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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS62 KRAH 181849
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
250 PM EDT TUE JUN 18 2013

.SYNOPSIS...
-- Changed Discussion --
A COLD FRONT WILL APPROACH FROM THE NORTHWEST LATE TODAY...AND CROSS
THE REGION TONIGHT. HIGH PRESSURE WILL BUILD INTO CENTRAL NC FROM
THE NORTH WEDNESDAY THROUGH THURSDAY.
-- End Changed Discussion --

&&

.NEAR TERM /THROUGH TONIGHT/...
-- Changed Discussion --
AS OF 250 PM TUESDAY...

SLIGHT TO MODERATELY UNSTABLE AIR MASS RESIDES OVER CENTRAL NC AT
MID-AFTERNOON THANKS TO PEAKS OF SUN HEATING UP AN AIR MASS WITH SFC
DEWPOINTS IN THE UPPER 60S TO LOWER 70S. UPSTAIRS...A VORT MAXIMUM
OVER THE CENTRAL APPALACHIANS CONTINUES TO ROTATE EASTWARD WITH
ATTENDANT SHEAR AXIS EXTENDING SWWD ALONG THE SPINE OF THE SOUTHERN
APPALACHIANS. THIS MID LEVEL FEATURE AIDING TO ENHANCE THE 925-850MB
FLOW WHICH IS ADVECTING ADDITIONAL MOISTURE INTO THE COLUMN. LATEST
SATELLITE TOTAL BLEND PRECIP WATER PRODUCT DEPICTS VALUES BETWEEN
1.8-2 INCHES OVER OUR FORECAST AREA. THOUGH MID LEVEL LAPSE RATES
ARE MEAGER...ENOUGH JUICE EXISTS IN THE ATMOSPHERE TO SUPPORT THE
DEVELOPMENT OF NUMEROUS SHOWERS AND SCATTERED THUNDERSTORMS LATE
THIS AFTERNOON THROUGH EARLY EVENING AS THE MID LEVEL SHEAR AXIS
CROSSES THE REGION. CURRENT 0-6KM SHEAR VALUES IN THE 30-40KT RANGE
OVER THE NW PIEDMONT SUPPORT THE IDEA OF CONVECTION FORMING INTO A
LINE AS IT MARCHES EAST-SE. CANNOT RULE OUT THE POSSIBILITY OF AN
ISOLATED STRONG-SEVERE STORM WITH WIND GUSTS 40-50 MPH. STILL
BELIEVE MAIN WEATHER HAZARD WILL BE TORRENTIAL DOWNPOURS WITH
RAINFALL RATES 2-3 INCHES PER HOUR POSSIBLE IN A FEW OF THE STORMS.
FORTUNATELY STEERING WINDS CLOSE TO 25KTS SO STORMS WITH THIS
MAGNITUDE OF RAIN SHOULD NOT SETTLE OVER ONE SPOT VERY LONG. BULK OF
CONVECTIVE ALLOWING MODELS AS WELL AS THE 11Z HRRR SUGGEST THE
BROKEN LINE OF CONVECTION CROSSING THE PIEDMONT BETWEEN
21Z-00Z...AND INTO THE SANDHILLS AND COASTAL PLAIN 23Z-02Z.

PLAN TO MAINTAIN CATEGORICAL POPS IN THE NW PIEDMONT LATE THIS
AFTERNOON THEN SPREAD THESE HIGHER POPS SEWD WITH TIME. WILL
INTRODUCE DECREASING POPS BY EARLY EVENING IN THE NW PIEDMONT...THEN
TREND POPS LOWER OVER THE REMAINDER OF THE FORECAST BETWEEN 02Z-06Z.

OVERNIGHT...SFC COLD FRONT WILL PROGRESS SEWD AND SHOULD LIE WSW-ENE
ACROSS OUR FAR SOUTHERN-SE COUNTIES AT DAYBREAK. THIS FEATURE
SHOULD INTERACT WITH AVAILABLE MOISTURE TO TRIGGER SCATTERED SHOWERS
OVERNIGHT. STILL MUGGY OVERNIGHT THOUGH THE FAR N-NW SECTIONS MAY
START TO FEEL A LITTLE LESS HUMID BY DAYBREAK. MIN TEMPS MID 60S TO
NEAR 70.
-- End Changed Discussion --

&&

.SHORT TERM /WEDNESDAY AND WEDNESDAY NIGHT/...
-- Changed Discussion --
AS OF 250 PM TUESDAY...

