-- Discussion containing changed information from previous version are highlighted. --
000
FXUS62 KRAH 170045
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
841 PM EDT SUN JUN 16 2013

.SYNOPSIS...
HIGH PRESSURE WILL MOVE OFFSHORE THIS EVENING...AHEAD OF AN UPPER
LEVEL DISTURBANCE THAT MOVES THROUGH THE REGION OVERNIGHT AND
MONDAY. A COLD FRONT SLOWLY APPROACHES FROM THE NORTHWEST LATE
MONDAY AND MOVES ACROSS THE REGION LATE TUESDAY INTO WEDNESDAY
MORNING.

&&

.NEAR TERM /THROUGH MONDAY/...
AS OF 250 PM SUNDAY...

THE NAM AND THE GFS ARE FAIRLY SIMILAR ON THE FORECAST DETAILS
DURING THE NEAR-TERM PERIOD...WITH THE AIR MASS GRADUALLY MOISTENING
AHEAD OF A MODEST MID-LEVEL SHORTWAVE THAT BOTH MODELS MOVE THROUGH
CENTRAL NORTH CAROLINA OVERNIGHT AND MONDAY. THE 12Z RAOB ANALYSIS
SHOWED AMPLE 850MB MOISTURE TO OUR SOUTHWEST WITH WIDESPREAD DEW
POINT IN THE TEENS CELSIUS...AND OVERNIGHT THROUGH MONDAY BOTH THE
NAM AND THE GFS FORECAST PRECIPITABLE WATER VALUES INCREASING TO
AROUND TWO INCHES. THE GFS IS ACTUALLY AS HIGH AS 2.25 INCHES...BUT
THAT MAY END UP BEING OVERDONE. REGARDLESS...WITH A MOISTENING AIR
MASS AND CONTINUED COOLING ALOFT AS HAS BEEN A CONSISTENT FORECAST
PARAMETER OVER THE LAST SEVERAL MODEL RUNS...CHANCES FOR
PRECIPITATION SHOULD INCREASE. THE GUIDANCE HAS ACTUALLY BECOME
NOTICEABLY MORE BULLISH WITH PRECIPITATION CHANCES FROM LATE THIS
EVENING THROUGH MONDAY...WITH THE NAM MOS INTRODUCING CATEGORICAL
POPS INTO THE TRIAD TONIGHT AND GENERALLY LOW LIKELY POPS THROUGHOUT
CENTRAL NORTH CAROLINA FOR MONDAY. AT LEAST OVERNIGHT...OF CONCERN
IS THE CAP STILL IN PLACE OVER A GOOD PART OF CENTRAL NORTH CAROLINA
AT THE MOMENT...AND THE PRECIPITATION FROM THE NORTHWEST TRYING TO
PUSH SOUTHEAST TOWARD A LINGERING 850MB RIDGE. MUCH OF THE AVAILABLE
WRF GUIDANCE...MOSTLY FROM NCEP...SUGGESTS THAT UPSTREAM
PRECIPITATION MAY ACTUALLY WANE AS IT TRIES TO PUSH SOUTHEAST
OVERNIGHT. WHAT MAY INDEED END UP HAPPENING IS THAT THE HIGH POPS OF
THE NAM ARE CORRECT IN THE TRIAD FOR LOW-QPF PRECIPITATION...WITH
WHATEVER PRECIPITATION REMAINS MAKING DIFFICULT HEADWAY SOUTHEAST.
THE MID-LEVEL DISTURBANCE...AS FORECAST...APPEARS STRONG ENOUGH WITH
MID-LEVEL COOLING AND INCREASING MOISTURE TO WARRANT CHANCE POPS
OVER AREAS MAINLY NORTH OF A LINE FROM ABOUT KVUJ TO KETC TONIGHT...
SLIGHT CHANCES FOR MOST AREAS TO THE SOUTH...KEEPING AREAS DRY ALONG
AND SOUTH OF A LINE FROM KMEB TO KGSB. OVERNIGHT LOWS CONTINUE TO
WARM IN INCREASING MOISTURE AND CLOUDS...MID TO UPPER 60S.

