Blizzard and High Wind in Alaska, December 6 to 7, 2011

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
500 AM AKST TUE DEC 6 2011

.ANALYSIS AND UPPER LEVELS...
THE MAJOR FEATURE IN ALASKAN WEATHER TODAY IS THE LARGE STACKED LOW
OVER THE WESTERN ALEUTIANS. A POTENT SHORTWAVE TROUGH IS WORKING
TOWARD THE CENTRAL ALEUTIANS ROTATES AROUND THE BASE OF THE UPPER
LOW. A LARGE RIDGE AXIS STRETCHES FROM THE ALASKAN PENINSULA THROUGH
THE NORTHERN BERING AND WRAPS AROUND THE UPPER LOW TOWARD KAMCHATKA.
MUCH OF MAINLAND ALASKA LIES IN A TEMPORARY WESTERLY ZONAL FLOW. AT
THE SURFACE...A BROAD HIGH ENCOMPASSES MUCH OF THE GULF AND
NORTHEASTERN PACIFIC. THE REST OF THE MAINLAND STAYS UNDER A VERY
WEAK PRESSURE GRADIENT. OUT WEST...A MATURE SURFACE LOW COVERS MUCH
OF THE BERING SEA WITH AN OCCLUDED FRONT WRAPPING AROUND THE LOW
EASTWARD TOWARD ST. PAUL THEN SOUTHEASTWARD OVER THE EASTERN
ALEUTIANS.

.MODEL DISCUSSION...
MODELS IN EXCELLENT AGREEMENT WITH THE UPPER LEVEL PATTERN AND THE
MAJOR FEATURES IN THE SHORT TERM. SEVERAL SHORTWAVE TROUGHS WILL
ROTATE AROUND THE UPPER LOW OVER THE CENTRAL BERING. THE SECOND...A
MUCH MORE POTENT WAVE WILL TAKE OVER AS THE MAIN UPPER LOW CENTER
TOWARD MID WEEK. WHILE THERE STILL IS SOME SPREAD IN THE MODELS
REGARDING THE POSITION OF THE UPPER LOW MODELS ARE MUCH CLOSER
TOGETHER TODAY THAN YESTERDAY. THE POSITION OF THE MAIN LARGE SCALE
TROUGH IS ALSO WELL AGREED UPON. THE SAME HOLDS TRUE AT THE SURFACE.
GUIDANCE DEVELOPS A TRIPLE POINT LOW WITH THE SHORTWAVE TROUGH
APPROACHING THE CENTRAL ALEUTIANS. AS THE LOW DEEPENS IT TOO WILL
TAKE OVER AS THE MAIN SURFACE LOW CENTER. AS THE NEW LOW TAKES SHAPE
IN THE BERING AN OCCLUDED FRONT WILL PUSH EAST TOWARD THE MAINLAND
BRINGING THE NEXT SHOT OF PRECIPITATION.

.SHORT TERM FORECAST...
SOUTH CENTRAL ALASKA...PARTLY CLEAR TO MOSTLY CLOUDY CONDITIONS THIS
MORNING OVER THE ANCHORAGE BOWL AND MATANUSKA VALLEY WILL CLEAR OUT
THROUGHOUT THE DAY LEAVING SOME PASSING HIGHER CLOUDS. THE NEXT
CHANCE FOR ACTIVE WEATHER ACROSS THE AREA IS A FRONT STEMMING FROM A
BERING SEA LOW. THE FRONT WILL OVERTAKE THE AREA ON WEDNESDAY
RETURNING CLOUDY CONDITIONS TO MUCH OF THE SOUTHERN MAINLAND ALONG
WITH A SURGE OF WARM AIR FROM THE SOUTH. NOT QUITE AS MUCH AS THE
LAST SYSTEM THOUGH. THE ANCHORAGE BOWL WILL GET DOWNSLOPED FROM THIS
EVENT AS STRONG EASTERLIES LIE OUT AHEAD OF THE WARM AIR.
PRECIPITATION IN THE FORM OF SNOW LOOKS MORE LIKELY AS THE FRONT
PASSES AND DOWNSLOPING DIES DOWN. THE NORTHWARD SURGE OF WARM AIR IS
GOING TO MAKE PRECIPITATION TYPE A TRICKY FORECAST AROUND THE KENAI
PENINSULA AND NORTHERN GULF COAST WHICH WILL LIE RIGHT AROUND THE
RAIN/SNOW LINE. AS THE UPPER TROUGH HANGS AROUND LIGHT SNOW WILL
LINGER FOR MUCH OF THE SOUTH CENTRAL THROUGH FRIDAY.

