Small Craft Advisory 869, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
400 PM AKST SUN NOV 1 2015

.ANALYSIS AND UPPER LEVELS...

IN THE UPPER LEVELS... A 135 KT JET STREAK IS MOVING ACROSS THE
ALEUTIANS AND SOUTHERN BERING THIS AFTERNOON...ROUGHLY ALIGNED
PARALLEL WITH THE ALEUTIAN CHAIN. A LEADING SHORTWAVE AND UPPER
LEVEL FRONT IN THE UPPER LEVEL FLOW ALONG WITH THE LEFT EXIT
REGION OF THE JET ARE ALL MOVING ACROSS SOUTHWEST ALASKA. THE
STRONGEST SUPPORT WITH THE SHORTWAVE AND UPPER LEVEL FRONT IS
MOVING INTO THE YUKON DELTA AND NORTON SOUND REGIONS WHILE THE
UPPER LEVEL SUPPORT IS NOT IN PHASE...REMAINING SOUTH ALONG THE
ALASKA PENINSULA. THIS HAS RESULTED IN WIDESPREAD PRECIPITATION
ASSOCIATED WITH THE BROAD LIFT WITH THESE TWO FEATURES...THOUGH
BECAUSE THE SHORTWAVE AND THE JET ARE NOT SUPPORTING EACH OTHER
WELL...THUS FAR THE PRECIPITATION INTENSITY HAS BEEN LIGHT. THIS
IS EVIDENCED BY THE RETURNS ON THE BETHEL AND KING SALMON RADARS.
THE MARINE AIR MOVING ALONG WITH THESE FEATURES IS WARM ENOUGH TO
KEEP THE LIONS SHARE OF THE PRECIPITATION IN THE LIQUID PHASE
ACROSS SOUTHWEST ALASKA...THOUGH AS IT HAS BEEN MOVING INLAND AND
ENCOUNTERING THE COLDER AIR IN PLACE...WINTRY PRECIPITATION HAS
BEEN FALLING IN AREAS SUCH AS SPARREVOHN...IGIUGIG...AND INTERIOR
BRISTOL BAY.

OVER THE BERING...A STRONG LOW IS CREATING A LONG FETCH OF WEST TO
SOUTHWEST WINDS OVER NEARLY THE ENTIRE BERING SEA. THIS FETCH IS
CAUSING HIGH SURF CONDITIONS OFF THE COAST OF THE KUSKOKWIM DELTA
WITH MINOR COASTAL FLOODING AND EROSION EXPECTED DUE TO LONG-FETCH
AS FAR SOUTH AS BRISTOL BAY. A FEW FACTORS ARE HELPING MITIGATE
COASTAL FLOODING WITH THIS EVENT...FIRST...THE MOON IS CURRENTLY
NEAR ITS LAST QUARTER PHASE...WHICH REDUCES THE HEIGHT OF THE HIGH
TIDES NATURALLY. SECONDLY...THE STORMS TRACK ACROSS THE NORTHERN
BERING HAS BEEN KEEPING THE HIGHEST SWELLS OVER THE CENTRAL AND
NORTHERN BERING...WITH FEWER IMPACTS ALONG THE ALEUTIAN CHAIN AND
EVENTUALLY SOUTHWEST ALASKA. FINALLY...THE STORM IS NOWHERE NEAR
AS STRONG AS SOME OF THE STORMS THAT HAVE CAUSED COASTAL FLOODING
IN THE PAST...THUS WHILE THE WINDS ASSOCIATED WITH THE STORM ARE
STRONG...THEY COULD BE QUITE A BIT STRONGER.

MUCH OF SOUTHCENTRAL ALASKA REMAINS QUIET THIS AFTERNOON AS
A RIDGE OF HIGH PRESSURE CURRENTLY OVER THE AREA RETREATS AHEAD OF
THE ACTIVE WEATHER CURRENTLY MOVING ACROSS SOUTHWEST ALASKA.

