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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS62 KRAH 231900
AFDRAH

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

.SYNOPSIS...
A COLD FRONT WILL APPROACH THE AREA FROM THE WEST TODAY...LEADING TO
UNSETTLED WEATHER MOST OF THE DAY. AFTER FRONTAL PASSAGE
TONIGHT...THE INTRODUCTION OF CANADIAN HIGH PRESSURE WILL BRING
COOLER AND MORE SETTLED CONDITIONS TO THE REGION THROUGH THE HOLIDAY
WEEKEND.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 240 PM THURSDAY...

UPPER LEVEL TROUGH CONTINUES TO DIG SOUTHWARD THIS AFTERNOON AIDED
BY A 50-75 KNOT UPPER JET OVER THE UPPER MISSISSIPPI VALLEY. THE
SURFACE COLD FRONT IS CURRENTLY MOVING ACROSS CENTRAL TENNESSEE AND
WILL TAKE ITS TIME MOVING ACROSS THE MOUNTAINS THIS EVENING. THE
MAIN 500 MB VORT MAX ASSOCIATED WITH THE FRONT WILL NOT ARRIVE UNTIL
CLOSER TO 00Z. FRONTAL PASSAGE WILL FINALLY OCCUR AFTER 00Z IN THE
NORTHWEST PIEDMONT...CLOSER TO 3Z IN THE TRIANGLE AREA...AND NEAR 6Z
FOR THE I-95 CORRIDOR.

CURRENT RADAR TRENDS SHOW A MYRIAD OF SURFACE BOUNDARIES LEFT OVER
FROM LAST NIGHTS CONVECTION AND DIFFERENTIAL HEATING THIS MORNING.
IN ADDITION A SMALL SHORTWAVE TROUGH IS MOVING NORTHWARD FROM
UPSTATE SOUTH CAROLINA. AT THIS TIME THE BOUNDARY INITIATING THE
MOST CONVECTION SPANS SW TO NE FROM THE ROCKINGHAM AREA TO ROANOKE
RAPIDS. AT THIS TIME INGREDIENTS FOR THUNDERSTORMS ARE A BIT
HEALTHIER THAN IN PREVIOUS DAYS. CURRENTLY THERE IS ABOUT 1000 ML
CAPE IN THE EAST WITH LOW LEVEL LAPSE RATES BETWEEN 7-8. EFFECTIVE
SHEAR IS AROUND 20 KNOTS. RAP SOUNDINGS SHOW VERY TALL SKINNY CAPE
IN THE HAIL GROWTH ZONE MAKING SEVERE HAIL UNLIKELY IN THIS SCENARIO
BUT PEA HAIL IS CERTAINLY POSSIBLE. STRAIGHT HODOGRAPHS WITH 20
KNOTS OF SHEAR SUPPORT A MORE LINEAR MULTICELLULAR CONVECTIVE MODE.
THERE IS A RELATIVELY DRIER LAYER NEAR 800 MB WITH A VERY MODEST
INVERTED V MAKING SEVERE WINDS A LITTLE BIT MORE POSSIBLE THAN IN
PREVIOUS DAYS BUT GUSTS WILL MORE LIKELY TOP OUT IN THE 30-40 KNOT
RANGE. CURRENT SPC ANALYSIS ALSO SHOWS AN AREA OF 500-700 J/KG OF
DCAPE ACROSS THE SOUTH CENTRAL PORTION OF THE CWA. DESPITE
PARAMETERS BEING RELATIVELY BETTER TODAY...MID LEVEL LAPSE RATES ARE
STILL VERY WEAK. OVERALL BULK SHEAR IS LOW. THERE IS ENOUGH LIFT IN
THE MID LEVELS TO SUPPORT MORE LIGHTNING THAN IN PREVIOUS DAYS BUT
ANY SEVERE THREAT WILL BE FAIRLY SUBDUED. AS THE VORT MAX APPROACHES
FROM THE NORTHWEST...DYNAMICS WILL IMPROVE SLIGHTLY AND IF THERE IS
STILL CONVECTION AROUND THE NORTHWEST PIEDMONT WOULD BE THE MOST
LIKELY LOCATION TO SEE SEVERE WEATHER.

