-- Discussion containing changed information from previous version are highlighted. --
000
FXUS62 KRAH 240218
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
1016 PM EDT THU MAY 23 2013

.SYNOPSIS...
A COLD FRONT WILL CROSS THE AREA OVERNIGHT AND EARLY FRIDAY MORNING.
A CANADIAN HIGH PRESSURE SYSTEM WILL BUILD INTO THE REGION WITH
CLEAR AND COOL CONDITIONS FOR MOST OF THE HOLIDAY WEEKEND.

&&

.NEAR TERM /THROUGH TONIGHT/...
-- Changed Discussion --
AS OF 1015 PM THURSDAY...

THE EFFECTIVE COLD FRONT IS CURRENTLY MOVING INTO THE NORTHWEST
PIEDMONT... GENERALLY DENOTED BY A LINE OF SHOWERS AND STORMS MOVING
INTO THE NORTHWEST PIEDMONT. THE SPC MESO PAGE IS STILL SHOWING
AROUND 1000 TO 1500 J/KG OF MLCAPE ACROSS OUR WESTERN PIEDMONT THIS
EVENING... OUT AHEAD OF THE LINE OF SHOWERS AND STORMS. HOWEVER...
THE NORTHERN PORTION OF THE LINE IS SHOWING A WEAKENING TREND (WITH
THE SOUTHERN PORTION STILL DEVELOPING AND GETTING READY TO PUSH INTO
OUR SOUTHWEST/WESTERN PIEDMONT)... WITH OUTFLOW PUSHING WELL OUT
AHEAD OF THE LINE... WHERE PERHAPS NOCTURNAL COOLING IS BEGINNING TO
STABILIZE THE BOUNDARY LAYER. THIS IS ALSO WHERE THE SPC MESO PAGE
IS DEPICTING THE LEAST INSTABILITY ACROSS WESTERN PORTIONS OF OUR
AREA (NORTHERN PIEDMONT). THE CURRENT INSTABILITY (MLCAPE) MAX IS
LOCATED ACROSS OUR SOUTHWESTERN PIEDMONT... AROUND 1500 MLCAPE. THIS
IS WHERE ANY MARGINAL SVR THREAT IS EXPECTED TO BE OVER THE NEXT FEW
HOURS (MAIN THREAT ISOLATED STRONG WIND GUSTS)... BEFORE THE SURFACE
COLD FRONT PUSHES THROUGH WESTERN PORTIONS OF OUR AREA FUELED BY A
LEAD MID LEVEL S/W TROUGH... WHICH IS NOW PUSHING EASTWARD OFF OF
THE HIGHER TERRAIN. AS THE LINE PUSHES EASTWARD INTO CENTRAL AND
EASTERN PORTION OF THE RAH CWA... EXPECTED THE LINE WILL WEAKEN
(DECREASE IN INTENSITY AND COVERAGE) WITH THE COOLING BOUNDARY LAYER
AND LACK OF DEEP LAYER SHEAR (GENERALLY 20 TO 25 KTS AT BEST).
THUS... WILL TREND POPS TO HIGH CHANCE/LIKELY WEST TO SLIGHT CHANCE
EAST. EXPECT THE SURFACE COLD FRONT SHOULD BE TO THE EAST OF THE
AREA BY 09Z. THIS SHOULD END ANY CHANCES FOR SHOWERS AND STORMS.
HOWEVER... WE WILL LIKELY CONTINUE TO SEE AT LEAST PARTLY CLOUDY
SKIES ACROSS THE AREA UNTIL THE MAIN MID LEVEL TROUGH AXIS MOVES
THROUGH THE AREA TOMORROW. WILL SHOW LOW TEMPS RANGING FROM THE
UPPER 50S NW TO MID 60S SE.
-- End Changed Discussion --

&&

.SHORT TERM /FRIDAY THROUGH SUNDAY NIGHT/...
AS OF 240 PM THURSDAY...

FRIDAY AND FRIDAY NIGHT...

