Small Craft Advisory 315, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
540 AM AKDT SAT APR 9 2016

.ANALYSIS AND UPPER LEVELS...

AN ACTIVE WEATHER PATTERN HAS SET UP ACROSS SOUTHWEST ALASKA AND
MUCH OF THE BERING SEA THIS MORNING AS A SERIES OF LOWS PUSH
THROUGH THE AREA. ONE OF THESE LOWS HAS STALLED JUST TO THE WEST
OF UNALASKA THIS MORNING WHICH HAS KEPT GUSTY SOUTHEASTERLY WINDS
ACROSS THE EASTERN HALF OF THE EASTERN ALEUTIANS LONGER THAN
PREVIOUS EXPECTED. THE FRONTAL OCCLUSION ASSOCIATED WITH THIS
FRONT HAS NEARLY PUSHED THROUGH THE PRIBILOF ISLANDS BUT SHOULD
QUICKLY PUSH THROUGH JUST PRIOR TO SUNRISE AND BRING AN END TO
PRECIPITATION AND GUSTY WINDS. A SECOND AREA OF LOW PRESSURE SPUN
UP EAST OF THE AFOREMENTIONED LOW JUST TO THE SOUTHEAST OF SAND
POINT. THIS LOW WAS HEAVILY INFLUENCED BY AN UPPER LEVEL SHORTWAVE
AND A PIECE OF JET ENERGY IN THE LEFT EXIT REGION BROUGHT UPPER
LEVEL SUPPORT TO A WEAK SFC BASED TROUGH. THIS DECENT MID AND
UPPER LEVEL JET HAS ALLOWED THE SFC LOW TO QUICKLY PUSH NORTHWARD
AND HAS ALREADY BEGUN TO BRING RAIN TO PARTS OF THE ALASKA
PENINSULA. RAIN ACROSS SOUTHWEST ALASKA WILL CONTINUE TO BE ON THE
UPSWING AS THE LOW MOVES INTO BRISTOL BAY BY MID MORNING.

LOOKING AT SOUTHCENTRAL ALASKA...THE RIDGE AXIS REMAINS ALONG THE
NORTHERN GULF COAST AND HAS BEEN STRENGTHENING A GOOD BIT DURING
THE OVERNIGHT HOURS. AS THIS COASTAL RIDGE HAS STRENGTHENED...GAP
WINDS THROUGH TURNAGAIN ARM...PORTAGE VALLEY...COPPER RIVER AND
THE KNIK RIVER VALLEY HAVE STRENGTHENED AS WELL. WINDS THROUGH
PORTAGE VALLEY AND TURNAGAIN ARM HAVE BEEN STEADILY INCREASING
OVERNIGHT AND LOOK TO PEAK DURING THE LATE MORNING/EARLY AFTERNOON.
OTHER GAP WINDS ALONG THE COPPER RIVER AND KNIK RIVER WILL WEAKEN
A BIT EARLY THIS MORNING BUT SHOULD QUICKLY INCREASE AFTER SUNRISE.
A FRONT HAS PUSHED ACROSS THE WESTERN GULF OF ALASKA AND CLASHED
THE COASTAL MOUNTAINS ON THE EASTERN KENAI PENINSULA AND HAS
BROUGHT RAIN SHOWERS TO MUCH OF SOUTHCENTRAL ALASKA THIS MORNING.

&&

.MODEL DISCUSSION...

MODELS ARE IN PRETTY GOOD AGREEMENT THIS MORNING OVERALL BUT DO
STRUGGLE A BIT OUT WEST WITH JUST HOW QUICKLY THE DEVELOPING LOW
SOUTHEAST OF SAND POINT MOVES INTO BRISTOL BAY THIS MORNING. THIS
BRINGS A CHALLENGE TO FORECAST PRECIPITATION TIMING AS WELL AS
NUMEROUS WIND SHIFTS THROUGHOUT THE DAY. MODELS REMAIN IN PRETTY
GOOD AGREEMENT THROUGH SUNDAY MORNING BUT THEN STRUGGLE TO RESOLVE
THE NEXT AREA OF LOW PRESSURE WORTH WATCHING WHICH SKIRTS SOUTH OF
THE ALEUTIAN ISLANDS AND MOVES INTO THE GULF OF ALASKA LATE MONDAY.
THE NAM WAS USED EARLY ON ACROSS THE EASTERN DOMAIN DUE TO THE
HIGHER RESOLUTION TO HELP MAP OUT THE PRESSURE GRADIENTS THROUGH
MANY GAPS TO HELP FORECAST STRONGER WINDS THROUGH TURNAGAIN ARM
AND PORTAGE VALLEY. OUT WEST A BLEND OF THE NAM AND GFS WAS USED
FOR THE TIMING OF THE DEVELOPING LOW AS THE ECMWF WAS A BIT SLOWER
BRINGING THE LOW INTO BRISTOL BAY THAN THE NAM...GFS AND ENSEMBLES.

&&

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

AN APPROACHING FRONT IS BRINGING GUSTS ACROSS THE NORTHERN COAST
OF THE GULF OF ALASKA THIS MORNING ALONG WITH WIDESPREAD SHOWERS.
AS THIS FRONT CONTINUES TO PUSH NORTHWARDS...PRESSURE GRADIENTS
ARE EXPECTED TO INCREASE SLIGHTLY. THIS WILL RE-ENFORCE THE
CURRENT GAP WINDS ACROSS TURNAGAIN ARM AND THE MATANUSKA VALLEY.
HOWEVER...PRESSURE GRADIENTS WILL STILL REMAIN WEAK ENOUGH TO KEEP
WIND GUSTS JUST AT OR BELOW STRONG WIND CRITERIA. THIS FRONT WILL
SUPPORT WIDESPREAD RAIN...WHICH WILL BE LIMITED IN DOWNSLOPE
REGIONS OF ANCHORAGE...THE MATANUSKA VALLEY AND WESTERN KENAI.

