Small Craft Advisory 991, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
507 AM AKST FRI DEC 12 2014

.ANALYSIS AND UPPER LEVELS...
THERE IS AN UPPER LEVEL LOW OVER THE NORTHERN GULF OF ALASKA WITH
A WEAK TROUGH STRETCHING NORTH-NORTHWEST INTO MAINLAND ALASKA.
WEAK SURFACE FLOW AND SOME CLEARING ALOFT OVER PARTS OF
SOUTHCENTRAL HAD LED TO FOGGY CONDITIONS AROUND THE AREAS
SURROUNDING COOK INLET. A WEAK UPPER LEVEL DISTURBANCE TRAVERSING
THE SOUTHWEST MAINLAND AROUND THIS TROUGH HAS KEPT SOME SCATTERED
SNOW SHOWERS ALIVE OVERNIGHT...AND ARE BEGINNING TO DIMINISH AS
WE HEAD INTO THE MORNING HOURS. THERE IS A WEAK UPPER LOW OVER THE
NORTHWEST BERING SEA WITH WEAK RIDGING OVER THE EASTERN BERING. AS
SEEN IN CURRENT OBSERVATIONS OVER THE CENTRAL AND EASTERN
ALEUTIANS/BERING...NORTHWEST FLOW OVER THE EASTERN HALF OF THE
BERING HAS BEGUN TO DIMINISH AS THE OVERALL PATTERN BEGINS TO
SHIFT TODAY. THERE IS A FAIRLY STRONG EASTWARD MOVING UPPER LOW
IS SOUTH OF THE EASTERN ALEUTIANS AND ANOTHER STRONG LOW NORTHEAST
OF JAPAN TRACKING TO THE WEST-NORTHWEST....WITH BOTH SYSTEMS BEING
ASSOCIATED WITH A FAIRLY STRONG SUBTROPICAL JET.

&&

.MODEL DISCUSSION...

MODELS ARE IN GOOD AGREEMENT WITH THE OVERALL PATTERN THROUGH
SATURDAY AFTERNOON...WHERE THEY BEGIN TO DIVERGE SLIGHTLY FROM A
COMMON SOLUTION. THE MAIN DIFFERENCE WORTH MENTIONING OVER THE
WEST WAS THE LOW FORMING OVER THE NORTH PACIFIC SATURDAY...AND
TRACKING OVER THE EASTERN ALEUTIANS BY SUNDAY MORNING. THE ECMWF
BECAME THE OUTLIER TODAY...BEING THE ONLY MODEL TO BRING THE
TRIPLE POINT LOW NORTH OF THE ALEUTIAN CHAIN. THE AMERICAN AND
CANADIAN MODELS ARE KEEPING THE SYSTEM SOUTH OF THE
ALEUTIANS...WHICH SEEMS TO BE THE MORE VIABLE SOLUTION. OVER THE
EAST DOMAIN...THE MAIN DISCREPANCY WAS REGARDING THE TIMING OF THE
LOW MOVING INTO THE GULF SATURDAY NIGHT. THE GFS WAS THE PREFERRED
SOLUTION HAVING BETTER RUN TO RUN CONSISTENCY REGARDING THIS
SYSTEM TRACKING INTO THE GULF...WITH THE NAM BEING THE SLIGHTLY
SLOWER OUTLIER AND THE ECMWF BEING MUCH SLOWER AND INCONSISTENT
FROM RUN TO RUN. OVERALL...FORECAST CONFIDENCE IS NEAR TO ABOVE
NORMAL THROUGH SATURDAY AFTERNOON...BECOMING BELOW NORMAL AS TIME
PROGRESSES AND MODEL SOLUTIONS DIVERGE FURTHER FROM EACH OTHER.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 THROUGH 3)...
THE MAIN FOCUS TODAY WILL BE FOG AND STRATUS AROUND THE COOK INLET
AND THE CHANCE FOR CONVECTIVE SNOW SHOWERS ALONG THE NORTHEAST
GULF COAST. HIGHER CLOUDS STREAMING OVERHEAD TONIGHT HAVE NOT DONE
MUCH TO MITIGATE LOW CLOUDS AROUND KNIK ARM THROUGH THE NORTHERN
KENAI PENINSULA. LOW LEVEL FLOW REMAINS PRETTY SLACK WHILE HIGHER
CLOUDS WILL MOVE OFF TO THE EAST GIVING THE OPPORTUNITY FOR
RADIATIONAL COOLING. THE STRATUS SHOULD STICK AROUND AND EVEN
BUILD AGAIN THIS EVENING INTO THE OVERNIGHT HOURS...BUT DRIER
CROSS-BARRIER FLOW WILL BEGIN TO PICK UP EARLY SATURDAY AND DRY
OUT THE LOW LEVELS.

AN UNSTABLE AIR MASS OVER THE NORTHERN GULF WILL COMBINE WITH AN
UPPER LOW PRESSURE TO SEND SNOW SHOWERS FROM CORDOVA THROUGH
VALDEZ TODAY WITH MINOR ACCUMULATIONS. THESE AREAS WILL SEE A
BREAK LATE TONIGHT INTO SATURDAY MORNING BEFORE THE NEXT FRONT/LOW
MOVE CLOSER.