A WEAK DISTURBANCE CURRENTLY LOCATED WELL SOUTH OF THE WESTERN
ALEUTIANS LOOKS TO BE THE NEXT WEATHER MAKER IS IT MOVES TOWARDS
MAINLAND ALASKA AND INTENSIFIES IN THE COMING DAYS.

&&

.MODEL DISCUSSION...

THE MODELS ARE IN LARGE AGREEMENT REGARDING THE PASSAGE OF THE
DISTURBANCE AND FRONT CURRENTLY OVER SOUTHWEST ALASKA AS THEY MOVE
OVER SOUTHCENTRAL TONIGHT. THE AGREEMENT IS THAT IN LARGE PART THE
DISTURBANCE RACES ACROSS THE AREA...LEAVING VERY LIMITED TIME FOR
PRECIPITATION...THOUGH DUE TO UPSLOPE AND OTHER LOCAL EFFECTS
WILL PRODUCE MEASURABLE SNOWFALL.

ADDITIONAL MODEL DIFFERENCES ARISE REGARDING THE NEXT STORM
SYSTEM. IT IS CURRENTLY WELL SOUTH OF THE WESTERN ALEUTIANS...BUT
IN TAKING ADVANTAGE OF THE 120 KT JET STREAK IN PLACE...WILL RACE
TOWARDS THE ALASKA MAINLAND MONDAY AND TUESDAY. GENERALLY IT
LOOKS LIKE THE MODEL AGREEMENT ON A STORM TRACK NEAR OR ALONG THE
ALASKA PENINSULA LATE MONDAY AFTERNOON...THEN MOVING INTO THE GULF
TUESDAY MORNING BEFORE PUSHING INTO THE SOUTHEAST ALASKA PANHANDLE
TUESDAY NIGHT IS GOOD. THE DETAILS OF HOW MUCH COLD AIR WILL BE IN
PLACE ACROSS SOUTHCENTRAL...HOW STRONG ANY INITIAL DOWNSLOPING
WILL BE AND HOW LONG LASTING IT WILL BE ARE STILL BEING IRONED
OUT. FOR NOW THE NAM AND GEM REGIONAL ARE THE PREFERRED MODELS
OWING TO THEIR HIGHER RESOLUTION AND BETTER HANDLING OF LOCAL
EFFECTS. FORECAST CONFIDENCE IS ABOVE AVERAGE.

&&

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

THE REGION IS TRANSITIONING INTO A WESTERLY FLOW PATTERN ALOFT AS
AN OCCLUDED FRONT MOVES EAST INTO SOUTH CENTRAL. THIS WILL
SUPPORT THE DEVELOPMENT OF LIGHT SNOW ACROSS THE INTERIOR THIS
EVENING AND TONIGHT...WITH A RAIN AND SNOW MIX ALONG THE COAST.
THIS GENERAL PATTERN TENDS TO BE ON THE DRIER SIDE IN TERMS OF
OVERALL PRECIPITATION AMOUNTS...WITH PRECIPITATION TENDING TO
FAVOR THE WEST FACING SLOPES OF THE MOUNTAINS. FOR
ANCHORAGE...ACCUMULATIONS WILL BE RATHER LIGHT ACROSS WEST
ANCHORAGE...WITH HIGHER AMOUNTS OVER THE HILLSIDE AND EAST
ANCHORAGE. THE FRONT WILL MOVE EAST MONDAY...WITH PRECIPITATION
TAPERING OFF FROM WEST TO EAST...LINGERING THE LONGEST ACROSS THE
COPPER BASIN. A STRONG BUT COMPACT LOW WILL TRACK INTO THE GULF OF
ALASKA MONDAY NIGHT AND TUESDAY...BRINGING WIDESPREAD RAIN TO
COASTAL LOCATIONS...AND A RAIN AND SNOW MIX FOR PORTIONS OF THE
INTERIOR. PRECIPITATION WILL BE LIGHTER ACROSS THE
INTERIOR...ESPECIALLY IMMEDIATELY DOWNWIND OF THE CHUGACH
MOUNTAINS WHERE DOWNSLOPE FLOW AND A WEAK NORTHEAST WIND WILL KEEP
THE AREA DRIER THAN NEAR THE COAST. THIS LOW WILL ALSO BRING
STRONG AND GUSTY STRONG GALE FORCE WESTERLY WINDS TO KODIAK ISLAND
AND THE GULF OF ALASKA AS IT MOVES EASTWARD.

