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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS62 KRAH 231055
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
652 AM EDT WED JUL 23 2014

.SYNOPSIS...ATLANTIC HIGH PRESSURE WILL EXTEND WESTWARD OVER THE
CAROLINAS TODAY. A COLD FRONT WILL APPROACH FROM THE NORTHWEST
TONIGHT... THEN PUSH SOUTHEAST THROUGH NORTH CAROLINA THURSDAY AND
THURSDAY NIGHT. WEAK HIGH PRESSURE WILL PUSH IN FROM THE NORTH ON
FRIDAY.

&&

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

FOR TODAY/TONIGHT: ISOLATED SHOWERS ON THE PERIPHERY OF THE ATLANTIC
RIDGE OFF THE SOUTHEAST COAST HAVE ALL BUT DIED OFF THIS MORNING.
PATCHY FOG AND STRATUS WILL HOLD UNTIL SOON AFTER DAYBREAK
(PRIMARILY OVER THE ERN HALF OF THE CWA)... FOLLOWED BY A TREND TO
PARTLY TO MOSTLY SKIES AS A LIGHT SW SURFACE BREEZE INDUCES MIXING
AND DISPERSION OF THE LOW LEVEL MOISTURE. DEEP LAYER SHEAR REMAINS
LOW TODAY (10-15 KTS) WITH MARGINAL INSTABILITY (MLCAPE PEAKING AT
500-1000 J/KG) WITH MODEST MID LEVEL LAPSE RATES OF 5.5-6.0 C/KM.
DYNAMICALLY WE SHOULD BE IN A RELATIVE LULL ZONE TODAY WITH THE MID
LEVEL RIDGE CENTERED OFF THE SE COAST CONTINUING TO NOSE WESTWARD
OVER THE SOUTHEAST... WHILE ENERGY DIVES FROM THE UPPER MIDWEST
SOUTHEASTWARD TOWARD THE WRN OH VALLEY... HELPING DIG THE TROUGH
JUST TO OUR NW TONIGHT AS THE ASSOCIATED SURFACE FRONT APPROACHES.
PW VALUES REMAIN ELEVATED (1.7-2.1)... SO STILL EXPECT SCATTERED
SHOWER/STORM ACTIVITY TODAY... BUT THE LACK OF DEEP SHEAR AND
CONVECTIVE FOCUS AND THE WEAK MID LEVEL FLOW WILL HAMPER STORM
ORGANIZATION AND STRENGTH. BOTH THE TRADITIONAL AND CONVECTION-
ALLOWING MODELS BEAR THIS OUT WITH LIMITED COVERAGE TODAY... ALONG
WITH A SHIFT IN BEST LOW LEVEL MOISTURE TRANSPORT TO COASTAL
SECTIONS. WILL KEEP POPS AT 25-35% TODAY... PEAKING DURING THE
TYPICAL MID-LATE AFTERNOON... AND TAPERING DOWN IN THE MID-LATE
EVENING AS THE BOUNDARY LAYER STABILIZES AND PW DIPS SLIGHTLY. HIGHS
89-93 WITH NEAR-NORMAL THICKNESSES AND SOME SUNSHINE. LOWS 69-74
UNDER PARTLY TO MOSTLY CLOUDY SKIES. -GIH

&&

.SHORT TERM /THURSDAY THROUGH THURSDAY NIGHT/...
AS OF 315 AM WEDNESDAY...

