Heavy Freezing Spray Warning 185, NWS Anchorage, AK

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
1155 AM AKST FRI NOV 16 2012

.ANALYSIS AND UPPER LEVELS...SATELLITE IMAGERY SHOWS A HIGH AMPLITUDE
PATTERN IN PLACE ACROSS THE ALASKA REGION WITH A VERY NARROW (SHORT
WAVE-LENGTH) RIDGE CENTERED OVER THE EASTERN BERING AND TROUGHS ON
EITHER SIDE OF IT. A STRONG SHORT-WAVE TROUGH OVER THE WESTERN BERING
IS TRACKING RIGHT INTO THE RIDGE...AIDED BY A STRONG SUBTROPICAL JET
(MAX SPEED AROUND 170 KT). THIS IS TRANSPORTING A LOT OF MOISTURE
AND WARM AIR ACROSS THE ALEUTIANS AND INTO THE SOUTHERN BERING.
PRECIPITATION IS FOCUSED ALONG A FRONTAL SYSTEM WHICH EXTENDS FROM
A SURFACE LOW NEAR THE KAMCHATKA PENINSULA TO THE CENTRAL BERING
AND ALEUTIANS. A TRIPLE POINT LOW HAS DEVELOPED NORTH OF ATKA...BUT
FURTHER DEVELOPMENT IS NOT EXPECTED.

A LARGE CYCLONIC CIRCULATION DOMINATES THE GULF OF ALASKA AND
NORTHEAST PACIFIC...WITH A VERY TIGHT PRESSURE GRADIENT BETWEEN
THE SURFACE LOW IN THE GULF AND SURFACE HIGH OVER NORTHERN ALASKA.
THIS IS CONTRIBUTING TO STRONG GAPS WINDS ALONG THE COAST. MEANWHILE
AN UPPER LEVEL SHORT-WAVE IS DIGGING SOUTHWARD ACROSS SOUTHCENTRAL...
ADVECTING ARCTIC AIR SOUTHWARD AND HELPING TO MIX STRONG WINDS DOWN
TO THE SURFACE. THIS FEATURE WILL STRENGTHEN THE GAP WINDS AS IT
CONTINUES SOUTHWARD INTO THE GULF THIS AFTERNOON.

.MODEL DISCUSSION...MODELS ARE IN VERY GOOD AGREEMENT WITH SYNOPTIC
SCALE FEATURES. THERE ARE SOME MINOR DIFFERENCES WITH THE TRACK OF
THE TRIPLE POINT LOW ACROSS THE CENTRAL BERING. BASED ON SATELLITE
TRENDS PREFER THE MORE SOUTHERLY TRACK AS SEEN IN THE ECMWF SOLUTION.

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...EXPECT WINDY CONDITIONS TO DEVELOP ACROSS
MOST OF SOUTHCENTRAL THIS AFTERNOON AS UPPER TROUGH CONTINUES TO
PASS OVERHEAD AND HIGHER LEVEL WINDS MIX DOWN TOWARD THE SURFACE.
GAP WINDS WILL BE STRONGEST...AIDED BY A STRONG PRESSURE GRADIENT
AND COLD AIR ADVECTION. AS UPPER LEVEL SUBSIDENCE DIMINISHES TONIGHT
IN THE WAKE OF THE TROUGH EXPECT WINDS TO DIMINISH IN MANY AREAS AS
THE SURFACE DECOUPLES FROM THE UPPER LEVELS AND INVERSIONS SET BACK
UP. MEANWHILE...GAP WINDS WILL CONTINUE TO BLOW. THIS WILL CREATE
LARGE DIFFERENCES IN TEMPERATURE BETWEEN WINDY AREAS AND NON-WINDY
AREAS...MAKING FOR A VERY CHALLENGING MINIMUM TEMPERATURE FORECAST.
ANOTHER UPPER LEVEL SHORT-WAVE WILL DROP INTO SOUTHCENTRAL
SATURDAY...EVOLVING INTO AN UPPER LOW AND TRACKING SOUTHWARD INTO
THE WESTERN GULF AS WE HEAD THROUGH THE WEEKEND. THIS TROUGH/LOW
WILL HELP FORM A NEW SURFACE LOW OVER THE GULF HELPING TO RE-ENFORCE
THE SURFACE PRESSURE GRADIENT AND KEEP GAP WINDS GOING. THIS WILL
ALSO BRING A CHANCE OF SNOW TO THE NORTH GULF COASTAL AREAS...
ALTHOUGH OFFSHORE LOW LEVEL FLOW WILL ENSURE ONLY LIGHT ACCUMULATION.