&&

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

THE NORTH/SOUTH FRONTAL BOUNDARY WILL CONTINUE PUSHING INLAND EARLY
OVER INTERIOR SOUTHWEST ALASKA. LINGERING COLD AIR IN THE
KUSKOKWIM VALLEY AND NORTHEAST GREATER BRISTOL BAY (ALONG THE
ALASKA RANGE) WILL PROMOTE PRECIPITATION STAYING AS SNOW WITH
TOTAL ACCUMULATIONS OF 1 TO 3 INCHES POSSIBLE. AN ACTIVE AND
UNSTABLE FLOW ALOFT WILL KEEP SCATTERED RAIN SHOWERS IN THE
FORECAST IN MOST OF THE MAINLAND LOCATIONS OVERNIGHT INTO MONDAY.
ON MONDAY...A DEVELOPING SYSTEM MOVING TOWARD THE ALASKA PENINSULA
WILL BRING ANOTHER ROUND OF PRECIPITATION TO THE BRISTOL BAY
REGION. THIS LOW HAS TRENDED SLIGHTLY SOUTHWARD WITH TIME...WITH
HEAVIEST PRECIPITATION EXPECTED LATE MONDAY THROUGH THE OVERNIGHT
BEFORE DEPARTING TO THE EAST TUESDAY. WITH IMPRESSIVE DYNAMICS
SETTING UP JUST NORTH AND WEST OF THE LOW TRACK...RAIN IS EXPECTED
TO CHANGEOVER TO HEAVY WET SNOW...MOST LIKELY FROM SOUTH OF KING
SALMON TO NEAR ILIAMNA. IN THESE AREAS...A WIDE RANGE OF SNOWFALL
ACCUMULATIONS ARE POSSIBLE DEPENDING ON THE EXACT TRACK OF THE LOW
AND HOW MUCH COOLING CAN OCCUR. FOR NOW WILL MENTION UP TO 2
INCHES BUT LOCALIZED HIGHER AMOUNTS ARE POSSIBLE. STAY TUNED FOR
FURTHER REFINEMENTS TO THE FORECAST.

BEHIND THE ORIGINAL FRONTAL BOUNDARY A LONG FETCH OF GALE FORCE
WINDS WILL BRING HIGH SEAS AND COASTAL STORM SURGE TO THE
KUSKOKWIM DELTA COAST. A HIGH SURF ADVISORY REMAINS IN EFFECT FOR
THESE AREAS WITH A SURGE OF 1 TO 2 FEET ABOVE HIGHEST ASTRONOMICAL
TIDE. WE WILL CONTINUE WITH A SPECIAL WEATHER STATEMENT FOR THE
BRISTOL BAY COASTAL COMMUNITIES WHERE A SURGE OF UP TO 1 FOOT IS
EXPECTED WITH THE HIGH TIDE CYCLE TONIGHT.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
GALE FORCE WINDS AND RAIN SHOWERS WILL TAPER OFF SOMEWHAT OVERNIGHT.
A QUICK AND COMPACT LOW PRESSURE SYSTEM WILL DEVELOP NEAR THE
EASTERN ALEUTIANS/ALASKA PENINSULA EARLY MONDAY MORNING BRINGING A
QUICK SHOT OF RAIN AND WIND. ANOTHER GALE-FORCE LOW AND
ASSOCIATED WEATHER FRONT WILL ENTER THE WESTERN BERING LATER
MONDAY AND THEN MOVE TO THE CENTRAL BERING AND PRIBILOF ISLANDS BY
LATE TUESDAY AFTERNOON.

