Small Craft Advisory 983, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
455 AM AKST WED DEC 9 2015

.ANALYSIS AND UPPER LEVELS...THERE HAS BEEN LITTLE CHANGE IN THE
PATTERN OVER THE PAST 24 HOURS. TWO VERTICALLY STACKED LOWS
CONTINUE TO LINGER OVER THE AREA...BUT THEY ARE STARTING TO
CONSOLIDATE INTO ONE LOW IN THE GULF OF AK. THE LOW THAT WAS NEAR
DUTCH HARBOR LEFT A FRONTAL BOUNDARY DRAPED ACROSS THE EASTERN
BERING. ONE ADDITIONAL WEAK SURFACE LOW IS SKIRTING THROUGH THE
WESTERN ALEUTIANS THIS MORNING...BUT IT WILL HAVE LIMITED IMPACT
AND SHOULD DISSIPATE BY LATER TODAY. THE UPPER LEVEL JET CONTINUES
TO REFLECT A VERY CLASSIC EL NINO PATTERN. IT IS CLIPPING ACROSS
THE ENTIRE NORTH PACIFIC AT ABOUT 170 KTS BEFORE CRASHING INTO THE
PACIFIC NORTHWEST NEAR THE WASHINGTON/CANADA BORDER. AS THE
STEERING FLOW REMAINS NEARLY NON-EXISTENT AROUND THE LOW IN THE
GULF...THIS SYSTEM IS JUST MEANDERING NORTHWARD. WHEN COUPLED
WITH THE HIGHER PRESSURE AND MODESTLY COLD AIR MASS OVER THE
MAINLAND...THIS IS KEEPING THE OFFSHORE GRADIENT FAIRLY TIGHT AND
PRODUCING MORE OFFSHORE WINDS. AGAIN...THE MOST VULNERABLE SPOTS
ARE THE NORTH TO SOUTH ORIENTED GAPS SUCH AS THOMPSON PASS AND
RESURRECTION BAY.

&&

.MODEL DISCUSSION...MODELS ARE IN MUCH BETTER AGREEMENT HANDLING
THE LOW IN THE GULF OF AK. THUS...HIGHER RESOLUTION MODELS WERE
USED FOR THE MORNING PACKAGE AND THERE IS HIGHER FORECAST
CONFIDENCE IN HANDLING THIS FEATURE. OUT WEST...MODELS CONTINUE TO
HANDLE THE SYNOPTIC PATTERN WELL. THE TRICKIEST PORTION OF THE
FORECAST THERE IS HOW THE FRONT SETS UP IN RELATION TO THE
PRIBILOF ISLANDS AND DUTCH HARBOR. THE TREND OVERNIGHT WAS TO
IMPROVE CONDITIONS AT THESE LOCATIONS WITH THE FRONT SHIFTING JUST
TO THEIR WEST. GOING FORWARD...THERE WILL BE SOME INTERESTING
CHALLENGES. FIRST...WED NIGHT SNOW FOR INLAND PORTIONS OF SOUTH
CENTRAL. MODELS ARE "WORKING" OUT THE DETAILS...BUT FOR NOW THE
NAM IS THE MOST AGGRESSIVE WITH A COLD TROUGH OVER THE SUSITNA
VALLEY AND SOME MOISTURE WRAPPING IN FROM THE GULF LOW. REGARDLESS
OF THE SOLUTION...IT DOES NOT LOOK LIKE AN OVERLY IMPRESSIVE
EVENT. NEXT UP WILL BE THE POTENTIAL FOR MORE SNOW FOR SOUTH
CENTRAL LATE FRI INTO SAT. MODELS ALL SHOW THE STACKED LOW FROM
THE GULF FINDING ITS WAY UP COOK INLET AND BRINING A FAIR AMOUNT
OF MOISTURE. THEY ALSO ALL SHOW VARYING DEGREES OF SOME COLDER AIR
WRAPPING AROUND THE WESTERN SIDE OF THE LOW. THE NAM THOUGH IS THE
MOST BULLISH WITH UPPER LEVEL SUPPORT WHICH COULD LEAD TO A MORE
SIGNIFICANT SNOW ACCUMULATIONS. WE TRENDED THE PRECIPITATION
FORECAST UP SOMEWHAT...BUT KEPT THINGS FAIRLY GENERALIZED UNTIL WE
SEE THE NEXT FEW MODEL RUNS.

