High Surf Advisory 1, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
554 AM AKDT WED SEP 30 2015

.ANALYSIS AND UPPER LEVELS...

THE VERY ACTIVE WEATHER ACROSS SOUTHERN ALASKA HAS CONTINUED TO
UNFOLD. A POWERFUL VERTICALLY STACKED LOW OVER THE NORTHERN GULF
HAS BROUGHT PRODIGIOUS AMOUNTS OF PRECIPITATION TO
SOUTHCENTRAL...BOTH IN LIQUID AND SOLID FORM. IR SATELLITE IMAGERY
SHOWS A WOUND-UP SWIRL ACROSS THE NORTHERN GULF...INDICATING THE
LOW HAS ALREADY PASSED THE MATURE STAGE IN ITS LIFE CYCLE. A
DEFORMATION ZONE IS EVIDENT ON IR SATELLITE IMAGERY ORIENTED ALONG
THE SPINE OF THE ALASKA RANGE. ADDITIONAL DEVELOPMENT ON SATELLITE
IS EVIDENT ACROSS THE MATANUSKA AND SUSITNA VALLEYS THROUGH THE
ANCHORAGE BOWL AND ALONG THE NORTHERN KENAI PENINSULA. FOR
ANCHORAGE...THE LOW HAS BEEN THE JEWEL CAPPING OFF AN EXTREMELY
WET MONTH. 7.52 INCHES OF PRECIPITATION HAS FALLEN FOR THE MONTH...AND
THE ANNUAL PRECIPITATION IS NOW 14.82 INCHES. THUS...MORE THAN
HALF OF THE PRECIPITATION THAT HAS FALLEN THUS FAR IN 2015 HAS
FALLEN IN SEPTEMBER. FOR HIGHER ELEVATIONS...THE SECOND HALF OF
THE STORM PRODUCED AS MUCH AS 6 INCHES OF SNOW ON THE SOUTHERN KENAI
PENINSULA...AND 4 INCHES THUS FAR ON THE ANCHORAGE HILLSIDE.

IN ADDITION...A STRONG HIGH SLOWLY RETREATING SOUTHWARD ACROSS THE
CENTRAL ALEUTIANS HAS CONTRIBUTED TO THE GENERATION OF A STRONG
PRESSURE GRADIENT ACROSS SOUTHWEST ALASKA...CAUSING HIGH WINDS.
GUSTS OVER 60 MPH WERE RECORDED DURING THE DAY TUESDAY ALONG SHELIKOF
STRAIT...THE WEST SIDE OF KODIAK ISLAND...AND THE SOUTHERN COOK
INLET NEAR THE BARREN ISLANDS. ON THE WEST SIDE OF THE
HIGH...ANOTHER STRONG FRONT IS MOVING EAST INTO THE FAR WESTERN
BERING.

UPPER LEVELS...THE VERTICALLY STACKED LOW OVER THE NORTHERN GULF IS
CURRENTLY BEING PASSED BY A JET STREAK SOUTHEAST OF THE LOW AND IS
GETTING INTO THE LEFT ENTRANCE REGION. THUS...WEAKENING OF THE
FEATURE IS NOW UNDERWAY. RIDGING ABOVE THE SURFACE HIGH OVER THE
CENTRAL ALEUTIANS IS INTENSIFYING AND BUILDING EASTWARD. SO
DESPITE THE WEAKENING UPPER LOW OVER THE GULF...THE PATTERN IS
REMAINING VERY AMPLIFIED. A NEARLY VERTICALLY STACKED LOW CENTERED
NEAR THE KAMCHATKA PENINSULA IS ADDING TO THE INTENSITY OF THE
STRONG FRONT MOVING INTO THE WESTERN ALEUTIANS...INTENSIFYING IN
THE LEFT EXIT REGION OF ANOTHER JET STREAK. THE BUILDING RIDGING
WILL HELP TO TRANQUILIZE THE WEATHER ACROSS SOUTHERN MAINLAND
ALASKA FOR THE FIRST COUPLE DAYS OF OCTOBER.

&&

.MODEL DISCUSSION...

THE MODELS ALL GENERALLY START OUT IN AGREEMENT. THE GULF LOW WILL
SLOWLY SHIFT EAST ALONG THE NORTHERN GULF COAST WHILE STEADILY
WEAKENING. THIS WILL SHUT OFF MOST PRECIPITATION ACROSS
SOUTHCENTRAL LATER ON THIS MORNING AND LEAD TO A DRAMATIC
REDUCTION OF THE WINDS ACROSS SOUTHWEST ALASKA AND KODIAK ISLAND
OVER THE COURSE OF THE DAY.

