Small Craft Advisory 306, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
536 AM AKDT TUE APR 7 2015

.ANALYSIS AND UPPER LEVELS...
THERE IS A CLOSED UPPER LEVEL LOW POSITIONED OVER NUNIVAK ISLAND
WITH A CUT-OFF LOW FORMING JUST SOUTH OF KODIAK ISLAND. THE
TROUGH ASSOCIATED WITH THIS LOW IS BECOMING NEGATIVELY TILTED IN
THE SOUTHWESTERN GULF. UPSTREAM THERE IS AN AMPLIFIED RIDGE
OVER THE SOUTHEAST ALASKA REGION EXTENDING TO THE NORTHWEST INTO
THE NORTHERN SLOPE. THIS IS RESULTING IN THE PRESSURE GRADIENTS
STRENGTHENING BETWEEN THESE TWO SYNOPTIC FEATURES. THE SURFACE
OBSERVATIONS FOR MCHUGH CREEK HAVE BEEN REPORTING GUSTY SOUTHEAST
WINDS RANGING FROM UPPER 50S TO UPPER 60S MPH THROUGH THIS EARLY
MORNING. AT THE SURFACE...THE TRIPLE POINT LOW IS POSITIONED IN
THE NORTHERN SHELIKOF STRAIT AREA WITH THE WARM FRONT ENTERING THE
NORTHERN GULF. THE SATELLITE IMAGERY IS SHOWING A LARGE PLUM OF
MOISTURE OVER THE WESTERN GULF SPREADING INTO THE NORTHERN GULF
COASTLINE...INLAND AREAS AND SPILLING OVER INTO THE SOUTHWEST
ALASKA REGION. THE NORTHERN GULF COAST AND THE SOUTHERN MAINLAND
WILL CONTINUE IN HEAVY PRECIPITATION THIS MORNING WITH
TEMPERATURES BEING REPORTED IN UPPER 40S. WHILE...THE ANCHORAGE
BOWL CONTINUES TO DOWNSLOPE OUT RESULTING IN DRIER CONDITIONS WITH
THE CROSS-BARRIER FLOW.

ON THE BERING SIDE...THERE IS A GALE FORCE LOW POSITIONED OVER
NUNIVAK ISLAND BRINGING ONSHORE FLOW TO THE SOUTHWEST REGION
WITH LOWER STRATUS AND SNOW SHOWERS ADVECTING INTO THE KUSKOKWIM
DELTA AREA. ON THE BACKSIDE OF THIS LOW FROM THE CENTRAL TO
EASTERN BERING SEA AND SOUTHWARD ALONG THE ALEUTIANS CHAIN...THERE
IS GUSTY NORTHWESTERLY FLOW. THE LATEST ASCAT SCATTEREOMETER WINDS
IMAGERY...SHOWED PREDOMINANTLY 30 KNOT NORTHWESTERLY WINDS THROUGH
THE AFOREMENTIONED REGION. WHILE...THE WESTERN BERING/ALEUTIANS
HAS AN UPPER LEVEL RIDGE OVER THE AREA.

&&

.MODEL DISCUSSION...
THE NAM/GFS WERE THE PREFERRED MODELS OF CHOICE WITH THE HANDLING
OF THE TRIPLE POINT LOW NEAR KODIAK ISLAND. THE ECMWF MODEL WAS
SLOWER WITH THE TRIPLE POINT AS IT MOVES INLAND THIS MORNING INTO
THE BRISTOL BAY INTERIOR. WHILE THE NAM/ECMWF MODELS WERE USED ON
THE BERING SIDE WITH HOW THEY WERE DEPICTING THE LOW POSITIONED
OVER THE NUNIVAK ISLAND REGION. THE AFOREMENTIONED MODELS IN THE
BERING...HANDLED THE KAMCHATKA LOW VERY WELL AND THE ASSOCIATED
FRONTAL BOUNDARY ENTERING THE WESTERN ALEUTIANS TODAY AS IT
PROGRESSES INTO THE ALASKA PENINSULA BY WEDNESDAY. THE FORECAST
CONFIDENCE REMAINS ABOVE AVERAGE HEADING INTO THE MIDWEEK.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
THE COLD FRONT AND STRONG UPPER LEVEL TROUGH WILL PUSH THROUGH
SOUTH CENTRAL ALASKA TODAY. THIS WILL BRING SOME WINDS AND
PRECIPITATION INLAND...WHICH WILL DIMINISH TONIGHT. THE UPPER LOW
CURRENTLY OVER THE KUSKOKWIM DELTA WILL MOVE EASTWARD AND INTO
SOUTH CENTRAL ALASKA LATE TONIGHT AND WEDNESDAY. THIS WILL BRING
ANOTHER SHOT OF "LIKELY" POPS TO THE ANCHORAGE AREA WEDNESDAY AS
THIS LOW SLIDES THROUGH...THOUGH IT OPENS UP AND WEAKENS AS A DEEPER
LOW OVER THE BERING SEA MOVES EAST TOWARDS THE WEST COAST OF
ALASKA. A FRONT FROM THAT LOW WILL MOVE ACROSS KODIAK AND INTO THE
GULF OF ALASKA WEDNESDAY NIGHT. THIS FRONT AND THE LOW FOLLOWING
LOOK LIKE THEY WILL NOT REACH AS FAR INLAND AS THE PREVIOUS
SYSTEMS MENTIONED ABOVE...MAINLY STAYING IN THE GULF AND ALONG
THE GULF COAST.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
SOUTHWESTERN ALASKA IS UNDER THE INFLUENCE OF TWO AREAS OF LOW
PRESSURE THIS MORNING. THE FIRST IS THE VERTICALLY STACKED AND
WEAKENING 982 MB LOW NEAR NUNIVAK ISLAND. THIS WILL BE MOVING
INTO THE KUSKOKWIM DELTA THIS MORNING. THE SECOND IS A 977 MB LOW
LOCATED NEAR THE EASTERN END OF SHELIKOF STRAIGHT WHICH WILL MOVE
INLAND TO MERGE WITH THE KUSKOKWIM LOW AND CONTINUE TO MOVE
TOWARDS THE SEWARD PENINSULA THROUGH LATE TUESDAY NIGHT. STEADY
SNOW WITH SOME RAIN OVER THE INTERIOR SECTIONS OF THE AREA WILL
CONTINUE THROUGH THIS AFTERNOON BEFORE TRANSITIONING OVER TO
MOSTLY SNOW SHOWERS BY LATE TODAY.

