Small Craft Advisory 364, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
346 PM AKDT WED APR 27 2016

.ANALYSIS AND UPPER LEVELS...

THE WEATHER STORY TODAY REMAINS LARGELY UNCHANGED AS A LARGE STACKED
LOW SOUTH OF THE ALEUTIANS THAT IS DRIFTING EAST CONTINUES TO
DOMINATE THE PATTERN. WITH THE JET STREAM REMAINING TO OUR SOUTH
OVER THE PACIFIC OCEAN...THE MAIN FEATURES ARE ONLY GRADUALLY
EVOLVING DAY TO DAY AS THEY HAVE BECOME CUTOFF FROM THE MAIN JET
SUPPORT. MOST OF THE WEATHER AFFECTING THE AOR CAN BE ATTRIBUTED
TO A SERIES OF UPPER WAVES AND SURFACE BOUNDARIES ROTATING AROUND
THE DOMINANT ALEUTIAN LOW. AN UPPER SHORTWAVE PUSHING NORTHWARD
THROUGH THE NORTHERN GULF IS SUPPORTING SOME SHOWERS AND GUSTY
WINDS FROM THE ALASKA RANGE THROUGH THE NORTHERN GULF COAST. A
DISSIPATING FRONT OVER BRISTOL BAY IS STALLING ALONG THE COAST.
WITH LIMITED MOISTURE AND ONLY A VERY WEAK BOUNDARY...IMPACTS
REMAIN LIMITED TO SOME GUSTY SOUTHEASTERLY WINDS AND SCATTERED
SHOWERS. AN OPEN WAVE AND SURFACE FRONT ADVANCING TOWARDS THE
SOUTHERN ALASKA PENINSULA AND SOUTHERN GULF IS TAPPING INTO A
MOISTURE STREAM WRAPPING AROUND THE LOW. THIS IS BRINGING RAIN TO
THE EASTERN ALEUTIANS...SOUTHERN ALASKA PENINSULA...AND SOUTHERN
KODIAK ISLAND.

&&

.MODEL DISCUSSION...

AS IS TYPICAL WITH A LESS DYNAMIC PATTERN IN PLACE SUCH AS THIS
ONE...MODELS REMAIN IN GOOD AGREEMENT SYNOPTICALLY. THE MAIN
DIFFERENCE IN THE SHORT TERM IS IN THE HANDLING OF THE OPEN WAVE
TRACKING NORTHWARD TONIGHT TOWARDS KODIAK ISLAND. THE AMERICAN
MODELS KEEP THE FEATURE AS AN OPEN WAVE OVERNIGHT WHILE THE GEM
PINCHES OFF A WEAK CLOSED CIRCULATION OVER THE SOUTHWESTERN GULF.
SATELLITE IMAGERY IS STARTING TO DEPICT SOME CIRCULATION WITHIN
THE WAVE OVER THE SOUTHERN GULF...WHICH WOULD LEND SUPPORT TO THE
GEM SOLUTION. AS SUCH...HAVE NUDGED TO THE GEM IN THE SHORT TERM
WITH A TREND TO THE NAM/GFS LATER IN THE FORECAST. IMPACTS OF
THESE DIFFERENCES ARE MINIMAL HOWEVER AND FORECAST CONFIDENCE IS
ABOVE AVERAGE.

