Special Weather Statement, NWS Raleigh, NC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
302 PM EDT FRI SEP 28 2012

.SYNOPSIS...
A SLOW MOVING COLD FRONT WILL APPROACH THE CAROLINAS FROM THE NORTH
TODAY...PUSH SOUTHWARD INTO THE AREA TONIGHT...THEN STALL OUT NEAR
THE COAST OVER THE WEEKEND.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 300 PM FRIDAY...

OVERVIEW:
AN AMPLIFYING UPPER LEVEL TROUGH IN VICINITY OF JAMES BAY CANADA IS
EXPECTED TO DIG SOUTH TOWARD THE GREAT LAKES AS A VIGOROUS UPPER
LEVEL LOW TONIGHT...WITH INCREASINGLY CYCLONIC FLOW ALOFT OVER THE
MID-ATLANTIC AND CAROLINAS. A COLD FRONT EXTENDING EAST NORTHEAST
FROM THE CENTRAL PLAINS INTO THE OHIO VALLEY AND MID-ATLANTIC AT 06Z
THIS MORNING IS EXPECTED TO SLOWLY APPROACH THE AREA FROM THE
NORTH/NW TODAY...PROGRESSING INTO CENTRAL NC TONIGHT. AS HAS BEEN THE
THEME OVER THE PAST 24-36 HOURS...LATEST ROUND OF MODEL ITERATIONS
CONTINUE TO SLOW DOWN THE FROPA THROUGH THE CAROLINAS...WITH WHAT
APPEARS NOW TO BE SOMETIME SATURDAY AFTERNOON.

COMPACT MID/UPPER LEVEL SHORTWAVE WILL CROSS THE AREA
THIS AFTERNOON IN THE WESTERLY FLOW ALOFT AT THE BASE OF THE
AMPLIFYING MID/UPPER LEVEL TROUGH. THIS WILL BE THE PRIMARY FORCING
MECHANISM ACROSS THE AREA THIS AFTERNOON....WITH GROWING SUSPICIONS
IF THE FRONT WILL MAKE IT INTO THE AREA PRIOR TO 06Z. WHILE AIR
COLUMN WILL UNDERGO BROAD MOISTENING THROUGHOUT THE DAY(PWATS
INCREASE AOA 1.5")...WEAK WESTERLY LOW-LEVEL FLOW OVER THE CAROLINAS
WILL PREVENT ANY SUBSTANTIAL LOW-LEVEL MOISTENING...AND THUS THERE
IS LOW CONFIDENCE ON HOW WELL THE AREA OF CONVECTION  WILL HOLD
TOGETHER AS IT MOVES THROUGH THE CWA BETWEEN 18Z FRIDAY TO 03Z SAT.
THE VARIOUS HI-RES CAM REFLECTIVITY SIMULATIONS ARE ALL HANDLING
HANDLING THE UPSTREAM CONVECTION WELL ATTM...AND ALL SHOW SOME
CONVECTION MOVING THROUGH THE AREA THIS AFTERNOON THROUGH THE EARLY
EVENING...BUT DIFFER A GREAT DEAL WITH SUGGESTIVE
COVERAGE/ORGANIZATION OF THE CONVECTION.

THE INCREASINGLY MOIST-ADIABATIC LAPSE RATES...AND LIKELY MORE
CRITICAL THE LACK OF STRONGER NEAR SURFACE THETA-E MOIST ADVECTION
DUE TO WEAK LOW-LEVEL WESTERLY WIND COMPONENT WILL HOLD SFC
DEWPOINTS IN THE LOWER TO MID 60S...LIMITING DESTABILIZATION THIS
AFTERNOON...WITH MLCAPE VALUES IN THE 500-1000 J/KG RANGE. THE
UNIDIRECTIONAL DEEP LAYER SHEAR OF 20 TO 25 KTS THIS AFTERNOON WILL
INCREASE TO AROUND 30KTS LATE(AT OR AFTER 00Z)...BY WHICH TIME
NOCTURNAL STABILIZING EFFECTS WILL BEGIN TO BE FELT. ALSO...WITH
LACK OF LOW-LEVEL FORCING AS FRONT REMAINS NORTH OF THE AREA IT
APPEARS THAT THE SEVERE THREAT WILL BE UNORGANIZED AND ISOLATED AT
BEST...WITH GREATEST THREAT COMING FROM ISOLATED DAMAGING WINDS
PRIMARILY BETWEEN 3-10 PM THIS AFT/EVE. THE FORECAST WILL REFLECT
PRECIP CHANCES INCREASING TO 50% FROM WEST-EAST FROM MID/LATE
AFTERNOON INTO THIS EVENING BEFORE DECREASING IN COVERAGE.

