-- Discussion containing changed information from previous version are highlighted. --
000
FXUS62 KRAH 170543
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
142 AM EDT FRI MAY 17 2013

.SYNOPSIS...
A COLD FRONT OVER THE OHIO VALLEY AND MID ATLANTIC WILL GRADUALLY
MOVE SOUTH INTO THE REGION...AS UPPER LEVEL LOW PRESSURE MOVES IN
FROM THE WEST. BOTH THE FRONT AND THE UPPER LEVEL LOW WILL LINGER
AROUND THE REGION THROUGH THE WEEKEND...AND INTO EARLY NEXT WEEK.
THIS WILL RESULT IN UNSETTLED WEATHER AT LEAST THROUGH TUESDAY.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 935 PM THURSDAY...

A COLD FRONT DRAPED ACROSS INDIANA/OHIO/SOUTHERN PENNSYLVANIA HAS
MADE LITTLE PROGRESS SOUTHWARD THIS EVENING...BUT WILL EVENTUALLY
BEGIN TO BEND AROUND THE APPALACHIANS AND SURGE SOUTH TOWARD
NORTHEASTERN NC LATER TONIGHT INTO FRIDAY.  SOUTH OF THE
FRONT...THE INITIAL AREA OF CONVECTION OVER CENTRAL VA HAS
DISSIPATED OVER THE CHESAPEAKE BAY...WHILE ITS ASSOCIATED OUTFLOW
APPEARS TO HAVE SETTLED JUST NORTH OF ROANOKE RAPIDS.  A SECOND
ROUND OF CONVECTION MOVING ALONG A MORE PRONOUNCED AXIS OF 850MB
MOISTURE OVER WEST VIRGINIA IS NOW BEGINNING TO REEMERGE EAST OF THE
APPALACHIANS OF VIRGINIA.  IT APPEARS THIS CONVECTION...OR WHAT
HOLDS TOGETHER OF IT...WILL TRACK EAST-SOUTHEAST TOWARD SOUTHEASTERN
VIRGINA OVERNIGHT...WHILE ITS OUTFLOW MAY SLIP SOUTH AND MERGE WITH
THE PREEXISTING BOUNDARY LINGERING NEAR THE NORTHERN COASTAL PLAIN.
THE AIRMASS OVER CENTRAL NC...BASED OVER 00Z RAOBS AND SPC
MESOANALYSIS...FEATURES RELATIVELY STEEP LAPSE RATES BUT RATHER DRY
AIR ABOVE THE DEVELOPING NOCTURNAL INVERSION.  THUS...IT REMAINS
QUESTIONABLE WHETHER THE LIFT FROM THE SOUTHWARD MOVING BOUNDARIES
WILL BE ABLE TO OVERCOME THE LACK OF MOISTURE BETWEEN 925 AND 850MB.
WILL MAINTAIN A SLIGHTER CHANCE POP BUT RESTRICT IT TO MAINLY THE
NORTHERN PIEDMONT/COASTAL PLAIN.

MEANWHILE... AN UPPER LEVEL DISTURBANCE EVIDENT ON WATER VAPOR AND
RUC 300MB VORTICITY IS CURRENTLY CROSSING SOUTHWESTERN NC...AND WILL
DRIFT ACROSS THE SOUTHERN TIER OF NC OVERNIGHT. THERE IS SOME
PARTIAL CLEARING BEHIND THIS FEATURE OVER WESTERN NC IN THE
ASHEVILLE VICINITY. WHILE MOST OF THE CWA WILL REMAIN MOSTLY CLOUDY
OVERNIGHT...BUT A FEW BREAKS IN CLOUD COVER MAY EVENTUALLY DEVELOP
OVER THE SOUTHERN PIEDMONT/SANDHILLS LATER TONIGHT.  THE CURRENT LOW
TEMPERATURE FORECAST FAVORS THE COOLEST LOWS IN THIS AREA...SO ONLY
MINOR ADJUSTMENTS WILL BE MADE TO TEMPS OVERNIGHT.

&&

.SHORT TERM /FRIDAY AND FRIDAY NIGHT/...
AS OF 300 PM THURSDAY...