THE COLD FRONT WILL SLOWLY MOVE OUT OF THE EASTERN AREAS OF THE CWA
DURING THE EARLY MORNING. AFTER FRONTAL PASSAGE WINDS WILL SHIFT TO
NORTHWESTERLY AND INCREASE IN SPEED TO 15 KNOTS SUSTAINED. A VERY
TALL MIXED LAYER DURING THE AFTERNOON AND THE PASSAGE OF A 30 KNOT
850 JET WILL HELP TRANSPORT SOME OF THOSE WINDS DOWN TO THE SURFACE
AND GUSTS OF 25-30 KNOTS ARE POSSIBLE FRIDAY AFTERNOON. SKIES WILL
GRADUALLY CLEAR OUT AND THICKNESSES SUPPORT HIGH TEMPERATURES IN THE
MID 70S IN MOST LOCATIONS. ON FRIDAY NIGHT WINDS WILL REMAIN
BLUSTERY WHICH WILL HELP TO OFFSET RADIATIONAL COOLING A BIT AS
THICKNESSES SUPPORT LOWS NEAR 40 DEGREES BUT WILL GO A BIT
CONSERVATIVE IN THE LOWER 40S. STILL VERY POSSIBLE TO BREAK THE LOW
TEMPERATURE RECORDS AT BOTH RDU AND GSO WHICH ARE BOTH 43 DEGREES.
-ELLIS

SATURDAY THROUGH SUNDAY NIGHT...

A DEEP UPPER LEVEL LOW WILL DRIFT NWD ALONG THE NORTHERN MID
ATLANTIC AND NEW ENGLAND COAST THROUGH SUNDAY. DUE TO THE EXTENSIVE
CIRCULATION ASSOCIATED WITH THIS SYSTEM IN TANDEM WITH AN AMPLIFYING
RIDGE OVER THE CENTRAL U.S....THE FLOW ALOFT ACROSS CENTRAL NC WILL
BE NWLY. AT THE SURFACE...COOL CANADIAN HIGH PRESSURE WILL BUILD
SEWD FROM THE GREAT LAKES INTO THE CAROLINAS. THE DEEP N-NW FLOW
WILL RESULT IN A DRY AND COOL HOLIDAY WEEKEND. THICKNESSES SATURDAY
AFTERNOON IN THE 1360S...SOME 30-35M BELOW NORMAL AND SUPPORTIVE OF
TEMPS UPPER 60S TO NEAR 70. ALLOWING FOR THE WARMTH OF A LATE MAY
SUN...FAVOR TEMPS IN THE LOW-MID 70S.

TEMPS WILL COOL OFF QUICKLY SATURDAY EVENING THEN STABILIZE AS MODEL
RH CROSS SECTIONS SUGGEST INCREASING MID-HIGH LEVEL CLOUDINESS AFTER
MIDNIGHT. THESE CLOUDS ASSOCIATED WITH DISTURBANCES IN THE NW FLOW
ALOFT. THIS TYPE OF PATTERN SUPPORTIVE OF OROGRAPHIC ENHANCED
CLOUDINESS...SO THE USUALLY TOO WET GFS MAY BE ONTO SOMETHING. THE
ARRIVAL OF THESE CLOUDS WILL PLAY A ROLE IN DETERMINING MIN TEMPS.
FAVOR COOLEST TEMPS NE WHERE CLOUDS WILL BE LESS/THINNER COMPARED TO
THE WEST-SW. IF CLOUDS ARE SLOW TO ARRIVE OR THIN...MIN TEMPS MAY
END UP BEING 2-3 DEGREES COOLER THAN FORECAST.

MODEST WARM UP EXPECTED SUNDAY AS THICKNESSES RECOVER INTO THE
1370S/LOW 1380S. EXPECT AFTERNOON TEMPS IN THE MID-UPPER 70S UNDER
PARTLY-MOSTLY SUNNY SKIES. SUNDAY NIGHT SHOULD BE A LITTLE MILDER AS
AIR MASS CONTINUES TO MODIFY. MOS GUIDANCE APPEARS TOO WARM BY A
CATEGORY. FAVOR MIN TEMPS NEAR 50 COOLER SPOTS TO LOW-MID 50S
ELSEWHERE. -WSS

&&

.LONG TERM /MONDAY THROUGH THURSDAY/...
AS OF 300 PM THURSDAY...

