High Wind in Alaska, December 30, 2012

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE ANCHORAGE AK
415 PM AKST SAT DEC 29 2012

UPDATED WATCH/WARNING SUMMARY

.ANALYSIS AND UPPER LEVELS...A MAJOR STORM WHICH MOVED ACROSS
SOUTHWEST ALASKA LAST NIGHT IS NOW WEAKENING OFF THE KUSKOKWIM
DELTA. STRONG GUSTY WINDS BEHIND THIS SYSTEM RELATED TO STRONG
PRESSURE RISES AND A TIGHT PRESSURE GRADIENT ARE WEAKENING ACROSS
THE SOUTHERN MAINLAND. THERE WON'T BE MUCH OF A BREAK BEFORE WINDS
BEGIN TO INCREASE AGAIN AHEAD OF AN EVEN STRONGER STORM SYSTEM
OVER THE NORTHEAST PACIFIC. THIS IS A MATURE CYCLONE WITH A CENTRAL
SURFACE PRESSURE APPROACHING 950 MB AND MULTIPLE CLOUD BANDS WRAPPED
AROUND THE CENTER. THUS...EXPECT IT TO BOTTOM OUT SOON AND THEN
BEGIN A VERY GRADUAL WEAKENING PROCESS. PRE-FRONTAL WINDS AND
PRECIPITATION ARE MAKING THERE WAY INTO THE SOUTHERN GULF EARLY
THIS AFTERNOON...SO EXPECT DETERIORATING CONDITIONS ACROSS MUCH
OF THE SOUTHERN MAINLAND AS WE HEAD INTO THE EVENING HOURS.

A LARGE COMPLEX SERIES OF UPPER LOWS ARE SPINNING OVER THE BERING
SEA AND ALEUTIANS...ALL RELATIVELY WEAK COMPARED TO THE NORTHEAST
PACIFIC SYSTEM.

.MODEL DISCUSSION...THERE HAS BEEN A TREND TOWARD A FURTHER EAST
TRACK OF THE PACIFIC LOW. HOWEVER...ALL OF THE MODELS ARE CURRENTLY
TOO FAR WEST WITH THE LOW POSITION BASED ON SATELLITE IMAGERY. WILL
CONTINUE TO MONITOR TRACK OF THE LOW AND MAKE THE NECESSARY
ADJUSTMENTS. FORECAST CHANGES ARE BASED PRIMARILY OFF THE GFS
WHICH INITIALIZED THE BEST IN ITS DEPICTION OF A SINGLE CONCENTRIC
LOW AND SEEMED TO BE CLOSE ON THE CENTRAL PRESSURE.

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...THE PRIMARY IMPACT OF THIS STORM FOR
SOUTHCENTRAL ALASKA WILL BE WIDESPREAD STRONG WINDS. HIGH WIND
WARNINGS ARE IN EFFECT FROM PORTAGE VALLEY AND TURNAGAIN ARM
AND INTO ANCHORAGE. THIS SYSTEM IS STRONGER THAN THE SYSTEM WHICH
TRACKED ACROSS SOUTHWEST ALASKA YESTERDAY AND LAST NIGHT. A FARTHER
EAST STORM TRACK IS ALSO FAVORABLE FOR STRONGER GAP WINDS OVER
SOUTHCENTRAL. THE OCCLUDED FRONT WILL GO ALOFT PRIOR TO REACHING
ANCHORAGE BUT STILL EXPECT PASSAGE OF AN UPPER LEVEL FRONT ALONG
WITH A STRONG MID-LEVEL JET TO ENHANCE WINDS AND HELP MIX THEM
DOWN TO THE SURFACE. THEREFORE...THE HIGH WIND WATCH WAS EXPANDED
THIS MORNING TO INCLUDE EAST ANCHORAGE AND THE LOWER HILLSIDE. IN
FACT...AS UPPER FRONT PASSES THROUGH AND SURFACE LOW MAKES NORTHWARD
PROGRESS OVER SOUTHWEST ALASKA LATER TOMORROW AFTERNOON EXPECT WINDS
TO SHIFT TO SOUTHEAST OVER ALL OF THE ANCHORAGE BOWL.

IN ADDITION TO THE STRONG WINDS THIS STORM WILL RESUPPLY THE WARM
AIR WHICH IS IN PLACE. EXPECT A RAIN EVENT FOR MOST OF SOUTHCENTRAL
WITH TEMPERATURES IN THE 40S OR EVEN INTO THE 50S IN A FEW LOCATIONS.
THE ONE NOTABLE EXCEPTION WILL BE THOMPSON PASS WHERE TEMPERATURES
SHOULD REMAIN JUST COLD ENOUGH TO PRODUCE HEAVY WET SNOW.

WINDS AND PRECIP WILL GRADUALLY DIMINISH SUNDAY NIGHT AS THE STORM
EXITS ACROSS THE SOUTHWEST ALASKA COAST. HOWEVER...YET ANOTHER STRONG
STORM SYSTEM WILL TAKE A SIMILAR TRACK TO THIS STORM MONDAY THROUGH
TUESDAY. THUS THERE IS A GOOD CHANCE THERE COULD BE VERY SIMILAR
IMPACTS.

SOUTHWEST ALASKA...THE PACIFIC STORM WILL TRACK RIGHT ACROSS
SOUTHWEST ALASKA WITH THE STRONGEST WINDS RIGHT AHEAD AND RIGHT
BEHIND THE LOW. THE STRONGEST PRESSURE GRADIENTS WILL BE TO THE
EAST OF THE LOW CENTER OVER THE GULF AND SOUTHCENTRAL...SO DON'T
EXPECT WINDS TO BE NEARLY AS STRONG OVER SOUTHWEST ALASKA. PRECIP
TYPE WILL BE PRIMARILY RAIN OVER BRISTOL BAY WITH A MIX OF PRECIP
TYPES OVER THE KUSKOKWIM VALLEY AND KUSKOKWIM DELTA AS WARMER AIR
MOVES IN WITH THE LOW. ANY FREEZING RAIN THAT FALLS SHOULD BE SHORT
LIVED WITH LITTLE OR NO IMPACT...SO DO NOT PLAN TO ISSUE ANY
ADVISORIES AT THIS POINT IN TIME.

BERING SEA/ALEUTIANS...A SERIES OF LOWS OVER THE BERING SEA AND
ALEUTIANS WILL ALL WEAKEN AND BE ABSORBED INTO THE FLOW ON THE
BACK SIDE OF THE MAJOR STORM TO THE EAST AS IT TRACKS TO SOUTHWEST
ALASKA ON SUNDAY. A STRONG FRONT WILL MOVE TO THE WESTERN ALEUTIANS
MONDAY AND THEN SLIDE EASTWARD TUESDAY TO THE SOUTH OF THE WEAKENING
LOW OFF THE KUSKOKWIM DELTA COAST.

.LONG TERM FORECAST...UPPER TROUGH LOOKS TO REMAIN CENTERED OVER
THE BERING SEA WITH A RIDGE OVER THE WESTERN U.S. THEREFORE...AN
ACTIVE PATTERN WILL PERSIST ACROSS THE REGION.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...HIGH WIND WARNING 101 125.
MARINE...STORM WARNING 120 125 130 132 138 150 155.
         GALE WARNING...128 129 140 141 160 165 175 176 185.
         HEAVY FREEZING SPRAY 185.
FIRE WEATHER...NONE.

SEB DEC 12