Blizzard in Alaska, December 10, 2010

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
500 AM AKST FRI DEC 10 2010

.ANALYSIS AND UPPER LEVELS...THE STABLE AND HIGHLY AMPLIFIED UPPER
LEVEL PATTERN CONTINUES...AND FEATURES A STRONG RIDGE OVER THE
WESTERN BERING AND A DEEP TROUGH OVER THE GULF OF ALASKA. BETWEEN
THESE FEATURES A 130 KT JET PLUNGES DOWN FROM THE NORTH ACROSS THE
WEST COAST OF THE STATE. AT THE SURFACE...A RELATIVELY WEAK LOW IN
THE NORTHWEST GULF IS DRIFTING NORTHWARD TOWARD THE KENAI PENINSULA.
ALMOST ALL PRECIPITATION WITH THIS LOW IS FALLING AS SNOW...AND HAS
SPREAD INTO PRINCE WILLIAM SOUND AS WELL AS THE EASTERN KENAI
PENINSULA. OUT WEST...SURFACE HIGH PRESSURE OVER THE WESTERN
ALEUTIANS IS CREATING VERY BENIGN CONDITIONS OVER MUCH OF THE BERING
SEA...WITH THE EXCEPTION OF STRONG NORTHERLY WINDS THAT ARE
CONTINUING OVER THE AKPEN AND SOUTHWEST MAINLAND.

.MODEL DISCUSSION...SHORT TERM MODELS ARE IN RELATIVELY GOOD
AGREEMENT AS LONGWAVE PATTERN REMAINS STABLE THROUGH EARLY NEXT WEEK.
BY MIDWEEK...GFS BREAKS DOWN THE UPPER RIDGE OVER THE BERING...WHILE
THE EC AND HPC GUIDANCE KEEP THE RIDGE INTACT. THIS DIFFERENCE ALSO
LEADS TO DIFFERENCES IN THE SPEED OF AN UPPER LOW DROPPING SOUTH
ACROSS THE MAINLAND AROUND MIDWEEK. AT THIS TIME...FORECAST RELIES
PRIMARILY ON HPC GUIDANCE WHICH SIDES WITH THE MORE STABLE EC
SOLUTION.

.SHORT TERM FORECAST...
.EAST OF THE ALASKA RANGE...PRIMARY FORECAST CHALLENGE TODAY WILL BE
COVERAGE OF SNOWFALL ASSOCIATED WITH THE LOW IN THE NORTHERN GULF.
CURRENT SATELLITE AND RADAR ECHOS SHOW A CONTINUED NORTHWARD MOVEMENT
WITH THE ENTIRE FEATURE...BRINGING WIDESPREAD SNOWFALL INTO PRINCE
WILLIAM SOUND AND THE EASTERN KENAI PENINSULA. SNOW HAS CHANGED TO
RAIN IN CORDOVA...BUT WILL LIKELY CHANGE BACK TO SNOW BY LATER TODAY.
MEANWHILE A BLIZZARD WARNING REMAINS IN EFFECT THROUGH THOMPSON
PASS...WHERE CONDITIONS HAVE DETERIORATED SIGNIFICANTLY OVERNIGHT AND
SIGNIFICANT SNOWFALL WILL CONTINUE THROUGHOUT THE DAY. THE MOST
UNCERTAINTY IN THE FORECAST INVOLVES HOW FAR WEST THE SNOW SHIELD
WILL SPREAD THIS AFTERNOON...WITH THE NAM AGGRESSIVELY BRINGING
MODERATE SNOW INTO ANCHORAGE...AND THE GFS KEEPING ANCHORAGE DRY
THROUGH SATURDAY MORNING. AT THIS POINT MOST LIKELY SCENARIO SEEMS TO
BE AN EXTENDED PERIOD OF FLURRIES OR LIGHT SNOW IN ANCHORAGE THAT MAY
ACCUMULATE A FEW INCHES BY MIDDAY SATURDAY.

.SOUTHWEST MAINLAND...CLEAR SKIES WILL PREVAIL ACROSS MOST OF THE
MAINLAND THIS MORNING. THE MOST SIGNIFICANT FEATURE WILL BE CONTINUED
WINDY CONDITIONS FROM THE AKPEN EASTWARD. COMBINED WITH VERY COLD
TEMPERATURES...WIND CHILLS ARE ALREADY 30 BELOW ZERO IN SOME
AREAS...AND WILL CONTINUE UNTIL WINDS DIMINISH TOMORROW AFTERNOON.

.BERING SEA AND ALEUTIANS...WINDY CONDITIONS WILL CONTINUE OVER THE
EASTERN BERING THROUGH THE WEEKEND AS THE PRESSURE GRADIENT REMAINS
TIGHT. FURTHER WEST...RELATIVELY BENIGN CONDITIONS PERSIST AS HIGH
PRESSURE REMAINS PARKED OVERHEAD.

.LONG TERM FORECAST...GENERAL PATTERN TO CONTINUE THROUGH AT LEAST
MIDWEEK. MODELS ARE BEGINNING TO COME INTO AGREEMENT ON AN ADDITIONAL
PUSH OF COLD AIR MOVING INTO SOUTHCENTRAL AROUND
MIDWEEK...POTENTIALLY BRINGING THE COLDEST AIR OF THE SEASON TO MANY
AREAS.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...BLIZZARD WARNING 131
MARINE...GALE 121 130 150 155 160 165 180 170 171
         HEAVY FREEZING SPRAY 121 140 150 160 180
FIRE WEATHER...NONE

AMD DEC 10