STRONGER S/W IN THE NORTHERN STREAM WILL CROSS THE NORTHERN
MID ATLANTIC WHILE THE TAIL END OF THE SHEAR AXIS APPROACHES OUR
NORTHERN COUNTIES BY EARLY EVENING. NLY FLOW BEHIND THE INITIAL MID
LEVEL TROUGH WILL ADVECT DRIER AND SLIGHTLY MORE STABLE AIR INTO
CENTRAL NC. WHILE CLOUDS WILL LIKELY STICK AROUND DUE TO RESIDUAL
MOISTURE AND CYCLONIC CURVATURE IN THE MID LEVEL FLOW...CONVECTIVE
COVERAGE SHOULD BE LESS NUMEROUS WEDNESDAY AFTERNOON AND NOT AS
ROBUST. EXPECT TWO MAIN AREAS OF PRECIP...ONE OVER THE FAR SOUTH IN
VICINITY OF THE NEARLY STATIONARY SFC FRONT...AND THE OTHER OVER THE
FAR NORTH AHEAD OF THE SWD ADVANCING MID LEVEL SHEAR AXIS. PLAN TO
CAP POPS NO HIGHER THAN 50 PERCENT (NEAR SC BORDER) WITH A 1-IN-3
CHANCE ACROSS THE NORTH. AS ATMOSPHERE STABILIZES IN THE EARLY
EVENING...EXPECT MAJORITY OF THE CONVECTION TO DISSIPATE THOUGH A
STRAY SHOWER MAY STILL OCCUR IN VICINITY OF THE SHEAR AXIS ACROSS
THE NORTH. THIS SHEAR AXIS WILL CONTINUE TO PROGRESS SE OVERNIGHT
AND EXIT THE REGION BY DAYBREAK THU. SUBSIDENCE BEHIND THIS FEATURE
WILL AID TO DISSIPATE THE CLOUD COVERAGE AFTER MIDNIGHT.

EXPECT A FAIRLY UNIFORM TEMP FIELD WEDNESDAY DUE TO CLOUD COVERAGE
AND LOW LEVEL COLD AIR ADVECTION. MAX TEMPS NEAR 80 NORTH TO LOWER
80S SOUTH. MIN TEMPS WEDNESDAY NIGHT IN THE MID 60S.
-- End Changed Discussion --

&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...
AS OF 215 PM TUESDAY...

THURSDAY THROUGH FRIDAY...HEIGHTS ALOFT RISE OVER CENTRAL NORTH
CAROLINA...WITH A SUBSIDENT AIR MASS IN PLACE OVER THE AREA.
PRECIPITABLE WATER VALUES REMAIN HIGHER THURSDAY RELATIVE TO
FRIDAY...BETWEEN AN INCH AND 1.5 INCHES ON THE FORMER COMPARED TO A
DECREASE FROM THE NORTHEAST TO AT OR BELOW AN INCH FRIDAY. BOTH THE
GFS AND NAM BUFR SOUNDINGS...AND PARTICULARLY THE LATTER...FORECAST
ENOUGH MOISTURE AROUND 850MB THURSDAY FOR AREAS OF CU TO FORM...MORE
LIKELY TOWARD THE WESTERN PIEDMONT WHERE THE 850MB MOISTURE IS
HIGHEST. K INDICES FALL FROM THE NORTHEAST AS WELL THURSDAY
AFTERNOON CONTINUING INTO FRIDAY...WITH K INDICES WELL INTO NEGATIVE
VALUES BY FRIDAY AFTERNOON. IN TERMS OF DEEP CONVECTION...AMPLE
OVERALL CIN AND GRADUAL WARMING ALOFT WITH CONVERGENCE ALOFT SHOULD
PRECLUDE THAT. THERE SHOULD BE A FEW MORNING GUSTS WITH INITIAL
MIXING THURSDAY IN THE LOWER TO MID TEENS KTS IN THE MODESTLY TIGHT
GRADIENT BETWEEN AN INVERTED TROUGH OFF OF THE COAST AND SURFACE
HIGH PRESSURE BUILDING IN FROM THE NORTHWEST...BUT OVERALL 925MB
WINDS ARE MAINLY AROUND 10KT. 1000-850MB THICKNESSES SUGGEST HIGHS
IN THE LOWER TO MID 80S BOTH DAYS...CLOSE TO OR ON THE LOWER SIDE OF
MOS GUIDANCE. OVERNIGHT LOWS THURSDAY NIGHT AROUND 60 TO THE MID
60S...MINS POSSIBLY TEMPERED A LITTLE OVER THE SOUTHWEST PIEDMONT BY
SLIGHTLY GREATER UPPER-LEVEL MOISTURE FORECAST BY BOTH THE NAM AND
THE GFS.