THE NEXT MAJOR WEATHER MAKER IS THE FRONT NOW MOVING INTO THE
WESTERN BERING. STEADY EASTWARD PROGRESS OF THE FRONT IS EXPECTED
WITH MOST MODELS INDICATING ROBUST CYCLOGENESIS IN THE
NORTHWESTERN BERING AS A JET STREAK PUSHES NORTHEASTWARD EARLY
THURSDAY. THIS WILL HELP TO BOTH FURTHER AMPLIFY THE RIDGE AND
PROGRESS THE RIDGE EASTWARD THROUGH WESTERN ALASKA EARLY ON
THURSDAY. MODEL DISCREPANCIES BECOME MORE PRONOUNCED AT THIS
POINT...PARTICULARLY CONCERNING THE SPEED OF EASTWARD MOVEMENT OF
THE FRONT. THE GLOBAL MODELS ARE A HAIR FASTER THAN THE LOCAL
MODELS...AND GIVEN THE MODEL AGREEMENT THAT WINDS IN THE CORE OF
THE JET WILL BE RACING NORTH OF 170 KTS...THE FASTER MOVEMENT OF
THE FRONT LEAD TO A PREFERENCE TOWARDS THE GLOBAL MODELS FOR THIS
FORECAST PACKAGE.

&&

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

RIVER LEVELS REMAIN HIGH OVER MOST OF THE REGION DUE TO THE HEAVY
RAINFALL THE PAST TWO DAYS. A FLOOD ADVISORY REMAINS IN EFFECT IN
THE SUSITNA VALLEY AND ALSO IN THE CORDOVA AREA.

THE SNOW OVER SOUTHCENTRAL ALASKA IS LINGERING OVER THE NORTHERN COOK
INLET AREA THROUGH THE SUSITNA VALLEY. THIS WILL DIMINISH THIS
MORNING AS THE STRONG LOW IN THE GULF MOVES EASTWARD. THIS WILL
ALSO KICK UP THE WINDS IN SEWARD AND WHITTIER AND OTHER AREAS THAT
COMMONLY BLOW WITH STRONG OUTFLOW WINDS. THE BREAK BETWEEN SYSTEMS
FOR THURSDAY STILL LOOKS ON TRACK TO GIVE A NICE DAY OVER MOST OF
SOUTHCENTRAL BEFORE THE NEXT FRONT MOVES INTO THE REGION FRIDAY
USHERING IN MORE RAINFALL.

&&

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

STRONG NORTHWESTERLY WINDS ALONG THE AKPEN WILL SLOWLY DIMINISH
THIS MORNING AS RIDGING MOVES IN FROM THE EASTERN ALEUTIANS. THIS
WILL ALSO CAUSE THE PERSISTENT SNOW THAT HAS BEEN FALLING OVER THE
ALASKA RANGE OVER THE PAST FEW DAYS TO BREAK UP AS WELL...THOUGH
A FEW ADDITIONAL INCHES SHOULD STILL FALL THIS MORNING. OTHERWISE
A SHORT LIVED PERIOD OF QUIETER WEATHER WILL MOVE INTO THE AREA BY
THIS AFTERNOON AS WEAK RIDGING BEGINS TO MOVE INTO THE AREA. THIS
WILL BE RELATIVELY SHORT LIVED HOWEVER AS A FRONTAL SYSTEM
CURRENTLY MOVING THROUGH THE WESTERN ALEUTIANS WILL BEGIN TO
IMPACT COASTAL COMMUNITIES BY THURSDAY EVENING WITH RAIN AND
STRONG SOUTHERLY WINDS. THIS SYSTEM WILL THEN BRING RAIN...GUSTY
SOUTHERLY WINDS AND WARMER TEMPERATURES TO THE AREA INTO THE END
OF THE WEEK.

&&

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

MUCH OF THE ATTENTION OVER THE BERING SEA CENTERS AROUND THE STORM
FORCE FRONT CURRENTLY ENTERING THE WESTERN ALEUTIANS. THIS FRONT
WILL CONTINUE TO INTENSITY TODAY...AND IS EXPECTED TO BRING STORM
FORCE WINDS AND POTENTIALLY HEAVY RAINFALL TO THE CENTRAL
ALEUTIANS AND PRIBILOF ISLANDS TONIGHT AND THURSDAY. THE WORST OF
THE WEATHER WILL HOWEVER BE RELATIVELY SHORT LIVED AS THE FRONT
WILL BE RELATIVELY FAST MOVING SYSTEM AS IT RIDES ALONG A 150 KT
JET STREAK MOVING INTO THE REGION. THIS FRONT SHOULD MOSTLY EXIT
THE REGION BY THURSDAY NIGHT WITH GUSTY SOUTHWESTERLY WINDS AND
RAIN SHOWERS CONTINUING.

