Small Craft Advisory 58, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
424 PM AKST SAT JAN 16 2016

.ANALYSIS AND UPPER LEVELS...

A STRONG VERTICALLY STACKED LOW CENTERED A COUPLE HUNDRED MILES
SOUTH OF THE SOUTHERN ALASKA PENINSULA REMAINS THE PRIMARY LARGE-
SCALE FEATURE AFFECTING THE AREA THIS AFTERNOON. THE LOW HAS BEEN
NEARLY STATIONARY FOR SEVERAL DAYS NOW...AND SLOW FILLING HAS
COMMENCED AS NEXT TO NO BAROCLINICITY REMAINS NEAR THE LOW CENTER.

TWO FRONTS ARE ASSOCIATED WITH THE LOW...ONE STRETCHING ALONG THE
LENGTH OF THE ALEUTIANS...AND THE OTHER MOVING INTO THE WESTERN
GULF COAST. WHILE NEITHER FRONT HAS AN ABUNDANCE OF MOISTURE WITH
IT...THE ONE OVER THE GULF IS TRANSPORTING WARMER...MORE MOIST AIR
BEHIND IT. THAT FRONT IS THUS WRINGING OUT STEADIER LIGHT
PRECIPITATION AS SHOWN BY THE MIDDLETON ISLAND RADAR THAT IS
MOVING INTO THE NORTHERN GULF COAST AND PRINCE WILLIAM SOUND.

THE FRONT ALONG THE ALEUTIANS HAS WINDS GUSTING TO 45 MPH AT
TIMES...BUT OTHER THAN SOME LOCALLY DEPRESSED CEILINGS AND A FEW
AREAS OF LIGHT RAINFALL...THOSE ARE MOST IMPACTFUL OF THE EFFECTS
ASSOCIATED WITH THE FRONT.

&&

.MODEL DISCUSSION...

THE BROAD AGREEMENT AMONG THE MODELS CONTINUES THIS AFTERNOON...AS
THE LARGE-SCALE PATTERN REMAINS BLOCKED. THE MAIN DIFFERENCES IN
THE MODELS ALSO CONTINUE TO BE TIMING DIFFERENCES WITH SMALLER
SCALE DISTURBANCES IN THE BROAD FLOW...NAMELY HOW QUICKLY AND HOW
STRONG A COUPLE FRONTS MOVING EAST TO WEST ACROSS THE WESTERN GULF
AND INTO SOUTHWEST ALASKA AND BRISTOL BAY END UP. SINCE THE
DISAGREEMENTS ARE SMALL...THE HIGHER RESOLUTION MODELS WERE CHOSEN
TO CAPTURE THE SMALL SCALE EFFECTS...TRANSITIONING TO THE GLOBAL
MODELS FURTHER OUT. FORECAST CONFIDENCE REMAINS HIGH.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
THE FRONT STRETCHING ACROSS THE NORTHERN GULF WILL CONTINUE TO
DRIVE THE WEATHER THROUGH THE WEEKEND...WITH ANOTHER WAVE
APPROACHING THE AREA COME MONDAY. CLOUDY CONDITIONS HAVE
INCREASED OVER MUCH OF SOUTHCENTRAL AS THE FRONT APPROACHES FROM
THE SOUTHEAST...WITH PRECIPITATION ALREADY STARTING UP ALONG THE
NORTHERN GULF COAST. MANY PLACES WILL START OUT AS SNOW BUT WILL
THEN BEGIN TO WARM ENOUGH TO SEE SOME RAIN MIX IN OVERNIGHT
TONIGHT...MAINLY OVER THE EASTERN KENAI PENINSULA...ALONG THE
NORTHERN GULF COAST...AND OVER THE WESTERN KENAI PENINSULA SOUTH
OF CLAM GULCH. THIS WILL LIMIT SNOW ACCUMULATIONS FOR THE MOST
PART OVER THESE AREAS. THERE IS GOOD POTENTIAL FOR SOME OF THIS
NEW SNOW TO BLOW THROUGH THOMPSON PASS THIS EVENING...SO BE
PREPARED FOR REDUCED VISIBILITIES AT TIMES IF TRAVELING THROUGH
THE PASS. SNOW WILL STRUGGLE TO MAKE IT OVER INLAND AREAS TONIGHT
AS THE FRONT WEAKENS AND SOME CROSS-BARRIER FLOW KEEPS THINGS
DRIER IN THE LEE OF THE MOUNTAINS. HOWEVER...WITH THE CROSS-
BARRIER FLOW WEAKENING AS THIS DECAYING FRONT PIVOTS FROM EAST TO
WEST INTO SUNDAY...SHOULD CAUSE SOME PRECIPITATION TO SPILL OVER
SOME INLAND AREAS. SNOW ACCUMULATIONS WILL REMAIN QUITE LIMITED AS
THIS FRONT IS DECAYING...AND THE OVERALL FLOW BEGINS TO SHIFT TO
THE EAST-NORTHEAST. WINDS WILL ALSO DIMINISH AS THE GRADIENT
WEAKENS OVERNIGHT TONIGHT.

