-- Discussion containing changed information from previous version are highlighted. --
000
FXUS62 KRAH 170007
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
807 PM EDT THU MAY 16 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 300 PM THURSDAY...

THE LATEST SURFACE ANALYSIS SHOWED A NEARLY STATIONARY FRONT ACROSS
INDIANA AND OHIO TOWARD SOUTHERN NEW YORK...WITH A NOTICEABLE
SURFACE TROUGH WEST-TO-EAST ACROSS CENTRAL VIRGINIA. IT WAS ALONG
AND NEAR THIS TROUGH WHERE SHOWERS AND THUNDERSTORMS HAD DEVELOPED
DURING THE MID-AFTERNOON...IN AN AREA OF SLIGHTLY GREATER 0-6KM
SHEAR AND SURFACE-BASED CAPE TO 1500J/KG ON THE LATEST SPC
MESOANALYSIS. OVER CENTRAL NORTH CAROLINA...CIN CONTINUED TO
DOMINATE...WITH NUMEROUS HIGH CLOUDS AHEAD OF A MID-LEVEL SHORTWAVE
MOVING INTO THE SOUTHERN APPALACHIANS.

OVERNIGHT...THE MID-LEVEL SHORTWAVE CONTINUES TO MOVE EAST AND
NORTHEAST ACROSS CENTRAL NORTH CAROLINA. BUFR SOUNDINGS MAINTAIN
DECENT LOW-LEVEL STABILITY...BUT THE SAME SOUNDINGS FROM BOTH THE
NAM AND THE GFS ALSO CONTINUE TO SHOW STEEPENING LAPSE RATES
ALOFT...BETWEEN 800MB AND 600MB. MLCAPE IS NOT COMPUTED ON THE
GUIDANCE UNTIL AFTER 00Z...WHEN THERE IS A SLIGHT INCREASE WITH THE
CLOSER APPROACH OF THE MID-LEVEL WAVE AND LIFTED INDICES GENERALLY
FALL TO AROUND 0C. K INDICES INCREASE FROM LOW DOUBLE DIGITS TO
ABOVE 30 OVERNIGHT AS PRECIPITABLE WATER VALUES INCREASE TO NEAR 1.5
INCHES...AROUND THE 75TH PERCENTILE FOR MID MAY. WHILE THE
LOW-LEVELS REMAIN STABLE...AS THE MOISTURE INCREASES AND LAPSE RATES
STEEPEN ALOFT...AND WITH THE POSSIBLE APPROACH OF OUTFLOW FROM THE
NORTH...AN ISOLATED SHOWER OR THUNDERSTORM COULD OCCUR. MOS GUIDANCE
POPS FROM THE MAV AND MET HAVE BOTH INCREASED NOTICEABLY...MOSTLY IN
THE SLIGHT CHANCE RANGE...AND SOME OF THE WRF GUIDANCE HAS NOTED A
FEW SHOWERS OVERNIGHT PARTICULARLY AWAY FROM THE AREA FROM KFAY TO
KCTZ. WILL MAINTAIN A SLIGHT CHANCE OF A SHOWER OR THUNDERSTORM
TONIGHT WITH THE HIGHER CHANCES RELATIVE TO THE REST OF CENTRAL
NORTH CAROLINA FROM THE TRIAD EAST ALONG THE VIRGINIA BORDER.
OVERNIGHT LOWS WERE FORECAST WITH A BLEND OF THE GUIDANCE...UNDER A
PARTLY-TO-MOSTLY CLOUDY SKY OVERALL...IN THE LOWER TO MID 60S.

&&

.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 /00Z FRIDAY THROUGH TUESDAY/...
-- Changed Discussion --
AS OF 805 PM THURSDAY...

MAINLY VFR CONDITIONS WILL PREVAIL THROUGH THE 00Z TAF PERIOD. THE
EXCEPTION WILL RESULT FROM SCATTERED SHOWERS AND STORMS FOCUSED
ALONG A SURFACE PRESSURE TROUGH FRIDAY AFTERNOON FROM TRIAD
TERMINALS TO KRDU AND KRWI. THERE IS ALSO A LOWER PROBABILITY OF A
SHOWER IN THE VICINITY OF KRWI BETWEEN 03-09Z TONIGHT...WHERE AND
WHEN A LIFT-PRODUCING OUTFLOW BOUNDARY FROM UPSTREAM CONVECTION OVER
WESTERN VA MAY SETTLE. CONFIDENCE OF CONVECTION AFFECTING ANY OF THE
CENTRAL NC TERMINALS IS RELATIVELY LOW...HOWEVER...SO ONLY VICINITY
SHOWERS FOR FRI AFTERNOON HAVE BEEN INCLUDED IN THE TAFS AT THIS
TIME RANGE. WINDS WILL REMAIN LIGHT AND VARIABLE OWING TO THE
APPROACH AND ARRIVAL OF THE SURFACE PRESSURE TROUGH...AND WILL
VEER FROM GENERALLY WESTERLY THIS EVENING TO SOUTHEASTERLY OR
SOUTHERLY ON FRI.

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. ISOLATED-TO-SCATTERED SHOWERS AND THUNDERSTORMS
ARE POSSIBLE FRIDAY AFTERNOON AND FRIDAY NIGHT...WITH
SCATTERED-TO-NUMEROUS SHOWERS AND THUNDERSTORMS OVER THE WEEKEND.
SCATTERED SHOWERS AND THUNDERSTORMS SHOULD CONTINUE EARLY NEXT WEEK.
OUTSIDE OF SHOWERS AND THUNDERSTORMS...THE CHANCE FOR LATE NIGHT AND
EARLY MORNING LOW CLOUDS AND FOG INCREASES INTO THE WEEKEND IN A
MOIST AIR MASS.
-- End Changed Discussion --

&&

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

&&

$$

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