MORE AND MORE MODELS ARE JUMPING ON BOARD IN SHOWING AN AREA OF
ANAFRONTAL PRECIP DEVELOPING ACROSS VIRGINIA AND NORTH CAROLINA
LATE TONIGHT/TOWARDS DAYBREAK AS FRONT ENTERS THE AREA AND HEIGHT
FALLS INCREASE OVER THE MID-ATLANTIC AS UPPER VORTEX/TROUGH DIGS
INTO THE OHIO VALLEY.  SREF PLUME DIAGRAMS ACROSS THE AREA REALLY
SHOW A MARKED INCREASE IN QPF/POPS LATE TONIGHT/TOWARDS DAYBREAK AND
CONTINUING INTO THE DAY ON SATURDAY. WILL MAINTAIN SMALL CHANCE POPS
OVERNIGHT. LOWS TONIGHT IN THE LOWER 60S NW TO MID 60S SOUTHEAST.
&&

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

MODELS HAVE TRENDED WETTER ACROSS CENTRAL NC DUE TO THE
AFOREMENTIONED SLOWER TIMING OF THE LOW-LEVEL FRONTAL ZONE THROUGH
THE AREA. THERE STILL REMAINS CONSIDERABLE SPREAD AS TO THE LOCATION
AND TIMING OF THE FRONT...AND SUBSEQUENT SPIN UP OF A WEAK SURFACE
WAVE ALONG THE FRONT IN RESPONSE TO DIGGING MID/UPPER LEVEL VORTEX
DIVING SOUTHWARD INTO THE GREAT LAKES REGION. UNFORTUNATELY...THE
FINER FORECAST DETAILS WILL BE DEPENDENT ON THE FRONTAL
POSITION/LOCATION AND THUS CONFIDENCE IN SATURDAY'S FORECAST IS
LOWER THAN AVERAGE.

SATURDAY:
SYNOPTIC SCALE H5 FALLS ON THE ORDER OF 30 TO 40 METERS WILL EXTEND
DOWN THE MID-ATLANTIC SEABOARD WITH CONTINUATION OF WEAK SHORT-WAVE
TROUGHS/DISTURBANCES MOVING THROUGH THE AREA AT THE BASE OF THE
DEEPENING EASTERN US TROUGH. THESE FEATURES WILL ENHANCE
ASCENT/CONVECTION ATOP THE MOIST SLOW-MOVING/STALLED LOW-LEVEL
FRONTAL ZONE IN PLACE ACROSS CENTRAL NC WITH LOCALLY ENHANCED
CONVERGENCE INVOF THE SURFACE WAVE. GIVEN THE DECENT AMOUNT OF
MOISTURE/CLOUDS EXPECTED...INSOLATION WILL BE GREATLY TEMPERED ALONG
AND WEST OF THE TRIANGLE...WITH AREAS EAST OF INTERSTATE 95/COASTAL
AREAS STANDING THE BEST CHANCES OF SEEING SOME HEATING AND THE
DEVELOPMENT OF WEAK INSTABILITY BETWEEN 500 TO 800 J/KG.
DEEP LAYER SHEAR REMAINS MARGINAL AS WELL...BUT LOW-LEVEL SHEAR
COULD BE ENHANCED IN PROXIMITY TO THE YET TO DEVELOP SURFACE WAVE.
IF THERE IS AN ISOLATED SEVERE THREAT...IT WILL LIKELY BE ACROSS THE
FAR SOUTHEASTERN ZONES ALONG THE BETTER LOW-LEVEL LAPSE RATES.
WILL HIGHLIGHT THE SANDHILLS/SOUTHERN COASTAL OUT FOR AN ISOLATED
SEVERE THREAT FOR DAMAGING WINDS SATURDAY AFTERNOON/EVENING.