&&

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

ONE OF THE MAIN PLAYERS IN THE FORECAST FOR MUCH OF SOUTHCENTRAL
ALASKA IN THE COMING DAYS IS A FRONTAL BOUNDARY THAT CURRENTLY
EXTENDS FROM A LOW SOUTHWEST OF THE EASTERN ALEUTIANS TO THE FAR
SOUTHWEST CORNER OF THE GULF OF ALASKA. RECENT SATELLITE IMAGES
AND SURFACE OBSERVATIONS HINT AT A WEAK AREA OF LOW PRESSURE
TRYING TO SPIN UP IN THE NORTH PACIFIC SOUTH OF KODIAK ISLAND
ALONG THIS FRONT. THIS LOW WILL MOVE NEAR KODIAK ISLAND TONIGHT
AND WILL HELP BRING SOME GUSTY WINDS TO KODIAK ISLAND AND SHELIKOF
STRAIT. THE FRONT WILL CONTINUE TO PUSH QUICKLY THROUGH THE GULF
OF ALASKA TONIGHT AND STEADY RAIN WILL BE SEEN ALONG THE GULF
COAST BY THURSDAY MORNING. THE FRONT IS EXPECTED TO LINGER ALONG
THE COASTAL RANGE AND MAKE LITTLE (IF ANY) PROGRESS INLAND AS THE
FRONT WEAKENS AND LOSES MUCH OF ITS UPPER LEVEL AND LOW LEVEL
SUPPORT. THIS WILL LEAD TO THE INTERIOR OF SOUTHCENTRAL ALASKA
REMAINING LARGELY ON THE DRY SIDE. THE FRONT WILL ALSO CLASH WITH
HIGH PRESSURE RESIDING OVER THE INTERIOR OF ALASKA LEADING TO A
COMPACT PRESSURE GRADIENT THAT WILL ALLOW WINDS TO REMAIN GUSTY
THROUGH THE TYPICAL GAPS AND PASSES.

