Blizzard in Alaska, December 31, 2010

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
555 AM AKST FRI DEC 31 2010

.MODEL DISCUSSION...

MODELS ARE IN OVERALL GOOD AGREEMENT. ONLY MINOR CHANGES NEEDED TO
THE EXISTING FORECAST FOR WINDS AND PRECIPITATION TYPE...ESPECIALLY
FOR THIS MORNING.

.ANALYSIS AND UPPER LEVELS...

A STRONG LOW PRESSURE SYSTEM IS CURRENTLY MOVING NORTH THROUGH THE
COOK INLET REGION HEADED FOR THE INTERIOR OVER THE NEXT 12 TO 24
HOURS. THE NEXT LOW IS IN THE NORTH PACIFIC SOUTH OF THE ALEUTIANS
AND APPEARS IMPRESSIVE ON INFRARED SATELLITE IMAGERY THIS MORNING.
THIS SYSTEM WILL MAKE A LEFT TURN AND HEAD NORTH JUST TO THE WEST OF
THE SOUTHWEST MAINLAND LATER TONIGHT THROUGH SATURDAY NIGHT. A STRONG
FRONTAL BOUNDARY WILL AGAIN MOVE NORTH AND EAST ACROSS THE REGION IN
ASSOCIATION WITH THIS LOW. A THIRD SYSTEM WILL FOLLOW ON THE HEELS OF
THE SECOND LOW AND AFFECT THE REGION FROM LATE SUNDAY THROUGH AT
LEAST MONDAY.

.SHORT TERM FORECAST...

SOUTH AND EAST OF THE ALASKA RANGE...

OBSERVATIONS IN THE COOK INLET REGION AND DATA FROM THE UPPER AIR
RADIOSONDE AT ANCHORAGE THIS MORNING INDICATE A DEEP WARM LAYER NEAR
THE SURFACE. TEMPERATURES IN THE 30S WITH RAINFALL IN ASSOCIATION
WITH THE LOW WILL ASSURE THAT MOST AREAS SEE RAIN...WITH ONLY
ISOLATED POCKETS OF FREEZING RAIN. THE WINTER STORM WARNING FOR SNOW
IN THE SUSITNA VALLEY IS ON TRACK AS SPOTTER REPORTS WOULD SUGGEST AT
LEAST A FOOT HAS ALREADY FALLEN SOME PLACES. AN ADDITIONAL 6 TO 12
INCHES WITH ISOLATED HEAVIER AMOUNTS IN THE NORTHERN VALLEY ARE
LIKELY THROUGH LATE THIS AFTERNOON.

THE NEXT SYSTEM MOVES INTO THE REGION TONIGHT. WITH THIS LOW MOVING
MOVING THROUGH THE FAR EASTERN BERING SEA...THIS SYSTEM WILL HAVE
MORE WARM AIR TO WORK WITH SUCH THAT LOCATIONS ALONG THE NORTHERN
GULF COAST WILL MIX WITH OR CHANGE OVER TO RAIN. SOUTH-SOUTHEASTERLY
FLOW INITIALLY WILL CAUSE DOWNSLOPE DRY HOLE OVER THE WESTERN SLOPES
OF THE CHUGACH...ESPECIALLY NORTH OF THE KENAI PENINSULA...BUT THEN
FLOW WILL VEER TO A MORE SOUTH-SOUTHWESTERLY DIRECTION SOMETIME AFTER
NOON THURSDAY WHICH WILL LIKELY HELP PRECIPITATION MAKE IT INTO THE
ANCHORAGE BOWL. STRONG WINDS WILL BE LIKELY THROUGH TURNAGAIN ARM AND
HIGHER ELEVATIONS BEGINNING EARLY SATURDAY AND LASTING INTO SUNDAY
AFTERNOON BEFORE DIMINISHING.

SOUTHWEST ALASKA...

THE CURRENT SYSTEM AFFECTING THE REGION WILL CONTINUE TO MOVE NORTH
AND EAST OUT OF THE AREA THIS MORNING. THE WINTER WEATHER ADVISORY
FOR THE KUSKOKWIM VALLEY WILL LIKELY BE ALLOWED TO EXPIRE AS FORECAST
TIMING OF THE SYSTEM APPEARS TO BE ON TRACK. ATTENTION THEN TURNS TO
THE NEXT BIG SYSTEM WHICH WILL BEGIN TO AFFECT THE REGION THIS
EVENING. MODEL FORECASTS ARE IN GOOD AGREEMENT THAT THIS MAY POSE
SOME SIGNIFICANT IMPACTS FOR MOST OF THE SOUTHWEST MAINLAND. THE
EVENT SHOULD BEGIN THIS EVENING AS SNOW...BUT STRONG WARMING JUST OFF
THE SURFACE WILL LIKELY ALLOW THE SNOW TO CHANGE OVER TO FREEZING
RAIN FOR A PERIOD OF TIME. THERE ARE STILL LOTS OF QUESTIONS AS TO
WHEN THE CHANGEOVER OCCURS AND HOW FAST IT OCCURS...BUT THERE IS THE
CHANCE THAT A QUARTER INCH OF ICE FALLS ACROSS MANY PLACES BEFORE AN
EVENTUAL CHANGEOVER TO ALL RAIN...ESPECIALLY NEAR DILLINGHAM. WITH
THE MORNING FORECAST PACKAGE WINTER STORM WATCHES HAVE BEEN ISSUED
FOR THE BRISTOL BAY AND KUSKOKWIM DELTA ZONES. AN ADDITIONAL WATCH
MAY BE NECESSARY LATER TODAY FOR THE MIDDLE KUSKOKWIM VALLEY.

BERING SEA/ALEUTIANS...

MAIN FORECAST CONCERN WILL BE THE POSSIBILITY OF BLIZZARD CONDITIONS
FOR THE PRIBILOFS LATE SATURDAY MORNING THROUGH THE AFTERNOON ON THE
BACK SIDE OF THE LOW WHICH WILL MOVE NORTH THROUGH THE EASTERN
BERING. THE MAIN SNOWFALL WILL OCCUR WITH WINDS IN THE 15 TO 25 MPH
RANGE...BUT WINDS WILL INCREASE SIGNIFICANTLY LATER IN THE MORNING
WHICH COULD CREATE BLOWING SNOW CONDITIONS. WILL STAY ON TOP OF THIS
AS THE EVENT DRAWS CLOSER. OTHERWISE...MAINLY COLD ADVECTION SHOWERS
WILL OCCUR ON THE BACK SIDE OF THE LOW PRESSURE SYSTEM MOVING BY TO
THE SOUTH AND EAST ACROSS THE ALEUTIAN CHAIN.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...WINTER STORM WARNING...145
         WINTER STORM WATCH...155 161
         WINTER WEATHER ADVISORY...152
MARINE...GALES...120 125 129 132 138 140 141 150 155 160 165 170 171
                 172 179 185
         STORMS...130
         HVY FRZG SPRY...179 185
FIRE WEATHER...NONE.

CC DEC 10