A RIDGE ALOFT IS FORECAST FRIDAY INTO FRIDAY NIGHT...WHILE CENTRAL
NORTH CAROLINA REMAINS IN A FAIRLY MOIST OVERALL AIR MASS WITH
PRECIPITABLE WATER VALUES LINGERING AROUND 1.5 INCHES. RELATIVE TO
THE REST OF THE REGION...AN 850MB THETA-E PERSISTS OVER AND NEAR
CENTRAL NORTH CAROLINA. AT THE SURFACE...THE PRIMARY BOUNDARY TO OUR
NORTH SLOWLY MOVES SOUTH TO NEAR THE VIRGINIA BORDER...POSSIBLY INTO
THE NORTHERN COASTAL PLAIN...FROM FRIDAY THROUGH 12Z SATURDAY. WINDS
ALOFT ARE GENERALLY LIGHT UNDER THE RIDGE...AND LIFT SEEMS TO BE
MAXIMIZED DIURNALLY UNDER MAXIMUM HEATING WITH MIXED-LAYER CAPE ON
THE ORDER OF 500-1500J/KG...HIGHEST TOWARD THE COASTAL PLAIN. WEAK
SHORTWAVES ARE FORECAST TO MOVE UNDERNEATH THE RIDGE SOUTH OF THE
SURFACE BOUNDARY...WHICH MAY RESULT IN ISOLATED-TO-SCATTERED SHOWERS
AND THUNDERSTORMS FRIDAY AFTERNOON THROUGH THE NIGHT. 0-6KM SHEAR IS
WEAK...TEENS KNOTS OR LESS...AND BUFR SOUNDINGS SHOW CAPE IS SLENDER
AS THE 800-600MB LAYER IS FORECAST A LITTLE WARMER THAN TONIGHT. THE
NAM AND THE GFS SHOW SOME QPF...AND WILL FORECAST SLIGHT CHANCE TO
CHANCE POPS...HIGHEST NORTH OF A LINE FROM ABOUT KEXX TO KGSB CLOSER
TO ANY SURFACE BOUNDARY AND WHERE K VALUES ARE FORECAST HIGHEST.
HIGH TEMPERATURES FRIDAY MOSTLY 85 TO 90...WITH THE HIGHER VALUES
OVER THE SOUTHWEST PIEDMONT THROUGH THE SANDHILLS AND SOUTHERN
COASTAL PLAIN. LEANED NEAR THE WARMER MET AND ECMWF MOS FOR FRIDAY
NIGHT...MOSTLY MID 60S.

&&

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

SATURDAY THROUGH MONDAY NIGHT: CONFIDENCE IN AN UNSETTLED WEATHER
PATTERN IS HIGH THROUGH MONDAY NIGHT...HOWEVER THE TIMING...COVERAGE
AND INTENSITY OF PRECIPITATION IS STILL AN ISSUE. A WEAK UPPER LEVEL
TROUGH WILL STALL OVER TN AND THE CAROLINAS DURING THIS PERIOD...
WITH RIDGING TO THE NORTH AND AN UPPER LEVEL LOW TO THE WEST OVER
THE NORTHERN PLAINS. THOUGH THE MODELS HANDLE THE CHARACTER OF THE
LOW DIFFERENTLY...DISTURBANCES ASSOCIATED WITH IT WILL YIELD
CONTINUING CHANCES FOR SHOWERS AND STORMS THROUGH MONDAY NIGHT
BEFORE THE LOW OVER THE PLAINS STARTS MOVING EAST. AT THE SURFACE...
THE GFS SHOWS A LOW DEVELOPING IN THE LEE OF THE ROCKIES THIS
WEEKEND AND DEEPENING AS IT MIGRATES SLOWLY EAST INTO THE DAKOTAS
AND MINNESOTA BY TUESDAY. WHILE THE MAIN TROUGH AXIS EXTENDS SOUTH
THROUGH TX...ANOTHER TROUGH AXIS...WITH A WEAKER SHORTWAVE LOW OVER
IN/KY ON SATURDAY...WILL EXTEND EAST TOWARD THE APPALACHIANS. WARM
MOIST SW FLOW OFF THE GULF WILL KEEP PWAT VALUES IN THE 1.5 TO 2.0
INCH RANGE THROUGH MONDAY NIGHT. WITH RESPECT TO THE UPPER LOW FOR
THE WEEKEND...THE 12Z GFS CUTS OFF THE LOW OVER KY WHILE THE 00Z
ECMWF INDICATES A S/W TROUGH EXTENDING INTO NC. BOTH HAVE BEEN
TRENDING TOWARD A STRONGER AREA OF LOW PRESSURE TO THE WEST OF THE
APPALACHIANS. THE GFS MAY BE A LITTLE STRONG AT THIS TIME...THUS
WILL USE A BLEND OF THE TWO MODELS...LEANING MORE TOWARD THE ECMWF
IN MOVING THE LOW OUT MONDAY NIGHT. MODEL GENERATED MLCAPE VALUES OF
1000-1500 J/KG SATURDAY THROUGH MONDAY...WITH THE MODEL SOUNDINGS
GENERATED VIA BUFKIT INDICATING TALL SKINNY CAPE. COMBINED WITH 0-6
KM BULK SHEAR VALUES OF 10-15 KTS EXPECT CONVECTIVE MODE TO BE
MAINLY DISORGANIZED PULSE TYPE STORMS...ALTHOUGH AN ISOLATED STRONG
STORM CANNOT BE RULED OUT. THE BIGGER IMPACT WILL LIKELY BE FROM
HEAVY RAINFALL...ESPECIALLY SUNDAY NIGHT WHEN THE HIGHEST PWAT
VALUES ARE EXPECTED. HIGH TEMPERATURES THROUGH THIS PERIOD WILL BE
DEPENDENT ON CLOUD COVER AND PRECIPITATION. FOR NOW...EXPECT HIGHS
IN THE UPPER 70S NW AND LOW TO MID 80S ACROSS THE EAST AND SOUTH.
OVERNIGHT LOWS WILL STAY MAINLY IN THE MID 60S.

