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000
FXUS62 KRAH 080818
AFDRAH

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
316 AM EST SUN DEC 8 2013

.SYNOPSIS...AS ARCTIC HIGH PRESSURE CONTINUES TO BUILD OVER THE
REGION...WARM AND MOIST AIR WILL RIDE ATOP THE LOW-LEVEL COLD DOME
TODAY PRODUCING FREEZING RAIN ACROSS THE WESTERN AND NORTHERN
PORTIONS OF THE STATE...WITH A COLD RAIN CENTRAL AND EASTERN AREAS.
A WEAK COASTAL LOW WILL LIFT UP THE MIDDLE ATLANTIC COAST LATE
TONIGHT AND MONDAY...FOLLOWED BY FRONTAL ZONE THAT WILL DRIFT
SLOWLY EAST THROUGH THE CAROLINAS MONDAY NIGHT AND TUESDAY.

&&

.NEAR TERM /THROUGH TONIGHT/...
AS OF 255 AM SUNDAY...

NO CHANGES TO CURRENT WARNING AND ADVISORY CONFIGURATION/LAYOUT
AS WE AWAIT FOR PRECIPITATION TO DEVELOP ACROSS THE AREA.

A COMPLEX PATTERN CURRENTLY UNFOLDING OVER THE EAST/SOUTHEASTERN US
AS MID-LEVEL HEIGHT FALLS ASSOCIATED WITH SHORTWAVE TROUGH LIFTING
FROM THE SOUTHERN-CENTRAL ROCKIES NORTHEASTWARD INTO THE UPPER GREAT
LAKES TONIGHT/EARLY MONDAY HAS BEGUN TO GIVE RISE TO WEAK SURFACE
LOW PRESSURE DEVELOPMENT NEAR NEAR THE TN VALLEY. MEANWHILE...A
PROGRESSIVE BUT STRONG 1035-1040 ARCTIC HIGH WILL CONTINUE TO BUILD
EAST...BECOME FIRMLY ENTRENCHED OVER THE REGION TODAY. AS
AFOREMENTIONED SURFACE WAVE LIFTS NORTHEASTWARD ALONG THE SOUTHERN
APPALACHIANS AND INTO THE SOUTHERN MID-ATLANTIC REGION...ZONE OF
STRONG LOW TO MID-LEVEL WARM MOIST AIR ADVECTION WILL LEAD TO THE RE-
DEVELOPMENT AND THEN EXPANSION OF A STRATIFORM PRECIP SHIELD OVER
THE SOUTHERN APPALACHIANS. AS PRECIPITATION BEGINS TO FALL INTO THE
SHALLOW WEDGE OF COLD ARCTIC NEAR THE SURFACE... CLASSICAL COLD AIR
DAMMING WILL BRING AN EARLY SEASON FREEZING RAIN THREAT TO PORTIONS
OF THE WESTERN/NORTHERN PIEDMONT COUNTIES.

MODELS REMAIN STEADY WITH THE THERMAL STRUCTURE...STILL DEPICTING
THE ABRUPT DEVELOPMENT OF A PROMINENT 6-8C WARM NOSE ATOP THE
STRENGTHENING CAD WEDGE...ELIMINATING ANY MEASURABLE/NOTEWORTHY
FROZEN-MIXED PPRECIP ACROSS CENTRAL NC. INSTEAD THE ACCURACY OF THE
FORECAST AND WHETHER WE WILL SEE ANY ICE ACCUMULATION WILL HINGE ON
MARGINALLY FREEZING SFC WET-BULB TEMPERATURES OF 31-32F WITHIN THE
WARNING AREA THAT EXTENDS ALONG A LINE FROM CLEMMONS-HIGHPOINT-
GREENSBORO-ALTAMAHAW-ROXBORO. MODELS HAVE BEEN PRETTY STABLE IN THAT
REGARD...SLOWLY RETREATING THIS NEAR FREEZING SFC WET-BULB LINE
THROUGHOUT THE DAY...AND LIFTING IT NORTH OF THE AREA BY 00Z TO 03Z.
GIVEN THE MARGINALLY FREEZING TEMPERATURES ONLY A FRACTION OF THE
AVERAGE MODEL LIQUID QPF OF 0.30-0.40 WILL GO TO FREEZING WITH
MAJORITY OF THE ICE ACCRUAL BEING ON ELEVATED SURFACES SUCH AS TREES
AND POWER-LINES.

