Small Craft Advisory 925, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
419 PM AKST SAT NOV 21 2015

.ANALYSIS AND UPPER LEVELS...
PROGRESSIVE UPPER LEVEL FLOW DOMINATES THE SOUTHERN TIER OF ALASKA
FROM THE BERING SEA TO THE SOUTHERN MAINLAND. AN UPPER LEVEL
SHORT-WAVE CONTINUES TO MAKE ITS WAY ACROSS SOUTHCENTRAL ALASKA
THIS MORNING PRODUCING AREAS OF SNOW FROM ANCHORAGE AND THE MAT-SU
TO THE COPPER RIVER BASIN. STRONG COLD AIR ADVECTION RIGHT BEHIND
THIS WAVE IS LEADING TO WIDESPREAD GALE TO STORM FORCE WINDS
ACROSS THE GULF OF ALASKA WATERS. SIMILARLY STRONG WINDS HAVE ALSO
DEVELOPED IN WHITTIER AND WESTERN PRINCE WILLIAM SOUND. A WEAKER
AND BROADER SHORT-WAVE IS HEADED INLAND ACROSS SOUTHWEST ALASKA
TODAY. SNOWFALL WITH THIS IS MUCH LIGHTER AND SPARSER THAN WHAT
IS FALLING OVER SOUTHCENTRAL. CONTINUING UPSTREAM ANOTHER COUPLE
UPPER LEVEL SHORT-WAVES ARE CROSSING THE CENTRAL BERING AND
CENTRAL ALEUTIANS. AS WITH THE SOUTHWEST ALASKA TROUGH THESE ARE
OF LOW AMPLITUDE AND PRODUCING GENERALLY LIGHT PRECIPITATION. THE
NEXT MAJOR STORM SYSTEM IS TAKING SHAPE SOUTH OF THE KAMCHATKA
PENINSULA...WHERE A STRONG UPPER LEVEL JET STREAK EXITING ASIA IS
LEADING TO RAPID DEEPENING OF A SURFACE LOW. AS THIS LOW DEEPENS
WE ARE JUST BEGINNING TO SEE RISING HEIGHTS DOWNSTREAM WHICH WILL
LEAD TO SIGNIFICANT AMPLIFICATION OF THE UPPER LEVEL PATTERN OVER
THE NEXT COUPLE DAYS...ULTIMATELY LEADING TO TRANSPORT OF MUCH
WARMER AIR NORTHWARD TO THE SOUTHERN ALASKA MAINLAND.

&&

.MODEL DISCUSSION...
MINOR DIFFERENCES CONTINUE WITH TRACK OF A COUPLE WEAK SURFACE
LOWS...ONE MOVING ONSHORE OF THE KUSKOKWIM DELTA TONIGHT AND
ANOTHER CROSSING THE NORTHERN GULF SUNDAY AND SUNDAY NIGHT. THESE
DIFFERENCES WILL AFFECT THE WINDS NEAR THE LOW CENTER...BUT WILL
HAVE LITTLE AFFECT ON THE FORECAST FOR THE LARGER REGION. WILL
GENERALLY USE AN AVERAGE POSITION OF ALL THE MODELS. AS FAR AS THE
MAJOR STORM SYSTEM TRACKING INTO THE BERING SEA THERE HAS BEEN A
DEFINITE MODEL TREND TOWARD A DEEPER LOW AND STRONGER WINDS...SO
WILL INCREASE WINDS ACROSS MOST OF THE BERING AND ALEUTIANS WITH
THE AFTERNOON FORECAST. WITH A STRONGER SYSTEM THE EASTWARD
PROGRESSION OF THE FRONTAL SYSTEM LOOKS A LITTLE SLOWER SO WILL
ALSO REFLECT THAT CHANGE IN THE LATEST FORECASTS. OVERALL FORECAST
CONFIDENCE IS ABOVE AVERAGE.

&&

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

WITH THE CURRENT FRONTAL SYSTEM EXITING THE AREA TO THE EAST
THE STRONG POST FRONTAL WESTERLY WINDS WILL GRADUALLY DIMINISH
OVERNIGHT AND SNOW SHOWERS WILL TAPER OFF. SNOW WILL PERSIST THE
LONGEST OVER THE COPPER RIVER BASIN MAINLY EAST OF THE RICHARDSON
HIGHWAY AND OVER THE ADJACENT MOUNTAINS. THE NEXT LOW PRESSURE
SYSTEM WILL TRACK OVER KODIAK ISLAND SUNDAY MORNING AND THEN INTO
THE NORTH CENTRAL GULF SUNDAY EVENING. WHILE MODELS HAVE BEEN
TRENDING MORE SOUTHERLY WITH THE SURFACE LOW...WHICH WOULD CONFINE
ITS PRECIPITATION TO THE GULF AND MORE SOUTHERN COAST AREAS...THEY
DO STILL SWING A PHASED TROUGH THROUGH SOUTH CENTRAL ALASKA
FURTHER NORTH. WHILE THE NORTHERN TROUGH IS NOT ALL THAT STRONG IT
SHOULD STILL BE ENOUGH TO BRING AND INCH OR TWO OF LIGHT SNOW TO
THE SOUTHERN SUSITNA VALLEY...MATANUSKA VALLEY AND ANCHORAGE AREAS
SUNDAY AFTERNOON AND EVENING.

