Small Craft Advisory 873, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
442 PM AKST MON NOV 2 2015

.ANALYSIS AND UPPER LEVELS...

THE DISTURBANCE THAT MOVED THROUGH SOUTHCENTRAL OVERNIGHT LAST
NIGHT IS NOW CLEARING THE EASTERN COPPER RIVER BASIN AT THIS TIME.
SNOWFALL AMOUNTS WERE MODEST...WITH ONLY A FEW INCHES OF SNOW IN
MOST AREAS AND LESS THAN AN INCH FOR MUCH OF ANCHORAGE. WITH THAT
STORM GONE...THE NEXT ONE ON THE TRAIN IS ALREADY MAKING ITS
PRESENCE KNOWN IN SOUTHWEST ALASKA...PARTICULARLY ALONG THE ALASKA
PENINSULA. TEMPERATURES ALL ACROSS SOUTHWEST ALASKA WITH THE
EXCEPTION OF INTERIOR BRISTOL BAY ARE ALL SAFELY ABOVE FREEZING.
RAIN HAS BEEN THE DOMINANT PRECIPITATION TYPE THUS FAR ALONG THE
EASTERN ALEUTIANS AND SOUTHERN ALASKA PENINSULA. AS IT MOVES INTO
THE GULF OVERNIGHT AND THROUGH THE DAY TOMORROW...IT WILL BRING
ACTIVE WEATHER TO PARTS OF SOUTHCENTRAL. MORE ON THAT BELOW...

A LOW CURRENTLY MOVING THROUGH THE BERING STRAIT HAS BEEN
PRODUCING HIGH SURF ALONG THE COAST FROM KIPNUK NORTH...THOUGH
SLOW RECESSION IN THE WAVE HEIGHTS IS EXPECTED.

ANOTHER LOW NEAR THE KAMCHATKA PENINSULA IS EXPECTED TO BE THE
NEXT WEATHER MAKER FOR THE NORTHERN BERING...AND A VERY STRONG
STORM SYSTEM OVER THE NORTHWEST PACIFIC WILL MOVE INTO THE BERING
FOR MID-LATE WEEK.

THIS PARADE OF STORMS IS MOVING ALONG AN ENERGETIC JET ORIENTED IN
A NEAR-ZONAL PATTERN ACROSS THE ALEUTIANS...ALASKA PENINSULA...AND
ALONG THE GULF COAST. THE CORE OF THE 130 KT JET STREAK IS MOVING
OVER THE WESTERN GULF. WEST OF THE JET STREAK ALONG THE ENTRANCE
REGION...A SHORTWAVE DISTURBANCE IN THE UPPER LEVELS IS HELPING
DEVELOP THE LOW CURRENTLY OVER THE SOUTHERN ALASKA PENINSULA. THE
LOW IS RACING NORTHEAST ALONG THE CORE OF THE AFOREMENTIONED JET
STREAK...HENCE THE VERY SHORT RETURN OF ACTIVE WEATHER FOR SOUTHERN
MAINLAND ALASKA. A SHORTWAVE COMING OFF THE ASIAN CONTINENT NOW
IS ALSO EXPECTED TO AMPLIFY AND ENERGIZE OVER THE COMING DAYS...WHICH
WILL REALLY HELP TO INVIGORATE THE FAST MOVING STORM EXPECTED TO DEVELOP
MID-LATE WEEK ALONG THE SOUTHERN BERING.

&&

.MODEL DISCUSSION...

THE MODELS ARE IN GENERAL AGREEMENT PERTAINING TO THE TRACK OF THE
NEXT STORM MOVING THROUGH SHELIKOF STRAIT AND INTO THE WESTERN
GULF ALONG...BUT SOME DIFFERENCES REMAIN ON THE EXTENT AND
DURATION OF THE EARLY DOWNSLOPING AS THE FLOW NORTH OF THE LOW
PASSES THROUGH THE CHUGACH. THIS HAS SOME IMPLICATIONS FOR HOW
MUCH SNOW IS SEEN IN THE ANCHORAGE BOWL AND WESTERN KENAI
PENINSULA LATE TONIGHT INTO TOMORROW MORNING. AS THE STORM PULLS
FURTHER EAST AND THE CENTER PASSES SOUTH OF PRINCE WILLIAM SOUND
ALL MODELS AGREE THAT ANY DOWNSLOPING WILL QUICKLY END. AGREEMENT
IS ALSO HIGH ON RELATIVELY BENIGN WEATHER RETURNING TO
SOUTHCENTRAL AS THE NEXT STORM SYSTEM DEVELOPS ACROSS THE BERING.
THE MAIN FORECAST CHALLENGE WITH THIS STORM IS THE STRENGTH AND
COVERAGE OF THE WIND FIELD. DUE TO THE UNCERTAINTY FUTURE UPDATES
SHOULD BE MONITORED FOR THE STORMS TRACK AND STRENGTH. WITH
GENERAL AGREEMENT FOR THE UPCOMING STORM SYSTEMS...FORECAST
CONFIDENCE IS ABOVE NORMAL.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...