MONDAY...THE MID-LEVEL SHORTWAVE IS FORECAST TO MOVE THROUGH CENTRAL
NORTH CAROLINA...LEAVING SOME SUBSIDENCE IN ITS WAKE LATE IN THE
DAY...MAINLY TOWARD THE TRIAD. THE NAM IS WEAKER WITH ITS
MIXED-LAYER CAPE...500-1000J/KG COMPARED TO THE 1000-1500J/KG OF THE
GFS. BOTH MODELS SHOW ONLY LIMITED DOWNDRAFT CAPE...MAINLY 200J/KG
OR LESS...UNDER WEAK 0-3KM SHEAR IN THE RANGE OF 15KT. 1000-500MB
LAPSE RATES ARE WEAK AS WELL...TO ABOUT 6C/KM BASED ON THE HIGHER
GFS. AS THE DISTURBANCE PASSES THROUGH WITH A WEAK SURFACE TROUGH IN
PLACE...WILL ESSENTIALLY CARRY HIGH CHANCE POPS FOR THE DAY...
CONFINING THOSE POPS MAINLY TO THE AFTERNOON IN THE FAR SOUTHEAST.
ANTICIPATING MORE CLOUDS...HAVE LOWERED MAXES FOR MONDAY TO THE
LOWER TO MID 80S.

&&

.SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY/...
AS OF 250 PM SUNDAY...

MONDAY NIGHT...BOTH THE NAM AND THE GFS FORECAST SOME SUBSIDENCE
BEHIND THE MID-LEVEL SHORTWAVE...PARTICULARLY FROM THE TRIANGLE
NORTHWEST AND NORTH OVERNIGHT. THIS MAY RESULT IN CHANCES FOR
PRECIPITATION BECOMING LIMITED IN THOSE AREAS. FARTHER SOUTH...
HIGHER MOISTURE AND INSTABILITY PERSISTS OVERNIGHT...WITH ANOTHER
MID-LEVEL SHORTWAVE SKIRTING THE AREA TO THE SOUTH. IF THIS
VERIFIES...CHANCES FOR SHOWERS AND ISOLATED THUNDERSTORMS COULD
LINGER INTO THE OVERNIGHT HOURS...ESPECIALLY ACROSS THE SANDHILLS
AND SOUTHERN COASTAL PLAIN. FOR THIS FORECAST...WILL SHOW A
DIMINISHING TREND TO PRECIPITATION CHANCES...ONLY SLIGHT CHANCE IN
THE TRIAD OVERNIGHT WITH CHANCES MAINLY ALONG AND SOUTH OF U.S. 64.
ONCE AGAIN...OVERNIGHT LOWS SHOULD BE WARM...WITHIN A DEGREE OR
THREE OF 70. -DJF

TUESDAY...A DAMPENING MID LEVEL S/W CROSSING CENTRAL NC DURING PRIME
HEATING SHOULD INTERACT WITH THE MOIST AND SLIGHTLY UNSTABLE AIR
MASS IN PLACE TO TRIGGER NUMEROUS-WIDESPREAD SHOWERS AND A FEW
T-STORMS...MAINLY TUESDAY AFTERNOON. LOW LEVEL CONVERGENCE WILL BE
MAXIMIZED ALONG A SWD DRIFTING SFC BOUNDARY WILL LIFT ALOFT A RESULT
OF THE WEAKENING S/W AND 300MB JET CROSSING SOUTHERN NEW ENGLAND
PLACING CENTRAL NC IN THE FAVORABLE RIGHT ENTRANCE REGION. DYNAMICS
NOT OVERLY IMPRESSIVE THOUGH 30KTS OF BULK SHEAR OCCUR IN THE
AFTERNOON ACROSS THE NORTH AND MLCAPE (GFS) REACHES 1000-1400 J/KG
IN THE AFTERNOON. AS ELUDED TO IN PREVIOUS FORECAST...POTENTIAL FOR
SHOWERS/STORMS TO PASS REPEATEDLY OVER THE SAME LOCATION AS MEAN
FLOW PARALLEL TO THE SWD DRIFTING SFC BOUNDARY. THIS MAY LEAD TO
LOCALIZED FLOODING ISSUES...MAINLY IN URBAN AREAS. ANY UPDRAFTS ABLE
TO SUSTAIN MORE THAN 20 MINUTES MAY PRODUCE A WET MICROBURST BUT A
MARGINAL WIND PROFILE AND DEEP MOISTURE (LACK OF DRY AIR
ENTRAINMENT) SUGGEST ANY DAMAGING WINDS WILL BE QUITE ISOLATED.

