Small Craft Advisory 972, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
511 AM AKST SUN DEC 6 2015

.ANALYSIS AND UPPER LEVELS...
THERE IS AN UPPER LEVEL TROUGH OVER THE WESTERN BERING SEA.
ASSOCIATED WITH THIS ARE TWO VERTICALLY STACKED LOWS...ONE SOUTH
OF THE WESTERN ALEUTIANS AND ON SOUTH OF THE EASTERN ALEUTIANS.
THERE IS ALSO A WEAK SHORT-WAVE OVER THE SOUTHEAST BERING AND
ALASKA PENINSULA...WHICH IS ESSENTIALLY A "BACK DOOR" WARM FRONT
MOVING TOWARD THE NORTHWEST. FURTHER EAST THERE IS AN UPPER LEVEL
RIDGE OVER SOUTHERN ALASKA WITH WEAK OFFSHORE FLOW AT THE LOWER
LEVELS. THERE IS AN UPPER LOW OVER THE SOUTHERN GULF OF ALASKA
WITH A SHORTWAVE TROUGH OVER THE EAST CENTRAL GULF MOVING TOWARDS
THE WEST. THERE IS ENOUGH MOISTURE OVER THE GULF TO BRING SOME
SHOWERS TO KODIAK ISLAND IN NORTHEAST FLOW.

OF NOTE FROM A LARGER WEATHER/CLIMATE PERSPECTIVE IS THE VERY
EXTENDED EAST ASIAN JET (EAJ). THIS IS RUNNING ALMOST DUE EAST
BETWEEN 35 AND 40 DEGREES NORTH LATITUDE FROM KOREA TO ABOUT 140
DEGREES WEST LONGITUDE. THE WINDS IN THIS JET EXCEED 190 KTS IN
PORTIONS OF THE WESTERN PACIFIC. THIS EXTENDED EAJ IS A COMMON
OCCURRENCE DURING EL NINO YEARS AND IS A SIGN THAT THE CURRENT EL
NINO IS WELL COUPLED WITH THE MID LATITUDE WEATHER AT THIS TIME.

&&

.MODEL DISCUSSION...
THE NUMERICAL MODELS ARE IN REASONABLY GOOD AGREEMENT FOR THE
SHORT TERM PORTION OF THE FORECAST. THERE ARE SOME DIFFERENCES IN
HOW THEY HANDLE THE INTERACTION OF THE VARIOUS LOWS OVER AND JUST
SOUTH OF THE EASTERN/CENTRAL ALEUTIANS AND ALASKA PENINSULA FROM
SUNDAY EVENING THROUGH MONDAY AFTERNOON. THIS DOES NOT HAVE A
LARGE IMPACT ON THE WEATHER FORECAST...BUT DOES INTRODUCE SOME
UNCERTAINTY. WITH THIS IN MIND...THE FORECAST CONFIDENCE IS NEAR
NORMAL FOR THE ALEUTIANS AND BERING SEA AND A BIT ABOVE NORMAL FOR
THE SOUTHWEST AND SOUTH CENTRAL ALASKA MAINLAND.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (DAYS 1 AND 2)...
MUCH OF THE FOG AND STRATUS IN THE ANCHORAGE AND MATANUSKA VALLEY
AREA DISSIPATED OVERNIGHT. THERE WERE SOME HIGH CLOUDS PASSING
OVERHEAD WHICH MAY HAVE CONTRIBUTED TO THIS. THE MORE LIKELY
CULPRIT IS THE INCREASE IN LOW LEVEL FLOW BEGINNING AT A FEW
HUNDRED FEET ABOVE THE SURFACE AS SEEN IN THE 12Z ANCHORAGE
SOUNDING. EXPECT SLIGHT WEAKENING OF THIS FLOW TODAY SO WE MAY
NOT BE COMPLETELY DONE WITH THE FOG/STRATUS. DO NOT EXPECT IT TO
BECOME WIDESPREAD BUT PATCHES WILL LIKELY CONTINUE TO FLOAT ALONG
KNIK ARM. THE OTHER PROBLEM AREA IS THE COPPER RIVER BASIN WHERE
STRATUS IS WIDESPREAD. THIS HAS KEPT TEMPERATURES STEADY OVERNIGHT.
WITH HIGH PRESSURE MOVING OVERHEAD THERE WILL NOT BE ANYTHING TO
MIX OUT THE LOW LEVEL MOISTURE. HAVE INCREASED TEMPERATURES WITH
THIS IN MIND...BUT STILL EXPECT SOME COOLING OVER THE NEXT COUPLE
DAYS. IF IT DOES CLEAR OUT TEMPERATURES WILL DROP QUICKLY. ASIDE
FROM THESE TWO ISSUES EXPECT MOSTLY CLEAR SKIES ACROSS SOUTHCENTRAL
WITH SEASONABLY COOL TEMPERATURES.