12Z GFS TRENDING TOWARD THE 00Z ECMWF. THE ECMWF HELD ONTO THE L/W
TROUGH ALONG THE EASTERN SEABOARD RESULTING IN A SLOWER WARMING
TREND WHERE AS THE GFS WITH ITS BUILDING MID-UPPER HEIGHTS
ADVERTISES A QUICKER/MORE NOTABLE WARM-UP. THE ECMWF SOLUTION OF A
LINGERING TROUGH NEAR OR OFFSHORE OF THE NEW ENGLAND COAST AND AN
AMPLIFYING RIDGE OVER THE MS RIVER VALLEY WILL MAINTAIN A NW FLOW
ALOFT OVER CENTRAL NC. THE ECMWF HINTS AT POSSIBLE DISTURBANCES
ASSOCIATED WITH MCS ACTIVITY THAT MAY OCCUR IN THE UPPER MID
WEST/GREAT LAKES TUESDAY-THURSDAY CROSSING OUR REGION. IF THIS WERE
TO OCCUR...COULD SEE A PERIOD OF UNSETTLED WEATHER ANYTIME BETWEEN
WEDNESDAY-THURSDAY. IF GFS WERE TO VERIFY WITH THE RIDGE BUILDING
CLOSER TO HOME...MCS ACTIVITY WILL BE SHUNTED MORE TO OUR NORTH. FOR
NOW...WILL KEEP POPS NO HIGHER THAN 20 PERCENT TUESDAY INTO
THURSDAY. LOW LEVEL THICKNESSES RETURN TO NEAR OR SLIGHTLY ABOVE
NORMAL VALUES TUESDAY ONWARD. WILL HAVE AFTERNOON TEMPS NEAR 80-LOWER
80S TUESDAY...AND LOW-MID 80S WEDNESDAY/THURSDAY. AGAIN...IF GFS
VERIFIES...WED/THU COULD SEE TEMPS IN THE UPPER 80S TO NEAR 90.


&&

.AVIATION /00Z FRIDAY THROUGH TUESDAY/...
AS OF 805 PM THURSDAY...

NUMEROUS SHOWERS AND STORMS DEVELOPED BETWEEN KRDU AND KRWI/KFAY
AROUND 18Z...AND HAVE SINCE PUSHED EAST INTO THE COASTAL
PLAIN...LEAVING VFR CONDITIONS ACROSS CENTRAL NC WITH A
SOUTH-SOUTHWESTERLY SURFACE WIND.  A SECOND LINE OF STORMS HAS
RECENTLY DEVELOPED AND EXTENDS FROM KRNK TO KTNB AS A COLD FRONT AND
UPPER LEVEL TROUGH APPROACHES FROM THE WEST.  IT APPEARS THIS LINE
OF STORMS SHOULD SWEEP ACROSS THE TRIAD AREA BETWEEN 00Z AND
02Z...MOVING TO KRDU BY 03-04Z...AND IF IT HOLDS TOGETHER...REACHING
KFAY/KRWI BY 05-06Z.  A STRONG WIND SHIFT TO WEST-NORTHWESTERLY
WINDS WILL ACCOMPANY THE LINE..AND CONFIDENCE IS FAIRLY HIGH THAT
GUSTS WILL EXCEED 30KT AT KGSO/KINT. IN ADDITION..CEILINGS AND VSBYS
MAY BRIEFLY FALL TO TO MVFR.  FURTHER EAST...MVFR CEILINGS MAY
DEVELOP AHEAD OF THE LINE DUE TO ABUNDANT LOW LEVEL MOISTURE...BUT A
SWITCH NORTHWESTERLY WINDS SHOULD HELP TO SCOUR CEILINGS BY FRIDAY
MORNING.

VFR CONDITIONS WILL CONTINUE ON FRIDAY WITH WINDS STRENGTHENING TO
NEAR 15KT AND GUSTING TO AT LEAST 25KT AS AN UPPER LEVEL TROUGH
SWINGS ACROSS THE AREA.

OUTLOOK...
VFR CONDITIONS ARE EXPECTED THROUGH THE WEEKEND.

&&

.CLIMATE...
MORNING LOW TEMPERATURES ON THE 25TH AND 26TH ARE EXPECTED TO BE
NEAR RECORD MIN TEMPS FOR THE DATE.

RECORD MIN TEMP/YEAR SET      MAY 25TH            MAY 26TH

RDU                           43 / 1967           43 / 1979

GSO                           43 / 1956           42 / 1930


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

&&

$$

SYNOPSIS...BLAES
NEAR TERM...BSD
SHORT TERM...ELLIS/WSS
LONG TERM...WSS
AVIATION...SMITH
CLIMATE...RAH