IN THE ADVISORY AREA...JUST SOUTH OF THE WARNING AREA...THE DURATION
OF NEAR FREEZING SFC WET BULBS WILL BE MUCH LESS...SUCCUMBING TO THE
INCREDIBLY WARM AIR ALOFT BY EARLY AFTERNOON WILL MINIMAL AND/OR
SHORT-LIVED IMPACTS.

THE PRECIPITATION WILL TAPER OFF TO DRIZZLE FROM SOUTH TO NORTH
DURING THE AFTERNOON AND INTO THE EVENING AS THE LLJ AND ASSOCIATED
ISENTROPIC LIFTS NORTH INTO THE MID-ATLANTIC REGION WITH A NEW
EXPANDING AREA OF PRECIP OFFSHORE ALONG A SECONDARY LOW PRESSURE
DEVELOPMENT OFF THE NORTH CAROLINA COAST.  TEMPERATURES WILL HOLD
STEADY OR INCH SLIGHTLY UPWARD ESPECIALLY LATE...AS THE ARCTIC RIDGE
SHIFTS OFFSHORE. TEMPERATURES IN THE LOWER 30S NORTH TO UPPER 30S
SOUTH.

&&

.SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
AS OF 315 AM SUNDAY...

THERE WILL BE A FRONT APPROACHING FROM THE WEST WITH LOW LEVEL
SOUTHWEST FLOW AHEAD OF THE FRONT ERODING THE WEDGE AIRMASS MONDAY.
EXPECT A WIDE TEMPERATURE RANGE ACROSS THE AREA AS A RESULT...WITH
HIGHS IN THE LOW 60S SOUTHEAST RANGING TO UPPER 40S IN THE NORTHWEST
WHERE LINGERING COOL AIR AND LIGHT RAIN/DRIZZLE WILL DELAY THE
PROCESS. THE FRONT WILL BE MOVING SLOWLY ACROSS THE AREA DURING THE
DAY...THUS TIMING LULLS IN THE PRECIP IS NOT A HIGH PERCENTAGE
FORECAST AT THIS POINT...SO WILL MAINTAIN LIKELY POPS ACROSS THE
AREA FROM MONDAY AFTERNOON INTO TUESDAY MORNING AS THE FRONT
SLOWS/STALLS IN THE VICINITY OF THE SOUTHEAST COAST MONDAY NIGHT.
RAINFALL AMOUNTS LOOK TO RANGE UP TO PERHAPS A HALF AN INCH THROUGH
THE PERIOD WITH GOOD MOISTURE ADVECTION UNDERWAY IN ADVANCE OF THE
FRONT...AND COULD BE HIGHER IN THE SOUTHEAST IN THE VICINITY OF THE
STALLED FRONTAL ZONE. MODEST COOL AIR ADVECTION WILL BE UNDERWAY
BEHIND THE FRONT MONDAY NIGHT WITH MINS FALLING INTO THE MID 40S
NORTHWEST TO MID 50S IN THE SOUTHEAST. WITH THE HEAVY CLOUDINESS AND
PRECIP...HIGHS TUESDAY WILL SHOW LITTLE DIURNAL INCREASE...WITH
HIGHS IN THE 40S ACROSS THE NORTHERN TIER TO THE 50S ACROSS THE
SOUTH. HIGH PRESSURE MIGRATING ACROSS THE OHIO VALLEY NUDGES THE
FRONT SOUTH TUESDAY NIGHT...SPREADING DRIER AIR INTO THE AREA...
WILL HAVE POPS DIMINISHING TO SLIGHT CHANCES OVERNIGHT WITH SOME
CLEARING TO ALLOW MINS TO FALL INTO THE UPPER 20S TO MID 30S.

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
AS OF 315 AM SUNDAY...

