Area Forecast Discussion
Issued by NWS Anchorage, AK

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FXAK68 PAFC 191318
AFDAFC

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
518 AM AKDT SUN OCT 19 2014

.ANALYSIS AND UPPER LEVELS...

THE UPPER AIR PATTERN IS DOMINATED BY A HIGH AMPLITUDE NEGATIVE
TILT UPPER LEVEL TROUGH STRETCHING FROM NORTHWEST ALASKA TO 40N
JUST WEST OF THE PACIFIC US COASTLINE. THE POLAR JET STREAM IS IN
FULL SWING ACROSS THE NORTH CENTRAL PACIFIC AS A SHARP BAROCLINIC
ZONE EXISTS OWING TO A CONTINUED PATTERN OF COLD ARCTIC AIR MOVING
INTO THE BERING FROM EASTERN SIBERIA AND THE BERING STRAIT. A
MOBILE SHORTWAVE TROUGH IS TRACKING OFF THE KAMCHATKA PENINSULA
INTO THE WESTERN BERING...WITH AN ASSOCIATED STATIONARY FRONT
DRAPED ACROSS THE WESTERN AND CENTRAL ALEUTIANS. CLOSER TO THE
MAINLAND...A 979 MB SURFACE LOW ASSOCIATED WITH THE AFOREMENTIONED
UPPER TROUGH WILL MERGE WITH AN ENERGETIC UPPER LEVEL SHORTWAVE
TROUGH THEN TRACK INLAND ACROSS WESTERN PRINCE WILLIAM SOUND AND
INTO COOK INLET. PRECIPITATION WILL SUBSEQUENTLY INCREASE ACROSS
THE NORTH GULF COAST AND PORTIONS OF SOUTHCENTRAL BEGINNING SUNDAY
EVENING AND LASTING THROUGH MONDAY.

&&

.MODEL DISCUSSION...

THE NUMERICAL GUIDANCE IS IN EXCELLENT AGREEMENT WITH THE LARGE
SCALE PATTERN THROUGH THE END OF THE WEEK...BUT THERE ARE SLIGHT
BUT IMPACTFUL DIFFERENCES WITH THE DEPICTION OF A LOW TRACKING
INTO SOUTHCENTRAL ON MONDAY...AND A STRONG LOW MOVING INTO THE
SOUTHERN GULF LATE TUESDAY AND WEDNESDAY. THE NAM AND CANADIAN
RDPS WERE SOUTHWARD OUTLIERS WITH THE FORMER...WITH THE
GFS...CANADIAN GDPS...AND ECMWF FAVORING A NORTHERLY AND FASTER
SOLUTION. A MIDDLE GROUND APPROACH WAS FAVORED...LEANING TOWARD
THE GLOBAL MODELS WHICH STAY NORTH. THE DIFFERENCES IN THE LATTER
LOW WILL BE HANDLED BY THE ECMWF AS THE GFS WAS AN OUTLIER WITH
RESPECT TO STRENGTH OF THE LOW. OTHERWISE...FORECAST CONFIDENCE
ACROSS THE REGION IS MODERATE THROUGH EARLY WEEK....AND HIGH
TOWARD THE END OF THE WEEK.