TUESDAY THROUGH THURSDAY: AS THE LOW/SHORTWAVE MOVES NE AWAY FROM
THE AREA ON TUESDAY...HIGH PRESSURE WILL BUILD INTO THE CAROLINAS
FROM THE ESE...WITH RETURN FLOW OFF THE ATLANTIC AND A SLIGHT
DECREASE IN FORECAST PWAT VALUES. DRY AIR WILL ADVECT IN AT THE MID
LEVELS WITH DECREASING RAINFALL CHANCES THROUGH WEDNESDAY. A LOW AND
ASSOCIATED TROUGH OVER THE MIDWEST WILL MOVE EAST DURING THIS
TIME...WITH INCREASING PRECIPITATION CHANCES AGAIN WEDNESDAY NIGHT
AND THURSDAY AS THE SYSTEM MOVES INTO THE MID ATLANTIC. HIGH TEMPS
TUESDAY AND WEDNESDAY IN THE MID 80S...DECREASING A FEW DEGREES FOR
THURSDAY...UPPER 70S TO MID 80S. OVERNIGHT LOWS REMAIN STEADY IN THE
MID TO UPPER 60S.

&&

.AVIATION /06Z FRIDAY THROUGH TUESDAY/...
-- Changed Discussion --
AS OF 140 AM FRIDAY...

MAINLY VFR CONDITIONS WILL PREVAIL THROUGH THE 06Z TAF PERIOD. THE
POSSIBLE EXCEPTION WILL RESULT FROM SCATTERED SHOWERS AND STORMS
FOCUSED ALONG A SURFACE PRESSURE TROUGH/REMNANT OUTFLOW THIS
AFTERNOON FROM TRIAD TERMINALS TO KRDU AND KRWI. IN ADDITION...
CANNOT RULE OUT A STAY SHOWERS OR TWO EARLY THIS MORNING AS A WEAK
DISTURBANCE ALOFT MOVES ACROSS THE AREA. HOWEVER... DO NOT
ANTICIPATE ANY SUB-VFR CONDITIONS FROM THESE POSSIBLE SHOWERS THIS
MORNING. WILL KEEP ONLY VICINITY SHOWERS MENTIONED IN THE TAFS FROM
THIS AFTERNOON INTO THE EVENING... GIVEN BOTH THE TIMING AND
COVERAGE UNCERTAINTY WITH ANY SHOWERS AND STORMS. GIVEN THE EXPECTED
WEAK SURFACE TROUGH/OUTFLOW MOVING INTO THE AREA NOW THAT IS
EXPECTED TO STALL ACROSS CENTRAL NC THIS MORNING (WHICH SHOULD BE
THE FOCUS FOR SHOWER AND THUNDERSTORM DEVELOPMENT THIS AFTERNOON)
WILL GO WITH A LIGHT AND VARIABLE WIND ACROSS THE THE NORTHERN TAF
SITES... WITH MORE OF A SOUTHWESTERLY WIND AT KFAY THROUGH EARLY
AFTERNOON... BEFORE OUTFLOW FROM SHOWERS AND STORMS TO THE NORTH MAY
RESULT IN VARIABLE WINDS FOR KFAY AS WELL.

LOOKING AHEAD: AS A COLD FRONT APPROACHES FROM THE NORTH...AND AN
UPPER-LEVEL LOW APPROACHES FROM THE WEST...THE CHANCES FOR UNSETTLED
WEATHER INCREASE. SCATTERED-TO-NUMEROUS SHOWERS AND THUNDERSTORMS
ARE EXPECTED OVER THE WEEKEND. SCATTERED SHOWERS AND THUNDERSTORMS
SHOULD CONTINUE EARLY NEXT WEEK AS WELL. THE CHANCE FOR LATE NIGHT
AND EARLY MORNING LOW CLOUDS AND FOG WILL INCREASE INTO THE WEEKEND
AND EARLY NEXT WEEK IN A MOIST AIR MASS AS WELL.
-- End Changed Discussion --

&&

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

&&

$$

SYNOPSIS...DJF
NEAR TERM...SMITH
SHORT TERM...DJF
LONG TERM...KC
AVIATION...BSD/MWS