Small Craft Advisory 134, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
410 PM AKST THU FEB 12 2015

.ANALYSIS AND UPPER LEVELS...
IN THE UPPER LEVELS A RIDGE IS SITTING OVER THE WESTERN U.S. WITH
RIDGE AXIS EXTENDING NORTHWEST TO MAINLAND ALASKA. A CORRESPONDING
TROUGH IS CENTERED OVER THE BERING SEA AND NORTH CENTRAL PACIFIC.
A MYRIAD OF UPPER LEVEL SHORT-WAVES ARE LIFTING NORTH FROM THE
PACIFIC TO MAINLAND ALASKA AND THE EASTERN GULF. ONE OF THESE WAVES
IS LIFTING NORTHWARD ACROSS SOUTHCENTRAL THIS MORNING...BRINGING
PRECIP TO MUCH OF THE REGION. SOUTHEASTERLY FLOW ACROSS THE KENAI
AND CHUGACH MOUNTAINS LAST NIGHT CREATED AN ABOVE FREEZING WARM
NOSE (AS SEEN IN THE 12Z ANCHORAGE SOUNDING). THIS HAS RESULTED
IN A WINTRY MIX OF PRECIP-TYPES IN ANCHORAGE...WITH SNOW...SLEET
AND FREEZING RAIN ALL BEING REPORTED.

THE PRIMARY SURFACE FEATURE OF INTEREST IS AN INVERTED SURFACE
TROUGH WHICH EXTENDS NORTHWARD FROM A WEAK SURFACE LOW SOUTH OF
THE ALASKA PENINSULA ACROSS THE EASTERN BERING SEA TO THE KUSKOKWIM
DELTA. SNOW IS FOCUSED ALONG AND AHEAD OF THIS BOUNDARY. ALTHOUGH
THE SNOW IS GENERALLY ON THE LIGHT SIDE STRONG NORTHERLY WINDS AND
COLD TEMPERATURES ARE COMBINING WITH THE FALLING SNOW TO PRODUCE
LOW VISIBILITIES IN BLOWING SNOW ON THE PRIBILOF ISLANDS. A WINTER
WEATHER ADVISORY FOR BLOWING SNOW HAS BEEN EXTENDED THROUGH 9 PM
THIS EVENING WITH STEADY SNOW EXPECTED TO CONTINUE AS THE SURFACE
TROUGH TRACKS TOWARD THE ISLANDS.

MEANWHILE...A SERIES OF FAIRLY WEAK SURFACE LOWS HAVE FORMED OVER
THE NORTHEAST PACIFIC CLOSER TO THE UPPER JET. THE CHALLENGE MOVING
FORWARD WILL BE THE TRACK OF THESE LOWS AS THEY MOVE NORTHWARD.

&&

.MODEL DISCUSSION...
MODELS SHOW THE SAME GENERAL EVOLUTION OF THE LARGE SCALE PATTERN
OVER THE NEXT FEW DAYS. HOWEVER...THEY ARE REALLY STRUGGLING WITH
INITIALIZATION/VERIFICATION OF THE MANY UPPER LEVEL WAVES AS WELL
AS THE SURFACE LOWS. SPECIFICALLY...MODEL SPREAD GROWS FAIRLY
LARGE WITH LOW TRACK OVER THE GULF FRIDAY THROUGH SATURDAY AS
WELL AS WITH HANDLING OF MULTIPLE WEAK LOWS IN THE EASTERN
BERING/EASTERN ALEUTIANS/SOUTHERN ALASKA PENINSULA REGION. WITH
ALL OF THE MODELS STRUGGLING TO SOME EXTENT...THERE REALLY IS NOT
A PREFERRED SOLUTION. FORECAST CONFIDENCE IS GENERALLY LOW.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
PRECIPITATION ACROSS SOUTHCENTRAL ALASKA WILL DIMINISH OVERNIGHT
WITH ANOTHER FRONT PUSHING INTO THE SOUTHERN GULF TONIGHT.
OFFSHORE FLOW INCREASES ALONG THE GULF COAST AND COOK INLET LATE
TONIGHT AS THE PRESSURE GRADIENT TIGHTENS AHEAD OF THE APPROACHING
SURFACE LOW IN THE GULF. THE FRONT PUSHES INTO THE NORTHERN GULF
FRIDAY MORNING BRINGING RAIN TO THE NORTHERN COASTS AND EASTERN
KENAI WITH A FEW A ISOLATED RAIN AND SNOW SHOWERS MAKING IT INLAND.
WINDS LOOK TO BE GUSTY AGAIN ON FRIDAY NIGHT INTO SATURDAY ALONG
THE WESTERN GULF...DEPENDING ON THE TRACK OF THE LOW IN THE GULF.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
A WEAKENING FRONT/INVERTED TROUGH EXTENDING FROM THE EASTERN
BERING AND OVER THE KUSKOKWIM DELTA WILL PUSH OFF TO THE WEST
OVERNIGHT TONIGHT. THIS WILL KEEP LIGHT SNOW OVER THE AREA
THROUGH THIS EVENING...AND TAPERING OFF TO SHOWERS OVERNIGHT.
ONCE THIS FEATURE DEPARTS THE AREA...A SERIES OF WEAK UPPER LEVEL
DISTURBANCES WILL GENERATE SCATTERED SHOWERS ACROSS THE SOUTHWEST
MAINLAND THROUGH FRIDAY AFTERNOON. HIGH PRESSURE WILL BEGIN TO
BUILD INTO THE INTERIOR FRIDAY AFTERNOON...BRINGING DRIER
CONDITIONS TO THE AREA THROUGH SATURDAY.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
AN UPPER LOW DROPPING SOUTHWARD THROUGH THE BERING WILL KEEP
SHOWERY CONDITIONS OVER MUCH OF THE REGION THROUGH FRIDAY
NIGHT...WITH THE BULK OF THE SENSIBLE WEATHER IMPACTS CONFINED TO
THE PRIBILOF ISLANDS AND SOUTHEASTERN BERING. BLOWING SNOW WILL
CONTINUE TO BE A CONCERN FOR THE PRIBILOFS INTO FRIDAY MORNING AS
THE FRONTAL BOUNDARY GRADUALLY WEAKENS OVERHEAD AND STRONG
NORTHEASTERLY WINDS REMAIN IN PLACE AT THE SURFACE. THE WORST
CONDITIONS ARE EXPECTED TO PERSIST THROUGH THIS EVENING...BEFORE
THE WINDS BEGIN TO DIMINISH OVERNIGHT AND VISIBILITIES IMPROVE AS
A RESULT. THEREFORE...A BLOWING SNOW ADVISORY REMAINS IN EFFECT
UNTIL 9 PM TONIGHT. A NORTH PACIFIC LOW TRACKING TOWARDS DUTCH
HARBOR WILL CONTINUE TO SPREAD RAIN OVER THE EASTERN ALEUTIANS AND
ALASKA PENINSULA THROUGH SATURDAY...BEFORE WEAKENING AND TRACKING
BACK INTO THE NORTH PACIFIC.

