Small Craft Advisory 922, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
436 PM AKST FRI NOV 20 2015

.ANALYSIS AND UPPER LEVELS...
THE MAIN FEATURE IS THE LARGE BROAD UPPER LEVEL TROUGH FROM THE
ARCTIC SOUTH ACROSS THE BERING SEA. A 100 KT JET IS ROUNDING THE
BASE OF THIS UPPER LEVEL TROUGH. AT THE SURFACE THE LOW AND
ASSOCIATED FRONT THAT MOVED THROUGH THE SOUTH CENTRAL REGION
THIS MORNING IS CONTINUING TO RAPIDLY MOVE OFF TO THE NORTHEAST.
THIS WILL BE RAPIDLY REPLACED BY A FAST MOVING LOW NOW OVER THE
WESTERN ALASKA PENINSULA THAT WILL MOVE INTO WESTERN PRINCE
WILLIAM SOUND TONIGHT. THIS STORM WILL BRING ANOTHER ROUND OF
PRECIPITATION TO KODIAK ISLAND AND SOUTH CENTRAL ALASKA INCLUDING
PRINCE WILLIAM SOUND AND THE COPPER RIVER BASIN. THE SECONDARY
CONCERN WITH THIS STORM IS THE STRONG GUSTY WEST WIND IN THE WEST
QUADRANT OF THE LOW THAT WILL BE ACCELERATED BY THE FAST MOVING
RIDGE FOLLOWING IN THE WAKE OF THIS LOW. THE POTENTIAL FOR
BLOWING SNOW IS OF CONCERN FOR THE KENAI PENINSULA ESPECIALLY IN
THE KACHEMAK BAY AREA TONIGHT INTO SATURDAY MORNING.

A WEAK LOW OVER THE WESTERN BERING SEA WILL RAPIDLY MOVE EAST TO
THE NUNIVAK ISLAND AREA BY SAT NIGHT. THIS SHOULD BRING ANOTHER
QUICK ROUND OF SNOW TO SOUTHWEST ALASKA SAT NIGHT AND SUN. THE
NEXT BIG WEATHER MAKER IS A WEAK LOW NOW SOUTH OF THE KAMCHATKA
PENINSULA THAT WILL RAPIDLY INTENSIFY INTO A LARGE STRONG STORM
SOUTH OF SHEMYA SAT THEN MOVE INTO THE CENTRAL BERING SEA SUN. WE
EXPECT THIS STORM TO CONTINUE TO MOVE NORTHEAST ACROSS THE BERING
SEA THROUGH MONDAY. THIS STORM WILL BRING WARMER CONDITIONS TO THE
SOUTHERN MAINLAND AND MORE IMPORTANTLY IT MAY DEVELOP A STORM
SURGE ALONG THE BERING SEA COAST NORTH OF CAPE NEWENHAM TO THE
BERING STRAIT.

&&

.MODEL DISCUSSION...
THE MODELS REMAIN IN GOOD AGREEMENT INTO THE MID TERM. THE
DETAILS IN THE HIGHER RESOLUTION MODELS IS PREFERRED WITH REGARD
TO THE FAST MOVING LOW THAT WILL IMPACT KODIAK ISLAND INTO SOUTH
CENTRAL ALASKA TONIGHT AND SAT. THERE ARE MODEL DIFFERENCES WITH
THE INTENSITY AND LOCATION OF THE STORM THAT WILL BE MOVING TO
THE NORTHERN BERING SEA MONDAY THAT WILL HAVE AN IMPACT ON THE
POTENTIAL FOR COASTAL STORM SURGE FLOODING DEPENDING ON THE
ORIENTATION OF THE FETCH. THIS WILL BEAR WATCHING. OVERALL
CONFIDENCE IS HIGH THROUGH THE MID TERM FOR THE SYNOPTIC SCALE.

&&

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

PRECIPITATION FROM THE NEXT FRONT WILL BEGIN SPREADING OVER THE
AREA THIS EVENING AS A MIX OF RAIN...SNOW AND ISOLATED POCKETS OF
FREEZING RAIN DUE TO WIDELY VARIED SURFACE TEMPERATURES.
TEMPERATURES IN AREAS IN CLOSE PROXIMITY TO EACH OTHER CURRENTLY
RANGE FROM THE UPPER TEENS AND LOWER TO MID 20S TO THE UPPER 30S
AND 40S THIS AFTERNOON. PRECIPITATION WILL GRADUALLY CHANGE OVER
TO ALL SNOW IN ALL BUT THE MOST COASTAL LOCATIONS THROUGH THE
EVENING HOURS THEN INCREASING IN INTENSITY AFTER MIDNIGHT WITH
SNOW CONTINUING IN MOST AREAS THROUGH SATURDAY MORNING.
ADDITIONALLY THE FRONT WILL BRING A BROAD AREA OF GALES AND STORM
FORCE WINDS TO GULF OF ALASKA AND COASTAL WATERS.

