High Wind in Alaska, December 7, 2011

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
500 AM AKST WED DEC 7 2011

.ANALYSIS AND UPPER LEVELS...
AFTER THE QUIET WEATHER OF THE PAST COUPLE DAYS THINGS ARE STARTING
TO GET INTERESTING AGAIN AS NICE PLUME OF MOISTURE IN SOUTHWESTERLY
FLOW HEADS TOWARD SOUTH CENTRAL ALASKA. CURRENTLY A DIPOLE SETUP
EXISTS IN THE UPPER LEVELS WITH A CLOSED HIGH PRESSURE OVER THE
NORTHEASTERN PACIFIC AND A CLOSED LOW OVER THE BERING SEA. THE
PACIFIC HIGH HAS BEEN ANCHORED THERE SINCE THE PATTERN CHANGE TWO
WEEKS AGO AND HAS A RIDGE EXTENDING THROUGH SOUTH CENTRAL ALASKA
CURVING UP THROUGH THE SEWARD PENINSULA AND THE CHUKCHI PENINSULA.
THE HIGH IS BROUGHT BY A NEGATIVE EASTERN PACIFIC OSCILLATION. THE
PREVIOUS EPISODES OF NEGATIVE EPO INDEX HAVE BEEN FAIRLY SHORT LIVED
SO DON'T EXPECT THE PATTERN TO HANG AROUND FOR LONG. THE FLOW BETWEEN
THESE TWO CENTERS FEATURES A STOUT 100KT JET FROM SOUTHWEST TO
NORTHEAST INTO THE SOUTHWESTERN MAINLAND. THE FRONT ASSOCIATED WITH
THE BERING SYSTEM HAS ALREADY BROUGHT SNOW...BLOWING SNOW AND BOUTS
OF BLIZZARD CONDITIONS TO THE YUKON DELTA AND BRISTOL BAY REGIONS. AT
THE SURFACE...A LARGE HIGH SPRAWLS OVER NORTHWEST TERRITORIES AND
YUKON. THE PRESSURE GRADIENT OVER THE MAINLAND IS TIGHTENING AS A
BOMBING LOW MOVES NORTH IN THE BERING SEA. THE LOW PRESSURE AND ITS
ASSOCIATED FRONT ALONG WITH A SURGE OF WARM MOIST AIR NORTHWARD WILL
BE THE FOCUS OF THE FORECAST IN THE COMING DAYS.

.MODEL DISCUSSION...
THE BIGGEST QUESTION IN THE SHORT TERM IS THE DEVELOPMENT OF A TRIPLE
POINT LOW IN THE GULF. RIGHT NOW ALL GUIDANCE POINTS TO AN OPEN
SURFACE TROUGH MOVING INTO THE GULF TONIGHT INTO THURSDAY MORNING.
GUIDANCE HANDLES THE UPPER LEVEL PATTERN VERY SIMILARLY FOR THE SHORT
TERM AND EVEN INTO EARLY NEXT WEEK FOR THE ALASKA REGION. THERE IS
SOME DISAGREEMENT WITH THE AMOUNT OF AMPLIFICATION OF A SHORTWAVE
TROUGH MOVING EASTWARD IN THE NORTHERN PACIFIC SOUTH OF THE GULF OF
ALASKA. THE EFFECT ON OUR WEATHER WOULD BE MINIMAL WITH THAT FEATURE.
THE SURFACE PATTERN AGREEMENT BREAKS DOWN A LITTLE SOONER. THE EXACT
POSITION OF THE SURFACE LOW IN THE NORTHERN BERING IS IN QUESTION AS
IT FILLS AND ROTATES AROUND...ANOTHER LOW IMPACT DISCREPANCY. TOWARD
THE WEEKEND THERE IS MORE UNCERTAINTY IN A BROAD LOW MOVING INTO THE
WESTERN BERING SEA. ALL GUIDANCE SHOWS A BROAD DEEP LOW BUT DISAGREE
WITH TIMING AND PLACEMENT OF BOTH THAT AND THE ASSOCIATED
FRONTS/TRIPLE POINT LOWS THAT DEVELOP.