&&

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

BEGINNING SUNDAY...A SIGNIFICANT PATTERN TRANSITION WILL MANIFEST
ITSELF AS A HIGH AMPLITUDE NORTH AMERICAN RIDGE AXIS BUILDS INTO
SOUTHERN ALASKA. DRIVING THIS WILL BE A STOUT NORTH PACIFIC
LOW...WITH AMPLE AMOUNTS OF MOISTURE AND WARM AIR. A PRETTY
SIGNIFICANT WEDGE OF WARM AIR WILL DRIVE INTO THE INTERIOR...AND
THIS WILL HELP PUSH TEMPERATURES WELL ABOVE AVERAGE ACROSS ALL OF
SOUTHERN ALASKA. HEAVY RAIN WILL IMPACT COASTAL LOCATIONS...WITH
SHOWERY CONDITIONS INLAND. AREAS CLOSE TO NORTH-SOUTH BARRIERS
SUCH AS THE CHUGACH AND WESTERN ALASKA RANGE WILL SEE HEAVY
DOWNSLOPING...ESPECIALLY ANCHORAGE NORTHWARD TOWARD THE MATANUSKA
VALLEY. THERE IS STILL SIGNIFICANT UNCERTAINTY WITH THE OVERALL
TRACK OF THE UPPER LEVEL SHORTWAVE TROUGH AND ASSOCIATED SURFACE
LOW...WITH THE GFS TRENDING EASTWARD AND WEAKER WHILE THE ECMWF
REMAINS STRONGER AND FARTHER WEST. THE OVERALL TRACK OF THESE
FEATURES IS IMPORTANT...ESPECIALLY REGARDING THE PRESSURE GRADIENT
AND ASSOCIATED WINDS THROUGH MAJOR GAPS...INCLUDING TURNAGAIN ARM.
THE ECMWF WOULD FAVOR A MORE SIGNIFICANT TURNAGAIN ARM WIND...AND
A MORE PRONOUNCED WARMUP TUESDAY AS THE TROUGH MOVES THROUGH
ACROSS PARTS OF SOUTHCENTRAL.

THE PATTERN ALOFT BECOMES MORE UNCERTAIN AFTER THE FIRST NORTH
PACIFIC LOW MOVES OUT ON TUESDAY...BUT THE GLOBAL GUIDANCE AS A
WHOLE CONTINUES TO HINT AT CONTINUED WARMER AND MORE ACTIVE
WEATHER INTO NEXT WEEKEND.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...WINTER WEATHER ADVISORY...179
MARINE...GALES...173-176 179
         HVY FRZG SPRY...179 185
FIRE WEATHER...NONE

&&

SYNOPSIS AND MODEL DISCUSSION...SEB
SOUTHCENTRAL ALASKA...KH
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...TP
LONG TERM...JA