Small Craft Advisory 963, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
506 AM AKST THU DEC 3 2015

.ANALYSIS...
THE UPPER LEVELS HAVE A WEAK NEGATIVE TILTED TROUGH OVER THE
BRISTOL BAY INTERIOR EXTENDING ACROSS THE ALEUTIAN RANGE INTO
THE BARREN ISLANDS REGION. THIS SYNOPTIC FEATURE WILL AFFECT
ANCHORAGE BY TONIGHT AS THE WEAK RIDGE OVER SOUTHCENTRAL MOVES TO
THE NORTH. THE SATELLITE IMAGERY IS SHOWING THIS FEATURE WITH A
SWATH OF MOISTURE ALONG THE SOUTHWEST ALASKA COASTLINE WITH
SURFACE OBSERVATIONS REPORTING LIGHT SNOW SHOWERS. THE MODIS
NIGHTTIME MICROPHYSICS IMAGERY IS SHOWING AREAS OF FOG ACCOMPANIED
BY LOW STRATUS THROUGH THE UPPER COOK INLET ALONG THE TURNAGAIN
ARM...THE LOWER SUSITNA VALLEY...THE MATANUSKA VALLEY AND THE
INTERIOR OF THE WESTERN KENAI PENINSULA THIS MORNING. WHILE THE
SOUTHWEST INTERIOR WILL BE UNDER THE INFLUENCE OF OFFSHORE FLOW
AND COOLER TEMPERATURES WITH MOSTLY CLEAR SKIES. THE EASTERN
ALEUTIANS/BERING SEA HAS A RIDGE AXIS JUST EAST OF SAINT MATTHEW
ISLAND EXTENDING THROUGH THE EASTERN ALEUTIANS INTO THE NORTH
PACIFIC. FARTHER UPSTREAM IS A BROAD CLOSED LOW NEAR ADAK WITH AN
ASSOCIATED TROUGH EXTENDING SOUTHWARD NEAR 40N. ON THE BACKSIDE OF
THIS SYSTEM AT 300 MB THERE IS A STRONG 185 KNOT NORTHWESTERLY JET
STREAM DIGGING INTO THE BASE OF THE LONGWAVE TROUGH. REFLECTED AT
THE SURFACE IS AN OCCLUDED 965 MB LOW JUST SOUTH OF SHEMYA WITH
THE OCCLUDED FRONT EXTENDING THROUGH THE WESTERN TO CENTRAL BERING
SEA BEFORE EXTENDING THROUGH DUTCH HARBOR. THIS IS BRINGING
TEMPERATURES IN THE MID TO UPPER 30S TO THE CHAIN AND THE SOUTHERN
BERING SEA. THE SATELLITE IMAGERY IS SHOWING A SHOWERY REGIME
BEHIND THE OCCLUDED FRONT WITH THE SOUTHWESTERLY WINDS REFLECTED
AT THE SURFACE.

