Special Weather Statement, NWS Raleigh, NC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
310 PM EDT WED JUL 24 2013

.SYNOPSIS...
A COLD FRONT WILL DROP SOUTHEASTWARD THROUGH CENTRAL NORTH CAROLINA
TONIGHT... AND STALL OUT JUST TO OUR SOUTH ON THURSDAY. WEAK HIGH
PRESSURE WILL BUILD INTO THE REGION BEHIND THIS FRONT THURSDAY...
AND REMAIN OVER THE AREA THROUGH FRIDAY.

&&

.NEAR TERM /THROUGH THURSDAY NIGHT/...
AS OF 300 PM WEDNESDAY...

THROUGH TONIGHT: LATEST SURFACE MAP SHOWS THE PREFRONTAL TROUGH
STRETCHING FROM THE NRN COASTAL PLAIN SW THROUGH THE SANDHILLS...
AND THE INCOMING COLD FRONT NOW EXTENDING THROUGH THE OH VALLEY. THE
LACK OF CLOUDS THIS MORNING AND DRY COLUMN HAVE ALLOWED FOR GOOD
HEATING TODAY... NEAR 90 TO THE LOWER 90S... WHICH HAS LED TO
MODERATE DESTABILIZATION (MUCAPE AROUND 2000 J/KG). WE'RE ALREADY
SEEING SCATTERED CONVECTIVE CELLS DEVELOPING... ALTHOUGH THE
SOMEWHAT LOW PW (1.4-1.6 IN.) AND POOR DEEP LAYER SHEAR HAVE LIMITED
COVERAGE AND STRENGTH OF UPDRAFTS THUS FAR. BUT AS THE COLD FRONT
APPROACHES... LOW LEVEL MASS CONVERGENCE AND DEEP LAYER SHEAR SHOULD
IMPROVE... AS WILL THE MID LEVEL LAPSE RATES (CURRENTLY AT OR UNDER
5.5 C/KM BUT EXPECTED TO RISE A BIT TO 6.0-6.25 C/KM TONIGHT) AS THE
MID LEVEL TROUGH DIGS JUST TO OUR WEST. THIS WILL INTRODUCE SOME
WEAK DPVA LATER TONIGHT... ALONG WITH WEAK UPPER DIVERGENCE WITH THE
JET OVER THE CENTRAL US NOSING TOWARD THE WRN CAROLINAS. THIS MEANS
THAT THE TIME OF PEAK HEATING THIS AFTERNOON WILL NOT LINE UP
IDEALLY WITH THE IMPROVING (DECENT FOR THIS TIME OF YEAR BUT STILL
NOT TREMENDOUS) DYNAMIC FORCING FOR ASCENT AND BETTER WIND FIELD
THROUGH THE COLUMN. BUT THE INSTABILITY ALONE AND REBOUNDING PW BACK
TO 1.8 INCHES OR GREATER STILL SUPPORTS GOOD CHANCE POPS THROUGH
TONIGHT... HIGHEST IN THE NORTH WHERE MID LEVEL WINDS WILL BE
STRONGER. WITH STRONG DOWNDRAFT CAPE AND STEEP LOW LEVEL LAPSE
RATES... STRAIGHT LINE WINDS WILL REMAIN THE PRIMARY SEVERE WEATHER
THREAT INTO TONIGHT... WITH A LESSER THREAT OF HAIL DUE TO THE
MARGINAL CAPE IN THE -10C TO -30C LAYER (JUST NEAR 300 J/KG
CURRENTLY DUE TO WARM TEMPS ALOFT... ALTHOUGH IT'S EXPECTED TO RISE
TO DECENT VALUES OF 600-800 J/KG EARLY THIS EVENING). NAM/GFS AGREED
WELL ON ISOLATED CONVECTION AREAWIDE FOLLOWED BY SCATTERED STORMS TO
OUR NW DROPPING TO THE ESE DURING THE EVENING... INCREASING IN
COVERAGE AS IT HEADS EASTWARD AND FEEDS ON BETTER MOISTURE IN PLACE
OVER THE COASTAL PLAIN. WILL TREND BACK DOWN TO A LOWER CHANCE LATE
TONIGHT AS LOW PRESSURE DEEPENS JUST OFF THE SE NC COAST LEADING TO
A MORE STABLE LOW LEVEL FLOW FROM THE NNE... BUT THE DIGGING TROUGH
INTO CENTRAL NC AND DPVA TOWARD DAYBREAK SHOULD BRING ENOUGH LARGE
SCALE LIFT TO CONTINUE AT LEAST LOW POPS LATE. EXPECT NO MORE THAN
AN INCH OF RAINFALL AT ANY ONE SPOT BUT THE GREATER TOTALS SHOULD BE
OVER THE NORTHCENTRAL AND NE CWA WHERE THE HIGHER LOW-LEVEL MASS
CONVERGENCE AND STRONGER DPVA WILL BE FOUND. WITH THE RELATIVELY
COOLER AIR NOT ARRIVING UNTIL VERY LATE... PERSISTENCE PROVIDES THE
BEST MIN TEMP GUIDANCE... SUPPORTING LOWS OF 67-72.