DIFFICULT TEMPERATURE FORECAST FOR SATURDAY...DEPENDENT ON
LOCATION/TIMING OF FRONT AND AREAL COVERAGE OF PRECIP. EXPECT
GENERALLY COOLER CONDITIONS ACROSS THE NORTH WHERE FRONT WILL BE
QUICKER TO CLEAR...WITH THE WARMEST READINGS ACROSS THE
SOUTH/SOUTHEAST. HIGHS NEAR TO LOWER 70S ACROSS THE NORTH TO UPPER
70/NEAR 80 SOUTH.

SATURDAY NIGHT:
SLOW SOUTHWARD/SOUTHEASTWARD DRIFT OF FRONT TOWARDS THE COAST AFTER
MIDNIGHT SATURDAY NIGHT SHOULD RESULT IN A DIMINISHING OF SHOWERS
ACROSS THE AREA OVERNIGHT. GIVEN LACK OF RUN-TO-RUN CONTINUITY
REGARDING THE TIMING OF THE FRONT...WILL HANG ON TO AT LAST
SLIGHT/SMALL CHANCE POPS EVERYWHERE SATURDAY NIGHT...BUT MUCH OF THE
FORECAST AREA COULD BE DRY BY MIDNIGHT SATURDAY NIGHT. WEAK COOL/DRY
AIR ADVECTION SHOULD BEGIN TO SEEP SOUTH INTO AT LEAST NORTHERN
PORTIONS OF THE FORECAST AREA BY DAYBREAK SUNDAY. LOWS IN THE
MID/UPPER 50S NORTH TO LOWER 60S SOUTH/SOUTHEAST.
&&

.LONG TERM /SUNDAY THROUGH FRIDAY/...
AS OF 302 PM FRIDAY...

NWP GUIDANCE IS STRUGGLING WITH AN EVOLVING WEATHER PATTERN DURING
THE EXTENDED RANGE BUT SOME CONSENSUS DEVELOPING ON A POTENTIALLY
WET START TO THE UPCOMING WEEK.

GUIDANCE IS IN GOOD AGREEMENT IN DEPICTING A SPLIT FLOW PATTERN WITH
A CLOSED VORTEX IN THE NORTHERN STREAM NEAR THE SOUTHERN GREAT LAKES
ON SUNDAY WITH A CONVERGENT WESTERLY TO NORTHWESTERLY FLOW ALOFT
OVER CENTRAL NC. A SLOW MOVING AND SOMEWHAT ILL DEFINED SURFACE
FRONT WILL LINGER NEAR THE CAROLINA COAST WITH SLIGHTLY COOLER AIR
BEING TRANSPORTED INTO THE REGION ON SUNDAY. THE POTENTIAL FOR
PRECIPITATION ON SUNDAY WILL BE GENERALLY CONFINED TO NEAR THE
SURFACE FRONT IN A REGION OF DEEPER MOISTURE AND SLIGHT ISENTROPIC
LIFT.