.MODEL DISCUSSION...
THE MODELS ARE IN GOOD AGREEMENT WITH THE NORTH PACIFIC LOW
LOCATED SOUTH OF SHEMYA IN THE EARLY PERIOD...BUT BY THURSDAY
NIGHT THE MODELS TRANSITION THIS LOW INTO A COMPLEX LOW WITH
MULTIPLE LOW CENTERS JUST SOUTH OF DUTCH HARBOR. THIS SYSTEM
CONTINUES TO MOVE EASTWARD AND REMAINS SOUTH OF THE GULF OF ALASKA
HEADING INTO THE WEEKEND. THE MODELS ARE STRUGGLING WITH PLACEMENT
OF THIS SYSTEM. BY FRIDAY ANOTHER SYSTEM TRACKS NEAR THE KAMCHATKA
PENINSULA AND REMAINS SOUTH OF THE WESTERN ALEUTIANS. THE MODELS
ARE HAVING DIFFICULTY WITH THE PLACEMENT AND STRENGTH OF THIS
SYSTEM AS WE HEAD INTO THE WEEKEND. THE FORECAST CONFIDENCE IS
AVERAGE BEFORE DIMINISHING AS THE NORTH PACIFIC LOW BECOMES A
BROAD COMPLEX LOW BY END OF THE WEEK.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
ALL GUIDANCE IS QUICKLY TRENDING TOWARD A MINOR SNOWFALL OVER MUCH
OF SOUTHCENTRAL ALASKA THIS AFTERNOON THROUGH TONIGHT. AN INVERTED
TROUGH EXTENDING FROM A DEEP LOW OVER THE NORTHEAST PACIFIC EXTENDS
NORTHWARD ACROSS THE CENTRAL GULF. THIS TROUGH IS MOVING SLOWLY
WESTWARD SPREADING MOISTURE NORTH AND WEST TOWARD SOUTHCENTRAL.
MEANWHILE...AN UPPER LEVEL TROUGH IS SWINGING THROUGH BRISTOL BAY
AND BEGINNING TO LIFT NORTHWARD AS IT HITS THE OPPOSING FLOW OVER
THE GULF. THIS TROUGH WILL TAKE ADVANTAGE OF THE MOISTURE IN PLACE
AS WELL AS DEEP LAYER WEAK INSTABILITY (AS SEEN IN THE ANCHORAGE
SOUNDING) TO PRODUCE WIDESPREAD SNOW SHOWERS. ALTHOUGH SNOW
ACCUMULATION IS EXPECTED TO BE LIGHT...IT DOES LOOK FAVORABLE FOR
MESOSCALE BANDS OF HEAVIER SNOW TO BRIEFLY SET UP SOMEWHERE OVER
THE WESTERN KENAI TO ANCHORAGE AREA. THUS THERE LIKELY WILL BE
SOME AREAS WHICH SEE SEVERAL INCHES OF SNOW. IN ADDITION...A
SURFACE LOW IS EXPECTED TO FORM OVER THE NORTHERN GULF AND DRIFT
INTO PRINCE WILLIAM SOUND. HEAVIER PRECIPITATION IS LIKELY IN THE
VICINITY OF THIS LOW. ALTHOUGH PRECIP WILL BE IN THE FORM OF SNOW
MOST PLACES...IT IS WARM ENOUGH IN THE CORDOVA AREA TO PRODUCE ALL
RAIN. ANOTHER MUCH WEAKER UPPER WAVE WILL FOLLOW DURING THE DAY
FRIDAY KEEPING A CHANCE OF SHOWERS IN THE FORECAST FOR MOST OF THE
REGION.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
A LINGERING UPPER TROUGH OVER THE BRISTOL BAY AREA WILL BRING
AREAS OF LIGHT SNOW TO MAINLY AREAS NORTH AND EAST OF KING SALMON
TODAY. THAT WILL BE THE ONLY THREAT OF PRECIPITATION OVER THE NEXT
COUPLE DAYS. LOW STRATUS HAS FILTERED INTO THE KUSKOKWIM VALLEY
AND DELTA WITHIN THE LIGHT NORTHERLY FLOW AND SHOULD CONTINUE TO
HANG AROUND AS THE WEAK OUTFLOW PATTERN CONTINUES THROUGH
SATURDAY. EXPECT GENERALLY LIGHT WINDS AND BELOW NORMAL
TEMPERATURES THROUGH THE SHORT TERM.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
THE DEEP LOW PRESSURE SYSTEM WILL PULL SOUTH OF THE CHAIN TODAY AS
A FRONTAL BOUNDARY ASSOCIATED WITH IT WEAKENS AS IT MOVES OVER
THE ALASKA PENINSULA AND PRIBILOF ISLANDS. SOME ACCUMULATING SNOW
IS POSSIBLE IN THESE PLACES...BEST CHANCES OVER SAINT GEORGE
ISLAND. ARCTIC AIR FILTERING IN BEHIND THIS FRONT OVER THE WESTERN
AND CENTRAL BERING WILL KEEP SCATTERED SNOW SHOWERS OVER MUCH OF
THE AREA. MOSTLY BENIGN CONDITIONS...WEAK FLOW AND NO MAJOR
FRONTS...WILL REMAIN IN PLACE THROUGH SATURDAY AS THE JET STAYS
WELL SOUTH OF THE CHAIN.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
THE FORECAST FOR THIS WEEKEND INTO NEXT WEEK IS CHARACTERIZED BY
BELOW AVERAGE CONFIDENCE AS MODELS CONTINUE TO STRUGGLE GREATLY
WITH THE EVOLUTION OF AN ELONGATED AREA OF LOW PRESSURE SOUTH OF
THE ALEUTIAN CHAIN. THERE IS A GENERAL CONSENSUS FOR THE
DEVELOPMENT OF A DOMINANT LOW CENTER WITHIN THE BROADER COMPLEX
LOW...HOWEVER 00Z GUIDANCE DIFFERS ON THE PLACEMENT OF THIS
FEATURE BY UPWARDS OF 400 MILES...MAKING IT VERY DIFFICULT TO
NARROW DOWN ANY SPECIFIC FORECAST DETAILS. THERE IS ALSO GENERAL
AGREEMENT ON A DEEP LOW APPROACHING THE SOUTHERN GULF EARLY TO MID
NEXT WEEK AS THE LONGWAVE TROUGH SHIFTS TO THE EAST...BUT THIS
SYSTEM IS ALSO POORLY HANDLED BY THE MODELS AT THIS TIME.

THIS PATTERN IS GENERALLY EXPECTED TO YIELD BENIGN CONDITIONS
ACROSS SOUTHERN ALASKA THROUGH MUCH OF THE NEXT WEEK AS THE MAIN
UPPER LEVEL JET REMAINS OVER THE NORTH PACIFIC SOUTH OF 50N AND
KEEPS THE STORM TRACK WELL TO THE SOUTH OF THE MAINLAND. THE BEST
CHANCES FOR PRECIPITATION WILL THEREFORE REMAIN CONFINED TO THE
GULF COAST...WITH INLAND AREAS OF SOUTHCENTRAL STAYING MOSTLY DRY
WITH TEMPERATURES NEAR SEASONAL NORMAL VALUES. OUT WEST...THE BULK
OF THE ACTIVITY SHOULD REMAIN CONFINED TO THE ALEUTIAN CHAIN IN
CLOSER PROXIMITY TO THE COMPLEX LOW...WITH A MORE SHOWERY REGIME
OVER THE REST OF THE BERING BENEATH BROAD CYCLONIC FLOW.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE
MARINE...GALE WARNING 178
		 HEAVY FREEZING SPRAY 160 180 181

&&

SYNOPSIS AND MODEL DISCUSSION...PLD
SOUTHCENTRAL ALASKA...SEB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...MTL
LONG TERM...CB