Small Craft Advisory 863, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
541 AM AKDT SAT OCT 31 2015

.ANALYSIS AND UPPER LEVELS...
THE LARGE SCALE UPPER LEVEL PATTERN CONSISTS OF A STRONG UPPER
LEVEL RIDGE CENTERED OVER THE BERING WITH AN UPPER LEVEL LOW
DIGGING SOUTH THROUGH THE WESTERN GULF AND INTO THE NORTH PACIFIC.
THE JET RUNNING NORTH TO SOUTH BETWEEN THESE TWO FEATURES HAD
BEEN STRETCHED ACROSS THE WESTERN ALASKA COAST...BRISTOL BAY AND
THE ALASKA PENINSULA...IS DROPPING SOUTH AND WEAKENING. AS THE
JET MOVES SOUTH...THE FOCUS OF THE STRONGEST NORTHERLY SURFACE
WINDS HAS BEEN SHIFTING SOUTH AS WELL WITH THE STRONGEST WINDS
CURRENTLY BEING DOWNSLOPED FROM THE MOUNTAINS AND CHANNELED
THROUGH THE GAPS AND PASSES OF THE ALASKA PENINSULA.

PRECIPITATION HAS ENDED OVER THE SOUTHWEST ALASKA MAINLAND WITH
THE EXCEPTION OF A FEW ISOLATED SNOW SHOWERS ALONG ALASKA RANGE.
OVER SOUTH CENTRAL ALASKA THE SAME TREND IS UNDERWAY WITH SHOWERS
ENDING INLAND AND BECOMING MORE SCATTERED ALONG THE COAST AS THE
UPPER LOW IN THE GULF DROPS SOUTH. NORTHERLY GAP FLOW HAS
INCREASED SUBSTANTIALLY THROUGH RESURRECTION BAY WITH WEST WINDS
BEGINNING TO INCREASE THROUGH WHITTIER AND PASSAGE CANAL. FURTHER
WEST A STRONG LOW IS BEGINNING TO SPIN UP OFF OF THE KAMCHATKA
PENINSULA WITH THE ASSOCIATED FRONTAL SYSTEM APPROACHING THE
WESTERN ALEUTIANS.

&&

.MODEL DISCUSSION...
MODELS REMAIN IN GOOD SYNOPTIC AGREEMENT FOR THE FIRST COUPLE OF
DAYS OF THE FORECAST PERIOD. HIGH RESOLUTION MODELS WERE PREFERRED AS
THE MOST SIGNIFICANT SHORT TERM FORECAST IMPACTS WILL BE TIED TO
THE STRENGTH AND TIMING OF THE GAP AND DOWNSLOPE WINDS THAT
DEVELOP AS OFFSHORE FLOW STRENGTHENS THROUGH THE FIRST HALF OF THE
WEEKEND.

&&

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

GAP WINDS ARE THE MAIN WEATHER CONCERN FOR SOUTHCENTRAL OVER THE
SHORT TERM. COLD AIR CONTINUES TO FILTER IN FROM THE WEST...WHILE
SURFACE HIGH PRESSURE CONTINUES TO BUILD IN WHILE A LOW PRESSURELINGERS
IN THE GULF. THE RESULTING PRESSURE GRADIENTS BETWEEN THESE TWO
FEATURES ARE EXPECTED TO INCREASE TODAY THROUGH TONIGHT...AND
SUPPORT NORTHERLY AND WESTERLY GUSTY WINDS THROUGH LOCAL GAPS. AN
APPROACHING UPPER LEVEL JET IS EXPECTED TO PROVIDE AN EXTRA BOOST
TO THESE WINDS THIS EVENING BEFORE WINDS SLOWLY BEGIN TO DIMINISH
EARLY SUNDAY MORNING.

THE CURRENT PROGRESSIVE PATTERN WILL BRING A QUICK CHANGE TO THE
REGION BY SUNDAY AFTERNOON...WITH A NEW FRONT BRINGING THE CHANCE
FOR INCREASING CLOUDS AND PRECIPITATION.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
THE MAINLAND BEGINS A TRANSITION FROM THE DEPARTING TROUGH AND
NORTHERLY JET TO AN APPROACHING FRONTAL BOUNDARY FROM THE BERING
SEA LATE TONIGHT. LINGERING ARCTIC AIR ALOFT...SLACKENING
WINDS...AND CLEARING SKIES WILL ALLOW FOR SOME OF THE COLDEST
OVERNIGHT TEMPERATURES OF THE SEASON SO FAR. A WEAKENING FRONT
WILL BRING A SLIGHT CHANCE OF FLURRIES TO THE KUSKOKWIM DELTA
TODAY. SOUTHERLY FLOW PICKING UP AHEAD OF THE STRONGER BERING
FRONT WILL RETURN MOISTURE AND LOW CLOUDS FIRST TO THE DELTA
TODAY...THEN TO THE BRISTOL BAY AREA OVERNIGHT. THE FRONT COMES
ASHORE LATE TONIGHT INTO SUNDAY FROM THE WEST...SOUTHERLY FLOW
SHOULD JUMP TEMPERATURES UP ABOVE FREEZING PRETTY FAST...BUT
PRECIPITATION COULD START AS SNOW BEFORE CHANGING OVER TO RAIN IN
THE AFTERNOON. THE KUSKOKWIM VALLEY SHOULD SEE SOME ACCUMULATING
SNOW WITH THIS FRONT SUNDAY AFTERNOON WITH 1 TO 3 INCHES POSSIBLE.
BEHIND THE FRONT ON SUNDAY NIGHT...A SHOWERY MIXED PRECIPITATION
REGIME WILL FOLLOW.