FRIDAY NIGHT THROUGH TUESDAY...UPPER RIDGING CONTINUES TO BUILD IN.
AROUND THE RIDGE...THERE COULD BE A WEAK MID-LEVEL SHORTWAVE OR TWO
THAT ATTEMPTS TO MOVE...OR HAS SOME SUCCESS MOVING...INTO CENTRAL
NORTH CAROLINA ESPECIALLY LATE IN THE WEEKEND AND EARLY NEXT WEEK.
THE MOISTURE OF THE MEAN AIR MASS...AND MOISTURE AT THE
SURFACE...INCREASE SUNDAY INTO MONDAY...WITH SURFACE DEW POINTS
EXPECTED TO INCREASE TO AROUND 70F BY MONDAY...CONTINUING INTO
TUESDAY. WITH SURFACE RIDGING OVER THE GULF CURRENTLY FORECAST...IT
SHOULD BE A GRADUAL MOISTURE INCREASE ESPECIALLY AT THE
SURFACE...AND COARSE MODEL SOUNDINGS AT LEAST INTO SUNDAY AFTERNOON
HAVE A GOOD CONSENSUS OF AT LEAST BEING WEAKLY CAPPED ALOFT. WILL
MAINTAIN THE DRY FORECAST FRIDAY NIGHT THROUGH THE WEEKEND...BUT
WITH INCREASING MOISTURE...SOME GUIDANCE SUGGESTING A WEAKNESS IN
THE MID-LEVEL HEIGHTS TRANSLATING INTO COOLING ALOFT...AT LEAST SOME
QPF BY MUCH OF THE CURRENT LONG-TERM GUIDANCE...AND MEX MOS POPS
NEAR OR ABOVE CLIMATOLOGY...WILL INTRODUCE A SLIGHT CHANCE OF
SHOWERS AND THUNDERSTORMS AT THE END OF THE PERIOD MONDAY AND
TUESDAY. FORCING SHOULD BE LIMITED TO WEAK SURFACE TROUGHINESS...SEA
BREEZE...AND/OR WEAK MID-LEVEL PVA AT TIMES...WHICH MAY BE ENOUGH
FOR ISOLATED SHOWERS AND THUNDERSTORMS IN A RELATIVELY MOIST AIR
MASS. 1000-850MB THICKNESSES GRADUALLY RISE...WHICH...ALONG WITH MOS
GUIDANCE...WOULD SUGGEST HIGHS RISING TO AT OR ABOVE NORMAL BY
SUNDAY. IF THE SURFACE DEW POINT IS A LITTLE HIGHER THAN FORECAST
PRIMARILY DUE TO SLIGHTLY LESS MIXING...MAXIMUM AFTERNOON HEAT
INDICES COULD RISE TO AROUND 100 BY MONDAY.

&&

.AVIATION /17Z TUESDAY THROUGH SUNDAY/...
AS OF 1210 PM TUESDAY...

A SURFACE COLD FRONT SLOWLY ADVANCING SOUTHEASTWARD WILL INTERACT
WITH THE MOIST AND SLIGHTLY UNSTABLE AIR MASS TO TRIGGER NUMEROUS
SHOWERS AND SCATTERED THUNDERSTORMS ACROSS CENTRAL NC LATER THIS
AFTERNOON THROUGH TONIGHT. THE SHOWER AND THUNDERSTORM COVERAGE IS
EXPECTED TO BE GREATEST BETWEEN 4 PM AND 10 PM. THE CONVECTIVE
ACTIVITY WILL CREATE WIDESPREAD MVFR CEILINGS/VISIBILITY WITH
POCKETS OF IFR CEILING/VISIBILITY IN THE HEAVIER SHOWERS.

THE COLD FRONT SHOULD CROSS THE TRIAD TERMINALS AROUND 10 PM...THE
KRDU/KRWI TERMINALS BETWEEN 1 AM AND 3 AM...AND THE KFAY VICINITY
BETWEEN 3-5 AM. AHEAD THE BOUNDARY EXPECT IFR CEILINGS ALONG WITH A
FEW SHOWERS. THE PASSAGE OF THE FRONT WILL BE NOTED BY SURFACE WINDS
VEERING FROM THE SW TO THE NORTH-NORTHWEST.

AVIATION CONDITIONS WILL BEGIN TO IMPROVE WEDNESDAY MORNING AS DRIER
MORE STABLE AIR FLOWS INTO THE REGION BEHIND THE EXITING FRONT.
EXPECT A RETURN TO VFR CONDITIONS THOUGH A STRATOCU DECK WILL LIKELY
DEVELOP WEDNESDAY AFTERNOON WITH BASES 3000-4000FT.

HIGH PRESSURE WILL BUILD INTO AND LINGER OVER CENTRAL NC WEDNESDAY
NIGHT THROUGH THE WEEKEND. THIS WEATHER SYSTEM WILL BRING DRY AND
STABLE CONDITIONS LEADING TO VFR PARAMETERS. THE EXCEPTION WILL BE A
BRIEF PERIOD OF MVFR VISIBILITY DUE TO FOG...MAINLY IN THE COASTAL
PLAIN.

&&

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

&&

$$

SYNOPSIS...WSS
NEAR TERM...WSS
SHORT TERM...WSS
LONG TERM...DJF
AVIATION...WSS