A FAST MOVING SHORTWAVE TROUGH CURRENTLY OVER THE EASTERN
ALEUTIANS WILL MOVE INTO THE GULF OF ALASKA TONIGHT AND
TUESDAY...STRENGTHENING TO STORM FORCE AS IT TRACKS THROUGH THE
NORTHERN GULF. THIS WILL ALSO SPREAD MOISTURE AND PRECIPITATION
ACROSS SOUTHCENTRAL...WITH SNOW INLAND AND RAIN AND SNOW ALONG THE
COAST. THIS PATTERN TENDS TO FAVOR THE HEAVIEST PRECIPITATION
ACROSS COASTAL AREAS...WITH MUCH LESS INLAND...ESPECIALLY NORTH
TOWARD THE ALASKA RANGE. A LOW LEVEL NORTHEAST TO NORTHWEST FLOW
WILL KEEP AREAS LIKE THE MATANUSKA VALLEY MUCH DRIER...WITH ONLY
LIGHT SNOW AMOUNTS TOWARDS ANCHORAGE. MOST SNOW WILL DEVELOP IN
THE LATE MORNING BEFORE DIMINISHING BY THE AFTERNOON. SNOW WILL
LINGER THE LONGEST IN THE COPPER RIVER BASIN BEFORE ENDING BY THE
AFTERNOON. CLEARING WILL DEVELOP TUESDAY NIGHT AND WEDNESDAY AS
THE LOW MOVES EAST...WITH AN OFFSHORE PRESSURE GRADIENT RAMPING UP
GAP WINDS ALONG THE COAST.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...

THE PRIMARY FOCUS OVER THE SOUTHWEST MAINLAND FOR THE SHORT-TERM
FORECAST REMAINS THE PRECIPITATION TYPE AND AMOUNTS THAT WILL
DEVELOP OVER PORTIONS OF THE BRISTOL BAY ZONE TONIGHT AND INTO
TOMORROW. MODELS ARE IN GOOD AGREEMENT WITH A DEEP NORTH PACIFIC
LOW PASSING THROUGH THE ALASKA PENINSULA AND INTO THE WESTERN GULF
LATE TONIGHT. THIS LOW TRACK WOULD PROMOTE AN AREA OF FAVORABLE
DYNAMIC SUPPORT FOR HEAVY PRECIPITATION OVER EASTERN PORTIONS OF
BRISTOL BAY...WITH COLDER NORTHERLY FLOW BEHIND THE SYSTEM
DROPPING TEMPERATURES ENOUGH TO START MIXING WITH SNOW OVER AREAS
NORTH AND EAST OF DILLINGHAM. HOWEVER TIMING IS EVERYTHING WITH
THIS SYSTEM...AND THERE IS STILL THE QUESTION OF HOW MUCH
AVAILABLE PRECIPITATION WILL BE LEFT BY THE TIME THE TEMPERATURES
DROP ENOUGH FOR IT TO FINALLY TRANSITION TO SNOW. CONFIDENCE
REMAINS HIGH THAT THERE WILL BE A TRANSITION TO A MIX OF RAIN AND
SNOW OVERNIGHT TONIGHT AND INTO TOMORROW MORNING. PRECIPITATION
WILL THEN QUICKLY TAPER OFF TO SHOWERS AS THE LOW RAPIDLY MOVES
OFF TO THE EAST ON TUESDAY. THESE SHOWERS WILL PERSIST OVER THE
SOUTHWEST MAINLAND THROUGH TUESDAY NIGHT AS MOIST AND UNSTABLE
SOUTHWEST FLOW AHEAD OF THE NEXT FRONT APPROACHES FROM THE BERING.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...

THE INITIAL FOCUS IN THE SHORT TERM REMAINS ALONG THE ALASKA
PENINSULA AND OVER THE FAR SOUTHEASTERN BERING...AS A STRONG LOW
TRACKS THROUGH THE ALASKA PENINSULA AND INTO THE WESTERN GULF
OVERNIGHT TONIGHT. THIS SYSTEM WILL CONTINUE TO BRING RAIN AND
GUSTY WINDS TO THE AREA...WHICH WILL EVENTUALLY SHIFT AROUND TO
THE NORTHWEST AS THE LOW MOVES OFF TO THE EAST. OTHERWISE...RAIN
SHOWERS AND GUSTY SOUTHWEST WINDS WILL CONTINUE ACROSS THE
REMAINDER OF THE BERING THROUGH TUESDAY NIGHT AS ANOTHER LOW
MOVING TOWARDS THE BERING STRAIT SWINGS A FRONT ACROSS THE WESTERN
AND CENTRAL BERING. THE FOCUS THEN SHIFTS TO A MUCH STRONGER LOW
APPROACHING THE CENTRAL ALEUTIANS FROM THE NORTH PACIFIC TUESDAY
NIGHT INTO WEDNESDAY...BRINGING THE POTENTIAL FOR STORM FORCE TO
MINIMUM HURRICANE FORCE GUSTS OVER PARTS OF THE SOUTHERN BERING
AND CENTRAL ALEUTIANS BY WEDNESDAY.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...

