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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS62 KRAH 150702
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
302 AM EDT SAT JUN 15 2013

.SYNOPSIS...
HIGH PRESSURE CONTINUES TO BUILD OVER THE REGION TODAY. THE HIGH
MOVES OFF OF THE SOUTHEAST COAST SUNDAY. THE AIR BECOMES
INCREASINGLY MOIST SUNDAY INTO MONDAY...AHEAD OF A COLD FRONT THAT
MOVES INTO THE REGION TUESDAY.

&&

.NEAR TERM /THROUGH TONIGHT/...
-- Changed Discussion --
AS OF 300 AM SATURDAY...

AS SURFACE HIGH PRESSURE BUILDS INTO CENTRAL NORTH CAROLINA FROM
THE NORTHWEST...THE LATEST WATER VAPOR IMAGERY SHOWED FAIRLY DRY AIR
ALOFT OVER THE AREA...WITH A MODEST INCREASE IN SOME MID-LEVEL
MOISTURE MOVING IN FROM THE NORTH AND HELPING TO PROVIDE FOR JUST A
FEW MID CLOUDS. THE 00Z UPPER-AIR ANALYSIS SHOWED GOOD HEIGHT RISES
ALOFT JUST NORTHWEST OF THE AREA AT 500MB AND HEIGHTS INDEED RISE
TODAY IN RESPONSE TO MID-LEVEL HIGH PRESSURE MOVING EAST ACROSS THE
GULF. NAM AND GFS BUFR SOUNDINGS MAINTAIN THE GOOD CAP AROUND 700MB
NOTED ON THE 00Z KGSO SOUNDING...THOUGH THEY ALSO SUPPORT...FOR MOST
OF CENTRAL NORTH CAROLINA...JUST ENOUGH MOISTURE AROUND 800MB FOR
MORE DIURNAL CU. THIS COINCIDES WITH THE 00Z 850MB ANALYSIS WHICH
SHOWED 850MB DEWPOINT DEPRESSIONS CLOSE TO ONLY 5C OVER MUCH OF THE
EAST...AND DURING THE DAY FRIDAY THERE WAS GOOD CU FORMATION OVER
MUCH OF THE EAST COAST. CU MAY NOT BE QUITE AS PLENTIFUL AS FRIDAY
ESPECIALLY TOWARD THE WESTERN PIEDMONT WHERE 850MB MOISTURE IS
FORECAST TO BE A LITTLE LESS RELATIVE TO THE REST OF CENTRAL NORTH
CAROLINA...BUT SUBSIDENCE SHOULD KEEP ANY CLOUDS SHALLOW OVERALL.
1000-850MB THICKNESSES...ALONG WITH THE GOOD TRACK RECORD OF LATE
FOR BOTH BIAS-CORRECTED MAXES FROM THE MAV AND MOS GUIDANCE...
SUPPORT MAXES CLOSER TO THE MET MOS IN MOST LOCATIONS. THIS WOULD
RESULT IN HIGHS IN THE MID 80S.

NAM AND GFS BUFR SOUNDINGS SHOW A RELATIVELY DRY AND CAPPED AIR MASS
PERSISTS OVERNIGHT. AS THE SURFACE HIGH QUICKLY MOVES SOUTHEAST...THE
NAM AND GFS BOTH INCREASE WINDS JUST OFF OF THE SURFACE APPRECIABLY
COMPARED TO CURRENT CONDITIONS. THIS SHOULD RESULT IN MORE MIXING
OVERNIGHT AND A MORE NOTICEABLE SOUTH OR SOUTHWEST BREEZE CERTAINLY
COMPARED TO THE CALM CONDITIONS OF EARLY THIS MORNING...ALTHOUGH NOT
SURE ABOUT THE WINDS BEING QUITE AS HIGH AS THE 10KT THE MOS
GUIDANCE SUGGESTS LATE TONIGHT. STILL...WITH A SOUTHWEST FLOW AND A
LITTLE MORE MIXING...EXPECT WARMER OVERNIGHT LOWS...60 TO 65 DEGREES.
-- End Changed Discussion --

&&

.SHORT TERM /SUNDAY AND SUNDAY NIGHT/...
-- Changed Discussion --
AS OF 300 AM SATURDAY...