THE FRONT WILL CONTINUE TO WEAKEN THROUGH FRIDAY WHEN MUCH OF THE
STEADY RAIN WILL HAVE ENDED AND UPSLOPE SHOWERS OVER THE COASTAL
RANGE WILL BE THE MAIN PRECIPITATION MODE. THE GUSTY WINDS THROUGH
THE TYPICAL GAPS AND PASSES WILL FLUCTUATE AS THE PRESSURE
GRADIENT CHANGES SUBTLY IN ORIENTATION THROUGHOUT THE PERIOD.
GUSTY WINDS IN THE ANCHORAGE BOWL...COPPER RIVER BASIN AND THE
KNIK RIVER VALLEY WILL BE MORE OF A DIURNAL INFLUENCE WHICH WILL
LEAD TO STRONGER WINDS DURING THE DAY AND LIGHTER WINDS AT NIGHT
AS THE BOUNDARY LAYER DECOUPLES WITH THE LOSS OF SURFACE HEATING.
TEMPERATURES WILL REMAIN SLIGHTLY ABOVE NORMAL THROUGH THE PERIOD
WITH NO SIGNIFICANT ADVECTION EXPECTED OVER THE NEXT TWO DAYS.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
BREEZY EAST WINDS WILL PERSIST ACROSS MUCH OF SOUTHWEST ALASKA
THIS AFTERNOON AND EVENING AHEAD OF A FRONTAL SYSTEM LIFTING NORTH
ACROSS THE ALASKA PENINSULA AND BRISTOL BAY. WITH DEW POINTS IN
THE 20S IN MIDDLE KUSKOKWIM VALLEY AND PORTIONS OF THE WESTERN
ALASKA RANGE EXPECTING TO SEE RELATIVE HUMIDITIES IN THE MID 20S
TO MID 30S THIS AFTERNOON AND EVENING IN INTERIOR AND DOWNSLOPING
LOCATIONS. ISOLATED TO SCATTERED SHOWERS PRIMARILY OVER MOUNTAINS
WILL TAPER OFF OVERNIGHT THEN PICK UP AGAIN PERIODICALLY AS
SHORTWAVE TROUGHS ROTATE OVER THE AREA THROUGH FRIDAY.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
THE VERTICALLY STACKED LOW JUST SOUTH OF THE CENTRAL ALEUTIANS
WILL TRACK SLOWLY EAST TONIGHT AND THURSDAY. THE LOW WILL BECOME
QUASISTATIONARY AND GRADUALLY DISSIPATE OVER THE WESTERN TIP OF
THE ALASKA PENINSULA THURSDAY NIGHT AND FRIDAY AS A STRONGER
DEVELOPING LOW IN THE NORTH PACIFIC TRACKS NORTHEAST TOWARDS THE
FAR WESTERN GULF. OVER THE BERING EAST TO NORTHEAST FLOW WILL
CONTINUE FOR THE DURATION.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
THE UPPER LEVEL LONGWAVE TROUGH REMAINS LOCATED OVER THE BERING
EXTENDING THROUGH THE CHAIN INTO THE NORTH PACIFIC OCEAN. THIS
WILL RESULT IN A SHOWERY WEATHER REGIME OVER THE BERING SEA AND
THE ALEUTIANS THROUGH THE WEEKEND. THE WESTERN ALEUTIANS WILL HAVE
A WEATHER FRONT MOVE THROUGH BY SATURDAY AFTERNOON. THIS SYNOPTIC
FEATURE WILL BRING GALE FORCE SOUTHEASTERLY WINDS AND RAIN
ACCOMPANIED BY WARMER TEMPERATURES THROUGH THE WEEKEND. THE LOW
PRESSURE SYSTEM UPSTREAM ASSOCIATED WITH THIS FRONT WILL TRACK
INTO THE WESTERN CHAIN BY MONDAY. THIS SYSTEM WILL TRACK ALONG THE
CHAIN HEADING INTO THE MIDWEEK TIMEFRAME AND BE LOCATED JUST WEST
OF UNALASKA BY TUESDAY. THIS WILL CONTINUE TO BRING A SHOWERY
WEATHER REGIME THROUGH EARLY NEXT WEEK WITH NORTHEASTERLY WINDS ON
THE BACKSIDE OF THIS SYSTEM. WHILE A NEGATIVE TILTED RIDGE OVER
THE SOUTHEAST PANHANDLE EXTENDING INTO THE EASTERN BROOKS RANGE
WILL BECOME MORE AMPLIFIED BY EARLY NEXT WEEK. THIS WILL COINCIDE
WITH A STRONG SOUTHERLY JET STREAM OVER THE GULF BRINGING WARMER
TEMPERATURES HEADING INTO EARLY NEXT WEEK. THE MODELS ARE IN
BETTER AGREEMENT AS THE NORTH PACIFIC LOW LOCATED SOUTH OF THE
EASTERN ALEUTIANS TRACKS TO THE LOWER SOUTHWESTERN GULF BY SATURDAY.
THE ASSOCIATED WEATHER FRONT WITH THIS SYSTEM WILL TRACK INTO THE
NORTHERN GULF RESULTING IN STORM FORCE SOUTHEASTERLY WINDS BY
LATE SATURDAY MORNING. THESE STORM FORCE WINDS WILL SHIFT MORE
EASTERLY TO NORTHEASTERLY BY SATURDAY AFTERNOON AND WILL EXTEND
FROM THE NORTHERN GULF INTO THE BARREN ISLAND REGION AND THE UPPER
SHELIKOF STRAIT. THE PRESSURE GRADIENTS WILL WEAKEN BY SATURDAY
EVENING WITH THE AFOREMENTIONED WINDS DIMINISHING TO GALE FORCE.
THIS SYNOPTIC FEATURE WILL BRING ABUNDANT MOISTURE WITH PERIODS
OF HEAVY RAIN MAINLY ALONG THE NORTHERN AND WESTERN COASTAL
COMMUNITIES THROUGH THE WEEKEND. BY MONDAY THIS SYSTEM WILL HAVE
MOVED INLAND AND DISSIPATED WITH LIGHT WINDS FOR THE SOUTHCENTRAL
REGION.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALES...119 131.

&&

SYNOPSIS AND MODEL DISCUSSION...RSD
SOUTHCENTRAL ALASKA...MC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...JR
LONG TERM...PD