MUCH OF THE CWA SHOULD SEE SHOWERS/STORMS AT SOME POINT THU. THE MID
LEVEL TROUGH DIGS JUST WEST OF THE FORECAST AREA EARLY THU... WITH
PROJECTED HEIGHT FALLS OF 30-50 M OVER NC. THE ACCOMPANYING SURFACE
FRONT IS EXPECTED TO REACH THE SPINE OF THE APPALACHIANS EARLY THU
MORNING... THEN EASE SLOWLY EASTWARD INTO CENTRAL NC DURING THE
AFTERNOON WITH SURFACE LOW PRESSURE FORMING ALONG THE FRONT AS DPVA
ALOFT STRENGTHENS. THIS IMPROVING DYNAMIC FORCING FOR ASCENT WILL
ATTEND STRENGTHENING MID LEVEL WINDS AND GREATER DEEP LAYER SHEAR OF
30-35 KTS. INSTABILITY COULD HOLD ON THE LOW SIDE HOWEVER... AS
MODELS SHOW MUCAPE TOPPING OUT AT 1000-2000 J/KG OVER THE
CENTRAL/ERN CWA... WHICH COULD BE A FUNCTION OF THE EARLY ARRIVAL OF
THE DYNAMIC LIFT AS SUGGESTED BY TRADITIONAL MODELS (WHICH SHOW GOOD
QPF COVERAGE OVER THE NRN/WRN CWA PRIOR TO 18Z) AS WELL AS THE HIGH-
RES WRF-NMM/ARW AND THE (NAM-HEAVY) SREF PROBABILITIES. WILL BRING
IN MID RANGE CHANCE POPS OVER THE NW CWA BY LATE MORNING...
SPREADING EAST OVER THE REST OF THE CWA DURING THE AFTERNOON...
BEFORE ENDING WNW TO ESE FROM LATE AFTERNOON THROUGH THE EVENING.
DID KEEP A LOW CHANCE OF LINGERING SHOWERS OVER THE SOUTHEAST CWA
THROUGH THE NIGHT GIVEN THAT THE FRONTAL ZONE COULD BECOME STALLED
OUT THERE... AND THE INCOMING SURFACE HIGH PRESSURE WILL STILL BE
CENTERED OVER IN/OH OVERNIGHT... NOT A FAVORABLE LOCATION FOR THE
MORE DENSE AIR TO BE ABLE TO GET OVER THE MOUNTAINS. THE RISK OF A
FEW SEVERE STORMS REMAINS... BOOSTED BY THE LARGE SCALE FORCING FOR
ASCENT AND THE IMPROVING KINEMATICS... BUT IF THE CONVECTION COMES
IN EARLIER IN THE DAY AS EXPECTED... THIS WILL CUT DOWN ON HEATING
AND RESULTING INSTABILITY OVER ALL BUT THE FAR SE CWA. AND MARGINAL
MID LEVEL LAPSE RATES (BARELY APPROACHING 6.0) SHOULD LIMIT THE
LARGE HAIL THREAT. BUT WITH THE RELATIVE VIGOROUS NATURE OF THIS
SYSTEM (FOR JULY) AND POSSIBLE MODERATE INSTABILITY... WILL CONTINUE
THE MENTION OF AN ISOLATED SEVERE STORM OR TWO ESPECIALLY FROM THE
TRIANGLE SOUTH AND EAST... HIGHLIGHTING DAMAGING WINDS AS THE
PRIMARY THREAT. HIGHS 84 NW TO 93 SE. LOWS 64 NW TO 73 SE.
-GIH

&&

.LONG TERM /FRIDAY THROUGH TUESDAY/...
AS OF 240 AM WEDNESDAY...

FRIDAY AND FRIDAY NIGHT: THE SURFACE FRONT AND THE UPPER LEVEL
TROUGH WILL MOVE EAST OF MUCH OF CENTRAL NC BY FRIDAY...WITH WINDS
VEERING TO THE NORTHWEST AND COOL HIGH PRESSURE BUILDING IN. IT
APPEARS THAT THE COOLEST AIR MAY ONLY MAKE IT INTO THE FAR NW ON
FRIDAY AS WEAK LOW PRESSURE IS EXPECTED TO SIT ALONG THE CAROLINA
COAST FRIDAY AND FRIDAY NIGHT. HIGHS ON FRIDAY IN THE MID TO UPPER
80 WITH LOWS IN THE MID 60S TO AROUND 70 DEGREES EXPECTED. GIVEN THE
LINGERING SFC LOW ALONG THE COAST AND THE FRONT STALLING IN THAT
GENERAL VICINITY...THERE WILL BE THE CHANCE FOR ADDITIONAL SHOWERS
AND STORMS ON FRIDAY...MAINLY ACROSS THE SOUTHEAST. PWATS WILL
DECREASE TO UNDER AN INCH FOR FRIDAY AS MID LEVEL DRY AIR IS
ADVECTED INTO THE REGION.