TUESDAY NIGHT INTO WEDNESDAY...MID LEVEL TROUGH AND ASSOCIATED SFC
BOUNDARY DRIFT SE AND EXIT THE REGION TUESDAY EVENING. THIS SUGGEST
A GRADUAL DIMINISHING IN CONVECTIVE COVERAGE FROM THE NORTH TUESDAY.
ON WEDNESDAY...S/W IN THE ACTIVE NORTHERN STREAM WILL CROSS THE MID
ATLANTIC WEDNESDAY. THIS FEATURE WILL SEND ANOTHER SFC FRONT SWD
ACROSS CENTRAL NC ON WEDNESDAY. WEAK CONVERGENCE ALONG THIS BOUNDARY
COUPLED WITH MODEST UPPER AIR SUPPORT MAY TRIGGER/SUSTAIN
ISOLATED-SCATTERED SHOWERS AND THUNDERSTORMS ON WEDNESDAY. COVERAGE
APPEARS TO BE BETTER SOUTH VERSUS NORTH AS AIR MASS ACROSS THE NORTH
WILL BE DRIER AND MORE STABLE.

HIGH TEMPERATURES TUESDAY DEPENDENT ON CONVECTIVE COVERAGE. IF
WIDESPREAD CONVECTION OCCURS SOONER THAN ANTICIPATED...MAX TEMPS MAY
BE 3-4 DEGREES TOO WARM. A SFC N-NE FLOW WILL SLOWLY ADVECT COOLER
AIR INTO CENTRAL NC WEDNESDAY. LOW LEVEL THICKNESSES SUPPORT MAX
TEMPS NEAR 80-LOWER 80S. -WSS

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/...
AS OF 250 PM SUNDAY...

WEDNESDAY NIGHT THROUGH THURSDAY NIGHT...SURFACE RIDGE WILL
STRENGTHEN OVER CENTRAL NC. RESULTANT LOW LEVEL NE FLOW WILL
MAINTAIN A RELATIVELY COOL AND STABLE AIR MASS OVER THE BULK OF
CENTRAL NC. THE EXCEPTION WILL BE THE FAR SOUTH AND WEST AS ENOUGH
LIFT/MOISTURE MAY EXIST AROUND THE PERIPHERY OF THE RIDGE TO PERMIT
ISOLATED CONVECTION TO OCCUR. AFTERNOON TEMPS THURSDAY WILL AGAIN
AVERAGE A FEW DEGREES BELOW NORMAL WITH MOST SPOTS IN THE LOWER 80S.
MIN TEMPS BOTH NIGHTS IN THE LOW-MID 60S.