FOR THURSDAY/THURSDAY NIGHT: THE FRONT IS EXPECTED TO SETTLE TO OUR
SOUTHEAST THURSDAY... MERGING WITH THE PRECEDING TROUGH WHILE THE
SURFACE LOW DEEPENS AND TRACKS NORTHEASTWARD OFF OUR COAST. THE HIGH
PRESSURE AREA ATTEMPTING TO BUILD IN FROM THE NORTH IS JUST AROUND
1019 MB BUT CONTAINS AIR THAT IS FAIRLY DENSE FOR THIS TIME OF
YEAR... WITH CORE DEW POINTS IN THE 40S. SO DESPITE THE FACT THAT
ACTUAL COLD FRONTAL PASSAGE WELL THROUGH CENTRAL NC IS A VERY RARE
OCCURRENCE FOR JULY... THIS FRONT MAY BEAT THIS TENDENCY AND SHOULD
PUSH JUST FAR ENOUGH SE OF THE CWA TO PUT US ALL IN THE STABLE NNE
LOW LEVEL FLOW. MODEL FORECAST SOUNDINGS DIFFER AS TO HOW STABLE
THIS INCOMING AIR MASS WILL BE... WITH A GENERAL ABSENCE OF GOOD
MOIST OVERRUNNING THAT WOULD ENHANCE SURFACE-BASED STABILITY. BUT
THIS MORNING'S UPPER AIR ANALYSES SHOWED ENOUGH 925-850 MB MOISTURE
TO OUR N AND NNW THAT SHOULD FILTER INTO CENTRAL NC TO PRODUCE
VARIABLE CLOUDY SKIES FOR MUCH OF THURSDAY... PARTICULARLY WITH
POTENTIAL INFLUX OF MARINE AIR AS THE STRENGTHENING LOW ENHANCES THE
NNE WINDS INTO THE AREA. HAVE LOW CONFIDENCE IN PRECIP CHANCES GIVEN
THE LOW LEVEL STABILITY AND FALLING PW AS DRIER AIR WORKS IN FROM
THE WEST. BUT THIS DOESN'T OCCUR UNTIL AFTERNOON ACCORDING TO THE
NAM/GFS WHICH KEEP PW ABOVE 1.5 INCHES IN THE EAST HALF OF THE CWA
UNTIL MID AFTERNOON. WILL RETAIN A CHANCE OF SHOWERS ACROSS THE EAST
AND FAR SOUTH INTO THE AFTERNOON... THEN NO POPS FROM EARLY EVENING
ON THROUGH THE NIGHT WITH FURTHER DRYING AND A WEAKENING WIND FIELD
AS THE TROUGH AXIS HEADS TO OUR EAST AND WEAKENS. TEMPS ARE QUITE
TOUGH WITH COLD AIR ADVECTION AND CLOUD COVER LEADING TO ATYPICALLY
LOW THICKNESSES. WILL STICK WITH HIGHS 81-86... A BLEND OF
STATISTICAL GUIDANCE. LOWS 63-70. -GIH

&&

.SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT /...
AS OF 305 PM WEDNESDAY...