OUR ATTENTION THEN SHIFTS TO ANOTHER SYSTEM TRACKING SOUTHEAST TO
NORTHWEST ACROSS THE EASTERN GULF TO START THE WORK WEEK. THIS
SYSTEM HOLDS THE POTENTIAL TO BRING GUSTY WINDS BACK UP ALONG
PRINCE WILLIAM SOUND AND THE NORTHERN GULF COAST...ALONG WITH MORE
PRECIPITATION.

&&

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

THE MAIN DRIVER OF THE WEATHER OVER THE NEXT SEVERAL DAYS WILL BE
A WEAKENING AREA OF LOW PRESSURE SOUTH OF THE ALASKA PENINSULA.
THIS ANCHOR LOW WILL GRADUALLY WEAKEN OVER THE NORTH PACIFIC AS IT
SLOWLY MEANDERS EASTWARD AS THE BULK OF THE JET ENERGY (STEERING
CURRENTS) PASSES WELL SOUTH OF THE AREA. THIS LOW WILL CONTINUE
TO ACT IN UNISON WITH AN AREA OF LOW PRESSURE IN THE ARCTIC TO ACT
AS A BLOCKING PATTERN...WHICH WILL KEEP MUCH OF SOUTHWEST ALASKA
ON THE QUIET AND CALM SIDE. A SMALL PIECE OF ENERGY FROM THE
NORTHERN STREAM HAS BROKEN OFF AND HAS PUSHED ACROSS SOUTHWEST
ALASKA (EVIDENT ON WATER VAPOR IMAGERY). THIS PIECE OF ENERGY WILL
HELP CREATE SOME SNOW SHOWERS OVER SOUTHWEST ALASKA THIS EVENING
BEFORE PUSHING OFFSHORE OVER THE BERING SEA. A LITTLE BIT OF JET
SUPPORT ATTACHED TO THIS UPPER WAVE WILL HELP GRADUAL STRENGTHENING
OVER THE BERING SEA UNTIL A SFC LOW DEVELOPS IN RESPONSE OVER THE
WESTERN ALEUTIANS ON MONDAY.

IN THE MEANTIME...AS THE SURFACE LOW SOUTH OF THE ALASKA PENINSULA
WEAKENS THE PRESSURE GRADIENT ACROSS SOUTHWEST ALASKA WILL FOLLOW
SUIT. THIS IS EVIDENT IN THE DECREASE OF WIND SPEEDS ACROSS
COASTAL LOCATIONS OF THE KUSKOKWIM DELTA. AREAS OF BLOWING SNOW
WILL CONTINUE ALONG THE KUSKOKWIM DELTA COAST THROUGH THIS EVENING
UNTIL WINDS WEAKEN SUFFICIENTLY ENOUGH TO NOT BE ABLE TO TRANSPORT
SNOW. VISIBILITIES COULD DROP AS LOW AS ONE HALF MILE BRIEFLY THIS
EVENING MAINLY NEAR THE TOKSOOK AREA WHERE THE STRONGEST WINDS ARE
BEING OBSERVED DUE TO THE FAVORABLE WIND DIRECTION.