WITH SEVERE POTENTIAL LOW...HEAVY RAIN AND FLOODING WILL AGAIN BE
THE LARGEST THREAT. WHILE ONLY A QUARTER TO A HALF OF AN INCH OF
WIDESPREAD PRECIPITATION IS EXPECTED...AREAS RECEIVING HEAVY RAINS
OVER THE PAST FEW DAYS WOULD BE A BIT MORE PRIMED FOR URBAN AND
SMALL STREAM FLOODING. CORFIDI VECTORS SHOW THAT STORMS SHOULD BE
PROGRESSIVE ENOUGH TO AVOID TRAINING BUT ORIENTATION OF INDIVIDUAL
BOUNDARIES COULD ALLOW FOR SOME TRAINING CELLS THIS AFTERNOON.
MOISTURE TRANSPORT...PW VALUES AND SURFACE CONVERGENCE ARE ALL BEST
IN THE COASTAL PLAIN THIS AFTERNOON...MAKING THIS THE MOST LIKELY
LOCATION FOR FLOODING TODAY.

SOUTH SOUTHWESTERLY WINDS TODAY WILL SHIFT TO NORTHWESTERLY AFTER
FRONTAL PASSAGE AND SUSTAINED WINDS WILL ELEVATE TO 10-15 KNOTS.
HIGHS TODAY WILL BE LARGELY DEPENDENT UPON CONVECTION AND CLOUD
COVER BUT IN GENERAL...UPPER 70S TO NEAR 80 IN THE NW AND LOWER TO
MID 80S IN THE SOUTH. LOWS WILL BE DEPENDENT UPON THE TIMING OF THE
FRONTAL PASSAGE UPPER 50S TO NEAR 60 IN THE NW AND MID 60S SE. SOME
MVFR CEILINGS OR VISIBILITIES COULD BE POSSIBLE IN THE EAST BEFORE
MAIN FRONT MOVES THROUGH EARLY FRIDAY MORNING.

&&

.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/...
-- Changed Discussion --
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.
-- End Changed Discussion --


&&

.AVIATION /18Z THURSDAY THROUGH TUESDAY/...
AS OF 140 PM THURSDAY...

24 HOUR TAF PERIOD: COMPLICATED LOW CONFIDENCE FORECAST FOR THIS
AFTERNOON. SEVERAL OUTFLOW AND DIFFERENTIAL HEATING BOUNDARIES HAVE
SET UP ACROSS CENTRAL NORTH CAROLINA THIS AFTERNOON. APPROACHING
FROM THE SOUTHWEST IS A SHORTWAVE TROUGH THAT WAS LOCATED OVER
NORTHERN GA THIS MORNING. ALL OF THESE SURFACE BOUNDARIES WILL BE
FOCI FOR THE GENESIS OF SHOWERS AND STORMS THIS AFTERNOON. THE MOST
PROMINENT BOUNDARY AT THIS TIME IS BISECTING THE CWA FROM SW TO NE
AND WILL BE AFFECTING KFAY AND KRWI IN THE NEXT COUPLE OF HOURS.
HEAVY RAIN AND GUSTY WINDS ARE LIKELY WITH THESE STORMS ALONG WITH
IFR/MVFR CEILINGS AND VISIBILITIES. OTHERWISE VFR CONDITIONS WILL
PREVAIL OUTSIDE OF STORMS WITH WINDS OUT OF THE SOUTH SOUTHWEST AT
5-10 KNOTS. LATER THIS AFTERNOON A MORE CONCENTRATED LINE OF SHOWERS
AND STORMS ASSOCIATED WITH THE PRE-FRONTAL TROUGH WILL MAKE THEIR
WAY ACROSS THE AREA WITH THE TRIAD TERMINALS AFFECTED JUST BEFORE
0Z. THIS LINE WILL SLOWLY PROGRESS EASTWARD GETTING TO KRDU AND KFAY
IN THE VICINITY OF 3Z AND KRWI CLOSER TO 6Z.

FOR FRIDAY CONDITIONS WILL RETURN TO VFR BUT STRONG GUSTY WINDS WILL
BE THE PROBLEM OF THE DAY WITH 15-20 KNOTS SUSTAINED OUT OF THE
NORTHWEST GUSTING TO 25-30 KNOTS. SKIES WILL GRADUALLY CLEAR
THROUGHOUT THE DAY.

LONG TERM: SATURDAY WILL SEE A PROLONGED RETURN TO VFR CONDITIONS
THROUGH MONDAY MAKING CONDITIONS VERY FAVORABLE FOR GENERAL AVIATION
THROUGH THE EXTENDED MEMORIAL DAY 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...ELLIS
NEAR TERM...ELLIS
SHORT TERM...ELLIS/WSS
LONG TERM...WSS
AVIATION...ELLIS
CLIMATE...RAH