Blizzard in Alaska, December 26, 2012

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
430 AM AKST WED DEC 26 2012

.ANALYSIS AND UPPER LEVELS...
THE ALASKAN DOMAIN HAS SETTLED INTO A STABLE OVERALL WEATHER PATTERN
THAT IS CHARACTERIZED BY A DEEP LONGWAVE TROUGH CENTERED OVER THE
BERING SEA WITH A RIDGE OVER THE EASTERN GULF OF ALASKA. THIS PUTS
MUCH OF THE MAINLAND UNDER SOUTHERLY FLOW WHICH HAS ALLOWED
TEMPERATURES TO WARM UP SIGNIFICANTLY COMPARED TO MUCH OF THE REST OF
THE MONTH SO FAR. THE REMNANTS OF THE UPPER TROUGH THAT BROUGHT SNOW
YESTERDAY TO SOUTHCENTRAL ARE LINGERING OVER PRINCE WILLIAM SOUND AND
THE WESTERN SUSITNA VALLEY...AND WILL CONTINUE TO DECREASE THROUGH
THE MORNING HOURS. THE NEXT MAJOR LOW IS ALREADY ROLLING TOWARD THE
ALASKA PENINSULA FROM THE SOUTH WITH A CENTRAL PRESSURE IN THE UPPER
950S. PRECIPITATION ASSOCIATED WITH THE MAIN WEATHER FRONT IS
KNOCKING ON THE DOORSTEP OF THE BRISTOL BAY ZONE AND KODIAK ISLAND.

.MODEL DISCUSSION...
MODELS ARE IN REASONABLY GOOD OVERALL AGREEMENT THROUGH THE FIRST 2
OR 3 DAYS. THE GFS IS A NOTABLE OUTLIER WITH RESPECT TO THE LONGEVITY
AND TRACK OF THE LOW CURRENTLY APPROACHING THE STATE. ALL THE OTHER
MODELS SUGGEST A WEAKENING LOW THAT DISSIPATED SOMEWHERE NORTH OF
KODIAK ISLAND THURSDAY EVENING. MEANWHILE...THE GFS KEEPS THE LOW
CIRCULATION INTACT AND MOVES IT INTO THE EASTERN GULF BEFORE
DISSIPATING. THE MAIN IMPACT OF THIS DISCREPANCY IS THE SPEED AND
DURATION OF WINDS FUNNELING THROUGH TURNAGAIN ARM AND AROUND THE COOK
INLET REGION AS THE GFS SOLUTION WOULD WEAKEN WINDS MUCH QUICKER.
BECAUSE IT IS SUCH AN OUTLIER...THIS SOLUTION WAS DISCARDED. OF
NOTE...THE 6Z GFS RUN HAS COME IN LINE WITH THE OTHER MODEL
SOLUTIONS...WHICH RAISES CONFIDENCE EVEN HIGHER. OUT WEST...BY THE
END OF THE SHORT TERM (84 HOUR) PERIOD...A PACIFIC LOW WILL MOVE INTO
THE CENTRAL ALEUTIANS AND STALL BY THE END OF THE WEEK. MODEL SUGGEST
THAT AS THE UPPER LEVEL CIRCULATION WEAKENS...THE CONSOLIDATED ENERGY
AT THE SURFACE WILL BREAK UP INTO MULTIPLE WEAKER SURFACE LOWS. THIS
SOLUTION MAKES SENSE AND IS STRONGLY FAVORED BY CLIMATOLOGY...BUT THE
DETAILS OF THESE LOWS ARE NOTORIOUSLY HARD TO PINPOINT MORE THAN
24-36 HOURS IN ADVANCE. THUS...WILL NOT TRY TO GET TOO FANCY WITH THE
MORNING FORECAST AND INSTEAD UTILIZE A BLEND OF MODEL SOLUTIONS TO
SMOOTH OUT SOME OF THE INDIVIDUAL DETAILS.

.SHORT TERM FORECAST...
SOUTHCENTRAL...PRIMARY FORECAST CHALLENGE OVER THE NEXT 24-36 HOURS
WILL BE THE APPROACH OF THE NEXT WEATHER FRONT...STARTING WITH KODIAK
ISLAND THIS MORNING AND SPREADING TOWARD PRINCE WILLIAM SOUND BY LATE
THIS AFTERNOON. EASTERLY WINDS WILL BE STRONG WITH THIS LOW...WHICH
SHOULD SET UP A CLASSIC UPSLOPE/DOWNSLOPE PATTERN ACROSS THE REGION.
THIS SHOULD KEEP ANCHORAGE MOSTLY DRY...WHILE THE WESTERN SUSITNA
VALLEY AND WHITTIER TO GIRDWOOD CORRIDOR SEE SUBSTANTIAL ACCUMULATING
SNOW ENHANCED BY THE MOUNTAINS. TEMPERATURES ARE STARTING OUT ABOVE
FREEZING AROUND PORTAGE AND WHITTIER...AND WITH ONSHORE WINDS
INCREASING THROUGHOUT THE DAY THINK BLIZZARD CONDITIONS WILL BE
AVOIDED AROUND PORTAGE...EVEN THOUGH THE INTENSITY OF THE SNOW WILL
STILL SIGNIFICANTLY RESTRICT VISIBILITY AROUND THE REGION.
MEANWHILE...NORTHERLY WINDS WILL STEADILY INCREASE FROM THE MATANUSKA
VALLEY TO KENAI AND HOMER AS THE PRESSURE GRADIENT AROUND COOK INLET
GRADUALLY INCREASES. THIS WILL ALSO HELP DISSIPATE AREAS OF LOW
CLOUDS AND FOG LINGERING AROUND COOK INLET THIS MORNING.