ONE FEATURE OF INTEREST THAT FORMS BEHIND THE INITIAL FRONT AND
AS THE SURFACE LOW SETTLES INTO PRINCE WILLIAM SOUND EARLY
SATURDAY MORNING IS A SEMI STATIONARY MESOSCALE BAND OF
PRECIPITATION THAT SETS UP STRETCHING FROM THE SOUTHERN TALKEETNA
MOUNTAINS...ACROSS THE MATANUSKA VALLEY AND OVER THE ANCHORAGE
AREA AND THE CHUGACH MOUNTAINS. THIS BAND COUPLED WITH GOOD COLD
AIR ADVECTION AND WESTERLY FLOW ALOFT AS WELL AS SOUTH TO
SOUTHWESTERLY FLOW UP COOK INLET HAS THE POTENTIAL TO BRING SOME
RATHER SUBSTANTIAL SNOW FALL RATES SATURDAY MORNING IN ADDITION
TO THE SNOW BECOMING INCREASINGLY FLUFFY AS TEMPERATURES COOL.

THE STEADIER SNOW WILL CHANGE TO SNOW SHOWERS DURING THE AFTERNOON
SATURDAY...THEN TAPER OFF OVERNIGHT SATURDAY NIGHT. ON SUNDAY...THE
WEAK LOW THAT IS EXPECTED TO MOVE INTO SOUTHWEST ALASKA EARLY SUNDAY
MORNING WILL MOVE THROUGH SOUTHCENTRAL AND INTO PRINCE WILLIAM
SOUND...GIVING ANOTHER QUICK SHOT OF SNOW SHOWERS TO SOUTH-CENTRAL
ALASKA.

&&

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

TO THE NORTH OF THE LOW...ENOUGH WARM AIR HAS WORKED INTO THE
STORM TO ALLOW FOR A COLD RAIN OVER THE BRISTOL BAY REGION...WITH
THE ONLY SNOW FURTHER INLAND NEAR SPARREVOHN. COLD AIR ASSOCIATED
WITH THE TROUGH IS BEING DRAWN SOUTHEASTWARD...BUT HAS GOTTEN
BOTTLED UP WEST OF THE AHKLUN MOUNTAINS. AS THE LOW MOVES INTO
THE GULF TONIGHT...THE POLAR AIR MASS WILL BE DRAWN INTO ALL OF
SOUTHWEST ALASKA. BROAD WEST TO NORTHWESTERLY WINDS WILL ALLOW
CONTINUED UPSLOPE SNOW SHOWERS ON THE WEST SIDES OF THE AHKLUN
MOUNTAINS AND THE ALASKA RANGE THROUGH THE NIGHT. MORE ISOLATED
SNOW SHOWERS ARE EXPECTED ON SATURDAY ACROSS THE REMAINDER OF
SOUTHWEST ALASKA AS A WEAK UPPER-LEVEL DISTURBANCE MOVES THROUGH.

A SECOND SOMEWHAT STRONGER DISTURBANCE LOOKS TO MOVE ACROSS THE
AREA STARTING SATURDAY EVENING FOR THE COASTAL REGIONS...WORKING
INLAND FOR THE DAY ON SUNDAY. INCREASED VORTICITY ADVECTION AHEAD
OF A SHORTWAVE LEADING A 110 KT NORTHWEST TO SOUTHEAST ORIENTED
JET STREAK IN THE UPPER LEVELS WILL PROVIDE THE FORCING FOR THIS
PARTICULAR LOW. BY THIS POINT COLD AIR WILL BE FIRMLY ENTRENCHED
ACROSS ALL OF SOUTHWEST ALASKA...SO SNOW WILL BE THE PRECIPITATION
TYPE FOR THIS EVENT EVERYWHERE. A PRIMARY INGREDIENT LACKING WITH
THIS SNOWFALL EVENT IS MOISTURE...AND AS SUCH A WIDE AREA OF ONLY UP
TO 2 INCHES OF SNOW IS EXPECTED FOR MOST LOCALES. THE STORM WILL
MOVE INTO THE GULF LATE SUNDAY AFTERNOON WITH ASSOCIATED SNOWFALL
ENDING SOON THEREAFTER ALONG THE WEST SLOPES OF THE ALASKA RANGE.

RIDGING AND WARMING TEMPERATURES ARE EXPECTED BY MONDAY AS A
POWERFUL LOW OVER THE BERING CAUSES WARM SOUTHERLY WINDS TO MOVE
INTO SOUTHWEST ALASKA.