IN A SOUTHWEST FLOW...MOISTURE GRADUALLY INCREASES SUNDAY INTO
SUNDAY NIGHT...WITH BOTH THE NAM AND GFS SUGGESTING THAT
PRECIPITABLE WATER VALUES INCREASING FROM AROUND AN INCH TO OVER 1.5
INCHES BY 00Z MONDAY. SUBSIDENCE PERSISTS THROUGH THE DAY SUNDAY
AHEAD OF A WEAK SURFACE FRONT THAT APPEARS TO BE MOVING NORTH FROM
THE GULF TOWARD CENTRAL NORTH CAROLINA LATE IN THE DAY. THIS FRONT
MAY SOMEHOW MERGE WITH A WEAK SURFACE TROUGH THAT THE NAM AND THE
GFS MOVE INTO CENTRAL NORTH CAROLINA FROM THE NORTH BY SUNDAY
EVENING...AND THERE IS ALSO AN 850MB TROUGH FORECAST TO MOVE INTO
THE AREA AS THE RIDGE ALOFT FLATTENS WITH WEAK MID-LEVEL SHORTWAVES
MOVING TOWARD THE MID-ATLANTIC AND CENTRAL NORTH CAROLINA. AS
COOLING ALOFT TAKES PLACE LATE SUNDAY AND ESPECIALLY SUNDAY NIGHT...
UNDER WEAK UVV...THERE MAY BE JUST ENOUGH MOISTURE AND LIFT TO
SUPPORT AN ISOLATED SHOWER OR THUNDERSTORM EITHER DEVELOPING OVER
THE AREA...OR MORE LIKELY A COMBINATION OF ISOLATED DEVELOPMENT AND
ISOLATED REMNANTS OF DEEP CONVECTION TO THE NORTH BEING ABLE TO
SUSTAIN THEMSELVES MOVING INTO THE AREA. IT IS INTERESTING HOW THE
MAV MOS POPS ARE JUST BELOW SLIGHT CHANCE SUNDAY NIGHT WHILE THE GFS
ITSELF PRODUCES FAIRLY WIDESPREAD...ALBEIT LIGHT...QPF OVER THE
ENTIRE AREA...AND THE NAM IS JUST THE CONVERSE...DRY WITH ITS QPF
YET SOLIDLY WITH SLIGHT CHANCE-TO-CHANCE POPS FOR CENTRAL NORTH
CAROLINA. FOR THIS FORECAST...WILL INTRODUCE A SLIGHT CHANCE OF A
SHOWER OR THUNDERSTORM SUNDAY NIGHT WITH THE LEAST POPS SOUTH AND
BARELY IN THE SLIGHT CHANCE RANGE WHERE THE MID-LEVEL CAP REMAINS
LONGER. THE CONSENSUS OF THE LATEST WRF MODELS OBSERVED SUGGEST AN
ALTERNATIVE TO MORE CHANCE POPS OVERNIGHT SUNDAY NIGHT ALONG AND
NORTH OF U.S. 64...AND MOSTLY DRY SOUTH.

SHOULD BE A LITTLE MORE CIRRUS SUNDAY...THOUGH MOSTLY THIN FOR A
LARGE PART OF THE DAY...AND 1000-850MB THICKNESSES SUPPORT HIGHS
GENERALLY A BLEND OF MAV AND MET MOS GUIDANCE...85 TO 90. THE
SURFACE GRADIENT TIGHTENS BEHIND HIGH PRESSURE AND AHEAD OF THE
SURFACE TROUGH SUCH THAT SOUTHWEST WINDS SHOULD SHOW A GUSTY
CHARACTER TO AROUND 20 TO POSSIBLY 25 MPH AT TIMES SUNDAY. SOME
CONTINUED BREEZE PLUS MORE CLOUDS SUNDAY NIGHT...MOSTLY CLOUDY OR
BECOMING MOSTLY CLOUDY AT LEAST WITH SOME MID- AND HIGH-LEVEL CLOUDS
MOVING IN FROM THE NORTHWEST...WILL RESULT IN AGAIN WARMER OVERNIGHT
LOWS...MOSTLY UPPER 60S.
-- End Changed Discussion --

&&

.LONG TERM /MONDAY THROUGH FRIDAY/...
-- Changed Discussion --
AS OF 300 AM SATURDAY...