SOUTHWEST...MAIN STORY IS THE FRONT MOVING IN FROM THE SOUTH. WITH
VERY COLD TEMPERATURES IN PLACE AT THE SURFACE...AND WINDS EXPECTED
TO REMAIN OFFSHORE AS THE FRONT APPROACHES THIS MORNING...CONFIDENCE
HAS INCREASED THAT THE WESTERN CAPES OF BRISTOL BAY AS WELL AS THE
COAST OF THE KUSKOKWIM DELTA WILL SEE BLIZZARD CONDITIONS AS THE
FRONT MOVES THROUGH. THUS...BOTH WATCHES HAVE BEEN UPGRADED TO
WARNINGS. BLIZZARD CONDITIONS SHOULD BE RELATIVELY SHORT-LIVED ALONG
THE WESTERN CAPES AS THE FRONT PUSHES THROUGH BY LATE THIS
AFTERNOON...BUT WILL LIKELY PERSIST INLAND NORTH AND WEST OF
DILLINGHAM. NORTHERLY WINDS ACROSS THE REGION WILL RAPIDLY DIMINISH
EARLY THURSDAY MORNING AS THE LOW CENTER LOSES ITS ALREADY-LIMITED
UPPER LEVEL SUPPORT AND WEAKENS RAPIDLY.

BERING SEA AND ALEUTIANS...WITH THE LOW TRACKING SOUTH OF THE ALASKA
PENINSULA THE MOST SIGNIFICANT IMPACT TO THE EASTERN HALF OF THE
BERING SEA WILL BE STRONG NORTHERLY WINDS AND AREAS OF SNOW DURING
THE DAY TODAY. TEMPERATURES AT DUTCH HARBOR AND AROUND COLD BAY WILL
COOL SLOWLY THROUGHOUT THE DAY...ALLOWING SOME AREAS OF BLOWING SNOW
TO DEVELOP THIS AFTERNOON AND EVENING. NOT EXPECTING BLIZZARD
CONDITIONS AT THIS TIME AS COLD ADVECTION IS NOT OVERLY IMPRESSIVE
AND SEA SURFACE TEMPERATURES ARE STILL FAIRLY WARM THIS TIME OF YEAR.
HOWEVER...SNOWFALL RATES SHOULD BE FAIRLY IMPRESSIVE WHICH WILL
LIKELY RESTRICT VISIBILITY IN SOME AREAS. FURTHER WEST...PARTLY
CLOUDY CONDITIONS AND SNOW SHOWERS WILL CONTINUE THROUGH THIS
AFTERNOON BEFORE TEMPERATURES WARM AND SNOW TURNS TO RAIN TONIGHT AS
PACIFIC LOW MOVES IN. THE FRONT WILL CLIP ONLY THE WESTERN ALEUTIANS
TONIGHT...BUT SHOULD BE STRONG ENOUGH TO BRIEFLY BRING WINDS UP TO
STORM-FORCE.

.LONG TERM FORECAST...
WHILE THE EXACT DETAILS OF THE FORECAST IN THE LONG RANGE HAVE BELOW
AVERAGE CONFIDENCE...THE OVERALL WEATHER PATTERN SHOULD REMAIN LOCKED
IN WITH A LONGWAVE TROUGH TO THE WEST OF THE MAINLAND AND A RIDGE TO
THE EAST. THIS WILL KEEP THE RELATIVELY WARM AND MOIST CONDITIONS
GOING ACROSS THE SOUTHERN MAINLAND AND ALASKA PENINSULA...WITH
GENERAL NORTHERLY FLOW AND A RAIN/SNOW MIX OVER THE WESTERN HALF OF
THE BERING.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...BLIZZARD WARNING 155 161
MARINE...STORM 120 130 138 176
         GALE 125 132 140 141 150 155 160 165 170 171 172 175 179 180
              185
         HEAVY FREEZING SPRAY 179 185
FIRE WEATHER...NONE

DIXON DEC 12

SPECIAL WEATHER STATEMENT
NATIONAL WEATHER SERVICE ANCHORAGE AK
927 AM AKST WED DEC 26 2012

AKZ101-121-125-271500-

...BACKCOUNTRY AVALANCHE WARNING FOR THE KENAI AND WESTERN CHUGACH
MOUNTAINS IN AND AROUND THE EASTERN TURNAGAIN ARM AREA...

THE CHUGACH NATIONAL FOREST AVALANCHE INFORMATION CENTER HAS ISSUED
AN AVALANCHE WARNING FOR THE KENAI AND WESTERN CHUGACH MOUNTAINS IN
AND AROUND THE EASTERN TURNAGAIN ARM AREA.

DANGEROUS HUMAN TRIGGERED AVALANCHES ARE LIKELY IN THE BACKCOUNTRY.
NATURAL AVALANCHES ARE LIKELY DURING PERIODS OF HEAVY SNOWFALL AND
HIGH WIND. PEOPLE WITHOUT EXPERT AVALANCHE SKILLS ARE URGED TO STAY
OUT OF THE BACKCOUNTRY.

THIS AVALANCHE WARNING IS IN EFFECT UNTIL 600 AM AKST 12-27-2012.

THIS WARNING DOES NOT INCLUDE SKI AREAS...HIGHWAYS...OR RAILROADS
WHERE AVALANCHE REDUCTION WORK IS EXECUTED.

FOR THE FULL ADVISORY VISIT WWW.CNFAIC.ORG OR CALL 907-754-2369.