SOUTHWEST ALASKA...TODAY'S FORECAST FOR THE SOUTHWEST REVOLVES AROUND
A COUPLE OF FRONTS. THE FIRST STRETCHES THE WIDTH OF THE BERING TO
THE WESTERN ALEUTIANS. THE FIRST FRONT WILL LIKELY ONLY AFFECT THE
KUSKOKWIM DELTA REGION AND THE SOUTHEASTERN SLOPE OF THE KILBUCKS.
THE MAIN IMPACT OF THE FIRST FRONT WILL BE BLIZZARD CONDITIONS IN THE
GUSTY SOUTHERLY WINDS. THE SECOND FRONT TO PUSH THROUGH WILL AFFECT
MOST OF THE SOUTHWEST ON TUESDAY EVENING INTO WEDNESDAY MORNING. THE
CHALLENGE WITH THE SECOND FRONT WILL BE HOW FAR INLAND THE WARM AIR
PUSHES. PRECIPITATION WILL LIKELY TURN FROM SNOW TO RAIN ON
WEDNESDAY AS THE FRONT PUSHES ONSHORE MOSTLY FOR COASTAL BRISTOL
BAY. MIXED PRECIPITATION WILL CONTINUE THROUGH LATE THURSDAY INTO
FRIDAY MORNING WITH INTERMITTENT BREAKS AFTER THE OCCLUDED FRONT
PASS TO THE COLD FRONT PASSAGE.

BERING SEA AND ALEUTIANS...WIDESPREAD RAIN CONTINUES FOR MUCH OF THE
CHAIN AS A NUMBER OF FEATURES AFFECT THE AREA. GUSTY WINDS OF GALE
FORCE AFFECT MUCH OF THE BERING AS THE SURFACE LOW SPINS OUT WEST.
THE FIRST OCCLUDED FRONT STRETCHES OVER THE EASTERN ALEUTIANS
BRINGING RAIN. THE FRONT WILL CONTINUE EAST AND QUICKLY BE REPLACED
BY A WARM FRONT WITH A DEVELOPING SURFACE LOW TO THE WEST. AS THE LOW
MOVES NORTH INTO THE BERING LATE TODAY THE SECOND OCCLUDED FRONT WILL
MOVE EASTWARD OVER THE EASTERN ALEUTIANS AND AKPEN BRINGING ANOTHER
SHOT OF RAIN. AS THE LOW SLOWLY FILLS IN THE BERING MIXED RAIN AND
SNOW SHOWERS WILL COVER MUCH OF THE BERING.

.LONG TERM FORECAST...
THE EXTENDED FORECAST LOOKS MUCH LIKE THE CURRENT PATTERN. LARGE
SCALE TROUGHING IN THE BERING WITH RIDGING FROM THE GULF OF ALASKA
THROUGH THE INTERIOR. STORM TRACKS FAVORED IN THIS REGIME ARE
DEVELOPING NORTHERN PACIFIC LOWS MIGRATING INTO THE BERING WITH
ASSOCIATED FRONTS/TRIPLE POINT LOWS PROGRESSING EASTWARD OVER THE
MAINLAND.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...BLIZZARD WARNING 155
MARINE...STORM 411 412 GALE 120 130 132 138 140 150 155 160 165 170
171 172 175 176 179 180 185 351 413 414 HEAVY FREEZING SPRAY 185
FIRE WEATHER...NONE

MTL DEC 11