THE NEXT SYSTEM TO IMPACT THE REGION WILL BE A VERY ROBUST AND
RAPIDLY DEEPENING 985 MB LOW CURRENTLY ABOUT 300 MILES NORTHWEST
OF SHEMYA THIS MORNING. THIS LOW HAS EXCELLENT JET SUPPORT WITH IT
WITH UPPER JET WIND SPEEDS IN EXCESS 100 KT REPORTED ON THE
SHEMYA SOUNDING THIS MORNING. THIS SYSTEM IS EXPECTED TO RAPIDLY
MOVE ACROSS THE BERING WITH THE FRONT BEGINNING TO IMPACT THE
SOUTHWEST COAST BY WEDNESDAY MORNING. AS WITH THE PREVIOUS
SYSTEM...A RAIN SNOW MIX IS EXPECTED OVER SOUTHERN PORTIONS OF THE
REGION WITH GENERALLY ALL SNOW FURTHER NORTH. MODEL SOLUTIONS ARE
NOT INDICATING AS MUCH WARM ADVECTION OR MOISTURE IN THE LOWER
ATMOSPHERE WITH THIS SYSTEM...SO PRECIPITATION SHOULD BE MOSTLY
SNOW AND IN LOWER AMOUNTS THAN THE PREVIOUS SYSTEM.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
THE MAIN DRIVER OF THE FORECAST FOR THE BERING SEA AND THE
ALEUTIANS OVER THE NEXT 48 HOURS IS THE RAPIDLY INTENSIFYING 985
MB LOW ABOUT 300 MILES NORTHWEST OF SHEMYA THIS MORNING. THIS LOW
AND ITS FRONT WILL MOVE VERY QUICKLY EASTWARD OVER THE BERING SEA
TO BE NEAR NUNIVAK ISLAND BY LATE WEDNESDAY NIGHT. WHILE THE
SYSTEM ONLY HAS MODEST COLD AIR ADVECTION IN THE LOWER
LEVELS...THE SUPERB DYNAMIC SUPPORT WITH THE SYSTEM SHOULD BRING A
VERY WIDE SWATH OF UPPER GALE FORCE WINDS ACROSS THE BERING SEA
AND THE ALEUTIAN CHAIN WITH STORM FORCE WINDS OVER THE SOUTH
CENTRAL BERING SEA. DUE TO THE LONG FETCH OF THIS SYSTEM...SEAS IN
EXCESS OF 25 FT ARE EXPECTED TO PUSH EASTWARD OVER THE BERING SEA
THROUGH THE FORECAST PERIOD.

&&

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

MODELS ARE IN GOOD AGREEMENT THAT THE ENERGY IN THE BERING LOW
WED NIGHT WILL CROSS THE AKPEN AND FORM A TRIPLE POINT LOW BETWEEN
THE KENAI PENINSULA AND KODIAK ISLAND ON THU. AN ASSOCIATED FRONT
WILL REACH THE NORTHEAST GULF COAST THU NIGHT. ALTHOUGH THE EXACT
POSITION IS STILL UNCERTAIN...THE TRIPLE POINT LOW WILL REMAIN
NEAR THE EASTERN KENAI THROUGH FRI...AND THEN A NEW LOW WILL
DEVELOP IN THAT AREA ON SAT BEFORE DRIFTING INTO THE GULF THROUGH
MON. THIS SCENARIO MEANS THE TRIPLE POINT LOW AND FRONT WILL BRING
WINDS TO CHANNELED TERRAIN AS WELL AS THE GULF WED NIGHT THROUGH
THU NIGHT. ABUNDANT RAIN WILL AFFECT THE GULF COAST THROUGH SAT
BEFORE TAPERING OFF BY MON. OF MORE IMPORTANCE IS THE POSSIBILITY
OF SNOW FOR INTERIOR AREAS OF SOUTHCENTRAL. THU NIGHT INTO FRI HAS
WARM AIR IN PLACE SO PRECIP WILL BE RAIN OR A MIX..BUT BEGINNING
FRI NIGHT COLD AIR SLIPS INTO THE AREA. ALTHOUGH FORECAST
PRECIPITATION AMOUNTS ARE LIGHT...ANYTHING THAT FALLS WILL BE
SNOW...ESPECIALLY AT NIGHT THROUGH MON.

MEANWHILE...AS THE LOWS ARE MOVING OUT OF THE BERING...COLD WEST
TO NORTHWEST FLOW WILL BECOME ENTRENCHED AND BRING SNOW SHOWERS TO
THE BERING...THE ALEUTIANS...AND SOUTHWEST AK INTO MON.

THE FORECAST RELIES ON THE EC AND WPC GUIDANCE.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...HIGH WIND WARNING 101.
MARINE...STORM WARNING 413.
         GALE WARNINGS 119 120 125 129 155 165 170 171 172
         173 174 175 176 177 178 179 351 411 412 414.
         HEAVY FREEZING SPRAY 185 412 414.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...PD
SOUTHCENTRAL ALASKA...BL
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...RLF
LONG TERM...DS