Small Craft Advisory 916, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
413 PM AKST WED NOV 18 2015

.ANALYSIS AND UPPER LEVELS...

A SIGNIFICANT WEATHER PATTERN CHANGE IS UNDERWAY ACROSS THE
ALASKAN DOMAIN. CLEAR AND COLD CONDITIONS WITH GUSTY "OUTFLOW"
WINDS ALONG THE GULF COAST ARE GIVING WAY TO MOIST SOUTHERLY FLOW
AND WARMER AIR OVER THE EASTERN BERING SEA AND SOUTHWEST
ALASKA...WITH SOUTHCENTRAL ALASKA NEXT ON THE AGENDA. A SERIES OF
STORMS ARE LINED UP OVER THE BERING AND NORTHWEST PACIFIC...ALL
RIDING ALONG A RESURGENT 175+ KT JET COMING OFF EASTERN RUSSIA.
THE FIRST STORM IS THE WEAKEST...AND IS ESSENTIALLY A MODERATE
STRENGTH FRONT THAT MADE LANDFALL OVER SOUTHWEST ALASKA LATE THIS
MORNING DROPPING SEVERAL INCHES OF SNOW. BLOWING SNOW ALONG THE
KUSKOKWIM DELTA COAST HAS DIMINISHED BEHIND THE FRONT WITH
TEMPERATURES ALREADY WARMING TO NEAR FREEZING AT SOME LOCATIONS IN
ONSHORE FLOW. THIS FRONT WILL CONTINUE TO WEAKEN AS IT CROSSES THE
ALASKA RANGE INTO COOK INLET THIS EVENING.

A SECOND AND STRONGER LOW IS EVIDENT ON SATELLITE IMAGERY MOVING
INTO THE FAR WESTERN BERING EARLY THIS AFTERNOON. THE ASSOCIATED
FRONT IS MOVING INTO THE CENTRAL ALEUTIANS WITH GALE-FORCE WINDS
AND RAIN. BECAUSE IT IS STRONGER THAN THE FIRST STORM...MORE WARM
AIR IS BEING ENTRAINED INTO THE CIRCULATION COMPARED TO THE FIRST
STORM. THIS WILL HOLD TRUE OVER THE NEXT 24-36 HOURS AS THIS
SECOND STORM QUICKLY TRACKS TOWARD MAINLAND ALASKA.

&&

.MODEL DISCUSSION...

THE MODELS ARE NOW IN GOOD AGREEMENT ON THE FIRST STORM (TONIGHT)
BRINGING WIDESPREAD MINOR ACCUMULATIONS OF SNOW TO SOUTHCENTRAL.
THERE HAS ALSO BEEN AN INCREASE IN AGREEMENT ON THE EVOLUTION OF
THE SECOND STORM ON THURSDAY/THURSDAY NIGHT...FEATURING A
NORTHWEST-TO-SOUTHEAST ORIENTED FRONT SWEEPING ACROSS SOUTHERN
ALASKA WITH A SURGE OF WARM AIR INTO SOUTHWEST ALASKA AND ALSO UP
COOK INLET. HEAVY SNOW WILL FALL IN THE COASTAL MOUNTAINS AND ALSO
IN THE SUSITNA VALLEY...WHERE THE HEAVY SNOW WATCH HAS BEEN
UPGRADED TO A HEAVY SNOW WARNING. THERE REMAIN MEANINGFUL
DIFFERENCES IN THE TRACK AND INTENSITY OF A THIRD LOW THAT WILL
RACE THROUGH THE AREA FRIDAY NIGHT INTO SATURDAY (SEE EXTENDED
DISCUSSION BELOW). FOR THE SHORT TERM FORECAST...THE GFS WAS
PREFERRED AND USED FOR THE AFTERNOON FORECASTS TODAY.

