Small Craft Advisory 865, NWS Anchorage, AK

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

.ANALYSIS AND UPPER LEVELS...
A LARGE AMPLITUDE PATTERN CURRENTLY IS IN PLACE WITH TROUGH OVER
THE EASTERN MAINLAND AND GULF OF ALASKA. A RIDGE IS SITUATED OVER
THE BERING SEA WITH A TROUGH OVER THE KAMCHATKA PENINSULA. AT THE
BASE OF THE TROUGH OVER THE WESTERN BERING SEA IS A JET OF 175
KT. THE JET ROUNDING THE RIDGE IN THE EASTERN BERING AND OVER THE
MAINLAND THIS MORNING IS AROUND 100 KT.

SOME LIGHT SNOW CONTINUES INTO THE LATE AFTERNOON OVER THE COPPER
RIVER BASIN WHICH SHOULD END EARLY THIS EVENING. WITH THE JET
MOVING OVERHEAD AND A DECENT SURFACE GRADIENT OVER
SOUTHCENTRAL...THERE REMAIN MODERATE TO STRONG NORTH AND WEST GAP
WINDS. OUT WEST...A WEAK SHORT WAVE ON THE FRONT SIDE OF THE RIDGE
IS BRINGING LIGHT SNOW SHOWERS TO PORTIONS OF SOUTHWEST ALASKA
THIS AFTERNOON. FURTHER WEST...A STACKED SURFACE LOW JUST EAST OF
THE KAMCHATKA PENINSULA WITH AN ASSOCIATED FRONT IS MOVING THROUGH
THE WESTERN BERING SEA THIS AFTERNOON WITH GALE FORCE WINDS AND
MODERATE PRECIPITATION.

&&

.MODEL DISCUSSION...
THE MODELS ARE IN VERY GOOD AGREEMENT ON THE LONG WAVE PATTERN
THROUGH FRIDAY. THE TROUGH CURRENTLY OVER EASTERN GULF OF ALASKA
AND EASTERN ALASKA WILL GIVE WAY TO THE RIDGE OVER THE BERING
SEA. THE AXIS OF THE RIDGE WILL TRANSITION OVER THE MAINLAND
TONIGHT AND SUNDAY BEFORE BEING FLATTENED OVER THE MAINLAND SUNDAY
NIGHT AS A SHORT WAVE TROUGH CROSSES SOUTHWEST ALASKA TOMORROW AND
INTO SOUTHCENTRAL ALASKA TOMORROW AFTERNOON AND NIGHT. THIS WILL
BRING MORE PRECIPITATION TO SOUTHWEST TOMORROW AND TO SOUTHCENTRAL
LATE TOMORROW AFTERNOON AND NIGHT. THE UPPER LOW AND ASSOCIATED
SURFACE NEAR KAMCHATKA WILL SWING INTO THE BERING STRAIT TOMORROW
NIGHT BRINGING A LONG FETCH OF SOUTHWEST FLOW TO THE BERING SEA.
THIS WILL BRING THE THREAT OF COASTAL STORM SURGE TO MOST OF THE
WEST COAST OF ALASKA. A SECONDARY LOW ON THE BACK SIDE OF THE
UPPER LOW WILL DEVELOP SOUTH OF ADAK SUNDAY NIGHT AND QUICKLY
DEEPEN OVER THE NORTH PACIFIC AND WORK TO THE ALASKA PENINSULA
MONDAY NIGHT. THE LOW WILL MOVE INTO THE NORTHERN GULF BY TUESDAY
MORNING. WESTERLY FLOW WILL CONTINUE ACROSS THE BERING THROUGH
MONDAY NIGHT AS WELL...CONTINUING THE THREAT OF COASTAL STORM
SURGE TO THE WEST COAST OF ALASKA. ANOTHER LOW AND ASSOCIATED
SHORT WAVE TROUGH MOVES INTO THE WESTERN BERING SEA MONDAY NIGHT.