THE LONG TERM FORECAST IS LARGELY DOMINATED BY A DEEP AREA OF LOW
PRESSURE OVER THE EASTERN ALEUTIANS. BY WEDNESDAY NIGHT...THE LOW
WILL BE ON A WEAKENING TREND AS IT PUSHES FROM DUTCH HARBOR TOWARD
KODIAK ISLAND BY THURSDAY EVENING. ALTHOUGH THE LOW WILL BE
WEAKENING...STRONG NORTHWESTERLY WINDS WILL BE OBSERVED ACROSS THE
ALEUTIAN CHAIN AS COLD AIR ADVECTION ALLOWS FOR STRONGER WINDS TO
MIX DOWN TO THE SURFACE. IN ADDITION...A WEAK ISALLOBARIC
COMPONENT WILL BE DEVELOPING OVER THE CENTRAL ALEUTAINS IN
RESPONSE TO WEAK SHORT WAVE RIDGING DEVELOPING BEHIND THE SURFACE
LOW. THIS WILL LEAD TO WIDESPREAD WIND GUSTS OF 60 TO 70 MPH WITH
POTENTIALLY STRONGER GUSTS THROUGH NORTHWEST FACING GAPS. SEAS
WILL ALSO BE A CONCERN AS THE LOW SKIRTS ACROSS THE ALEUTIANS.
WAVE HEIGHTS OF 25 TO 35 FEET ARE EXPECTED ON THE PACIFIC SIDE OF
THE ALEUTIANS WHILE THE SOUTHERN BERING SEA COULD EXPERIENCE SEAS
OF 15 TO 25 FEET.

PRECIPITATION TYPE WITH THIS SYSTEM LOOKS PRETTY SIMPLE AS A STOUT
WARM FRONT SLAMS INTO SOUTHWEST ALASKA LATE WEDNESDAY INTO
THURSDAY. 850 MB TEMPERATURES WILL QUICKLY WARM TO 0 TO -2 DEGREES
CELSIUS WHICH SUPPORTS PRECIPITATION TO DEVELOP AS RAIN.
HOWEVER...A FEW LOCATIONS NEAR THE ALASKA RANGE AND THE LOWER
KUSKOKWIM VALLEY MAY HOLD ONTO COLD AIR LONG ENOUGH TO SUPPORT
SNOW BEFORE EVENTUALLY CHANGING OVER TO RAIN. THE SAME CAN BE SAID
FOR SOUTHCENTRAL WHERE PRECIPITATION ON THURSDAY AND FRIDAY WILL
LIKELY FALL AS RAIN WITH WARMING 850 MB TEMPERATURES. EVENTUALLY
COLDER AIR WILL BEGIN FILTERING IN BEHIND THE LOW AND GRADUALLY
CHANGE PRECIP FROM RAIN TO SNOW STARTING ACROSS SOUTHWEST ALASKA
ON FRIDAY AND SOUTHCENTRAL ALASKA ON SATURDAY. DOWNSLOPING
CONDITIONS WILL NEED TO BE MONITORED ON THE LEE SIDE OF THE
ALEUTIAN RANGE AND CHUGACH MOUNTAINS WITH A STOUT LOW LEVEL JET
PASSING ACROSS THE MOUNTAINS.

ATTENTION WILL THEN TURN BACK TO THE BERING SEA AS ANOTHER NEAR
GALE FORCE FRONT WILL PUSH ACROSS THE BERING SEA ON SUNDAY AS A
DEVELOPING AREA OF LOW PRESSURE PUSHES OFF OF KAMCHATKA. MODELS
ARE IN A BIT OF DISAGREEMENT WITH TIMING AT THIS TIME BUT IT IS
ALSO 7 DAYS OUT. REGARDLESS...THE UPPER LEVEL PATTERN CONTINUES TO
FAVOR AN ACTIVE PATTERN AND NO PATTERN CHANGE APPEARS IN SIGHT AT
THIS TIME.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...HIGH WIND WATCH 187.
MARINE...STORM WARNING 132
         GALE WARNING 119 120 130 131 136 137 138 139 150 155 176 177 178.

&&

SYNOPSIS AND MODEL DISCUSSION...BC
SOUTHCENTRAL ALASKA...JA
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...TP
LONG TERM...MC