DRIER COOLER AIR WILL BE SPREADING INTO THE AREA...AND MODELS ARE
TRENDING TOWARDS A SURFACE WAVE ALONG THE FRONT OFFSHORE THAT COULD
PRODUCE ISENTROPIC LIFT OVER THE COOL AIR AND PERHAPS SOME LIGHT
SHOWER ACTIVITY IN THE EAST THROUGH MUCH OF WEDNESDAY. AT THIS POINT
WILL HOLD OFF THE POPS TO ACCOUNT FOR UNCERTAINTY IN JUST HOW FAR
SOUTHEAST OF THE ARE THE FRONT IS NUDGED. MEANWHILE...THE COOL
AIRMASS LOCKING INTO PLACE WILL PRODUCE HIGHS IN THE 40S WEDNESDAY
THROUGH FRIDAY...WITH GOOD RADIATIONAL CONDITIONS ALLOWING MINS TO
FALL INTO THE MID AND UPPER 20S EACH NIGHT.

LOOKS LIKE THE CAD CYCLE MAY RELOAD AS THE WEEKEND APPROACHES...WITH
THE COLD AIR REGIME OVER THE AREA LATE WEEK ASSUMING A
CLIMATOLOGICAL ORIENTATION WITH AN INVERTED TROF ALONG THE COAST IN
THE MARITIME BAROCLINIC ZONE. RESULTING CYCLOGENESIS WOULD PRODUCE
ISENTROPIC LIFT AND RAIN SATURDAY.

&&

.AVIATION /06Z SUNDAY THROUGH WEDNESDAY/...
AS OF 1230 AM SUNDAY...

24-HR TAF PERIOD:
AVIATION CONDITIONS WILL BEGIN TO DETERIORATE BETWEEN 06 TO 12Z...
BECOMING PREDOMINATELY MVFR AND POSSIBLY IFR AT SOME LOCATIONS BY
DAYBREAK AS A WARM RAIN BEGINS TO OVERSPREAD AND FALL INTO A SHALLOW
DOME OF COLD AIR AT THE SURFACE. THEREAFTER...IFR/LIFR WILL REMAIN
LOCKED IN ACROSS THE FORECAST AREA AS PRECIP STRENGTHENS THE COLD
AIR DAMMING WEDGE OVER CENTRAL NC. PRECIP IS EXPECTED TO TRANSITION
TO FZRA AT THE INT/GSO TERMINALS AROUND OR SHORTLY AFTER SUNRISE
(~12Z)...AND PERSIST AS FZRA/FZDZ THROUGH MUCH OF THE DAY BEFORE
TRANSITIONING BACK TO RAIN SUNDAY EVENING/TONIGHT. A VERY BRIEF
PERIOD OF FZRA WILL ALSO BE POSSIBLE AT THE RDU TERMINAL SUNDAY
MORNING BETWEEN 12-17Z...THOUGH UNCERTAINTY IS HIGH WITH REGARD TO
DURATION/IMPACT. FURTHER EAST/SOUTH AT THE RWI/FAY TERMINALS...
EXPECT ONLY RAIN. ONCE THE RAIN TAPERS OFF LATE THIS EVENING BETWEEN
00 TO 06Z...AREAS OF DENSE FOG WILL BE POSSIBLE WITH A CONTINUATION
OF IFR/LIFR CONDITIONS.

LOOKING AHEAD: EXPECT ADVERSE AVIATION CONDITIONS TO PERSIST THROUGH
TUESDAY/WEDNESDAY. VFR CONDITIONS SHOULD RETURN BY WED/THU AS HIGH
PRESSURE BUILDS INTO THE REGION IN THE WAKE OF A COLD FRONTAL
PASSAGE. -VINCENT

&&

.RAH WATCHES/WARNINGS/ADVISORIES...
FREEZING RAIN ADVISORY FROM 4 AM TO 7 PM EST SUNDAY FOR
NCZ008>010-024-025-038>040.
ICE STORM WARNING FROM 4 AM SUNDAY TO MIDNIGHT EST SUNDAY NIGHT
FOR NCZ007-021>023.

&&

$$

SYNOPSIS...PWB/MWS
NEAR TERM...CBL
SHORT TERM...MLM
LONG TERM...MLM
AVIATION...CBL/VINCENT