&&

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

NORTHERLY FLOW ALOFT AND AN OFFSHORE PRESSURE GRADIENT IS
PROMOTING DRY AND LARGELY CLEAR SKY CONDITIONS ACROSS SOUTHCENTRAL
THIS EVENING. SOME LOW AND MID LEVEL CLOUDS HANGING OVER PARTS OF
THE COPPER BASIN AND MATANUSKA VALLEY WILL GRADUALLY CLEAR OUT AS
DRIER AIR CONTINUES TO INFILTRATE THE REGION. THE STRONGEST
PRESSURE GRADIENT WILL OCCUR THROUGH LATE THIS EVENING AND INTO
THE OVERNIGHT BEFORE RAPIDLY WEAKENING SUNDAY MORNING. THIS WILL
KEEP MARGINALLY STRONG OUTFLOW WINDS ACROSS VALDEZ...SEWARD...AND
WHITTIER THROUGH TONIGHT. DRY WEATHER WILL PERSIST THROUGH THE
MORNING TOMORROW BEFORE A FAST MOVING FRONT MOVES INTO THE REGION.
RAIN WILL MIX ALONG THE COAST...BUT THE COLD DOME OF AIR OVER
INTERIOR ALASKA WILL KEEP PRECIP TYPE ALL SNOW. WITH A WESTERLY
FLOW DIRECTION ALOFT...SNOW WILL FAVOR WEST FACING SLOPES OF THE
CHUGACH AND TALKEETNA MOUNTAINS. SNOW WILL BECOME MORE STEADY
SUNDAY EVENING AND INTO THE OVERNIGHT...AND THIS IS WHEN SNOW
ACCUMULATIONS ARE EXPECTED BEFORE RAPIDLY TAPERING OFF AND LARGELY
ENDING BY MONDAY MORNING. SNOW WILL CONTINUE ACROSS THE COPPER
BASIN THROUGH THE DAYTIME PERIOD MONDAY.

&&

.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. SOUTHERLY FLOW
PICKING UP AHEAD OF THE STRONGER BERING FRONT WILL CONTINUE TO RETURN
MOISTURE AND LOW CLOUDS THROUGH THE OVERNIGHT FOR COASTAL
LOCATIONS...THEN MOVE INLAND 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. AREAS NORTH AND/OR EAST OF AN ANIAK-TO-ILIAMNA
LINE 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 BEFORE A
NEW LOW APPROACHES AND BRINGS A RENEWED SHOT AT RAIN AND SNOW
MAINLY TO BRISTOL BAY FOR MONDAY INTO TUESDAY.

.MARINE IMPACTS...A HIGH SURF ADVISORY HAS BEEN ISSUED FOR THE
KUSKOKWIM DELTA COAST WITH SEAS OF 10 TO 15 FEET PEAKING MONDAY
MORNING AND A COASTAL SURGE OF 1 TO 2 FEET ABOVE HIGHEST
ASTRONOMICAL TIDE. FOR BRISTOL BAY...ANY COASTAL SURGE SHOULD BE
NO MORE THAN 1 FOOT ABOVE HIGHEST ASTRONOMICAL TIDE. THIS WILL BE
COVERED BY A SPECIAL WEATHER STATEMENT.

THE BROAD LOW THAT WILL TRACK ACROSS THE BERING SEA STARTING LATE
TONIGHT WILL PUSH A LARGE AREA OF SOUTH TO SOUTHWESTERLY 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 ALASKA 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 WITH THE HIGH TIDE SUNDAY NIGHT...BUT WILL
PERSIST INTO MONDAY NIGHT FOR THE COAST FROM NUNIVAK ISLAND
NORTH.

&&

.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 THEN INTO 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.
LATE SUNDAY NIGHT AN UPPER DISTURBANCE WILL BRING A COMPACT SYSTEM
TO THE CENTRAL ALEUTIANS...WHICH WILL THEN TRACK NORTH AND EAST
THROUGH THE EASTERN ALEUTIANS AND ALASKA PENINSULA MONDAY.