&&

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

THE EXTENDED PERIOD IS LARGELY DOMINATED BY A DEEP AREA OF LOW
PRESSURE THAT DEVELOPS OVER THE NORTH PACIFIC AND MOVES ACROSS
THE SOUTHERN BERING SEA WEDNESDAY THROUGH THURSDAY NIGHT AND
EVENTUALLY INTO THE GULF OF ALASKA BY FRIDAY MORNING. MODELS HAVE
REALLY LOCKED ONTO THIS SOLUTION OVER THE PAST SEVERAL DAYS AND
THE UPDATED FORECAST REFLECTS THE CONFIDENCE WITH STORM FORCE
WINDS ACROSS THE PACIFIC SIDE OF THE ALEUTIAN ISLANDS. THIS STORM
WILL LIKELY HAVE HURRICANE FORCE WINDS ASSOCIATED WITH IT AS IT
RAPIDLY DEEPENS OVER THE MIDDLE OF THE WEEK...HOWEVER THE UPPER
LEVEL JET WHICH WILL SUPPLY THE STORM WITH THE ENERGY NEEDED TO
RAPIDLY DEVELOP WILL REMAIN OVER THE NORTHERN PACIFIC. THIS WILL
LEAD TO THE HURRICANE FORCE WINDS REMAINING A BIT SOUTH OF OUR
AREA OF RESPONSIBILITY. HOWEVER...HIGH SEAS EXCEEDING 30 FT WILL
BE POSSIBLE ALONG THE PACIFIC SIDE OF THE ALEUTIAN ISLANDS AND
SEAS OF 20 TO 25 FT COULD MAKE IT INTO THE SOUTHERN BERING SEA AND
EVENTUALLY INTO THE GULF OF ALASKA. THE ONE ASPECT OF THIS SYSTEM
THAT NEEDS TO BE MONITORED IS THE COLD AIR ADVECTION THAT HAPPENS
ON THE BACK SIDE OF THE SURFACE LOW. COLDER AIR FILTERING IN FROM
SIBERIA WILL STEEPEN THE LOW LEVEL LAPSE RATES WHICH WILL HELP
BRING DOWN GUSTS OF 60 TO 65 MPH THROUGH THE GAPS OF THE CENTRAL
ALEUTIANS...EASTERN ALEUTIANS AND POSSIBLY PORTIONS OF THE ALASKA
PENINSULA.

A STOUT WARM FRONT WILL PUSH ACROSS THE SOUTHWEST MAINLAND ON LATE
WEDNESDAY INTO THURSDAY WHICH SHOULD KEEP THE MAJORITY OF
PRECIPITATION THAT FALLS AS RAIN. THE ONLY PLACE WHERE SNOW LOOKS
LIKE A POSSIBILITY WOULD BE THE LOWER KUSKOKWIM VALLEY WHERE COLD
AIR TENDS TO BE ENTRENCHED AND TAKE SOME TIME TO BE DISPLACED.
PRECIPITATION TYPE BECOMES A BIT OF A CHALLENGE ACROSS SOUTHCENTRAL
ALASKA LATE THURSDAY THROUGH A GOOD PART OF THE UPCOMING WEEKEND.
THE FRONT SHOULD MODIFY A BIT AS IT CROSSES SOUTHWEST ALASKA BUT
SHOULD STILL RAISE 850 MB TEMPS TO 0 TO -2 DEGREES CELSIUS WHICH
WOULD FAVOR MORE RAIN THAN SNOW. COLD AIR SHOULD QUICKLY REPLACE
THE WARMER AIR WHICH WOULD LIKELY LEAD TO A TRANSITION OF A
RAIN/SNOW MIX OR ALL SNOW. THAT IS SOMETHING THAT WILL BECOME MUCH
CLEARER ONCE THE SYSTEM IS SAMPLED BY THE ALASKA UPPER AIR
NETWORK...OBSERVATIONS AND SATELLITE DATA. NEEDLESS TO SAY AN
ACTIVE PERIOD OF WEATHER LOOKS TO UNFOLD AND IT LOOKS LIKE THIS
PERIOD OF ACTIVE WEATHER SHOULD CONTINUE WELL PAST THE LONG TERM
FORECAST.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE WARNING 132 150 155 177 178 179 180 181 185.

&&

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