MONDAY THROUGH TUESDAY NIGHT: WITHIN A BROAD TROUGH ALOFT EAST OF
THE ROCKIES...A LOW AMPLITUDE SOUTHERN STREAM SHORTWAVE TROUGH WILL
MOVE EASTWARD FROM THE CENTRAL PLAINS TO TN VALLEY MON...FOLLOWED
QUICKLY BY A MORE SUBSTANTIAL NORTHERN STREAM ONE FROM THE UPPER
MIDWEST TO THE CENTRAL APPALACHIANS MON NIGHT. THE FORMER FEATURE IS
OVER-AMPLIFIED BY GRID SCALE FEEDBACK ON (AT LEAST) THE PAST COUPLE
OF RUNS OF THE DETERMINISTIC GFS...AND INCLUDES A WRAPPED-UP
SUB-1000 MB LOW TRACKING THROUGH THE MIDDLE ATLANTIC REGION BY
TUE-TUE NIGHT. SUCH A SOLUTION HAS LITTLE TO NO SUPPORT FROM ANY
OTHER NWP GUIDANCE...WHICH RENDERS THE GFS MODEL MOSTLY UNUSABLE
BEYOND THE SHORT TERM.

IN THE LOW LEVELS...INSTEAD OF THE STRONG MID-ATLANTIC SURFACE LOW
DEPICTED BY THE GFS...A LEE TROUGH WILL DEVELOP OVER THE WESTERN
CAROLINAS MON...WHILE A WEAKENING SURFACE FRONT STALLS TO OUR NW. A
STRONGER COLD FRONT ATTENDING THE AFOREMENTIONED NORTHERN STREAM S/W
TROUGH IS THEN FORECAST TO OVERTAKE THE WEAKENING LEAD ONE AS THE
MERGED BOUNDARY THEN SETTLES INTO CENTRAL NC TUE AND TUE NIGHT. WITH
PRECIPITABLE WATER VALUES STEADILY INCREASING TO AT OR SLIGHTLY
ABOVE 1.75 INCHES...THE HEIGHT FALLS IN ADVANCE OF THE SHORTWAVE
TROUGHS ALOFT AND LOW LEVEL CONVERGENCE PROVIDED BY THE LEE TROUGH
WILL SUPPORT AN INCREASING CHANCE OF SHOWERS AND STORMS MON...WITH
HIGHEST CHANCES AROUND 50 PERCENT INVOF THE LEE TROUGH OVER THE
WESTERN PIEDMONT. GENERALLY WEAK MID LEVEL FLOW/BULK SHEAR...ON THE
ORDER OF ABOUT 15-25 KTS FROM SOUTH TO NORTH ACROSS THE CWA SUGGESTS
MULTI-CELL STORM ORGANIZATION...WITH ASSOCIATED STRONG WIND GUSTS.
CONVECTION WILL THEN LIKELY DIMINISH IN COVERAGE AND INTENSITY OVER
NC MON NIGHT...BEFORE BECOMING NUMEROUS TO WIDESPREAD AS THE SURFACE
COLD FRONT SETTLES INTO OUR AREA ON TUE. WSW MEAN FLOW ALIGNED
PARALLEL TO THE UNDERLYING SURFACE FRONT SUGGESTS HEAVY RAIN/
LOCALIZED FLOODING IN TRAINING STORMS ALONG THE BOUNDARY SHOULD
PROVIDE THE GREATEST IMPACT.

