Small Craft Advisory 989, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
445 PM AKST FRI DEC 11 2015

.ANALYSIS AND UPPER LEVELS...
SOUTHCENTRAL...A GULF LOW THAT HAS MEANDERED OVER THE WESTERN
GULF FOR THE BETTER PART OF WEEK NOW IS FINALLY BEGINNING TO MOVE
ONSHORE INTO THE KENAI PENINSULA THIS AFTERNOON. THE KENAI AND
MIDDLETON ISLAND RADARS SHOW WIDESPREAD SHOWER ACTIVITY FROM THE
SOUTHERN KENAI NORTH AND EAST THROUGH NEARLY ALL OF PRINCE WILLIAM
SOUND. A NEAT FEATURE IN THE RADAR REFLECTIVITY IS THE CLEAR
DOWNSLOPING OCCURRING ON THE KENAI PENINSULA AS THE ECHOES
DISAPPEAR UPON CROSSING THE KENAI MOUNTAINS. OBSERVATIONS EAST OF
ANCHORAGE SHOW THE LIONS SHARE OF THE OBS ARE BELOW
FREEZING...INDICATIVE OF A COOLING OF THE WARM LAYER ALOFT THAT
WAS ALSO NOTED COMPARING ANCHORAGES MOST RECENT 12Z VERSES 00Z
SOUNDINGS.

SOUTHWEST...SNOW CONTINUES THIS AFTERNOON AROUND THE KING SALMON
AREA AS A WEAK LOW OVER BRISTOL BAY COMBINED WITH A NEARLY
STATIONARY UPPER LEVEL DISTURBANCE OVER THE AREA GENERATES THE
LIFT NEEDED FOR CONTINUED SNOWFALL. LIGHT SNOW SHOWER ACTIVITY
ASSOCIATED WITH THE SAME UPPER LEVEL FEATURE IS ONGOING OVER THE
KUSKOKWIM DELTA AS WELL. OVER THE PAST DAY OR SO TEMPERATURES HAVE
CLIMBED BACK ABOVE ZERO FOR MOST AREAS OUTSIDE OF THE LOWER
KUSKOKWIM VALLEY AS WINDS HAVE SHIFTED TO A SOMEWHAT WARMER
NORTHWESTERLY DIRECTION BEHIND THE LOW OVER BRISTOL BAY.

BRISTOL BAY...WEAK HIGH PRESSURE OVER THE CENTRAL BERING IS
CENTERED BETWEEN THE LOW OVER BRISTOL BAY AND A WEAK FRONT
APPROACHING THE CENTRAL BERING. THE TIGHT GRADIENT BETWEEN THE
HIGH AND THE LOW OVER THE EASTERN BERING IS CAUSING GUSTY COLD
NORTHWEST WINDS WITH NUMEROUS SNOW SHOWERS ACROSS THE EASTERN
ALEUTIANS AND SOUTHERN ALASKA PENINSULA. OVER THE CENTRAL AND
WESTERN ALEUTIANS...THE FRONT IS PRODUCING A FEW SHOWERS AND GUSTY
WINDS...BUT IS NOTHING IN COMPARISON WITH A VERY POWERFUL LOW
CURRENTLY MOVING ACROSS THE PACIFIC TAKING AIM AT THE CENTRAL AND
WESTERN ALEUTIANS AND THE BERING FOR THE WEEKEND.

&&

.MODEL DISCUSSION...

THE MODELS ARE CONVERGING ON A COMMON SOLUTION WITH THE RAPIDLY
DEVELOPING LOW MOVING ACROSS THE NORTH PACIFIC. THE GFS/ECMWF
HAVE A SIMILAR INTENSIFICATION TREND AND TIMING OF THE LOW CENTER
CROSSING THE ALEUTIANS ON SAT. THE GFS OVERALL IS PREFERRED AND
WILL BE USED WITH THIS FEATURE.