.MARINE IMPACTS...THE BROAD LOW THAT WILL TRACK ACROSS THE BERING
SEA STARTING LATE TONIGHT WILL PUSH A LARGE AREA OF SOUTHERLY
WINDS INTO THE COAST. THESE WINDS COULD HELP SOME WATER TO BUILD
UP ALONG THE COAST...ESPECIALLY IN SOUTH FACING COMMUNITIES.
THEN...AFTER THE COLD FRONT MAKES IT TO THE COAST LATE SUNDAY
MORNING...THE FLOW WILL SHIFT TO A WEST TO SOUTHWEST DIRECTION.
THE LOW ITSELF WILL ALSO TRACK FROM THE SOUTHWEST (NEAR KAMCHATKA)
TO THE NORTHEAST (THE BERING STRAIT). THIS WILL LEAVE MUCH OF THE
BERING OPEN TO A LONG DYNAMIC FETCH FOR SIGNIFICANT SEAS TO BUILD.
THIS WEST TO SOUTHWEST FLOW WILL THEN PERSIST THROUGH MONDAY
MORNING. THIS WILL RESULT IN SEVERAL COMMUNITIES ALONG THE
SOUTHWEST AK COAST EXPOSED TO RELATIVELY HIGH WATER AND ROUGH
SURF FOR UP TO 36 HOURS. AT THIS POINT IT LOOKS LIKE THE WORSE
CONDITIONS WOULD BE MONDAY MORNING. COASTAL RESIDENTS SHOULD
FOLLOW THIS SITUATION AND STAY ALERT IF ANY ADVISORIES OR WATCHES
SHOULD BE NEEDED.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
WHILE THE EASTERN BERING QUIETS DOWN FOR TODAY...THE WESTERN
BERING IS GETTING ACTIVE WITH A GALE FORCE FRONT MOVING INTO THE
CENTRAL BERING SEA THIS EVENING FOLLOWED BY THE EASTERN BERING
SUNDAY MORNING. BEHIND THE FRONT...ANOTHER BROAD SWATH OF GALE
FORCE WINDS AND LARGE SEAS WILL ENCOMPASS MOST OF THE BERING SEA.
ON LATE SUNDAY NIGHT AN UPPER DISTURBANCE WILL BRING A COMPACT
SYSTEM TO THE CENTRAL ALEUTIANS.

&&

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

THE EXPECTED WARM-UP EARLY NEXT WEEK LOOKS LESS PROMISING TODAY
AS A DEEP UPPER LEVEL TROUGH OVER THE BERING SEA LOOKS TO KEEP
HIGH PRESSURE FURTHER SOUTH AND EAST. A QUICK SHORTWAVE RIDGE
LOOKS TO QUICKLY SLIDE ACROSS SOUTHWEST AND SOUTHCENTRAL ALASKA
THROUGHOUT THE DAY MONDAY WHICH WILL BE THE TURNING POINT
TEMPERATURE WISE. AS MENTIONED EARLIER...THE WARM-UP LOOKS LESS
PROMISING BUT IS STILL EXPECTED TO OCCUR (JUST TO A LESSER
MAGNITUDE).