WHILE THIS FRONT WILL BEGIN TO DISSIPATE THIS EVENING ALONG THE
COAST...A NEW WEAKER FRONT WILL APPROACH SUNDAY. THIS WILL REINFORCE
BROAD MOIST SOUTHERLY FLOW ACROSS THE GULF COAST...AND AN UPPER
LEVEL JET WILL PROVIDE ADDITIONAL SUPPORT FOR RAIN. MODELS ARE
TRENDING TOWARDS RAIN WHICH COULD BE HEAVY AT TIMES STARTING
TODAY THROUGH SUNDAY ACROSS THE EASTERN KENAI.

&&

.FIRE WEATHER...
THERE ARE NO SIGNIFICANT FIRE WEATHER CONCERNS OVER THE NEXT
COUPLE OF DAYS.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
A LOW BEGINNING TO CROSS THE AKPEN INTO SOUTHWEST ALASKA WILL
BRING RAIN AND GUSTY EASTERLY WINDS TO THE AREA TODAY. THE
STRONGEST OF THESE WINDS SHOULD OCCUR THIS AFTERNOON/EVENING ALONG THE
ALEUTIAN RANGE THIS AFTERNOON AS THE LOW CENTER MOVES INTO BRISTOL
BAY...BRINGING PRESSURE FALLS BETWEEN IT AND RIDGING OVER THE
GULF. BY LATE THIS EVENING...THIS LOW WILL MOVE INTO THE NORTHERN
BERING...BRINGING PARTIAL CLEARING TO SOME AREAS TONIGHT. ITS POSSIBLE
THAT THIS PARTIAL CLEARING BEHIND WIDESPREAD RAIN TONIGHT WILL
BRING PATCHY LOW STRATUS/FOG TO INTERIOR AREAS TONIGHT...HOWEVER
WITH THE FAST MOVING NATURE OF AN APPROACHING SHORTWAVE AND LACK
OF STRONG RIDGING THIS IS NOT EXPECTED TO BE WIDESPREAD IF IT
DOES FORM. THIS WILL BE SHORT LIVED HOWEVER AS A SHORTWAVE WILL
QUICKLY APPROACH THE AREA ON SUNDAY...BRINGING THE NEXT CHANCE OF
RAIN WITH OTHERWISE LIGHT WINDS.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
THE BROAD UPPER LEVEL TROUGH OVER THE CENTRAL BERING WILL CONTINUE
TO BRING RAIN SHOWERS BUT WITH WINDS FALLING BELOW GALE FORCE
THROUGHOUT THE AREA. THIS TROUGH WILL CONTINUE TO SLOW WEAKEN
THROUGH SUNDAY...ALLOWING FOR SHOWERS AND WINDS TO CONTINUE TO
DIMINISH. LATE ON SUNDAY A GALE FORCE FRONT WILL BEGIN TO APPROACH
THE EASTERN ALEUTIANS/AKPEN...WHICH BRINGING RAIN BACK INTO THOSE
AREAS FOR EARLY NEXT WEEK.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
THE PATTERN THROUGH EARLY NEXT WEEK WILL BE CHARACTERIZED BY A
BROAD NEGATIVELY TILTED LONGWAVE TROUGH ENCOMPASSING THE BERING
SEA. THIS WILL KEEP A GENERALLY SHOWERY REGIME IN PLACE OVER THE
BERING AND GULF REGIONS...WITH ENHANCED CHANCES FOR PRECIPITATION
OVER SOUTHCENTRAL AK IN THE SUNDAY NIGHT TIME FRAME AS A
SHORTWAVE TROUGH ROTATES INLAND FROM THE GULF. ATTENTION THEN
TURNS TO A DEEP NORTH PACIFIC LOW POISED TO APPROACH THE WESTERN
ALEUTIANS MONDAY NIGHT. MODELS ARE IN GENERAL AGREEMENT THAT THIS
LOW WILL DEEPEN INTO THE MID 960 MB RANGE...BUT THEY CONTINUE TO
STRUGGLE GREATLY WITH THE POSITION OF THIS FEATURE AS THE WEEK
PROGRESSES. EUROPEAN AND CANADIAN GUIDANCE HAVE BEEN FAIRLY
CONSISTENT IN TRACKING THE LOW ALONG OR SOUTH OF THE ALEUTIAN
CHAIN THROUGH THURSDAY AND THUS KEEPING MOST OF THE IMPACTS
CONFINED TO THE BERING. RECENT GFS RUNS HAVE BEEN TAKING THE LOW
INTO THE BERING AND STALLING IT NEAR NUNIVAK ISLAND AROUND THE
MIDDLE OF THE WEEK...WHICH WOULD REPRESENT A MORE SIGNIFICANT
THREAT OF STRONG GAP WINDS FOR PORTIONS OF SOUTHCENTRAL AK AS THE
PRESSURE GRADIENT BECOMES MORE FAVORABLE. THE CURRENT EXTENDED
FORECAST REFLECTS A PREFERENCE CLOSER TO THE EC SOLUTION GIVEN THE
BETTER OVERALL CONSISTENCY...HOWEVER THE LARGE MODEL SPREAD LENDS
A LOWER DEGREE OF CONFIDENCE TO THE FORECAST. THE EVOLUTION OF
THIS FEATURE WILL CONTINUE TO BE CLOSELY MONITORED IN THE COMING
DAYS.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE 119 120 125 130 131 132 139.

&&

SYNOPSIS AND MODEL DISCUSSION...MMC
SOUTHCENTRAL ALASKA...EN
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...DEK
LONG TERM...CB