FRI-SUN:  MEDIUM RANGE GUIDANCE DIFFER IN THE UPPER AIR PATTERN OVER
THE CAROLINAS AT THE END OF THE WEEK. GFS DEPICTION OF A SERIES OF
S/W CROSSING THE OH VALLEY INTO THE NORTHERN MID ATLANTIC EXTENDING
SWD INTO CENTRAL NC  FRI-SAT WOULD SUGGEST A THREAT OF SCATTERED
CONVECTION OVER OUR REGION. MEANWHILE...ECMWF DEPICTS AN ELONGATED
UPPER LEVEL LOW/SHEAR AXIS OFF THE SE U.S. COAST THAT MOVES LITTLE
FRI-SAT. THIS FEATURE ALONG WITH THE MAIN STORM TRACK ACROSS THE
LOWER GREAT LAKES INTO THE NORTHERN MID ATLANTIC PERMITS A NARROW
RIDGE OF HIGH PRESSURE TO EXTEND ACROSS THE CAROLINAS FROM AN
ANTI-CYCLONE POSITIONED OVER THE SOUTHERN PLAINS/LOWER MS VALLEY.
THIS SCENARIO WOULD KEEP CENTRAL NC DRY FRI AND SAT. DIFFICULT TO
SAY AT THIS TIME WHICH SCENARIO MOST LIKELY TO VERIFY AS EACH
SCENARIO HAS AN EQUAL CHANCE TO VERIFY. BY SUNDAY....MODEL CONSENSUS
KEYS ON UPPER RIDGE EXPANDING EWD INTO THE CAROLINAS FROM THE
TN-LOWER OH VALLEY. ANY SHEAR AXES ASSOCIATED WITH CONVECTION
OCCURRING ALONG THE STORM TRACK FROM THE GREAT LAKES INTO THE
NORTHERN MID ATLANTIC WOULD BRUSH OUR FAR NE COUNTIES.

AIR MASS WILL GRADUALLY MODIFY THIS PERIOD WITH AFTERNOON TEMPS
RETURNING TO NEAR OR SLIGHTLY ABOVE NORMAL LEVELS BY SUNDAY.

&&

.AVIATION /00Z MONDAY THROUGH FRIDAY/...
-- Changed Discussion --
AS OF 825 PM SUNDAY...

MID LEVEL RIDGE AXIS (OF HIGH PRESSURE) IS CURRENTLY PUSHING TO THE
EAST OF THE AREA THIS EVENING. MEANWHILE... A WEAK DISTURBANCE IS
EXPECTED TO PUSH INTO THE AREA OVERNIGHT. THIS MAY ALLOW FOR SOME
SHOWERS TO MOVE INTO NORTHWESTERN PORTIONS OF CENTRAL NC VERY LATE
THIS EVENING/EARLY MONDAY MORNING. THUS... HAVE INCLUDED A TEMPO
GROUP FOR SHOWERS AND POSSIBLY MVFR CIGS AND VISBYS IN THE 06-09Z
TIME FRAME AT KGSO AND KINT. ELSEWHERE.... EXPECT VFR CONDITIONS
WILL CONTINUE THROUGH AT LEAST 12Z MONDAY. UNSETTLED WEATHER IS
EXPECTED ON MONDAY. FOR NOW WILL SHOW VFR CONDITIONS AT ALL TAF
SITES OUTSIDE OF THE NORTHWEST (KGSO/KINT)... AS CONFIDENCE IS NOT
HIGH ENOUGH OF SUB-VFR CONDITIONS OUTSIDE OF ANY SCATTERED SHOWERS
AND STORMS. HOWEVER... EXPECT WE MAY HAVE PERIODS OF SHOWERS AND
STORMS MID MORNING THROUGH THE LATE AFTERNOON (WEST)/REST OF THE 00Z
TAF PERIOD (EAST)... AND POSSIBLE MVFR/IFR CONDITIONS ASSOCIATED
WITH THE MOIST CONDITIONS AND WITH SHOWERS AND STORMS.

WE MAY BRIEFLY SEE A PERIOD OF DRY CONDITIONS MONDAY EVENING INTO
EARLY TUESDAY MORNING... BEFORE ADDITIONAL DISTURBANCES MOVE ACROSS
THE AREA ALONG WITH A WEAK COLD FRONT LATE TUESDAY THROUGH
WEDNESDAY. UNTIL THEN EXPECT PERIOD OF SHOWERS AND STORMS... WITH
POSSIBLE SUB-VFR CONDITIONS. VFR CONDITIONS ARE GENERALLY EXPECTED
FROM THURSDAY ONWARD... OUTSIDE OF POSSIBLY SOME EARLY MORNING
STRATUS AND OR FOG DURING THE PRE-DAWN HOURS OF EACH MORNING.
-- End Changed Discussion --

&&

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

&&

$$

SYNOPSIS...KMC/DJF
NEAR TERM...DJF
SHORT TERM...DJF/WSS
LONG TERM...WSS
AVIATION...BSD