IN THE EAST...MODELS ARE SIMILAR ACROSS THE GULF AND SOUTHCENTRAL
ON THE SYNOPTIC SCALE. THE NAM HOWEVER WAS PRIMARILY USED TO
CAPTURE THE MESOSCALE FEATURES.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
A WEAKENING LOW HAS MOVED INTO COOK INLET THAT WILL START TO SHIFT
THE NORTHERLY FLOW TO A MORE SOUTHERLY DIRECTION. THIS WILL HELP
TO MOVE SNOW UP THE INLET AND TOWARDS THE MATANUSKA VALLEY
TONIGHT. WEAK EASTERLY WINDS OUT OF PRINCE WILLIAM SOUND WILL
CAUSE SOME WEAK CONVERGENCE OVER THE ANCHORAGE AREA. THIS COULD
ALLOW FOR A COUPLE INCHES OF SNOW WITH THE HEAVIEST EARLY SATURDAY
MORNING. SNOW WILL THEN CLEAR OUT THROUGH THE DAY SATURDAY AS THE
LOW DISSIPATES AND RIDGING MOVES IN. ON SUNDAY A FRONT WILL
APPROACH THE AREA FROM THE SOUTHWEST AND MAKE IT OVER THE
SOUTHCENTRAL SUNDAY EVENING.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
THE FRONT OVER THE SOUTHWEST MAINLAND WILL PUSH OUT OF THE BRISTOL
BAY AREA...LINGERING ACCUMULATING MAINLY ALONG THE ALASKA RANGE
TONIGHT. BEFORE THE UPPER LOW PRESSURE WEAKENS AND EXITS...A
DISTURBANCE ROTATING AROUND WILL KEEP SNOW GOING FOR INLAND AREAS
OF THE KUSKOKWIM DELTA BEFORE TAPERING OFF IN THE MORNING ON
SATURDAY. THE PATTERN WILL CHANGE PRETTY QUICKLY OVER THE WEEKEND
AS A STRONG SYSTEM ENTERS THE EASTERN BERING LATE SATURDAY NIGHT.
THE FRONT FROM THAT SYSTEM WILL OVERSPREAD THE MAINLAND ON SUNDAY
BRINGING MOSTLY SNOW...HOWEVER SOME RAIN WILL MIX IN NEAR THE
COAST.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
THE FOCUS FOR TONIGHT'S FORECAST TURNS TO THE DEVELOPING STORM IN
THE NORTHWEST PACIFIC. THE FRONT WILL SPREAD OVER THE WESTERN AND
CENTRAL ALEUTIANS TONIGHT...FIRST BRINGING SNOW...FOLLOWED BY
RAIN. THE WESTERN ALEUTIANS WILL STAY ON THE COLD SIDE OF THE LOW
WHERE PRECIPITATION WILL REMAIN ALL SNOW. THE BIGGER STORY WITH
THIS SYSTEM WILL BE THE WIND FIELD. AS THE SYSTEM IS PROGGED TO
GET INTO THE MID-920 MB RANGE...WIDESPREAD HURRICANE FORCE WINDS
ARE LIKELY. THE STRONGEST PORTION OF THE WIND FIELD WILL NOT THE
THE LEADING WARM FRONT...BUT WITHIN THE STING JET ON THE SOUTH
SIDE OF THE SYSTEM WHERE WINDS IN THE LOW LEVELS WILL APPROACH THE
80 TO 100 MPH RANGE. THE PEAK OF THE EVENT WILL BE TOMORROW
EVENING...HOWEVER WARNING LEVEL WINDS WILL CONTINUE THROUGH
SUNDAY AFTERNOON OVER THE CENTRAL ALEUTIANS.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7)...
THE VERY STRONG WESTERLY WINDS WILL SLOWLY DIMINISH ALONG THE
WESTERN/CENTRAL ALEUTIANS SUNDAY NIGHT AND MONDAY AS THE COLDER
AIR BEING PULLED DOWN ON THE BACKSIDE FROM THE EASTERN ASIA
REGION GETS WOUND UP IN THE LOW. THE BOUNDARY LAYER WINDS ARE
SHOWING 70 KNOTS LATE SUNDAY AFTERNOON WITH THE GFS MODEL DEPICTING
THIS LOW AT AROUND 937 MB AFTER BOTTOMING OUT AT 929 MB EARLIER IN
THE DAY. THIS SYSTEM WEAKENS AND TRACKS TO THE NORTHERN BERING
SEA BY MONDAY. THIS SYSTEM WILL MOVE TO THE CENTRAL BERING SEA BY
SUNDAY EVENING. AS THIS SYSTEM MOVES FARTHER NORTH INTO THE
BERING THE COLDER AIR WILL FILTER IN ON THE BACKSIDE OF THE LOW
RESULTING IN TEMPERATURES AT FREEZING OR BELOW WITH A SHOWERY
WEATHER REGIME AS WE HEAD INTO THE MIDWEEK. BY TUESDAY THIS
WEATHER SYSTEM WILL BE WEAKENED TO A GALE FORCE LOW POSITIONED
JUST WEST OF SAINT LAWRENCE ISLAND WITH PREDOMINANTLY WESTERLY
SMALL CRAFT WINDS IN THE BERING SEA. BY THURSDAY MORNING A GALE
FORCE LOW DROPS DOWN FROM THE KAMCHATKA PENINSULA WITH A WEATHER
FRONT EXTENDING THROUGH THE WESTERN ALEUTIANS. THIS WILL BRING
TEMPERATURES ABOVE FREEZING IN THE LOW 40S BEFORE SPILLING OVER
INTO THE WESTERN TO CENTRAL BERING BY THURSDAY AFTERNOON.