A SUBSTANTIALLY LARGER AND WARMER FRONTAL SYSTEM WILL BEGIN
SHIFTING THE PREVAILING FLOW MORE SOUTHERLY IN THE WESTERN
PORTIONS OF SOUTH CENTRAL ALASKA MONDAY AFTERNOON. PRECIPITATION
WILL INITIALLY SPREAD ACROSS THE ALASKA RANGE AND INTO THE
SUSITNA VALLEY WITH THE SOUTHERLY UP VALLEY FLOW FAVORABLE TO
PRODUCE A GOOD BIT OF SNOW IN THAT AREA WHILE TEMPERATURES REMAIN
COLD. FURTHER EAST...STRENGTHENING LOW LEVEL SOUTHEASTERLY FLOW
AND DOWN SLOPE DRYING WILL COMPETE WITH THE OVERRUNNING
PRECIPITATION...KEEPING PRECIPITATION LIGHT AND SPOTTY FROM THE
MATANUSKA VALLEY TO ANCHORAGE METRO AREA.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
A QUICK-MOVING UPPER LEVEL DISTURBANCE AND ASSOCIATED WEAK
SURFACE LOW MOVES ACROSS SOUTHWEST ALASKA TONIGHT INTO SUNDAY
AND BRINGS A SHOT OF SNOW TO THE AREA TONIGHT...WITH THE HIGHEST
ACCUMULATIONS FOCUSED OVER THE KUSKOKWIM DELTA WHERE UP TO 3
INCHES WILL BE POSSIBLE THROUGH SUNDAY MORNING. ON THE BACK SIDE
OF THIS SYSTEM AS SNOW ENDS...NORTH TO NORTHWEST WINDS GUSTING AS
HIGH AS 25 MPH COULD CAUSE LOCALIZED BLOWING SNOW ADVISORY
CONDITIONS...ESPECIALLY ALONG THE COAST. THE NEXT SYSTEM QUICKLY
APPROACHES SUNDAY NIGHT AND WILL BRING POSSIBLE BLIZZARD
CONDITIONS TO THE KUSKOKWIM DELTA ZONE NORTH AND WEST OF BETHEL.
ANY POTENTIAL BLIZZARD CONDITIONS WILL BE SHORT LIVED...LASTING
GENERALLY NO MORE THAN 3 TO 6 HOURS...BEFORE A WARM FRONT MOVES
THROUGH AND CAUSES SNOW TO MIX WITH OR CHANGE OVER TO RAIN.

ANOTHER CONCERN WITH THIS STORM WILL BE THE POTENTIAL FOR HIGH
SURF CONDITIONS FOR COASTAL COMMUNITIES FROM KUSKOKWIM BAY NORTH
ALONG THE COAST...BEGINNING WITH THE HIGH TIDE CYCLE AROUND MIDDAY
MONDAY. CURRENT GUIDANCE SUGGESTS SEAS REACHING 2.5 TO 3 FEET
ABOVE MAX ASTRONOMICAL TIDE FOR SEVERAL CONSECUTIVE HIGH TIDE
CYCLES NORTH OF CAPE NEWENHAM. GIVEN NO REPORTED IMPACTS FROM
PREVIOUS HIGH SURF ADVISORIES ISSUED IN THE LAST FEW WEEKS FOR
THIS REGION...WE WILL HOLD OFF ISSUING ANYTHING FOR THIS PACKAGE
BUT WILL REVISIT AS THE EVENT APPROACHES.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
A POWERFUL LOW PRESSURE SYSTEM MOVES INTO THE WESTERN BERING SEA
TONIGHT. A HIGH-END GALE TO STORM-FORCE FRONT WILL MOVE ACROSS THE
WESTERN ALEUTIANS LATER TONIGHT...WITH PRECIPITATION QUICKLY
CHANGING OVER TO RAIN AS WARMER AIR IS DRAWN IN FROM THE NORTH
PACIFIC. THE FRONT WILL WEAKEN SLIGHTLY AS IT CONTINUES EASTWARD
THROUGH MONDAY BUT WILL STILL MAINTAIN STRONG GALE FORCE WINDS AS
IT MOVES OVER THE ALEUTIANS AND ALASKA PENINSULA.
MEANWHILE...ANOTHER ROUND OF HIGH-END STORM FORCE TO HURRICANE-FORCE
WINDS WILL BE IN STORE FOR THE WESTERN ALEUTIANS AS STRONG COLD
ADVECTION COMMENCES ON THE BACKSIDE OF THE LOW. THIS LOW WILL
WEAKEN MONDAY INTO TUESDAY YET STILL REMAIN QUITE STRONG AS IT
MOVES NORTH INTO THE NORTHERN BERING SEA BY MONDAY EVENING.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
AT THE START OF DAY 3...THE DOMINATE FEATURE WILL BE THE LARGE LOW
IN THE BERING SEA...LOCATED JUST WEST OF ST MATTHEW ISLAND
TUESDAY EVENING. THE FRONT BY THIS TIME WILL BE SWEEPING INTO THE
SOUTHWEST MAINLAND...WITH PRECIPITATION STAYING AS MOSTLY RAIN
OVER THE SOUTHWEST COAST WITH A RAIN/SNOW MIX INLAND MONDAY NIGHT.
WINDS OVER THE CENTRAL BERING AND THE PRIBILOF ISLANDS ARE
EXPECTED TO CONTINUE TO BE AT STORM FORCE MONDAY EVENING BEFORE
SLOWLY FALLING TO STRONG GALE FORCE BY TUESDAY MORNING. WINDS WILL
CONTINUE TO DECREASE OVER THE BERING SEA ON WEDNESDAY AS THE LOW
MOVES NORTHWARD TO NEAR ST LAWRENCE ISLAND. THE FRONT WILL
CONTINUE TO PUSH THROUGH THE ALASKA RANGE AND INTO SOUTHCENTRAL
TUESDAY MORNING...BUT BY THIS TIME THE NORTHEASTERN PACIFIC RIDGE
WILL BE FIRMLY IN PLACE OVER THE EASTERN GULF OF ALASKA...WHICH
WILL PREVENT THE FRONT FROM PUSHING MUCH FURTHER EAST THAN ABOUT
145W.