OVER THE WEEKEND A LOW PRESSURE SYSTEM WILL DEVELOP IN THE GULF
BRINGING RAIN TO THE GULF COAST AREAS AS WELL AS A GALE TO STORM
FORCE FRONT ACROSS THE NORTHERN GULF. THE COOK INLET REGION SHOULD
REMAIN DOWNSLOPED WITH INCREASING CROSS BARRIER FLOW BUT MOST
MODEL GUIDANCE IS HINTING AT THE DEVELOPMENT OF A DEFORMATION
BETWEEN THE DEVELOPING SYSTEM AND THE OPEN WAVE PASSING TO THE
NORTH. THE BEST CHANCES TO SEE PRECIPITATION WITH THIS FEATURE
WILL BE AROUND KACHEMAK BAY AND PARTS OF THE KENAI PENINSULA WITH
THE ANCHORAGE AREA THROUGH THE MATANUSKA VALLEY REMAINING DRIER.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (FRIDAY THROUGH SUNDAY)...
A WEAK SHORTWAVE PASSING OVER THE KUSKOKWIM DELTA WILL CONTINUE TO
BRING SNOW FROM THE BETHEL AREA INTO THE LOWER KUSKOKWIM VALLEY
THROUGH LATE THIS MORNING...WITH LIGHT ACCUMULATIONS EXPECTED.
ANOTHER ROUND OF SNOW WILL THEN DEVELOP LATE TONIGHT ALONG THE
SOUTHWEST COAST IN ADVANCE OF AN APPROACHING UPPER LEVEL TROUGH
CURRENTLY OVER THE CENTRAL BERING. THIS FEATURE WILL THEN SPREAD
SNOWFALL THROUGHOUT THE SOUTHWEST MAINLAND FOR MOST OF THE DAY
SATURDAY...THOUGH ACCUMULATIONS SHOULD BE LIMITED TO AN INCH OR
TWO IN MOST INTERIOR LOCATIONS. CHANCES FOR WIDESPREAD SNOW WILL
THEN MOSTLY END ON SUNDAY UNDER CLEARING SKIES. WINDS WILL REMAIN
LIGHT AND VARIABLE THROUGH THE WEEKEND...AIDING IN THE DEVELOPMENT
OF NOCTURNAL FOG AND STRATUS.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (FRIDAY THROUGH SUNDAY)...
A FRONT CURRENTLY APPROACHING THE WESTERN ALEUTIANS WILL BRING
RAIN/SNOW AND GALE FORCE WINDS TO THE WESTERN ALEUTIANS
TODAY...FOLLOWED BY CENTRAL ALEUTIANS THIS EVENING...AND LASTLY
INTO THE EASTERN ALEUTIANS AND PRIBILOFS AS IT DISSIPATES ON
SATURDAY. A TRIPLE POINT LOW WILL THEN DEVELOP ALONG THIS FRONT TO
THE SOUTH OF ADAK AND ATKA LATE ON SATURDAY BEFORE MOVING OVER THE
DUTCH HARBOR/UNALASKA AREA SUNDAY MORNING. THIS WILL ALLOW FOR A
PERIOD OF GALE FORCE WINDS AND HEAVIER PRECIPITATION TO IMPACT THE
EASTERN ALEUTIANS AND THE SOUTHERN TIP OF THE ALASKA PENINSULA
OVER THE WEEKEND AS THE NEWLY FORMED LOWED CONTINUES TO PUSH
EASTWARD.

&&

.LONG TERM FORECAST (SUNDAY THROUGH THURSDAY)...

A VERY COMPLEX AND BROAD AREA OF LOW PRESSURE WILL SET UP ACROSS
THE BERING SEA AND MUCH OF THE ALASKA MAINLAND LATE THIS WEEKEND
AND INTO EARLY NEXT WEEK. THE MOST PROMINENT LOW CENTER WITHIN
THIS COMPLEX PATTERN WILL BE THE REMNANTS OF A TRIPLE POINT LOW
THAT DRIFTS FROM THE EASTERN ALEUTIANS TO NEAR KODIAK...WITH A
FRONT DRAPING ACROSS MUCH OF THE GULF OF ALASKA BY MONDAY
AFTERNOON. THE PATTERN IS NOT EXPECT TO SHIFT UNTIL WEDNESDAY
MORNING WHEN A DEVELOPING AREA OF LOW PRESSURE OVER THE NORTH
PACIFIC PUSHES INTO THE SOUTHERN GULF OF ALASKA AND BRING GALE
FORCE WINDS AND INCREASED PRECIPITATIONS CHANCES BACK TO
SOUTHCENTRAL ALASKA. AT THE SAME TIME...AN AREA OF LOW PRESSURE
WILL PUSH OFF THE KAMCHATKA PENINSULA AND DRIVE A FRONT ACROSS
THE WESTERN ALEUTIANS ON WEDNESDAY. WEAK RIDGING WILL DEVELOP
ACROSS FROM THE CENTRAL ALEUTIANS TO THE GULF OF ALASKA BETWEEN
THE TWO LOW PRESSURE SYSTEMS.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...HEAVY FREEZING SPRAY...185
         GALE...119 170 172 173 174 175 176 177 178 179 185.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...TP
SOUTHCENTRAL ALASKA...MTL/JR
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...DEK
LONG TERM...MMC