SOUTHCENTRAL ALASKA WILL BE UNDER THE INFLUENCE OF UPPER LEVEL
RIDGE SUNDAY NIGHT. BY MONDAY MORNING THERE WILL BE A SHORTWAVE
TROUGH MOVING THROUGH THE AREA BEFORE EXITING THE AOR BY LATE
MONDAY AFTERNOON. THE TEMPERATURES WILL BE MID TO UPPER 30S ALONG
THE COASTLINES WITH COOLER TEMPERATURES INLAND. SO THE COASTAL
COMMUNITIES WILL HAVE A WINTRY MIX...WHILE IT SHOULD BE ALL SNOW
FOR THE INLAND AREAS. THE MODELS ARE HANDLING THIS SYNOPTIC
FEATURE WELL WITH CONTINUES ONSHORE FLOW HEADING INTO THE MIDWEEK.
THE GULF WILL HAVE A STRONG 120 KNOT SOUTHWESTERLY JET STREAK
BEFORE EXITING THE NORTHEASTERN GULF BY WEDNESDAY. UPSTREAM THERE
WILL BE A STRONG 110 KNOT ZONAL JET STREAM SOUTH OF THE EASTERN
ALEUTIANS. THIS WILL TRACK A NORTH PACIFIC LOW INTO THE LOWER GULF
BY WEDNESDAY AFTERNOON. THE MODELS ARE STRUGGLING WITH THE
STRENGTH AND PLACEMENT OF THIS LOW. THE GFS TRACKS THIS LOW TO THE
FAR EASTERN GULF AND THE ECMWF MODEL HAS THE LOW IN THE LOWER
SOUTHWESTERN GULF. WE USED THE WPC MODEL TO KEEP A MORE
CONSISTENT TRACK WITH THIS SYSTEM AND THIS MODEL KEEPS THE SYSTEM
JUST EAST OF KODIAK AS IT TRACKS INTO THE CENTRAL GULF BY
THURSDAY. THEREFORE...THE FORECAST CONFIDENCE IS LOW WITH THE
UNCERTAINTY FOR THE STORM TRACK OF THIS SYSTEM.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...HIGH WIND WARNING 187 191.
MARINE...HURRICANE FORCE WIND 173 175 176 177 178. STORM WARNING
170 172 174 179 180 181 185. GALE WARNING 155 160 165 171. HEAVY
FREEZING SPRAY 130 160 180 181 185.

&&

SYNOPSIS AND MODEL DISCUSSION...JW
SOUTHCENTRAL ALASKA...DK
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...ML
LONG TERM...PD