&&

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...
A GENERALLY QUIET WEATHER REGIME WILL BE ONGOING ACROSS
SOUTHCENTRAL SUNDAY. LOCAL FOG ACROSS THE COPPER BASIN AND
PORTAGE VALLEY WILL LINGER THROUGH MID MORNING BEFORE LIFTING AS A
GULF LOW TRACKS NORTH TOWARD THE COAST. RAIN WILL SPREAD ALONG THE
GULF COAST FROM PRINCE WILLIAM SOUND EAST BY AFTERNOON AND EARLY
EVENING...WITH LIGHT SNOW SHOWERS ACROSS PORTIONS OF THE SOUTHERN
COPPER BASIN AND TOWARD MENTASTA PASS. RAIN...POSSIBLY MIXED WITH
WET SNOW DOWN TO THE SURFACE...WILL MOVE INTO ANCHORAGE AND PARTS
OF THE NORTHERN KENAI PENINSULA SUNDAY NIGHT INTO MONDAY MORNING.
THERE REMAINS DISCREPANCY IN BOTH PLACEMENT OF THE LOW AND HOW
MUCH COLD AIR THERE WILL BE IN PLACE BY MONDAY MORNING...WHICH
MAKES FOR A SOMEWHAT UNCERTAIN FORECAST. FOR NOW...SNOW
ACCUMULATIONS WILL LIKELY REMAIN ELEVATED. HOWEVER...THERE IS A
SMALL PROBABILITY THAT SOME LIGHT ACCUMULATIONS COULD DEVELOP AT
SEA LEVEL AROUND ANCHORAGE AND THE NORTHERN KENAI SHOULD BANDING
DEVELOP. PRECIPITATION BECOMES SHOWERY BY MONDAY AFTERNOON AND
EVENING...THEN DRIES OUT BY TUESDAY AS A DEVELOPING LOW IN THE
SOUTHERN GULF SETS UP AN OFFSHORE FLOW PATTERN ACROSS
SOUTHCENTRAL.

SOUTHWEST ALASKA...
LIGHT SNOW SHOWERS WILL BE A THREAT ACROSS ALL OF SOUTHWEST
ALASKA THROUGH MONDAY EVENING BEFORE THINGS TAPER OFF TUESDAY. THE
BEST CHANCE FOR LIGHT ACCUMULATIONS WILL COME MONDAY AS AN UPPER
DISTURBANCE TRACKS OVER THE REGION. THE PATTERN BECOMES LARGELY
DRY AND OFFSHORE TUESDAY AND WEDNESDAY.

BERING SEA/ALEUTIANS...
A SURFACE LOW AND ASSOCIATED FRONT WILL SKIRT ALONG THE WESTERN
AND CENTRAL ALEUTIANS TODAY BEFORE MOVING INTO THE NORTH PACIFIC.
PRECIPITATION WILL MAINLY IMPACT LOCATIONS FROM UNALASKA
WEST...WITH SHOWERY CONDITIONS ELSEWHERE. COLD AIR WILL SPILL
ACROSS THE ENTIRE ALEUTIAN CHAIN AS THE FRONT TRACKS SOUTH TUESDAY
AND WEDNESDAY...WITH WIDESPREAD RAIN AND SNOW SHOWERS ACROSS THE
CENTRAL AND EASTERN BERING AND ALEUTIANS.

&&

.LONG TERM FORECAST...

IT IS NOW LIKELY THAT A NORTH PACIFIC LOW EARLY NEXT WEEK WILL
STRUGGLE TO REACH AS FAR NORTH AS THE EXTREME SOUTHERN GULF.
BECAUSE OF THIS CONFIDENCE IS INCREASING THAT THE SOUTHERN
MAINLAND WILL SEE A CLEARING...DRYING...AND COOLING TREND STARTING
ON TUESDAY THAT WILL CONTINUE FOR A MAJORITY OF THE UPCOMING
WEEK. THIS SYSTEM WILL ALSO DRAG DOWN SOME OF THE COLDEST AIR OF
THE SEASON BY LATE IN THE WEEK...POSSIBLY DIPPING BELOW ZERO IN
THE COPPER RIVER BASIN AND NORTHERN SUSITNA VALLEY.

OUT WEST LITTLE HAS CHANGED IN THE LONG TERM FORECAST. GUSTY
NORTHWESTERLY WINDS AND SHOWERS WILL BEGIN TO DIMINISH ON
WEDNESDAY IN ADVANCE OF RIDGING THAT WILL EVENTUALLY SPREAD ONTO
THE SOUTHERN MAINLAND. BY LATE IN THE WEEK...A FRONT ASSOCIATED
WITH A KAMCHATKA WILL BRING THE NEXT ROUND OF RAIN AND WINDS TO
THE WESTERN BERING AND ALEUTIANS.

-DEK

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE 178 185.
FIRE WEATHER...NONE.

&&

$$

AHSENMACHER OCT 14


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