Blizzard in Alaska, December 7 to 8, 2012

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
200 PM AKST FRI DEC 7 2012

.ANALYSIS AND UPPER LEVELS...
A MUCH MORE ACTIVE PATTERN IS SETTING UP OVER SOUTHERN ALASKA AND
THE BERING SEA/ALEUTIAN ISLANDS. A STRONG LOW IS SPINNING UP SOUTH
OF THE ALEUTIANS AND MOVING NORTH. AN UPPER LOW OVER MAINLAND ALASKA
IS RETREATING NORTHWARD. THERE IS A TRANSIENT RIDGE BETWEEN THESE
TWO LOWS THAT STRETCHES FROM THE PRIBILOFS ACROSS THE ALASKA
PENINSULA (AKPEN) AND SOUTHEASTWARD INTO THE EASTERN PACIFIC.

THERE ARE SEVERAL FRONTS ASSOCIATED WITH THE ALEUTIAN LOW. THERE
IS AN OCCLUDED FRONT THAT STRETCHES FROM THE CENTRAL ALEUTIANS
EASTWARD ALONG 50 DEGREES NORTH LATITUDE TO ABOUT 155 DEGREES WEST
LONGITUDE. FROM THAT "TRIPLE POINT" A WARM FRONT STRETCHES EAST AND
A COLD FRONT TRAILS TO THE SOUTH.

.MODEL DISCUSSION...
GUIDANCE IS IN GOOD AGREEMENT UNTIL ABOUT 60 HOURS INTO THE FORECAST
WHEN THEY START TO DIVERGE ON HOW THEY HANDLE THE TRANSITION OF THE
MAJOR LOW AS IT MOVES INLAND...AND HOW THEY HANDLE DEVELOPMENT OF
OTHER LOWS AROUND ITS PERIPHERY. FORECASTS GENERALLY FOLLOW THE NAM
FOR THE GULF AND SOUTH CENTRAL...AND THE ECMWF FOR SOUTHWEST ALASKA
AND THE BERING SEA/ALEUTIANS.

.SHORT TERM FORECAST...
THE ALEUTIAN LOW WILL MOVE NORTH THROUGH SATURDAY THEN SLOWLY TURN
NORTHEAST BEFORE MOVING INLAND SUNDAY AFTERNOON. AT THAT POINT IT
BECOMES AN OPEN WAVE AND WESTERLY FLOW ALOFT DEVELOPS ACROSS THE
AREA. CYCLONIC FLOW WILL CONTINUE OVER SOUTHERN ALASKA ON MONDAY
WITH A WEAK RIDGE BUILDING OVER THE CENTRAL ALEUTIANS AND BERING
SEA.

FOR SOUTHWEST ALASKA/ALEUTIANS/BERING SEA...SEVERE WINTER WEATHER
WILL AFFECT MOST OF THE AREA DURING THE WEEKEND AS THE LOW AND
OCCLUDED FRONT MOVE ACROSS THE AREA. THE OCCLUDED FRONT WILL MOVE
INTO THE CENTRAL ALEUTIANS AND AKPEN THIS EVENING...INTO THE
PRIBILOFS AND BRISTOL BAY AREA SATURDAY MORNING...THEN INTO THE
KUSKOKWIM DELTA SATURDAY AFTERNOON. BLIZZARD CONDITIONS ARE POSSIBLE
IN THESE AREAS AS THE FRONT MOVES THROUGH. BEHIND THE FRONT WARMER
AIR WILL CHANGE PRECIPITATION TO RAIN FOR THE AKPEN AND EASTERN
ALEUTIANS.

FOR SOUTH CENTRAL ALASKA/NORTHERN GULF OF ALASKA...
PRECIPITATION ASSOCIATED WITH THE WARM/OCCLUDED FRONT WILL MOVE INTO
THE NORTHERN GULF OF ALASKA TONIGHT. AS THE FRONT MOVES INTO SOUTH
CENTRAL ALASKA ON SATURDAY AND SATURDAY NIGHT MOST AREAS WILL SEE
SOME SNOW. HIGHEST AMOUNTS WILL BE ON THE EASTERN KENAI PENINSULA
WITH ONE TO TWO FEET OF SNOW POSSIBLE OVER THE HIGHER ELEVATIONS FOR
THE WEEKEND. FOR ANCHORAGE AND THE MATANUSKA VALLEY AMOUNTS WILL BE
GENERALLY LESS THAN TWO INCHES.

BLIZZARD CONDITIONS ARE POSSIBLE IN THE PORTAGE VALLEY WITH THE
ONSET OF THE SNOW AND WINDS STARTING LATE SATURDAY MORNING...THEN
THROUGH THOMPSON PASS BEGINNING SATURDAY AFTERNOON.

THE PRECIPITATION WILL LIKELY TURN TO RAIN FOR AREAS ALONG THE GULF
COAST...PROBABLY MAKING THE SWITCH SATURDAY MORNING ON KODIAK AND
SATURDAY NIGHT NEAR CORDOVA. PRECIPITATION TYPE SHOULD STAY ALL SNOW
FOR MOST INLAND LOCATIONS.

PRECIPITATION WILL CONTINUE FOR SUNDAY AND SUNDAY NIGHT AS THE UPPER
LOW OPENS UP AND ALLOWS SOUTHWESTERLY FLOW ALOFT INTO THE AREA.
PRECIPITATION WILL TAPER OFF TO MAINLY SCATTERED SHOWERS FOR MONDAY.

.LONG TERM FORECAST...
THERE WILL BE A BRIEF BREAK IN THE WEATHER ON TUESDAY AS A SHORT
WAVE RIDGE MOVES ACROSS THE AREA. FOR THE REST OF THE WEEK THE
WEATHER WILL BE MORE ACTIVE AS PROGRESSIVE WESTERLY FLOW WILL SEND A
SERIES OF SYSTEMS ACROSS THE AREA.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...BLIZZARD WARNING 181 185 187 195.
         BLIZZARD WATCH 125 131 155 161.
MARINE...STORM WARNING 120 130 138 150 155 170 172 179.
         GALE WARNING 132 140 160 165 175 176 180 185.
         HEAVY FREEZING SPRAY 126 127 140 160 179 185.
FIRE WEATHER...NONE.

LUDWIG DEC 12