Special Weather Statement, NWS Raleigh, NC

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
330 PM EDT WED APR 4 2012

.SYNOPSIS...
A STRONG COLD FRONT PUSHES THROUGH THE REGION FROM THE NORTH TONIGHT
AND EARLY THURSDAY...BEING LOCATED ALONG OR JUST SOUTH OF THE SOUTH
CAROLINA BORDER THURSDAY AFTERNOON. LOW PRESSURE DEVELOPING ALONG
THE FRONT WILL MOVE OFF INTO THE ATLANTIC ON FRIDAY. HIGH PRESSURE
BUILDS IN FOR THE WEEKEND.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 250 PM WEDNESDAY...

THE LATEST SURFACE ANALYSIS SHOWED A SURFACE FRONT LOCATED OVER FAR
SOUTHERN WEST VIRGINIA AND CENTRAL VIRGINIA...WITH SURFACE-BASED
INSTABILITY INCREASING ALONG THE FRONT AS LIFTED INDICES HAVE FALLEN
TO AROUND -5C WITH A SURFACE MOISTURE POOL STARTING TO TAKE SHAPE
JUST SOUTH OF THE FRONT NEAR THE VIRGINIA BORDER. SPC MESOANALYSIS
SHOWS THE 0-6KM SHEAR HAS INCREASED TO JUST OVER 30KT...AND SOUTH OF
THE FRONT AND ALONG A SURFACE TROUGH ANALYZED OVER THE FOOTHILLS...
SCATTERED SHOWERS AND THUNDERSTORMS HAVE DEVELOPED. IN THE
STEEPENING LAPSE RATES...AROUND 7C/KM FROM 1000-500MB THIS
AFTERNOON...EXPECT SHOWERS AND THUNDERSTORMS TO CONTINUE TO INCREASE
IN COVERAGE AND INTENSITY. MESOSCALE MODELS HAVE BEEN CONSISTENT IN
SHOWING A CLUSTER OR TWO OF THUNDERSTORMS PROGRESSING SOUTHEAST OVER
OR NEAR CENTRAL NORTH CAROLINA THROUGH THE EVENING HOURS...EXITING
AROUND 03Z IN THE COASTAL PLAIN. WITH SEVERE THUNDERSTORM WATCH 140
IN EFFECT UNTIL 10 PM OR 02Z...THE PRIMARY THREAT SHOULD BE DAMAGING
WINDS...ALTHOUGH WET-BULB ZERO HEIGHTS ARE LOW ENOUGH THAT LARGE
HAIL IS ALSO A THREAT. ALREADY...THERE HAS BEEN A REPORT OR TWO OF
SMALL HAIL...TO PEA SIZE...JUST WEST OF THE YADKIN RIVER.

LATE TONIGHT...THE 850MB FRONT PROGRESSES SOUTH TO NEAR THE VIRGINIA
BORDER AS THE SURFACE FRONT MOVES INTO THE SANDHILLS AND SOUTHERN
COASTAL PLAIN. OVERNIGHT LOWS TOWARD THE SOUTH CAROLINA BORDER MAY
ACTUALLY OCCUR AT OR JUST AFTER 12Z AS THE FLOW TURNS NORTHEAST
BEHIND THE FRONT OVERNIGHT. BUFR SOUNDINGS STABILIZE OVERNIGHT AND
DRY SOME IN THE MID- AND UPPER-LEVELS BEFORE MOISTENING TAKES PLACE
AGAIN LATE TONIGHT...BETWEEN 09Z AND 12Z. MAINTAINED A CHANCE FOR
SHOWERS OVERNIGHT WITH THE HIGHER CHANCES MAINLY ALONG AND NORTH OF
U.S. 64 CLOSER TO THE 850MB FRONT AND WHERE THE BUFR SOUNDINGS SHOW
THE BEST MID-LEVEL MOISTENING RENEWED LATE. OVERNIGHT LOWS...MID 50S
NEAR THE VIRGINIA BORDER TO LOWER 60S TOWARD THE SOUTH CAROLINA
BORDER.

&&

.SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
AS OF 300 PM WEDNESDAY...