IN THE WAKE OF THE COASTAL LOW MOVING OFF TO THE NORTHEAST
FRIDAY...A WEAK EAST-NORTHEASTERLY LOW LEVEL FLOW AND RELATIVELY
STABLE AIRMASS SHOULD KEEP MOST OF FRIDAY DRY WITH A BRIEF PERIOD OF
SHORTWAVE RIDGING ALOFT AS ANOTHER PAIR OF SHORTWAVES APPROACH FROM
THE WEST.  WITH BETTER INSOLATION FRIDAY...HIGHS ARE EXPECTED TO
REBOUND A FEW DEGREES OVER THURSDAYS VALUES INTO THE MID TO UPPER
80S.  ALL MODELS SHOW A SOUTHERN WAVE...LIKELY CONVECTIVELY
ENHANCED...MOVING ACROSS THE DEEP SOUTH FRIDAY NIGHT....WHILE A
DEEPER NORTHERN STREAM SHORTWAVE BECOMES A CLOSED LOW OVER THE
NORTHERN GREAT LAKES. THE GFS IS FASTER THAN ANY OTHER
MODEL WITH THE SOUTHERN WAVE AND THE NAM APPEARS TO BE TOO STRONG
WITH A SURFACE WAVE INDUCED ALONG THE REMNANT FRONTAL ZONE OFF THE
SOUTHEAST COAST.   BASED ON A SLOWER TIMING OF THESE
FEATURES...EXPECT CONVECTION TO BE MOSTLY DRIVEN BY RETURN FLOW AND
FOCUSED ALONG THE SEABREEZE AND HIGHER TERRAIN ON SATURDAY.  HIGHS
IN THE UPPER 80S.  LOWS IN THE UPPER 60S TO AROUND 70.

&&

.LONG TERM /SUNDAY THROUGH WEDNESDAY/...
AS OF 305 PM WEDNESDAY...

THE EXTENDED PERIOD WILL FEATURES A WEAK UPPER LOW OVER THE NORTHERN
GREAT LAKES AND SOUTHERN CANADA...WITH A DEEP TROUGH OVER THE
EASTERN US AND A RIDGE OVER THE WESTERN US.  A COLD FRONT WILL
APPROACH FROM THE NORTHWEST SUNDAY AND IS FORECAST TO MOVE INTO OUR
BY MONDAY...WHILE THE POSSIBLE REMNANTS OF A SOUTHERN
WAVE SHEARS OUT ACROSS THE SOUTHEAST STATES AND CAROLINAS.  THIS
WILL LEAD TO AN ACTIVE PERIOD SUNDAY INTO MONDAY...THOUGH THERE ARE
STILL SOME MODEL DIFFERENCES REGARDING THE DETAILS OFF THE CLOSED
LOW AND TIMING OF THE FRONTAL ZONE.  HIGHS WILL CONTINUE TO BE
ABOUT A CATEGORY BELOW NORMAL WITH WIDESPREAD CLOUD COVER AND
LOWER HEIGHTS ALOFT. SOME MODERATION IS POSSIBLE TOWARD THE MIDDLE
OF NEXT WEAK IF THE UPPER TROUGH DEAMPLIFIES AND THE RIDGE EXPANDS
EAST...AS MODELS SUGGEST COULD OCCUR.