LOOKING AT THE BIG PICTURE...THE AFOREMENTIONED SHORTWAVE RIDGE
WILL BE QUICK TO MOVE ACROSS THE AREA ON MONDAY AS A POTENT
SHORTWAVE IS EXPECTED TO DIG OUT OF THE UPPER LEVEL TROUGH AND
AMPLIFY THE LONGWAVE PATTERN. THIS WAVE WILL SPIN UP A WEAK SFC
BASED LOW WHICH WILL MOVE INLAND NEAR BRISTOL BAY TUESDAY MORNING.
THIS SHOULD KEEP INCREASE RAIN CHANCES AS WELL AS BRING GALE FORCE
WINDS TO THE ALEUTIAN ISLANDS AND ALASKA PENINSULA LATE MONDAY AND
EARLY TUESDAY. THIS LOW WILL MOVE INTO SOUTHCENTRAL ALASKA EARLY
TUESDAY AND LIKELY PRODUCE PERIODS OF RAIN AND SNOW. CURRENTLY IT
APPEARS ANYTHING NORTH OF KENAI WOULD BE IN THE SNOW ZONE WITH
JUST COASTAL AREAS REMAINING RAIN. MODELS ARE STRUGGLING A TOUCH
WITH THE POSITION OF THE UPPER LEVEL WAVE AND SFC LOW...WHICH WILL
HAVE A LOT TO DO WITH HOW MUCH PRECIPITATION WILL BE OBSERVED.

THE MOST SIGNIFICANT (POSSIBLY) YET THE MOST INCONSISTENT FEATURE
WILL BE THE POSSIBILITY OF A SIGNIFICANT LOW DEVELOPING SOUTH OF
THE CENTRAL ALEUTIANS ON WEDNESDAY AND THURSDAY. THE REASON FOR
THE INCONSISTENCY IS THAT THE ARCTIC JET AND NORTH PACIFIC JET
APPEAR TO PHASE TOGETHER BRIEFLY WHICH CREATES A VERY POTENT JET
STREAK. THIS JET STREAK COULD QUICKLY DEVELOP AN UPPER LEVEL AND
SFC LOW THAT COULD EXCEED 24 MB STRENGTHENING IN 24 HOURS.
HOWEVER...THE JET STREAMS COULD ALSO HAVE LITTLE PHASING AND THE TWO
SEPARATE JET STREAKS COULD CLASH AND CREATE A WEAKER SFC LOW. THE
ONE THING OF NOTE IS THAT MODELS ARE TRENDING FURTHER NORTH WITH
LOW DEVELOPMENT POSSIBLY IN THE SOUTHERN BERING SEA. SHOULD THIS
SOLUTION PAN OUT...A PERIOD OF HEAVY RAIN FOR THE ALEUTIANS AND
ALASKA PENINSULA COULD BE SEEN AS WELL AS A LARGE AREA OF STORM
FORCE WINDS ACROSS THE ALEUTIANS AND BERING SEA.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALES 150 155 165 170 172 173 174 175 176 177 178 179 185
132 131 130 127 121.

&&

SYNOPSIS AND MODEL DISCUSSION...JER
SOUTHCENTRAL ALASKA...EN
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...MTL/MSO
LONG TERM...MC

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE ANCHORAGE AK
1025 AM AKDT SAT OCT 31 2015

AKZ155-161-312358-
KUSKOKWIM DELTA-BRISTOL BAY-
INCLUDING THE CITIES OF...BETHEL...HOOPER BAY...NUNIVAK ISLAND... KING
SALMON...DILLINGHAM...NAKNEK...PILOT POINT
1025 AM AKDT SAT OCT 31 2015

...HIGH SURF POSSIBLE ALONG THE COAST OF SOUTHWEST ALASKA SUNDAY
NIGHT THROUGH MONDAY NIGHT...

MULTIPLE STORMS WILL PUSH ACROSS THE BERING SEA THROUGH MONDAY AND
BRING ELEVATED WATERS LEVELS TO THE SOUTHWEST COAST OF ALASKA.
THIS INCLUDES BRISTOL BAY AND KUSKOKWIM BAY WHERE WATER LEVELS COULD
RANGE FROM ONE TO TWO FEET ABOVE HIGH ASTRONOMICAL TIDE. THESE
ELEVATED WATER LEVELS ARE EXPECTED TO CREATE HIGH SURF SUNDAY
NIGHT THROUGH MONDAY NIGHT FOR LOCATIONS WITH A SOUTHERLY OR
WESTERLY FACING COASTLINE. THERE IS A SMALL POSSIBILITY OF MINOR
COASTAL FLOODING ALONG THE SOUTHWEST COAST...MAINLY IN THE
PROXIMITY OF KUSKOKWIM BAY. HOWEVER...THERE IS STILL SOME
UNCERTAINTY ON TRACKS THAT THE MULTIPLE STORMS MOVING ACROSS THE
BERING SEA WILL TAKE...WHICH LEADS TO SOME UNCERTAINTY IF FLOODING
WILL OCCUR.

A HIGH SURF ADVISORY OR COASTAL FLOOD WATCH OR WARNING MAY BE
NEEDED FOR SUNDAY NIGHT AND/OR MONDAY NIGHT. INTERESTS ALONG THE
SOUTHWEST COASTLINE SHOULD MONITOR FOR UPDATES TO CONDITIONS.