THE 850MB FRONT GRADUALLY MAKES PROGRESS SOUTH THURSDAY AND THURSDAY
NIGHT...BEING NEAR THE SOUTH CAROLINA BORDER BY THURSDAY EVENING.
JET SUPPORT ACTUALLY IMPROVES LATE THURSDAY AND THURSDAY EVENING...
WITH ALMOST A COUPLED JET STRUCTURE AT 250MB AS THE RIGHT ENTRANCE
REGION OF ABOUT A 95KT JET IS LOCATED JUST OFFSHORE OF VIRGINIA...
WHILE THE LEFT EXIT REGION IS OVER THE SOUTHEAST STATES. WITH
PRECIPITABLE WATER VALUES FROM 1.25 TO 1.5 INCHES...THERE WILL BE A
CHANCE OF SHOWERS JUST NORTH OF THE SURFACE FRONT AND ALONG THE
850MB BOUNDARY ON THURSDAY UNDER CONSIDERABLE CLOUDINESS. THE BEST
CHANCES THURSDAY COULD BE EARLY IN THE DAY...AND THEN AGAIN
DEVELOPING LATE...COINCIDENT WITH THE ADVECTION OF MID-LEVEL
MOISTURE ON BUFR SOUNDINGS. DECENT CHANCES FOR RAIN AND SHOWERS...IN
THE LIKELY RANGE...ARE FORECAST THURSDAY NIGHT AS THE 850MB FRONT IS
LOCATED NEAR THE SOUTH CAROLINA BORDER...AND WHERE THE GFS FORECASTS
AN 850MB LOW MOVING EAST ALONG THAT FRONT AND THE NAM ALSO PROVIDES
FOR ITS OVERALL HIGHEST QPF AND 850MB LIFT. DIFFLUENCE ALOFT SHOULD
ALSO INCREASE WITH THE APPROACHING MID-LEVEL LOW. WHILE
SURFACE-BASED CAPE SHOULD BE SOUTH OF CENTRAL NORTH CAROLINA...FOR A
BRIEF PERIOD VERY LATE THURSDAY AFTERNOON AND THURSDAY EVENING
ELEVATED INSTABILITY IS SUCH...PARTICULARLY ON THE KFAY BUFR
SOUNDING FROM THE NAM...THAT ELEVATED THUNDER IS POSSIBLE ESPECIALLY
FROM KAFP AND KRCZ EAST THROUGH FAYETTEVILLE INTO THE FAR SOUTHERN
COASTAL PLAIN. THE GFS IS SLOWER WITH DRYING THAN THE NAM...AND AS
SUCH WILL MAINTAIN LIKELY CHANCES FOR PRECIPITATION FOR ESSENTIALLY
THE ENTIRE NIGHT...WITH SOME DIMINISHING IN CHANCES VERY LATE TOWARD
SUNRISE. HIGHS ON THURSDAY SHOULD RISE ONLY 5 TO 10 DEGREES OR SO...
DESPITE THE NORTHEAST WIND HELPED BY CLOUDS NOT EXPECTED TO BE TOO
LOW...IN THE LOWER 60S TOWARD KIXA TO 70 TO 75 BY THE SOUTH CAROLINA
BORDER. OVERNIGHT THURSDAY...LOWS SHOULD BE IN THE MID 40S TO AROUND
50. -DJF

MODEL CONSENSUS CONTINUES TO INDICATE MORE RAPID DRYING ON FRIDAY AS
SURFACE LOW PRESSURE TAKES SHAPE OFFSHORE OF THE SC COAST... THEN
MOVES ON OUT TO SEA DURING THE DAY. CENTRAL NORTH CAROLINA WILL BE
ON THE BACK SIDE OF THE GRADUAL DEPARTING/WEAKENING SOUTHERN BRANCH
MID/UPPER LEVEL TROUGH AS IT GETS PICKED UP BY THE AMPLIFYING POLAR
TROUGH EXITING OFF THE NEW ENGLAND COAST FRIDAY. CLEARING SKIES ARE
NOW ANTICIPATED AS EARLY AS FRIDAY MORNING... SPREADING TO THE COAST
BY AFTERNOON. A GOOD CAA PATTERN WILL CONTINUE INTO THE AFTERNOON
WITH LOW LEVEL THICKNESSES SUPPORTING THE COOLER GUIDANCE EVEN WITH
SUNSHINE DURING THE AFTERNOON. HIGHS GENERALLY 60-66 EXPECTED.