&&

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

A MAJOR WEATHER CHANGE IS IN STORE FOR SOUTHCENTRAL AK AS A SERIES
OF WEATHER SYSTEMS BEGINS TO INFLUENCE THE REGION. THE FIRST...IN
THE FORM OF A WEAK WEATHER FRONT...WILL SPREAD CLOUDS AND LIGHT
SNOW OVER MOST OF THE AREA TONIGHT. A STRONGER FRONT WILL SPREAD
HEAVY SNOW OVER THE SUSITNA VALLEY THU INTO FRI AND OVER NORTHEAST
PRINCE WILLIAM SOUND THU NIGHT INTO FRI MORNING. LESSER AMOUNTS
ARE EXPECTED OVER THE REST OF THE REGION. SIGNIFICANT WARMING
ALONG THE COAST AND AS FAR INLAND AS ANCHORAGE WILL CHANGE SNOW TO
RAIN LATER ON FRI AND FRI EVENING...WHILE INTERIOR ZONES REMAIN
COLD ENOUGH TO KEEP SNOW IN THE FORECAST. ON SAT PRECIPITATION
WILL REVERT TO SNOW SHOWERS ACROSS ALL OF SOUTHCENTRAL AS COLDER
AIR FILTERS INTO THE AREA BEHIND THE SECOND FRONT.

&&

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

THE FIRST ROUND OF SNOW AND WIND HAS CLEARED THE COAST AND WILL
CONTINUE TO MOVE INLAND THROUGH EARLY THIS EVENING. THE SECOND AND
STRONGER FRONT WILL QUICKLY MOVE INTO THE COAST DURING THE EVENING
HOURS...ACCOMPANIED BY ADDITIONAL WARM AIR PULLED UP FROM THE
SOUTH. THE HEAVIER PRECIPITATION WITH THIS SECOND STORM WILL FALL
INITIALLY AS SNOW...BUT TRANSITION TO RAIN OVER BRISTOL BAY AND
COASTAL PORTIONS OF THE DELTA. THINKING AT THIS POINT IS THAT
ENOUGH COLD AIR WILL REMAIN IN PLACE TO RESULT IN ALL-SNOW OVER
THE LOWER KUSKOKWIM VALLEY...WITH SEVERAL INCHES OF SNOW LIKELY
BUT PROBABLY STAYING BELOW ADVISORY LEVELS. THE OTHER SIGNIFICANT
COMPONENT OF THIS STORM WILL BE THE STRONG AND PROLONGED ONSHORE
WINDS THAT ARE LIKELY TO RESULT IN SOME WATER "PILING UP" ALONG
THE COAST. A HIGH SURF ADVISORY REMAINS IN EFFECT FOR BOTH THE
BRISTOL BAY AND DELTA COASTLINES DURING THE DAY THURSDAY.

COLDER AIR QUICKLY RETURNS FROM THE NORTH THURSDAY NIGHT AND
FRIDAY MORNING BEFORE ANOTHER STORM MOVES UP FROM THE NORTH
PACIFIC AND SPREADS SNOW BACK INTO THE BRISTOL BAY AREA BY FRIDAY
AFTERNOON.
&&