THE STATIONARY FRONT NEAR THE COAST BEGINS TO SLOWLY EASE NORTH AS A
WARM FRONT ON SUNDAY NIGHT AND ESPECIALLY MONDAY. THIS IS IN
RESPONSE TO A SOUTHERN STREAM WAVE WITH AN 85KT JET THAT CARVES OUT
A SECONDARY TROUGH OVER THE LOWER MISSISSIPPI VALLEY THAT LEADS TO
THE DEVELOPMENT OF A WEAK SURFACE WAVE ON THE NORTHERN GULF COAST.
AS THIS SURFACE WAVE LIFTS NORTH INTO THE LOWER TENNESSEE VALLEY ON
MONDAY NIGHT...A STRENGTHENING LOW LEVEL FLOW AND INCREASED MOISTURE
TRANSPORT SHOULD RESULT IN SATURATION AND AN INCREASED THREAT OF
PRECIPITATION. THE NAM/GFS SUGGEST THAT A SURGE OF LOW LEVEL FLOW
WILL RESULT IN AREAS OF LIGHT RAIN/SHOWERS ACROSS SOUTH-CENTRAL NC
SUNDAY EVENING THAT SHOULD SPREAD NORTH OVERNIGHT. THE ISENTROPIC
LIFT AS DEPICTED BY THE NAM/GFS IS FOCUSED IN THE 295-305K LAYER AND
IT BECOMES MORE GRADUAL DURING THE DAY MONDAY AS IT LIFTS NORTH.
HAVE INCREASED POPS TO THE LIKELY RANGE FOR PORTIONS OF THE CWA ON
SUNDAY NIGHT AND MONDAY. THE AIR MASS MAY BECOME SUFFICIENTLY
UNSTABLE TO SUPPORT A FEW THUNDERSTORMS IN THE FAR SOUTH AND
SOUTHEAST. LOW TEMPS ON SUNDAY MORNING WILL RANGE IN THE UPPER 60S
TO LOWER 70S WITH HIGHS ONLY IN THE LOWER TO MID 70S BECAUSE OF
CLOUDS AND PRECIPITATION.

THE SURFACE LOW WILL CONTINUE TO LIFT NORTH INTO THE OHIO VALLEY
WEST OF THE MOUNTAINS ON MONDAY NIGHT AND TUESDAY. THIS WILL
EVENTUALLY RESULT IN THE WARM FRONT LIFTING WELL NORTH OF THE REGION
ALONG WITH A DECREASE OF POPS INTO THE CHANCE RANGE AND A CHANGE IN
CHARACTER OF PRECIPITATION INTO A MORE SHOWERY NATURE. AS THE WARM
FRONT LIFTS NORTH AND MOVES INLAND AS A PSEUDO COASTAL FRONT IN A
LOW CAPE ENVIRONMENT WITH DEW POINTS NEAR 60 BUT A DECENT FLOW ALOFT
AND GOOD BULK SHEAR...THERE IS SOME POTENTIAL FOR THUNDERSTORMS THAT
COULD BE ORGANIZED.

AS THE SOUTHERN STREAM SHORT WAVE SHEARS OUT AND THE AND SURFACE LOW
MOVES INTO THE MID ATLANTIC...THE ASSOCIATED COLD FRONT SHIFTS INTO
THE PIEDMONT ON WEDNESDAY AND TOWARD THE COAST ON THURSDAY AND
FRIDAY. THE FRONT MAY BE ACCELERATED EAST AWAY FROM THE REGION ON
FRIDAY AS A NORTHERN STREAM WAVE...MORE EMPHATICALLY SHOWN ON THE
GFS...APPROACHES FROM THE NORTHWEST ON FRIDAY. WE WILL GRADUALLY
TAPER POPS DOWN AND THEN SHIFT THEM EASTWARD ON WEDNESDAY AND
THURSDAY WITH A DRY FORECAST ON FRIDAY. TEMPERATURES WILL RANGE NEAR
SEASONABLE VALUES ON WEDNESDAY THROUGH FRIDAY WITH HIGHS IN THE MID
70S TO AROUND 80 AND LOWS IN THE UPPER 50S TO LOWER 60S. -BLAES

&&

.AVIATION /18Z FRIDAY THROUGH WEDNESDAY/...
AS OF 130 PM FRIDAY...

24-HR TAF PERIOD:
AN UPPER LEVEL DISTURBANCE WILL CROSS THE REGION THIS
AFTERNOON...AND WILL EXIT THE AREA AOA 03Z. THIS WILL SUPPORT
A BAND OF WEST TO EAST MOVING BAND OF SHOWERS AND THUNDERSTORMS
THROUGH THE AREA.  THE BEST CHANCE FOR SHOWERS/STORMS WILL BE
BETWEEN 18-21Z AT THE INT/GSO TERMINALS...21-01Z AT THE RDU AND
22-03Z AT THE RWI TERMINAL. A BRIEF PERIOD OF SUB-VFR CONDITIONS
AND GUSTY WINDS WILL BE POSSIBLE WITH THE STRONGER STORMS.
OTHERWISE...OUTSIDE OF CONVECTION EXPECT VFR CONDITIONS TO
PREDOMINATE.

