Gale Warning 872, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
444 PM AKST SAT DEC 5 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 ONE 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)...

AN UPPER LEVEL JET STREAK AND ATTENDANT SHORTWAVE DISTURBANCE WILL
USHER HIGH LEVEL CLOUDS ACROSS THE REGION TONIGHT. DEPENDING ON
THE AMOUNT OF INSOLATION PROVIDED...FOG WHICH HAS DEVELOPED AROUND
SUNSET THIS AFTERNOON...OR IN SOME PLACES HAS PERSISTED SINCE
THIS MORNING...MAY DIMINISH IN COVERAGE AS THESE CLOUDS MOVE
OVERHEAD TONIGHT. AS OF 3 PM...VIIRS NPP POLAR SATELLITE DETECTED
THIS FOG EXTENDING FROM THE KNIK AND LOWER MATANUSKA RIVER VALLEYS
SOUTH ALONG THE WESTERN CHUGACH RANGE TO EAST ANCHORAGE...THEN
DEVELOPS AGAIN FROM POTTER MARSH THROUGH TURNAGAIN ARM DOWN TO
PORTAGE AND PERHAPS TURNAGAIN PASS. ANOTHER BATCH OF LOW CLOUDS
AND FOG EXISTS ALONG THE STERLING HIGHWAY FROM NEAR SOLDOTNA EAST
TO NEAR COOPER LANDING. A DENSE FOG ADVISORY HAS BEEN ISSUED FOR
THE IMPACTED AREAS IN ANCHORAGE AND THE MATANUSKA VALLEY UNTIL 6
AM AKST TO ACCOUNT FOR THIS FOG...WITH THE MAIN IMPACTS BEING
SLICK ROADS FROM THE FOG DEPOSITING ICE ON THE ROADWAYS...MAINLY
ALONG THE GLENN HIGHWAY...AND REDUCED VISIBILITY.

HIGH PRESSURE WILL BUILD OVER SOUTHCENTRAL THROUGH THE REMAINDER
OF THE WEEKEND INTO EARLY NEXT WEEK...WITH A CUT-OFF HIGH SETTING
UP DIRECTLY OVER THE NORTH GULF COAST. WITH MOSTLY CLEAR SKIES
THIS WILL BE IDEAL CONDITIONS FOR SIGNIFICANT COOLING OF THE AIR
MASS. EXPECT COOLING TEMPERATURES REGION-WIDE...WITH THE COLDEST
TEMPERATURES IN THE COPPER RIVER BASIN SUNDAY NIGHT AND MONDAY
MORNING.

CONTINUED ACTIVITY ACROSS THE GULF OF ALASKA AND NORTHEAST
PACIFIC COMBINED WITH COOLING OVER INTERIOR SOUTHCENTRAL IS
LEADING TO TIGHTENING PRESSURE GRADIENTS AND DEVELOPMENT OF GAP
WINDS ALONG PRINCE WILLIAM SOUND AND THE NORTH GULF COAST. THERE
WILL NOT BE MUCH IN THE WAY OF UPPER LEVEL SUPPORT TO ADVECT THE
COLDER AIR OFFSHORE. THEREFORE...GENERALLY EXPECT THIS TO BE A
WEAK EVENT WITH THE STRONGEST WINDS THROUGH THE GAPS AND IN THE
IMMEDIATE EXIT OF THE GAPS...BUT NOT MUCH FARTHER. WITH THE
COLDEST AIR SETTING UP IN THE COPPER RIVER BASIN...THE VALDEZ TO
THOMPSON PASS AREA CAN EXPECT SOME OF THE STRONGEST GAP WINDS.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (DAYS 1 AND 2...SUN AND
MON)...WEATHER WILL REMAIN COLD AND RELATIVELY CALM...ESPECIALLY
FOR DECEMBER...FOR THE NEXT COUPLE OF DAYS. AS THE BROAD LONGWAVE
TROUGH REMAINS OVER THE CENTRAL ALEUTIANS...A WEAK SHORTWAVE
RIDGE WILL ACTUALLY BUILD OVER THE MAINLAND. WITH THE COLD AIR
ALREADY IN PLACE OVER THE SOUTHWEST...THIS WILL CREATE A MODERATE
OFFSHORE SURFACE GRADIENT. THIS WILL CAUSE THE NORTH TO EAST WINDS
TO CREEP UP SLOWLY OVER THE NEXT 24 HOURS...ESPECIALLY ALONG THE
WESTERN CAPES OF BRISTOL BAY AND THE ALASKA PENINSULA. A WEAK WARM
FRONT WILL SLIDE THROUGH THE EASTERN ALEUTIANS AND ALASKA
PENINSULA LATE SUN INTO MONDAY. THIS COULD BRING A SHOT OF LIGHT
SNOW INTO THOSE AREAS. BUT AS IT USHERS IN THE WARMER AIR...EXPECT
THE SNOW TO CHANGE QUICKLY TO RAIN. THIS FRONT WILL ALSO HELP
TEMPERATURES OVER THE MAINLAND TO SLOWLY MODIFY TO START THE WEEK.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (DAYS 1 AND 2...SUN AND
MON)...THE BEST WAY TO SUM UP THE WEATHER FOR THE NEXT COUPLE OF
DAYS IS COMPLICATED BUT LOW-IMPACT. A BROAD UPPER LEVEL LOW WILL
SET-UP IN THE VICINITY OF DUTCH HARBOR. ON THE EAST SIDE OF THE
LOW THERE WILL BE SOUTH TO SOUTHEAST WINDS AND WARMER AIR BEING
ADVECTED FROM THE NORTH PACIFIC. SNOW SHOWERS WILL TURN TO RAIN
SHOWERS AS FAR NORTH AS THE PRIBILOF ISLANDS. ON THE WEST
SIDE...THERE WILL BE COLD AIR SNOW SHOWERS AND GUSTY NORTH TO
NORTHEAST WINDS. SEVERAL WEAK PIECES OF ENERGY WILL ROTATE ACROSS
THE BERING IN A CYCLONIC/COUNTER-CLOCKWISE FASHION AROUND THE LOW
CENTER. MODELS ARE SHOWING THAT SOME OF THIS ENERGY COULD PRODUCE
A POLAR LOW OVER THE NORTHWEST BERING ON SUNDAY. THIS WILL LIKELY
BRING A NARROW BAND OF STORM FORCE WINDS AND HEAVIER SNOW SHOWERS
THROUGH THE WESTERN ALEUTIANS LATE SUN.

&&

.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...DENSE FOG 101 111.
MARINE...GALES 130 138 160 177 178 180 181 185
         HEAVY FREEZING SPRAY 160 180 181 185.

&&

SYNOPSIS AND MODEL DISCUSSION...BL
SOUTHCENTRAL ALASKA...CC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...MO
LONG TERM...DEK