.SHORT TERM FORECAST...
SOUTH CENTRAL ALASKA...AHEAD OF THE APPROACHING FRONT MID AND HIGH
LEVEL CLOUDS HAVE STREAMED OVER MUCH OF THE AREA. EXPECT THE OVERCAST
TO CONTINUE AS CEILINGS WILL LOWER THROUGHOUT THE DAY. PRECIPITATION
WILL SPREAD NORTHWARD TODAY ESPECIALLY FOR THE NORTHERN GULF COAST.
FORECAST CHALLENGES WITH THIS REGIME WILL MAINLY BE WHERE THE
RAIN/SNOW LINE SETS UP FOR THE GULF COAST AND TIP OF THE KENAI
PENINSULA. MUCH OF THE SOUTH CENTRAL WILL STAY COLD ENOUGH FOR
PRECIPITATION TO REMAIN SNOW. THE HOMER AREA WILL BE THE EDGE OF THE
WARM AIR AND WILL LIKELY SEE A MIX OF PRECIPITATION BEFORE CHANGING
TO MOSTLY RAIN. WESTERN PRINCE WILLIAM SOUND LOOKS TO STAY SOLIDLY IN
SNOW WHILE THE EASTERN SOUND WILL SEE A MIX OF PRECIPITATION SOME
AREA GETTING ALL RAIN. THE ANCHORAGE BOWL AND MAT-SU WILL STAY
DOWNSLOPED AND MOSTLY DRY IN THE SOUTHEASTERLY FLOW THROUGH THE DAY.
CHANCES FOR SNOW WILL INCREASE IN THE EVENING AND INTO THE OVERNIGHT
HOURS AS THE SOUTHEAST FLOW BEGINS TO SLACKEN. LIGHT SNOW WILL
CONTINUE INTO THURSDAY MORNING. ANOTHER ROUND OF SNOW IS IN STORE
THURSDAY AFTERNOON INTO FRIDAY MORNING.

SOUTHWEST ALASKA...SNOW CONTINUES FOR A GOOD PORTION OF THE MAINLAND
AS WARM ADVECTION CONTINUES ALONG WITH GUSTY EASTERLY WINDS. THE
FORECAST HERE TODAY WILL REVOLVE AROUND THE EXTENT AND NORTHEASTWARD
PUSH OF WARM AIR FROM THE COAST. RAIN IS LIKELY TO MIX WITH SNOW FOR
MOST LOCATIONS. THE WARM AIR WON'T STICK AROUND FOR LONG AS A COLD
AIR STREAMS BACK IN FROM THE WEST EARLY THURSDAY MORNING TURNING
THINGS BACK TO ALL SNOW. PRECIPITATION WILL TURN SHOWERY THROUGHOUT
THE DAY TODAY AS THE WARM AIR SURGES NORTHWARD.

BERING SEA AND ALEUTIANS...THE BRUNT OF PRECIPITATION AND WINDS HAS
PASSED OFF TO THE NORTH AND EAST THOUGH RAIN SHOWERS REMAIN POSSIBLE
FOR MOST LOCATIONS. COLDER AIR WILL RETURN TO THE WESTERN CHAIN TODAY
BRINGING THE POSSIBILITY FOR SNOW TO MIX IN WITH THE RAIN. RAIN
SHOWERS WILL STAY THE NORTH FOR THE CENTRAL AND EASTERN ALEUTIANS
WITH LIGHTER WINDS.

.LONG TERM FORECAST...
FOR THE EXTENDED FORECAST THE PATTERN BEGINS TO CHANGE SLIGHTLY AS
THE NORTHEAST PACIFIC RIDGE MIGRATES EASTWARD. THE LARGE SCALE
TROUGHING OVER THE BERING WILL BE IN PLACE WITH A WEST/SOUTHWEST FLOW
FROM THE ALEUTIANS TO THE MAINLAND KEEPING A SIMILAR STORM TRACK IN
PLACE. LARGE LOWS IN THE BERING SEA WITH FRONTS/TRIPLE POINT LOWS
MOVING OVER THE GULF AND MAINLAND WILL BE THE PATTERN FOR THE TIME
BEING.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...BLIZZARD WARNING 155
MARINE...STORM 120 GALE 130 132 140 170 172 175 176 179 185 351 352
411 412 413 HEAVY FREEZING SPRAY 185
FIRE WEATHER...NONE

MTL DEC 11