&&

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

STACKED LOW IN THE GULF WILL SLOWLY TRACK INTO THE WESTERN GULF
AND AS IT DOES IT WILL BRING A PUSH OF WARMER AND MOISTER AIR OVER
SOUTHCENTRAL. THE MAIN IMPACT FROM THIS WILL BE INCREASING SNOW
CHANCES ALONG THE NORTH GULF COAST. WITH THE SUPPORT OF AN UPPER
LEVEL TROUGH APPROACHING FROM THE NORTHWEST AND A SECOND FROM THE
EAST TODAY...SOME LIGHT SNOW OR FLURRIES WILL TRY TO MAKE ITS WAY
PAST THE COASTAL RANGES TODAY...WITH THE MAIN CULPRIT AGAINST
ACCUMULATING SNOW BEING PERSISTENT LOW-LEVEL DRY AIR IN PLACE
UNDER THE INVERSION ACROSS THE POPULATED LOW-LYING AREAS. ANOTHER
DISTURBANCE WILL MOVE NORTHWEST ACROSS SOUTHCENTRAL THURSDAY...BUT
WITH SNOW BYPASSING THE ANCHORAGE AND PALMER AREAS WITH DOWNSLOPE
SOUTHEAST FLOW IN PLACE.

NORTH TO SOUTH ORIENTED GAP WINDS WHICH HAVE BEEN OCCURRING WILL
BEGIN TO DIMINISH BY THIS EVENING. THROUGH THOMPSON PASS...THESE
STRONGER WINDS COMBINED WITH THE INCOMING SNOW PROVIDE THE
POSSIBILITY FOR BLOWING SNOW. HOWEVER...WITH FAIRLY LOW NEW
SNOWFALL FORECAST AMOUNTS AND LITTLE TO NO TRANSPORTABLE SNOW
THROUGH THE PASS...VISIBILITIES ARE EXPECTED TO STAY ABOVE
CRITICAL LEVELS (GENERALLY ONE MILE OR GREATER).

&&

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

THE PERSISTENT PATTERN OF RIDGING ALOFT AND OFFSHORE FLOW WILL
PERSIST THROUGH THURSDAY MORNING. HIGHLIGHTS WILL CONTINUE TO BE
RELATIVELY STRONG NORTHERLY WINDS AND VERY COLD TEMPERATURES AND
WIND CHILLS VALUES AS LOW AS 35 BELOW ZERO. OTHERWISE...DRY AND
LARGELY CLEAR WILL DOMINATE. ON THURSDAY AFTERNOON...A TROUGH
MOVING ACROSS THE BERING WILL MERGE WITH A GULF LOW...SPREADING
CLOUDS AND SHOWERS INTO SOUTHWEST ALASKA...BRINGING ACCUMULATING
SNOW THREATS TO THE REGION INTO FRIDAY.

&&

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

A STALLED FRONTAL BOUNDARY OVER THE PRIBILOF ISLANDS WILL MOVE
EASTWARD THROUGH THURSDAY NIGHT...WITH COLDER AIR SPREADING BEHIND
THE FRONT...AND RAIN AND SNOW SHOWERS IMPACTING MOST OF THE
CENTRAL AND EASTERN BERING/ALEUTIANS AS IT TRACKS EAST. A WEAK
TROUGH WILL MOVE THROUGH THE WESTERN BERING SEA THURSDAY INTO
FRIDAY...WITH SNOW SHOWERS IMPACTING THE WESTERN BERING. NORTHWEST
FLOW SNOW SHOWERS WILL PERSIST OVER THE EASTERN ALEUTIANS AND
PRIBILOF ISLANDS THROUGH FRIDAY AS THE UPPER TROUGH STALLS OVER
THE EASTERN BERING SEA.