&&

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

AN UNCHARACTERISTIC PERIOD OF QUIET WEATHER LOOKS TO CONTINUE
ACROSS MUCH OF THE BERING SEA THROUGH SUNDAY NIGHT AS THE STORM
TRACK KEEPS ANY MAJOR SYSTEMS WELL SOUTH OF THE AREA. COME MONDAY
NIGHT...THE AFOREMENTIONED UPPER LEVEL DISTURBANCE WILL DEVELOP A
SURFACE REFLECTION AND HELP COMPACT THE PRESSURE GRADIENT TO
PRODUCE GALE FORCE WINDS ACROSS THE WESTERN BERING SEA AND PARTS
OF THE CENTRAL BERING SEA. RAIN AND SNOW WILL BE SHOWERY IN NATURE
DUE TO THE LACK OF ANY LARGE SCALE LIFTING MECHANISMS UNTIL
MONDAY NIGHT WHERE PRECIPITATION NEAR THE DEVELOPING SURFACE LOW
WILL BE MORE STRATIFORM IN NATURE. PRECIPITATION TYPE WILL LARGELY
FAVOR SNOW ON SUNDAY BUT TRANSITION TO RAIN FROM EAST TO WEST ON
MONDAY WITH THE LOW MOVING WESTWARD ACROSS THE BERING SEA. QUITE A
FEW LAND AREAS COULD EXPECT TO SEE UPWARD TO AN INCH OF SNOW FROM
TONIGHT THROUGH SUNDAY...ESPECIALLY ALONG THE EASTERN ALEUTIANS
AND PRIBILOF ISLANDS.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
BY MONDAY EVENING THE VERY LARGE UPPER LEVEL LOW COMPLEX ROTATING
AROUND THE VERTICALLY STACKED LOW SOUTH OF KODIAK ISLAND WILL BE
CENTERED NEAR 53N. THE UPPER TROUGH TO THE NORTH WILL BE SWINGING
OVER THE KENAI PENINSULA AROUND THIS TIME WITH ASSOCIATED SURFACE
LOW WEAKENS AND DISSIPATES. THERE IS STILL A FAIR BIT OF MODEL
DISAGREEMENT REGARDING THE TRACK OF THIS SURFACE FEATURE WHICH
COULD HAVE SIGNIFICANT IMPACTS TO WINDS IN THE NORTHERN GULF
COASTAL WATERS AND PRINCE WILLIAM SOUND. GIVEN THE BROAD SCALE
UPPER LOW TO THE SOUTH...PREFERRING A TRACK THAT TAKES THE LOW
INLAND AROUND THE CENTRAL KENAI PENINSULA. TO THE EAST THE NEXT
LOW WILL ROTATE NORTH JUST OFFSHORE OF HAIDA GWAII MONDAY NIGHT
WITH A COLDER UPPER LOW TO THE WEST CENTERED AROUND AMCHITKA PASS.

A RATHER STRONG LOW DEEPENING AS IT TRACKS EAST ALONG 40N WILL
BRING THE BEGINNINGS OF A PATTERN SHIFT AS IT CROSSES FROM 170W TO
160W MONDAY NIGHT AND BECOMES CAUGHT UP IN THE BROAD LOW COMPLEX.
THIS NEW SYSTEM WILL QUICKLY TAKE OVER AS THE DOMINANT
CIRCULATION RAPIDLY WEAKENS OUT THE OLDER LOWS AND TROUGHS TO THE
NORTH. AS THE SOUTHERN LOW BECOMES VERTICALLY STACKED AROUND
TUESDAY IT WILL MAKE A TURN TO THE NORTHEAST...LIFTING INTO THE
SOUTHERN GULF FOR THE WEDNESDAY/THURSDAY TIME PERIOD AND TO
CENTRAL GULF BY THURSDAY NIGHT OR FRIDAY. UPSTREAM THE RESULT WILL
BE A SHIFT TO THE NORTH OF THE STORM TRACK FOR THE NEW SYSTEMS
COMING IN FROM THE WEST PARALLEL BUT SOUTH OF THE ALEUTIANS
THROUGH THE END OF WEEK. AS WE MOVE INTO THE WEEKEND AND EARLY
NEXT WEEK...MORE OF A SOUTHWESTERLY GENERAL FLOW PATTERN WILL
PUSH INTO THE GULF WITH THE POTENTIAL FOR A MORE ACTIVE STORM
TRACK INTO THE GULF FOLLOWING.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE 119 130 131 138 139 179-185.
 		 HEAVY FREEZING SPRAY 160 180-185.

&&

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