&&

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

BROAD UPPER TROUGHING AND NORTHWEST LOW LEVEL FLOW WILL BE THE
DOMINANT WEATHER MODE THROUGH SATURDAY BEFORE ATTENTION SHIFTS TO
A LARGE AND STRONG STORM FORCE LOW WHICH WILL ENTER THE WESTERN
BERING SATURDAY NIGHT. SATELLITE IMAGERY DEPICTS BROAD AREAS OF
CONVECTIVE SHOWERS AS COLDER AIR POURS INTO THE EASTERN AND
SOUTHERN BERING. A DEVELOPING LOW OVER THE WESTERN BERING WILL
MAKE EAST PROGRESS TOWARD THE MAINLAND THROUGH SATURDAY
NIGHT...SUPPORTING ENHANCED RAIN AND SNOW SHOWERS AS IT MOVES
EAST. SATURDAY NIGHT...A STRONG OCCLUDED LOW MOVES INTO THE
WESTERN BERING...WHICH WILL BRING IN A HEALTHY DOSE OF WARMER
NORTH PACIFIC AIR AND STRONG SOUTHERLY TO SOUTHWESTERLY WINDS INTO
THE 60 MPH RANGE. THE FRONT WILL PROGRESS TO THE CENTRAL ALEUTIANS
AND PRIBILOF ISLANDS BY SUNDAY EVENING.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
AS PREVIOUSLY DISCUSSED...THE MODELS ARE IN GENERALLY GOOD
AGREEMENT WITH THE HANDLING OF LARGE LOW OVER THE BERING SEA AND
THE OVERALL PATTERN THROUGH EARLY TUESDAY MORNING. STORM FORCE
WINDS ARE EXPECTED OVER A GOOD PORTION OF THE BERING SEA LONG THIS
FRONT WITH AN SECOND SWATH OF STORM FORCE WINDS ALONG THE BACKSIDE
OF THE LOW AS IT MOVES INTO THE NORTHERN BERING SEA. THE STRONG
SOUTHERLY PUSH IS STILL EXPECTED WITH THIS SYSTEM...SO
TEMPERATURES OVER THE SOUTHWEST MAINLAND ARE EXPECTED TO QUICKLY
RISE WITH PRECIPITATION TURNING TO MOSTLY RAIN OVER THE REGION BY
MONDAY MORNING.

AT THE SAME TIME...THE AXIS OF THE ROBUST NORTHEAST PACIFIC RIDGE
WILL PASS THROUGH SOUTHCENTRAL ALASKA...GIVING A QUICK BLAST OF
COLD AIR OVER THE REGION WITH TEMPERATURES WELL BELOW ZERO INLAND
AND IN THE SINGLE DIGITS IN THE ANCHORAGE AREA AND TEENS ELSEWHERE
EXCEPT THE IMMEDIATE COASTAL AREAS. THESE TEMPERATURES WILL BE
SHORT LIVED HOWEVER AS THE RIDGE PUSHED EASTWARD TUESDAY MORNING.

AT THIS POINT...MODELS BEGIN TO DIVERGE THROUGH THE REMAINDER OF
THE PERIOD. BROADLY...THE MODELS ARE IN GROSS AGREEMENT IN
DEVELOPING A BROAD AND DEEP TROUGH OVER THE EASTERN BERING THAT
EXTENDS ALL THE WAY DOWN TO ABOUT 40N...SETTING UP DEEP SOUTHERLY
FLOW OVER THE SOUTHWEST MAINLAND AND MOST OF SOUTH-CENTRAL ALASKA.
THEY ALSO AGREE IN A DEEP UPPER LOW OVER NORTHEAST RUSSIA...SETTING
UP A BROAD AND FLAT TROUGH OVER THE REMAINDER OF THE BERING SEA
WITH ZONAL FLOW OVER THE NORTHERN PACIFIC. THE DIFFICULTIES ARE
WITH SURFACE FEATURES AS THE MODELS ARE STILL PROVIDING
SIGNIFICANTLY DIFFERENT SOLUTIONS WITH THE REMNANTS OF TYPHOON IN-
FA...WITH A ROUGH LOCATION SOMEWHERE SOUTH OF THE CENTRAL
ALEUTIANS ON WEDNESDAY. MODELS ARE ALSO STRUGGLING WITH A LOW
THAT IS EXPECTED TO DEVELOP ALONG A FRONT JUST NORTH OF HAWAII
SUNDAY NIGHT. IN GENERAL...THE GLOBAL MODELS ARE DEVELOPING THIS
LOW AND MOVING IT NORTHWARD ALONG THE WESTERN SIDE OF THE
NORTHEASTERN PACIFIC RIDGE AND INTO THE WESTERN POTIONS OF KODIAK
ISLAND SOMETIME LATE TUESDAY NIGHT THROUGH EARLY THURSDAY MORNING.
BECAUSE THE WIDE SPREAD OF SOLUTIONS WITH THIS LOW AND ITS
POTENTIAL INTERACTION WITH IN-FA...WPC GUIDANCE WAS USED IN DAYS
4-7...WHICH LEANED HEAVY ON ENSEMBLE GUIDANCE.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...STORM WARNING 119 120 131 132 177 178.
 GALE WARNING 129 130 136 137 138 139 141 150 155 160 165 175 176
180.
 HEAVY FREEZING SPRAY 181.

&&

SYNOPSIS AND MODEL DISCUSSION...SA
SOUTHCENTRAL ALASKA...JR
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...JA/JW
LONG TERM...RF

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE ANCHORAGE AK
1130 PM AKST FRI NOV 20 2015

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

1125 PM     SNOW             EAGLE RIVER             61.32N 149.57W
11/20/2015  M4.5 INCH                           AK   NWS EMPLOYEE

            4.5 INCHES OF NEW SNOW. STILL SNOWING AT TIME OF REPORT.

&&

RDUELL