TEMPERATURES IN THE MIDDLE TO UPPER 80S MON...THE WARMEST DAY OF THE
WEEK...WILL TREND 3-5 DEGREES COOLER IN MOSTLY CLOUDY AND STORMY
CONDITIONS TUE. LOWS IN THE MID-UPPER 60S.

WEDNESDAY THROUGH FRIDAY: GIVEN CONTINUED FRONT-PARALLEL FLOW ALOFT
IN THE BASE OF BROAD EASTERN CONUS TROUGH...THE SURFACE FRONT WILL
LIKELY LINGER OVER SOUTHERN NC WED...BEFORE DRIFTING SOUTHWARD AND
DIFFUSING BY THU. WILL ACCORDINGLY INDICATE ANOTHER DAY OF HIGH
CHANCE OF DIURNALLY-ENHANCED SHOWERS AND STORMS OVER THE SOUTHERN
TIER WED...TAPERING TO JUST A SLIGHT CHANCE ACROSS THE NORTH TO
ACCOUNT FOR UNCERTAINTY IN PLACEMENT OF THE FRONT. WILL THEN KEEP
THE FORECAST DRY FOR THU-FRI...THOUGH DEVELOPING WEAK SOUTHEASTERLY
LOW LEVEL FLOW AND ASSOCIATED IMPROVING LOW LEVEL MOISTURE...AND A
LEE TROUGH...MAY ULTIMATELY SUPPORT A FEW STORMS FRI AFTERNOON.
COOLER THAN AVERAGE OWING TO THE PRESENCE OF THE BROAD EASTERN
TROUGH...WITH HIGHS ABOUT A CATEGORY BELOW AVERAGE - GENERALLY
LOWER 80S...TO PERHAPS MIDDLE 80S BY FRI.
-- End Changed Discussion --

&&

.AVIATION /06Z SATURDAY THROUGH WEDNESDAY/...
AS OF 125 AM SATURDAY...

VFR CONDITIONS OCCUR DURING THE 06Z VALID TAF PERIOD...OUTSIDE OF
SOME AREAS OF MAINLY MVFR FOG ESPECIALLY TOWARD KRWI AND POSSIBLY
KFAY. EXPECT DIURNAL CU TO DEVELOP ONCE AGAIN THIS AFTERNOON ACROSS
CENTRAL NORTH CAROLINA...POSSIBLY NOT AS MUCH AS OCCURRED FRIDAY
AFTERNOON IN MOST PLACES BUT STILL FEW-TO-SCATTERED DURING THE
AFTERNOON. VARIABLE SURFACE WINDS BECOME WEST-SOUTHWEST DURING THE
MORNING...BUT WITH HIGH PRESSURE OVERHEAD 10KT OR LESS...AND A FEW
TYPICAL MIXING GUSTS IN THE LOWER TEENS KNOTS DURING DAYLIGHT HOURS.

BEYOND THE 06Z VALID TAF PERIOD...THE AIR BECOMES INCREASINGLY MOIST
IN CENTRAL NORTH CAROLINA SUNDAY INTO MONDAY. AN ISOLATED SHOWER OR
THUNDERSTORM IS POSSIBLE SUNDAY NIGHT...WITH CHANCES FOR SHOWERS AND
THUNDERSTORMS...AND ASSOCIATED LOCAL SUB-VFR CONDITIONS...INCREASING
ALONG WITH THE MOISTURE MONDAY INTO TUESDAY. THERE IS SOME
PROBABILITY OF LOW CLOUDS LATE MONDAY NIGHT INTO TUESDAY MORNING
BASED ON THE MODEL SOUNDINGS OF THE GFS. CHANCES FOR SHOWERS AND
THUNDERSTORMS CURRENTLY SEEM TO DIMINISH WEDNESDAY RELATIVE TO
MONDAY AND TUESDAY...WITH THE BETTER POTENTIAL FOR ISOLATED SHOWERS
AND STORMS TOWARD KFAY COMPARED TO OTHER CENTRAL NORTH CAROLINA TAF
SITES.

&&

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

&&

$$

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