A SLOW MOVING COLD FRONT WILL THEN MOVE INTO THE AREA OVERNIGHT AND
WILL EVENTUALLY STALL OUT OVER EASTERN AND SOUTHERN PORTIONS OF THE
CAROLINAS THROUGH EARLY NEXT WEEK. THIS WILL KEEP A CHANCE OF SHOWERS
ACROSS THE AREA OVERNIGHT AND THROUGH THE DAY ON SATURDAY.

LOOKING AHEAD:
ALTHOUGH SOME UNCERTAINTY REMAINS...AFOREMENTIONED STALL FRONT
WILL RESULT IN AT LEAST INTERMITTENT SUB-VFR CONDITIONS INTO
SATURDAY NIGHT/EARLY SUNDAY WITH A LULL ON SUNDAY BEFORE A SOUTHERN
WAVE AND INFLUX OF GULF MOISTURE LIFTS NORTHWARD ON
MONDAY...RESULTING IN MORE WIDESPREAD ADVERSE CONDITIONS THROUGH
TUESDAY.

&&

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

&&

SYNOPSIS...CBL
NEAR TERM...CBL
SHORT TERM...CBL
LONG TERM...BLAES
AVIATION...CBL

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SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE RALEIGH NC
313 PM EDT FRI SEP 28 2012

NCZ021-282015-
FORSYTH-
313 PM EDT FRI SEP 28 2012

...A STRONG THUNDERSTORM WILL MOVE ACROSS FORSYTH COUNTY THROUGH 415
PM EDT...

AT 313 PM EDT...DOPPLER RADAR INDICATED A STRONG THUNDERSTORM OVER
HUNTSVILLE...OR ABOUT 9 MILES SOUTH OF EAST BEND...MOVING EAST AT 15
MPH.

SOME LOCATIONS AFFECTED BY THIS STORM INCLUDE...LEWISVILLE...
CLEMMONS...PFAFFTOWN...WINSTON-SALEM.

HAZARDS INCLUDE...
GUSTY WINDS OF 30 TO 40 MPH.
DEADLY CLOUD TO GROUND LIGHTNING.
HEAVY RAINFALL AND MINOR FLOODING.

THIS INCLUDES INTERSTATE 40 BETWEEN EXITS 182 AND 203.

SEEK SHELTER IN A NEARBY BUILDING OR VEHICLE. STRONG WINDS ARE
CAPABLE OF KNOCKING DOWN SMALL TREES AND BLOWING AROUND TRASH CANS...
POTTED PLANTS...LAWN FURNITURE AND OTHER LIGHT OUTDOOR OBJECTS.

IF YOU SEE LIGHTNING OR HEAR THUNDER...YOU ARE AT RISK. TAKE SHELTER
INDOORS IMMEDIATELY. IF YOU CANNOT FIND SHELTER IN A BUILDING A
VEHICLE PROVIDES SAFETY FROM LIGHTNING.

THIS STORM WILL PRODUCE HEAVY RAINFALL...WHICH WILL CAUSE MINOR
FLOODING OF LOW LYING AREAS INCLUDING DITCHES...CREEKS...ROADWAYS AND
AREAS OF POOR DRAINAGE. AVOID THESE AREAS AND DO NOT CROSS FLOODED
ROADS. MOTORISTS SHOULD ALSO REDUCE DRIVING SPEEDS TO AVOID
HYDROPLANING.

&&

LAT...LON 3611 8051 3614 8044 3622 8044 3626 8045
      3626 8003 3601 8005 3603 8021 3600 8022
      3600 8032 3597 8040 3599 8043 3601 8042
      3606 8047 3604 8048 3605 8051 3609 8053
TIME...MOT...LOC 1913Z 273DEG 14KT 3609 8051

ELLIS