SATURDAY THROUGH TUESDAY: THERE MAY BE A LINGERING CHANCE FOR SOME
CONVECTION IN THE EAST SATURDAY WITH A SURFACE TROUGH AND WARM
SOUTHERLY FLOW SETTING UP ALONG THE CAROLINA COAST. OTHERWISE...
EXPECT MAINLY DRY WEATHER FOR MUCH OF THE AREA AS THE UPPER LEVEL
TROUGH SHIFTS OFFSHORE. HIGHS WILL BE GENERALLY IN THE UPPER 80S TO
LOW 90S AND LOWS IN THE UPPER 60S TO LOW 70S. THE PIEDMONT TROUGH
WILL REMAIN IN PLACE SUNDAY AND SUNDAY NIGHT AS ANOTHER FRONTAL
SYSTEM APPROACHES FROM THE WEST. EXPECT INCREASING CHANCES FOR
CONVECTION...DIURNAL IN NATURE...SUNDAY AND MONDAY AS THE FRONT
APPROACHES. ALTHOUGH THE TIMING OF THIS SYSTEM IS STILL A BIT
UNCERTAIN...AS IS THE MODEL FORECAST PRECIPITATION...EXPECT THE BEST
CHANCE OF CONVECTION ON MONDAY. AS OF THE LATEST (00Z) GFS MODEL
RUN...THE FRONT SHOULD MOVE THROUGH THE AREA MONDAY NIGHT...WITH
COOLER AND DRIER CONDITIONS FOR TUESDAY. SUNDAY SHOULD BE THE
WARMEST DAY...HIGHS IN THE LOW TO MID 80S AND LOWS IN THE LOW TO MID
70S. TEMPERATURES ON MONDAY WILL DEPEND ON THE TIMING OF THE FRONT
AND ITS ASSOCIATED CONVECTION...BUT FOR NOW WILL FORECAST HIGHS A
FEW DEGREES COOLER THAN SUNDAY...MID 80S TO AROUND 90 DEGREES.
NOTICEABLE TEMPERATURE CHANGE MONDAY NIGHT AND TUESDAY...WITH LOWS
IN THE MID 60S TO AROUND 70 DEGREES AND HIGHS IN THE LOW TO MID 80S.

&&

.AVIATION /12Z WEDNESDAY THROUGH SUNDAY/...
AS OF 652 AM WEDNESDAY...

AT INT/GSO... VFR CONDITIONS HAVE PREVAILED... WHILE CIGS/VSBYS HAVE
DROPPED TO IFR/LIFR AT RDU/FAY/RWI OVER THE LAST SEVERAL HOURS DUE
TO WET GROUND AND LIGHT WINDS. THESE POOR AVIATION CONDITIONS WILL
GRADUALLY IMPROVE THROUGH 14Z... RISING TO MVFR THEN VFR WITH THE
ONSET OF HEATING AND MIXING TO DISPERSE THE FOG AND STRATUS. VFR
CONDITIONS ARE LIKELY FROM 15Z ON THROUGH THE DAY AS CIGS LIFT AND
BREAK UP WITH MIXING... WITH SURFACE WINDS FROM THE SW AT 8-12 KTS.
ANY SHOWERS/STORMS WILL BE ISOLATED OR IN SMALL CLUSTERS... AND THE
CHANCE OF THEM AFFECTING TAF SITES IS TOO SMALL TO INCLUDE IN THE
TAFS AT THIS TIME. VFR CONDITIONS SHOULD PREVAIL THROUGH 06Z EXCEPT
AT RWI... WHICH MAY SEE MVFR VSBYS IN FOG AFTER 03Z. EXCEPT FOR THIS
LIGHT FOG AT RWI... VFR CONDITIONS SHOULD HOLD ELSEWHERE OVERNIGHT
WITH A LIGHT BREEZE FROM THE SW.

LOOKING BEYOND 12Z EARLY THU MORNING... AN APPROACHING COLD FRONT
WILL BRING NUMEROUS SHOWERS AND STORMS WITH SUB-VFR CONDITIONS
STARTING LATE THU MORNING (15Z-18Z) AT INT/GSO BEFORE SPREADING EAST
TO RDU DURING THE EARLY AFTERNOON AND TO RWI/FAY DURING THE MID-LATE
AFTERNOON. THE FRONT MAY SLOW DOWN OVER COASTAL SECTIONS THU
NIGHT/FRI... KEEPING A CHANCE OF SUB-VFR SHOWERS/STORMS FRI
AFTERNOON... BUT OTHERWISE VFR CONDITIONS ARE EXPECTED FRI-SAT AS
HIGH PRESSURE NOSES IN FROM THE NORTH. AN UPPER LEVEL DISTURBANCE
WILL MOVE IN FROM THE NORTHWEST ON SUNDAY... POTENTIALLY BRINGING
ANOTHER ROUND OF SHOWERS/STORMS. -GIH

&&

.RAH WATCHES/WARNINGS/ADVISORIES...
DENSE FOG ADVISORY IN EFFECT UNTIL 9 AM FOR
NCZ007>011-023>028-040-041-043-076.

&&

$$

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