&&

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

THE NEXT STRONG FRONTAL SYSTEM WILL BE STRETCHED ACROSS WESTERN
AND SOUTHWEST ALASKA FRIDAY MORNING WITH AN UPPER LEVEL RIDGE OVER
SOUTHCENTRAL ALASKA. THE RIDGE ALOFT WILL SHIFT EAST THROUGH THE
DAY FRIDAY ALLOWING THE FRONTAL SYSTEM TO SPREAD PRECIPITATION
EAST INTO SOUTH CENTRAL ALASKA AS WELL AS INCREASING SOUTHEASTERLY
GAP WINDS. INITIALLY PRECIPITATION IN THE SUSITNA VALLEY MAY BEGIN
AS SNOW FRIDAY MORNING BUT IS EXPECTED TO QUICKLY MIX OVER TO RAIN
AS THE LONG SOUTH SOUTHWESTERLY FETCH OF THE FRONTAL SYSTEM WILL
BRING A GOOD BIT OF WARM AIR UP INTO THE AREA AS WELL AS ABUNDANT
MOISTURE. THE FRONT WILL REMAIN SPRAWLED ACROSS MUCH OF MAINLAND
ALASKA WITH A BROAD UPPER LEVEL TROUGH AS IT WEAKENS THROUGH
SATURDAY.

AN UPPER LEVEL RIDGE WILL MOVE INTO WESTERN ALASKA ON SUNDAY AND
THEN PUSH EAST SUNDAY NIGHT...USHERING IN A PERIOD OF DRIER
WEATHER ACROSS SOUTHERN ALASKA INTO MONDAY. THEREAFTER...THERE IS
GOOD AGREEMENT WITH A BROAD LOW MOVING INTO THE BERING EARLY NEXT
WEEK...BUT LESS CERTAINTY ON HOW FAR EAST IT MOVES BY MIDWEEK...WITH
SOME NUMERICAL GUIDANCE (THE GFS) HINTING AT STRONGER HIGH PRESSURE
ALOFT KEEPING MOST OF THE ACTIVITY OVER THE BERING. THE ECMWF ALSO
HINTS AT THIS...BUT LESS AGGRESSIVELY WITH THE FRONT MAKING
EASTWARD PROGRESS INTO SOUTHERN ALASKA TUESDAY AND WEDNESDAY. THIS
FORECAST WILL TAKE AN ENSEMBLE BLENDED WPC APPROACH...WHICH KEEPS
SOME CHANCES FOR RAIN BY TUESDAY AND WEDNESDAY INTO SOUTHERN
ALASKA. TEMPERATURES WILL REMAIN NEAR NORMAL...WITH NO BIG STORMS
OR HIGH IMPACT WEATHER EVENT ANTICIPATED.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...STORM WARNING 170 173 174 175 176 177 179 181 185.
         GALES 120 121 127 130 131 132 150 151 165 171 172
               178 180.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...JW
SOUTHCENTRAL ALASKA...EZ
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...DEK
LONG TERM...JER/JA

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PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE ANCHORAGE AK
1049 AM AKDT WED SEP 30 2015

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1035 AM     SNOW             8 NW PALMER             61.69N 149.24W
09/30/2015  M1.5 INCH                           AK   TRAINED SPOTTER

1035 AM     SNOW             SUTTON                  61.72N 148.88W
09/30/2015  E0.2 INCH                           AK   TRAINED SPOTTER

1035 AM     SNOW             2 N WILLOW              61.77N 150.07W
09/30/2015  E2.8 INCH                           AK   TRAINED SPOTTER

1035 AM     SNOW             CANTWELL                63.37N 148.92W
09/30/2015  E10.0 INCH                          AK   DEPT OF HIGHWAYS

            DOT CANTWELL ESTIMATES 8-10 INCHES OF SNOWFALL FELL IN
            THE CANTWELL AREA.

1035 AM     SNOW             TALKEETNA               62.34N 150.09W
09/30/2015  E1.5 INCH                           AK   DEPT OF HIGHWAYS

1035 AM     SNOW             7 S TALKEETNA           62.23N 150.09W
09/30/2015  E2.5 INCH                           AK   DEPT OF HIGHWAYS

&&

RDUELL