SOUTHWEST ALASKA...AS SEEN IN THE 12Z KING SALMON SOUNDING
TEMPERATURE INVERSIONS OVER SOUTHWEST ALASKA ARE KEEPING MUCH
STRONGER WINDS ALOFT FROM MIXING DOWN TO THE SURFACE. AN UPPER
LEVEL WAVE WILL PASS THROUGH THE KUSKOKWIM VALLEY LATER TODAY AND
DOWN INTO BRISTOL BAY TONIGHT. THERE MAY BE JUST ENOUGH DOWNWARD
MOMENTUM WITH THIS WAVE TO BREAK THROUGH THE INVERSION IN SOME
LOCATIONS...BUT EXPECT ANY WINDS THAT DO DEVELOP TO BE LOCALIZED.
THAT WILL CHANGE AS WE HEAD THROUGH THE WEEKEND AS A MORE SIGNIFICANT
UPPER LOW DEVELOPS OVER SOUTHCENTRAL AND DIGS SOUTHWARD INTO THE
GULF. THE COMBINATION OF STRONGER DOWNWARD MOTION AND LOW LEVEL
COLD ADVECTION WILL BE ENOUGH TO PRODUCE MORE WIDESPREAD WINDS
SATURDAY NIGHT THROUGH MONDAY.

BERING SEA/ALEUTIANS...THE STRONG UPPER LEVEL JET WILL BARGE RIGHT
THROUGH THE RIDGE AXIS AND CONTINUE OFF TO THE NORTHEAST PACIFIC.
THIS WILL CAUSE FRONTAL SYSTEM TO ELONGATE AND SHEAR APART TONIGHT
AND SATURDAY. A NEW RIDGE WILL THEN DEVELOP AHEAD OF THE NEXT SYSTEM
MOVING OUT OF ASIA ON SUNDAY WHILE AN UPPER LEVEL LOW SETS UP OVER
THE WESTERN GULF. THIS WILL SET UP A COLD ADVECTION EVENT OVER THE
EASTERN BERING/EASTERN ALEUTIANS/ALASKA PENINSULA RESULTING IN
STRONG GUSTY NORTHERLIES AND SNOW SHOWERS. AS THE RIDGE MOVES
EASTWARD ON MONDAY ANOTHER FRONTAL SYSTEM WILL MOVE INTO THE
ALEUTIANS AND WESTERN BERING.

.LONG TERM FORECAST...EXPECT A FAIRLY STABLE PATTERN IN THE DAY 4
THROUGH 7 PERIOD WITH A MEAN RIDGE OVER THE BERING AND A MEAN LOW
IN THE GULF. THIS MEANS MAINLAND ALASKA WILL STAY ON THE DRY AND
COLD SIDE WITH GAP WINDS PERSISTING ACROSS PORTIONS OF SOUTHCENTRAL
AND SOUTHWEST ALASKA. STORMS COMING OUT OF ASIA WILL BE FORCED
NORTHWARD UP THE WEST SIDE OF THE BERING RIDGE...MAINTAINING AN
ACTIVE PATTERN OVER THE WESTERN ALEUTIANS.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...GALE WARNING...127 128 155 165 170 172 176 179 180 185.
         HEAVY FREEZING SPRAY WARNING...121 129 140 160 180.
FIRE WEATHER...NONE.

SEB NOV 12