FRIDAY NIGHT WILL BRING A CONCERN OF SCATTERED FROST FOR SOME PARTS
OF THE REGION. OF PARTICULAR INTEREST WILL BE THE CLIMATOLOGICALLY
COLDER AREAS OF THE PIEDMONT AND COASTAL PLAIN AWAY FROM URBAN
AREAS. CLEAR SKIES AND WINDS BECOMING LIGHT SUPPORT THE COLDER
GUIDANCE LOWS IN THE MID 30S TO AROUND 40... WITH THE COLDER
READINGS SUPPORTIVE OF SCATTERED FROST DEVELOPMENT. THIS WILL BE
MENTIONED IN THE HAZARDOUS WEATHER OUTLOOK.

FOR SATURDAY... HIGH PRESSURE WILL BE DOMINATE AS MOVES FROM THE
OHIO VALLEY TO THE MID-ATLANTIC SEABOARD. EXPECT MOSTLY SUNNY
CONDITIONS WITH SEASONABLE TEMPS IN THE 65-70 RANGE. -PWB

&&

.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
AS OF 325 PM WEDNESDAY...

...POTENTIAL FROST/FREEZE ISSUES EARLY TO MID NEXT WEEK AS THE
PATTERN CONTINUES TO COOL...

AFTER VIEWING THE 12Z EC AND ENSEMBLE GUIDANCE AVAILABLE AT 305
PM... TO GO WITH THE REST OF THE EARLY ARRIVING 12Z GUIDANCE... IT
CONTINUES TO CONFIRM A VERY INTERESTING PATTERN CHANGE THAT HAS BEEN
TAKING PLACE IN THE PAST WEEK. THE UPPER AIR PATTERN CHANGE HAS BEEN
SUBTLE THUS FAR BUT IT HAS LED TO SURFACE COOLING ALONG THE EASTERN
SEABOARD IN THE PAST WEEK. THIS CHANGE MAY NOT BE SO SUBTLE IN THE
COMING WEEK TO 10 DAYS AS THE COOLING TREND EXPANDS OVER THE EASTERN
THIRD OF THE UNITED STATES.

IRONICALLY... AS WE ARE LEAVING THE WINTER SEASON GOING INTO
SPRING... THE TEMPERATURES HAVE BEEN COOLING SINCE LATE MARCH OVER
THE NEW ENGLAND STATES DOWN INTO THE MID-ATLANTIC STATES INCLUDING
NC. THIS COOLING TREND IS OWING TO THE CHANGE IN THE UPPER AIR FLOW
PATTERN THAT HAD BEEN PERSISTENT FOR MUCH OF THE WINTER SEASON. A
STRONG UPPER RIDGE WHICH HAS BEEN LOCKED IN PLACE BETWEEN GREENLAND
AND THE U.K. IS RETROGRADING BACK TOWARD EASTERN CANADA AND SHOULD
BE IN THAT LOCATION BY TUE-WED NEXT WEEK. THE TROUGH AXIS THAT HAS
BEEN LOCATED OUT IN THE WESTERN ATLANTIC OCEAN... IS FORECAST TO
RETROGRADE BACK TO A POSITION THAT SHOULD ALIGN FROM HUDSON BAY INTO
THE GREAT LAKES AND OHIO VALLEY FOR MUCH OF NEXT WEEK. THIS WILL
ALLOW THE DELIVERY OF MODIFIED POLAR AIR FROM CANADA SOUTHWARD
ACROSS THE GREAT LAKES... NEW ENGLAND... AND MID-ATLANTIC STATES
INCLUDING NC. A COUPLE OF SURFACE COLD FRONTS WILL BE THE LEADING
EDGE OF THE COOLER AIR MASSES... ONE PASSAGE EXPECTED LATE SUNDAY...
FOLLOWED BY A MORE IMPORTANT BOUNDARY MONDAY AFTERNOON OR EVENING.