&&

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

WITH EACH SUBSEQUENT MODEL RUN...IT APPEARS MORE AND MORE LIKELY
THAT SOUTHWEST AND SOUTHCENTRAL ALASKA ARE HEADING INTO QUITE AN
ACTIVE WEATHER PATTERN STARTING FRIDAY. WE WILL START ACROSS
SOUTHCENTRAL ALASKA WHERE AN AREA OF LOW PRESSURE SITUATED BETWEEN
KODIAK ISLAND AND THE KENAI PENINSULA BEGINS TO ELONGATE WHILE
BECOMING ATTACHED TO A DECAYING LOW OVER THE SOUTHWEST MAINLAND.
GENERALLY A FEATURE SUCH AS THIS WOULD LEAD BE FAIRLY BENIGN WITH
JUST SHOWERS EXPECTED ACROSS THE REGION. HOWEVER...RIDGING
DEVELOPING AHEAD OF A DEEPENING LOW OVER THE BERING SEA WHICH WILL
BE DISCUSSED LATER WILL AMPLIFY THE UPPER LEVEL PATTERN OVER
SOUTHCENTRAL ALASKA. THIS WILL HELP PUSH THE UPPER LEVEL TROUGH
ACROSS SOUTHCENTRAL ALASKA (MAINLY THE COOK INLET REGION) WHICH
SHOULD HELP BOLSTER SNOW CHANCES. THERE IS A BIT OF DISPARITY
AMONGST THE GUIDANCE IN REFERENCE TO HOW MUCH JET ENERGY ACCOMPANIES
THE TROUGH LATE FRIDAY INTO SATURDAY WITH THE NAM BEING BY FAR THE
STRONGEST. WHILE MODEL QPF FIELDS ARE PRETTY LIGHT WITH ONLY LIGHT
SNOW ACCUMULATION ACROSS THE REGION...THERE IS THE POTENTIAL FOR A
BIT MORE SNOW THAN THE MODELS ARE HANDLING. WITH COLD AIR ADVECTION
ACCOMPANYING THIS TROUGH...IT LOOKS LIKE THE ENTIRE COLUMN COULD
BE LIFTED WHILE SATURATED WHICH COULD LEAD TO MESOSCALE BANDING
AND POCKETS OF HEAVIER SNOW. THIS EVENT IS STILL QUITE A FEW DAYS
OUT BUT IT IS SOMETHING THAT NEEDS TO BE MONITORED. IT LOOKS LIKE
THE MOST OF THE SNOWFALL WOULD LIKELY FALL ACROSS THE KENAI
PENINSULA MAINLY NEAR HOMER AND KACHEMAK BAY...BUT SNOW UP TOWARD
ANCHORAGE AND PARTS OF THE MATANUSKA AND SUSITNA VALLEYS WILL BE
POSSIBLE.

OUT WEST...A RAPIDLY EVOLVING LOW (CURRENTLY JUST A WEAK WAVE
NEAR THE EAST CHINA SEA) WILL INTERACT WITH A 140+ KNOT JET STREAK
AND RAPIDLY APPROACH THE WESTERN ALEUTIANS ON SATURDAY. MODELS ARE
SLOWLY CONVERGING ON A DEEP SOLUTION (927-933 MB) THAT CONTINUES
TO STRENGTHEN AS IT CROSSES INTO THE WESTERN BERING SEA. WITH
MODELS IN BETTER AGREEMENT AND WITH DECENT RUN-TO-RUN CONSISTENCY
THE FORECAST PACKAGE WILL ACCOMMODATE LARGE SWATHS OF STORM FORCE
WINDS WITH SEAS IN EXCESS OF 45 FT. IT IS VERY POSSIBLE THAT THESE
WINDS AND WAVE HEIGHTS ARE ON THE LIGHT SIDE AS ALL GUIDANCE
CONTINUES TO HINT AT HURRICANE FORCE WINDS ACROSS THE WESTERN AND
CENTRAL ALEUTIANS. MODEL AGREEMENT IS NOT GOOD ENOUGH TO JUMP ON
BOARD JUST YET BUT A CONTINUING TREND OF UPPING WINDS IN THE
FORECAST WILL LIKELY BE SEEN AS MODELS GET INTO BETTER AGREEMENT.
THE GFS IS GENERALLY THE OUTLIER AS IT WRAPS UP MUCH QUICKER WITH
A STRONGER MID-LEVEL JET. HOWEVER...THE ECMWF HAS BEEN SLOWLY
SHIFTING WESTWARD AND A LOT OF THE ENSEMBLE GUIDANCE CONTINUES TO
TREND WESTWARD. ANOTHER CONCERN ASSOCIATED WITH THIS LOW WILL BE
COASTAL FLOODING ALONG THE WEST COAST OF ALASKA. WITH THE TRACK OF
THE LOW UP IN THE AIR AS IT CROSSES THE BERING SEA...IT IS DIFFICULT
TO JUDGE THE IMPACTS OF COASTAL FLOODING. HOWEVER...THERE SHOULD
BE A NICE PERIOD OF WESTERLY WINDS AT SOME POINT OR ANOTHER AND
WITH LARGE FETCH COULD SEE HIGH SEAS APPROACH THE WEST COAST OF
ALASKA. IT WILL BE INTERESTING TO SEE WHAT IMPACTS THE SEA ICE
DEVELOPING ALONG THE COAST OF ALASKA WILL HAVE ON THE POTENTIAL SURGE.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...HEAVY FREEZING SPRAY...160 180 181 185.
         GALE...119 120 127 131 132 172 174-176 180 181 185

&&

SYNOPSIS AND MODEL DISCUSSION...MSO
SOUTHCENTRAL ALASKA...CC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...JA
LONG TERM...MMC