARE LIKELY TO DOMINATE THROUGH THE WEEKEND WITH HIGH
PRESSURE BUILDING IN... FOLLOWED BY A RESUMPTION OF SOUTHWEST FLOW
AND PIEDMONT TROUGH LATE IN THE WEEKEND. A COLD FRONT WILL APPROACH
FROM THE NW EARLY NEXT WORK WEEK... BRINGING THE POTENTIAL FOR SUB-
VFR SHOWERS/STORMS... PARTICULARLY MONDAY. -GIH

&&

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

&&

$$

SYNOPSIS...HARTFIELD
NEAR TERM...HARTFIELD
SHORT TERM...HARTFIELD
LONG TERM...MWS
AVIATION...HARTFIELD


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