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

A STRONG STORM FORCE LOW OVER THE WESTERN BERING WILL CONTINUE TO
SLOWLY MOVE EAST TONIGHT AND THURSDAY...WITH THE ASSOCIATED FRONT
MOVING INTO THE SOUTHWEST ALASKA COAST DURING THE AFTERNOON
TOMORROW. THE STRONGEST CORE OF STORM FORCE WINDS ARE CURRENTLY
IMPACTING THE WESTERN ALEUTIANS...AND WILL SLOWLY WEAKEN TO STRONG
GALES TO MIN STORM FORCE AS THEY TRACK TOWARD THE CENTRAL AND
EASTERN ALEUTIANS. ANOTHER GALE FORCE LOW WILL MOVE INTO THE FAR
SOUTHERN BERING AND CLIP THE CENTRAL AND EASTERN ALEUTIANS
THURSDAY AFTERNOON INTO FRIDAY...BRINGING RAIN AND SNOW AND COLDER
NORTHWEST WINDS BEHIND THE LOW.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
MODELS HAVE COME INTO BETTER...ALTHOUGH LESS THAN OPTIMAL...AGREEMENT
WITH THE LOW EXPECTED TO MOVE THE NORTHERN GULF OF ALASKA AND INTO
SOUTH CENTRAL ALASKA FRIDAY NIGHT INTO SATURDAY. BROADLY...THE 12Z
MODEL RUNS PLACE A SURFACE LOW FRIDAY NIGHT OVER SOUTH-CENTRAL
ALASKA WITH THE 12Z GFS/NAM PLACING A LOWER 980S MB LOW OVER THE
NORTH CENTRAL GULF COAST THAT MOVES INTO THE COPPER RIVER BASIN
OVERNIGHT FRIDAY. ON THE OTHER HAND...THE ECMWF IS SLOWER WITH A
DEEPER LOW OVER THE BRISTOL BAY REGION THAT MOVES FURTHER INLAND
BEFORE CURVING EASTWARD INTO THE YUKON. THE 18Z RUN OF THE GFS IS
APPROXIMATELY THE SAME STRENGTH AND POSITION AS THE 12Z RUN...SO
ON DAY 3 THE GFS GUIDANCE IS PREFERRED. THUS...USING THE GFS
SOLUTION...SNOW IS EXPECTED ALONG THE HIGHER ELEVATIONS OF PRINCE
WILLIAM SOUND ON FRIDAY EVENING THROUGH SATURDAY MORNING. IN THE
COOK INLET REGION...PRECIPITATION IS EXPECTED TO BEGIN EARLY FRIDAY
EVENING AS A RAIN/SNOW MIX BEFORE RAPIDLY TRANSITIONING TO ALL
SNOW AS THE LOW MOVES EASTWARD AND THE REGION FALLS INTO THE
BACKSIDE OF THE LOW. ACCUMULATING SNOW IS EXPECTED IN THE
ANCHORAGE AREA...BUT DUE TO THE UNCERTAINLY IN THE TRACK OF THE
LOW...IT IS TOO EARLY TO DISCUSS POTENTIAL SNOW AMOUNTS IN THE
COOK INLET REGION AT THIS TIME. AS THIS LOW MOVES INTO THE YUKON
TERRITORY ON SATURDAY...MOST OF SOUTHERN ALASKA WILL STAY IN A
COLD SHOWERY PATTERN AS A RIDGE BUILDS IN OVER THE EASTERN BERING
SEA THROUGH EARLY MONDAY MORNING.

FURTHER WEST...MODELS ARE IN GOOD AGREEMENT IN DEVELOPING A STRONG LOW
IN THE WESTERN BERING SEA NEAR THE COMMANDER ISLANDS LATE SATURDAY
NIGHT. THIS LOW IS EXPECTED TO MOVE INTO THE NORTHWEST BERING SEA
BY TUESDAY WHILE ITS ASSOCIATED FRONT ARCS EASTWARD THROUGH THE
BERING SEA AND WILL BEGIN TO IMPACT SOUTHWEST ALASKA TUESDAY
AFTERNOON. THIS FRONT WILL BRING AT LEAST GALE FORCE WINDS WITH
HIGH SEAS THROUGH MOST OF THE BERING AS IT PROGRESSES EASTWARD.
THIS FRONT IS EXPECTED TO HAVE A DEEP SOUTHERLY CONNECTION TO THE
SUB-TROPICS.

FINALLY...AT THE END OF THE EXTENDED PERIOD...THE REMNANTS OF EX-
TYPHOON IN-FA WILL BEGIN TO ENTER THE NORTHERN PACIFIC OCEAN. AS
WITH MOST FORMER TROPICAL SYSTEMS...MODELS ARE STRUGGLING WITH THE
EXTRA-TROPICAL TRANSITION AND TRACK. DUE TO THE LOW CONFIDENCE IN
THE DETAILS WITH THIS SYSTEM AT DAY 7...LITTLE DETAIL WAS INCLUDED
IN THE FORECAST OVER THE WESTERN BERING SEA FOR THIS FORECAST
PACKAGE.

THE GFS WAS USED FOR MOST OF THE FORECAST AREA ON DAY 3 AS A
MIDDLE GROUND SOLUTION BEFORE TRANSITIONING TO WPC GUIDANCE FOR
DAYS 4-7.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...STORM WARNING 150 155 170 173 175 177 178 185.
 GALE WARNING 119 120 130 131 132 136 137 138 139 141 160 165 172
174 176 179 180.
 HEAVY FREEZING SPRAY 127.

&&

SYNOPSIS AND MODEL DISCUSSION...AD
SOUTHCENTRAL ALASKA...DS
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...JA/AD
LONG TERM...RF