MEANWHILE...A FRONT WHICH HAS BEEN TRACKING WESTWARD ACROSS THE
GULF WILL CROSS KODIAK ISLAND TODAY BRINGING STEADY RAIN. COLDER
AIR OVER INTERIOR SOUTHCENTRAL COMBINED WITH PASSAGE OF THE FRONT
TO THE SOUTH HAS KICKED UP GAP WINDS ALONG THE PRINCE WILLIAM
SOUND AND THE GULF COAST...BUT EXPECT SOME SLACKENING OF PRESSURE
GRADIENTS AND WINDS TODAY THROUGH TONIGHT AS THE FRONT EXITS.
KODIAK WILL CONTINUE TO SEE PERIODS OF RAIN ON THE NORTHEAST
PERIPHERY OF A LOW COMPLEX SITTING OVER THE ALEUTIANS AND NORTH
CENTRAL PACIFIC.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2)...
THE SOUTHWEST ALASKA REGION HAS AN UPPER LEVEL RIDGE POSITIONED
OVER THE AREA WITH CONTINUED OFFSHORE FLOW. THIS WILL RESULT IN
COLD TEMPERATURES WITH MOSTLY CLEAR SKIES FOR SUNDAY. BY LATE
SUNDAY A WARM FRONT WILL TRACK INTO THE ALASKA PENINSULA AND
TRACK TO THE NORTHWEST AS WE HEAD INTO MONDAY. THIS WILL BRING IN
WARMER TEMPERATURES WITH THE MAJORITY OF THE PRECIPITATION FALLING
ALONG THE ALASKA PENINSULA AND THE SOUTHWEST COASTLINE. THE
PRECIPITATION WILL BE ALL RAIN ALONG THE ALASKA PENINSULA AND A
BRIEF TRANSITION ZONE OF WINTRY MIX...EXCEPT ALL SNOW FROM
DILLINGHAM NORTH AND WEST ALONG THE SOUTHWEST COASTLINE.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2)...
AT THE SURFACE THERE IS A BROAD AREA OF LOW PRESSURE LOCATED SOUTH
OF THE CENTRAL ALEUTIANS THAT WILL TRACK OVER DUTCH HARBOR BY LATE
SUNDAY NIGHT BEFORE MOVING NEAR NIKOLSKI BY MONDAY AFTERNOON. THIS
SYSTEM WILL BRING PREDOMINANTLY GALE FORCE NORTHWESTERLY WINDS
FROM THE NORTHERN TO LOWER WESTERN BERING SEA THROUGH THE WESTERN
TO CENTRAL ALEUTIANS. THE WINDS WILL INCREASE TO STORM FORCE IN
THE WESTERN BERING SEA BY LATE SUNDAY NIGHT AND MOVING INTO THE
WESTERN ALEUTIANS BY MONDAY. THESE NORTHWESTERLY WINDS WILL BRING
COLDER TEMPERATURES RESULTING IN A SHOWERY WEATHER REGIME. WHILE
DOWNSTREAM FROM THIS SYSTEM THERE WILL BE WARMER TEMPERATURES OVER
THE EASTERN ALEUTIANS THAT WILL SPILL OVER INTO THE EASTERN BERING
SEA. ALL THIS WARM AIR ADVECTION WILL INCREASE THE PRESSURE
GRADIENTS RESULTING IN GALE FORCE SOUTHEASTERLY TO EASTERLY WINDS
THROUGH THE EASTERN BERING SEA AND THE BRISTOL BAY REGION HEADING
INTO MONDAY.

&&

.LONG TERM FORECAST (DAYS 3 THROUGH 7...MON THROUGH FRI)...
THE LONG WAVE TROUGH OVER THE EASTERN BERING THAT HAS BEEN A
SEMI-PERMANENT FEATURE LATELY WILL BEGIN TO SHIFT INTO THE GULF
AND DEEPEN EARLY NEXT WEEK. THIS WILL BRING A GALE (OR POTENTIALLY
STORM FORCE) LOW INTO THE GULF BY LATE MONDAY WHICH WILL PERSIST
IN THE GULF AND SLOWLY WEAKEN OVER THE COURSE OF NEXT WEEK UNDER
THE UPPER LEVEL TROUGH. THIS WILL KEEP MUCH OF THE ACTIVE WEATHER
CONFINED TO THE GULF AND EASTERN BERING THROUGH THE MIDDLE OF NEXT
WEEK. OVER SOUTHCENTRAL THIS WILL BRING GENERALLY OFFSHORE FLOW
AND CLEAR SKIES FOR MUCH OF SOUTHCENTRAL...WHILE OVER THE
BERING...BROAD NORTHERLY GALE FORCE WINDS WILL BRING COLD AIR
ADVECTION SNOW SHOWERS TO THE AREA. BY LATE NEXT WEEK THERE IS
VERY GOOD MODEL AGREEMENT THAT THE GULF LOW WILL DISSIPATE
SOMEWHERE AROUND THE NORTH GULF COAST...BRINGING INCREASING
CHANCES FOR SNOWFALL TO THE SOUTH MAINLAND.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...HEAVY FREEZING SPRAY 160 180 181 185.
         STORM WARNING 178 411.
         GALE WARNING 130 138 160 165 175 176 177 179 180 181 185.

&&

SYNOPSIS AND MODEL DISCUSSION...JA
SOUTHCENTRAL ALASKA...SB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...PD
LONG TERM...DEK