&&

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

AN ACTIVE WEATHER PATTERN LOOKS TO BE ON THE HORIZON AS A SERIES
OF SIGNIFICANT STORM SYSTEMS PUSH ACROSS MUCH OF THE FORECAST
AREA. THE FIRST STORM OF NOTE BEGINS MONDAY NIGHT AS A SHORTWAVE
ENHANCED TROUGH INTERACTS WITH A WEAK SURFACE LOW SOUTH AND WEST
OF THE ALASKA PENINSULA. THE JET DYNAMICS ARE QUITE IMPRESSIVE
WITH THIS SHORTWAVE AND SHOULD QUICKLY SPIN A DECENT SURFACE LOW
UP DURING THE OVERNIGHT HOURS MONDAY HEADING INTO TUESDAY. THERE
WILL BE A GOOD BIT OF WARM FETCH ASSOCIATED WITH THIS LOW WHICH
SHOULD DRIVE A WARM FRONT ACROSS SOUTHWEST ALASKA. THE MAJORITY OF
PRECIPITATION LOOKS LIKE IT WILL FALL AS RAIN BUT THE LOWER
KUSKOKWIM VALLEY LOOKS LIKE IT WILL INITIALLY SEE SNOW AS THE
VALLEY TRAPS IN SOME COLDER AIR AND IT TAKES A WHILE TO BE
DISPLACED. THIS LOW WILL CONTINUE INTO SOUTHCENTRAL ALASKA TUESDAY
MORNING AND LOOKS LIKE A DECENT SNOWFALL EVENT WILL UNFOLD FOR
MOST INLAND LOCATIONS. INITIALLY...IT LOOKS LIKE DOWNSLOPING WILL
KEEP THE NORMAL LOCATIONS ALONG THE CHUGACH AND KENAI MOUNTAINS
DRY. HOWEVER...AS THE LOW MOVES TOWARD PRINCE WILLIAM SOUND...LOW
LEVEL FLOW SHOULD SWITCH TO THE NORTH WHILE UPPER LEVEL FLOW KEEPS
THE MOISTURE FEED FROM THE SOUTHWEST. THIS COULD LEAD TO A QUICK
COUPLE OF INCHES ACROSS THE ANCHORAGE BOWL AND MAT-SU VALLEYS.
OTHER LOCATIONS ACROSS SOUTHCENTRAL ALASKA WILL SEE DECENT SNOW
AMOUNTS BUT IT IS A BIT TOO EARLY TO GARNER A FAIR ESTIMATE.

ONCE THIS SYSTEM EXITS TO THE EAST TUESDAY NIGHT...THE NEXT SYSTEM
WILL HAVE ALREADY BEGUN TO SPIN UP SOUTH OF SHEMYA. NOW THIS
SYSTEM LOOKS QUITE IMPRESSIVE THROUGH MODEL DATA AS A SPLIT JET
MERGES TWO JET STREAKS TOGETHER AND DEVELOPS A VERY DEEP LOW OVER
A SHORT DURATION (RAPID CYCLOGENESIS). THIS LOW WILL MOVE
EAST/NORTHEAST TOWARD THE CENTRAL ALEUTIANS ON WEDNESDAY AND
CONDITIONS WILL RAPIDLY DETERIORATE AS THE LOW APPROACHES. IN THE
CURRENT FORECAST...WIDESPREAD GALES HAVE BEEN INTRODUCED TO THE
COASTAL WATERS OF THE ALEUTIANS. STORM FORCE WINDS WILL BE LIKELY
BUT MAY IMPACT SOUTH OF OUR AREA OF RESPONSIBILITY. THE TRACK OF
THE LOW WILL BE CRUCIAL WHEN IT COMES TO FORECASTING WINDS ACROSS
THE EASTERN HALF OF THE BERING SEA. MARINERS SHOULD MONITOR THIS
SYSTEM CLOSELY OVER THE NEXT SEVERAL DAYS. IN ADDITION TO THE
WINDS...HEAVY RAIN (SNOW OVER THE LOWER KUSKOKWIM VALLEY) LOOKS
POSSIBLE OVER THE ALEUTIANS AND SOUTHWEST ALASKA WITH A LARGE TAP
INTO SOME SUBTROPICAL MOISTURE. LAST BUT NOT LEAST...THIS LOW
CURRENTLY LOOKS TO PUSH INLAND OVER SOUTHWEST ALASKA THURSDAY
NIGHT WHICH COULD CREATE SOME STORM SURGE AND COASTAL FLOODING
ISSUES. THE DETAILS WILL CONTINUE TO BE IRONED OUT OVER THE COMING
DAYS BUT IT SEEMS A CHANGE IN WEATHER PATTERN IS UPON US.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE WARNING 121 127 129 131 132 150 155 165 170 172 173
 174 175 176 177 178 179 180 181 185.

&&

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