THE FROST AND POSSIBLY FREEZE POTENTIAL WILL RISE FOR NEXT WEEK
GIVEN THIS CRITICAL PATTERN CHANGE WHICH ALLOWS MODIFIED POLAR AIR
TO SURGE INTO THE REGION. THE EXACT NIGHTS THAT WILL BE CRITICAL
NIGHTS FOR FROST/FREEZE POTENTIAL ARE TOO EARLY TO PIN-DOWN AT THIS
TIME DUE TO THE DISAGREEMENT ON THE TIMING OF SPECIFIC FEATURES THAT
WILL BE ASSOCIATED WITH THE TROUGH ALOFT NEXT WEEK. HOWEVER... THIS
COOL DOWN COMES AT A CRITICAL TIME FOR OUR AGRICULTURAL AND OTHER
WEATHER PARTNERS THAT HAVE BEGUN SPRING PLANTINGS ETC... PREPARATIONS
SHOULD BE MADE NOW FOR THE EXPECTED COLD SPELL NEXT WEEK.

THE INCREASING FROST/FREEZE POTENTIAL FRIDAY NIGHT... AND ALSO FOR
NEXT WEEK WILL BE MENTIONED IN THE HAZARDOUS WEATHER OUTLOOK.

SENSIBLE WEATHER WILL INCLUDE...

A SLIGHT CHANCE OF SHOWERS WITH THE AFOREMENTIONED COLD FRONTAL
PASSAGES... OTHERWISE MOSTLY CLEAR AT NIGHT AND PARTLY SUNNY DURING
THE AFTERNOONS THIS WEEKEND INTO MID NEXT WEEK. LOWS MID 30S TO
LOWER 40S. (SAT AND TUE-WED MORNINGS ARE TARGET MORNINGS FOR THE
HIGHEST FROST POTENTIAL) WHEN LOWS OF 30-35 WILL BE POSSIBLE.
MORNINGS HIGHS GENERALLY IN THE 60S (LOWER TO MID 70S SUNDAY)... AND
SOME 50S IN THE NW-N ZONES BY WED.

&&

.AVIATION /18Z WEDNESDAY THROUGH MONDAY/...
AS OF 150 PM WEDNESDAY...

PRIMARY IMPACT THROUGH THE 18Z VALID TAF PERIOD WILL BE SCATTERED TO
NUMEROUS SHOWERS AND THUNDERSTORMS. ALREADY DURING THE EARLY
AFTERNOON SHOWERS WERE DEVELOPING CLOSER TO THE HIGHER ELEVATIONS
AND THE COLD FRONT...AND THESE SHOULD CONTINUE TO DEVELOP AND
INCREASE IN COVERAGE AS THEY MOVE SOUTHEAST DURING THE AFTERNOON.
EXPECT AT ALL TAF SITES POTENTIALLY FOR LOCALLY GUSTY WINDS WITH ANY
THUNDERSTORM AT OR ABOVE 30KT...WITH BRIEFLY IFR CONDITIONS. SUCH
CONDITIONS SHOULD DIMINISH BY 03Z IN CENTRAL NORTH CAROLINA.
OVERNIGHT INTO EARLY THURSDAY...WINDS WILL QUICKLY VEER TO NORTHEAST
BEHIND A COLD FRONT...WITH PATCHY RAIN EXPECTED UNDER CONSIDERABLE
CLOUDS IN THE VFR RANGE.

BEYOND THE 18Z VALID TAF PERIOD...A COLD FRONT WILL LIE JUST SOUTH
OF CENTRAL NORTH CAROLINA BY MID-MORNING THURSDAY. THUNDERSTORMS MAY
DEVELOP ALONG AND NEAR THE FRONT LATE THURSDAY AFTERNOON AND
EVENING...POSSIBLY GETTING CLOSE TO KFAY BUT LIKELY REMAINING JUST
SOUTH OF THERE. BEST POTENTIAL FOR IFR LOW CLOUDS WILL BE THURSDAY
NIGHT INTO EARLY FRIDAY...AND THEN PARTICULARLY TOWARD KFAY...AND
EXPECT THE LIKELIHOOD OF RAIN THURSDAY NIGHT. CONDITIONS GRADUALLY
IMPROVE FRIDAY INTO SATURDAY...WITH PREDOMINANT VFR CONDITIONS OVER
THE WEEKEND INTO EARLY NEXT WEEK.

&&

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

&&

SYNOPSIS...DJF
NEAR TERM...DJF
SHORT TERM...DJF/BADGETT
LONG TERM...BADGETT
AVIATION...DJF

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