&&

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

VFR CONDITIONS WILL HOLD THROUGH SUNSET... BUT SUB-VFR CONDITIONS
ARE THEN EXPECTED TO DEVELOP OVERNIGHT... LIKELY TO LAST THROUGH
EARLY THU AFTERNOON. A WEAK SURFACE TROUGH WILL CONTINUE TO SIT
ACROSS THE SANDHILLS/ERN PIEDMONT THE REST OF THE AFTERNOON AS A
COLD FRONT SLOWLY APPROACHES FROM THE NW. SCATTERED STORMS ARE
EXPECTED AHEAD OF THE FRONT... AND THESE COULD AFFECT ANY CENTRAL NC
TAF SITE AT ANY TIME THIS AFTERNOON THROUGH EVENING... BUT ARE MOST
LIKELY TO AFFECT INT/GSO 18Z-21Z... RDU 21Z-03Z... FAY 22Z-03Z...
AND RWI 23Z-04Z. BRIEF MVFR-IFR CONDITIONS WITH HEAVY DOWNPOURS AND
STRONG GUSTY WINDS ARE POSSIBLE IN AND NEAR ANY OF THESE STORMS.
OTHERWISE... CLOUD BASES SHOULD REMAIN ABOVE 3 KFT AGL UNTIL AFTER
MIDNIGHT. AFTER THE FRONT MOVES THROUGH (EXPECTED TO OCCUR FROM
03-05Z AT INT/GSO... 05Z-07Z AT RDU... 07Z-09Z AT RWI... AND 09Z-12Z
AT FAY)... WINDS WILL SHIFT TO BE FROM THE NNE AND INCREASE TO
AROUND 8-12 KTS WITH A FEW GUSTS OVER 15 KTS POSSIBLE. SCT-BKN
CLOUDS BASED AT 1-3 KFT ARE ALSO EXPECTED TO DEVELOP LATE TONIGHT...
LIFTING SLOWLY TO VFR BETWEEN 14Z AND 18Z THU MORNING.

LOOKING BEYOND 18Z THURSDAY... CONDITIONS WILL REMAIN GENERALLY VFR
THROUGH THURSDAY NIGHT ALTHOUGH A FEW STORMS ARE POSSIBLE NEAR
RDU/RWI/FAY FROM MID AFTERNOON THROUGH MID EVENING. THE FRONT WILL
WASH OUT AND DISSIPATE TO OUR SOUTHWEST ON FRIDAY. EXPECT VFR
CONDITIONS TO PREVAIL FRIDAY THROUGH SATURDAY... THEN CHANCES FOR
SUB-VFR CONDITIONS INCREASE AS ANOTHER FRONT APPROACHES FROM THE NW
SATURDAY NIGHT... THEN HOLDS OVER THE AREA THROUGH MONDAY.
OCCASIONAL MVFR CONDITIONS WITH SCATTERED SHOWERS AND STORMS ARE
POSSIBLE FROM LATE SATURDAY THROUGH MONDAY. -GIH

&&

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

&&

SYNOPSIS...WSS/GIH
NEAR TERM...HARTFIELD
SHORT TERM...BLS
LONG TERM...BLS
AVIATION...HARTFIELD

HAZARDOUS WEATHER OUTLOOK
NATIONAL WEATHER SERVICE RALEIGH NC
527 AM EDT WED JUL 24 2013

NCZ007>011-021>028-038>043-073>078-083>086-088-089-250930-
PERSON-GRANVILLE-VANCE-WARREN-HALIFAX-FORSYTH-GUILFORD-ALAMANCE-
ORANGE-DURHAM-FRANKLIN-NASH-EDGECOMBE-DAVIDSON-RANDOLPH-CHATHAM-WAKE-
JOHNSTON-WILSON-STANLY-MONTGOMERY-MOORE-LEE-HARNETT-WAYNE-ANSON-
RICHMOND-SCOTLAND-HOKE-CUMBERLAND-SAMPSON-
527 AM EDT WED JUL 24 2013

THIS HAZARDOUS WEATHER OUTLOOK IS FOR CENTRAL NORTH CAROLINA.

.DAY ONE...TODAY AND TONIGHT.

ISOLATED SEVERE THUNDERSTORMS ARE POSSIBLE THIS AFTERNOON THROUGH
THIS EVENING....MAINLY BETWEEN 3 PM AND 11 PM. THE MAIN SEVERE
WEATHER HAZARDS WILL BE LOCALIZED DAMAGING WIND GUSTS AND HAIL TO
THE SIZE OF QUARTERS. IN ADDITION...SOME OF THE STORMS WILL
PRODUCE A LARGE NUMBER OF LIGHTNING STRIKES.

.DAYS TWO THROUGH SEVEN...THURSDAY THROUGH TUESDAY.

HAZARDOUS WEATHER IS NOT EXPECTED AT THIS TIME.

.SPOTTER INFORMATION STATEMENT...

SKYWARN SPOTTERS ARE ENCOURAGED TO REPORT ANY SEVERE OR
SIGNIFICANT WEATHER IMMEDIATELY TO THE NATIONAL
WEATHER SERVICE.

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