AT THIS POINT...THE POSITION OF THE RIDGE WILL ALLOW FOR MOSTLY
SOUTH TO SOUTHWESTERLY FLOW OVER SOUTHCENTRAL ALASKA WITH A
SOUTHEASTERLY FLOW AT THE LOWER LEVELS OVER PRINCE WILLIAM
SOUND...WHICH SHOULD KEEP PRECIPITATION IN THE FORECAST FOR THE
SUSITNA VALLEY AND THE GULF COAST. THE SOUTHEASTERLY FLOW IN THE
LOWER LEVELS IN THE PRINCE WILLIAM SOUND AREA WILL GENERALLY KEEP
THE ANCHORAGE AREA DOWN-SLOPED...AND THE CURRENT FORECAST
REFLECTS THIS THROUGH DAY 3 WITH LIGHT PRECIPITATION IN THE
ANCHORAGE BOWL TUESDAY. PRECIPITATION TYPE WILL AGAIN BE AN ISSUE
WITH THE FLOW UP COOK INLET FAVORABLE FOR A CHANGE TO A RAIN/SNOW
MIX ALL THE WAY NORTH INTO THE SUSITNA VALLEY LATE TUESDAY.

AS HAS BEEN THE CASE FOR THE LAST SEVERAL DAYS...THE FORECAST FOR
WEDNESDAY ONWARD HAS BEEN DIFFICULT. MODELS ARE BEGINNING TO
CONVERGE ON A SOLUTION FOR EX-TYPHOON IN-FA WITH A 965 TO 975 MB
LOW MOVING ALONG THE ALEUTIAN CHAIN THURSDAY THROUGH EARLY
SATURDAY. THE MODELS HAVE NOT SIGNIFICANTLY IMPROVED HOWEVER ON
THE HANDLING OF THE LOW THAT IS ABOUT 700 MILES NORTH OF OAHU
THIS AFTERNOON. AT LEAST PORTIONS OF THIS FEATURE...IN WHATEVER
FORM IT WILL TAKE...SHOULD MOVE NORTHWARD ALONG THE WESTERN SIDE
OF THE RIDGE AND INTO THE THE ALASKA PENINSULA TO KODIAK REGION IN
THE WEDNESDAY TO THURSDAY TIME FRAME...BUT EVEN THIS IS NOT
CERTAIN AS THE MODELS ARE INCONSISTENT WITH SURFACE FEATURES AS
WELL AS WHAT TO DO WITH THE ENERGY ASSOCIATED WITH THIS LOW. BOTH
THE EC AND THE GFS HINT THAT WHATEVER REMAINS OF THIS ENERGY WILL
LIKELY INTERACT WITH THE REMAINS IN-FA ON DAY 6-7. WITH THIS BEING
SAID...AGAIN WPC GUIDANCE WAS USED HEAVILY IN THE DAY 4-7 TIME
FRAME TO ACCOUNT FOR THE HIGH DEGREE OF UNCERTAINTY IN THESE TWO
FEATURES.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...BLIZZARD WATCH 155.
 SNOW ADVISORY 141.
MARINE...HURRICANE FORCE WARNING 178.
 STORM WARNING 175 176 177 181 185.
 GALE WARNING 119 120 129 130 131 150 155 165 170 171 172 173 174
179 180.

&&

SYNOPSIS AND MODEL DISCUSSION...SB
SOUTHCENTRAL ALASKA...JR
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...CC
LONG TERM...RF