High Wind Warning 18, NWS Anchorage, AK

252 
WWAK71 PAFC 221358
NPWAER

URGENT - WEATHER MESSAGE
NATIONAL WEATHER SERVICE ANCHORAGE AK
458 AM AKST TUE FEB 22 2011

AKZ125-221500-
/X.CAN.PAFC.HW.W.0018.000000T0000Z-110222T2100Z/
WESTERN PRINCE WILLIAM SOUND-
INCLUDING THE CITIES OF...WHITTIER...SEWARD...GIRDWOOD...
MOOSE PASS
458 AM AKST TUE FEB 22 2011

...HIGH WIND WARNING IS CANCELLED...

THE NATIONAL WEATHER SERVICE IN ANCHORAGE HAS CANCELLED THE HIGH
WIND WARNING. 

WINDS ARE EXPECTED TO INCREASE THIS MORNING BUT ARE NO LONGER
EXPECTED TO REACH WARNING CRITERIA. GUSTS TO 60 MPH NEAR WHITTIER
ARE POSSIBLE THROUGH THIS EVENING. 

$$

SOUTHCENTRAL AND SOUTHWEST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ANCHORAGE AK
1230 PM AKST MON FEB 21 2011

.ANALYSIS AND UPPER LEVELS...A TROUGH OVER EASTERN ASIA IS BEGINNING
TO DIG SOUTHEASTWARD INTO THE NORTHWEST PACIFIC AND WESTERN BERING.
THIS IS BEGINNING TO CAUSE AMPLIFICATION OF SHORT-WAVE RIDGE OVER
THE BERING SEA. AT THE MOMENT THE BERING AND SOUTHERN MAINLAND ARE
UNDER THE INFLUENCE OF STRONG ZONAL FLOW ON TOP OF A HIGH AMPLITUDE
RIDGE OVER THE NORTHEAST PACIFIC. 12 SOUNDINGS FROM BETHEL...
MCGRATH...AND ANCHORAGE ALL SHOW A 150KT+ JET UP AROUND 250 MB.
THE JET IS BEGINNING TO WEAKEN AND SHIFT TO THE SOUTHEAST AS
HEIGHTS RISE OVER THE BERING SEA. AT THE SURFACE HIGH PRESSURE IS
BUILDING OVER THE EASTERN BERING AND SOUTHWEST ALASKA AS WELL AS
INTO INTERIOR SOUTHCENTRAL. THIS IS CAUSING LOW LEVEL FLOW TO
SHIFT TO NORTHWESTERLY WHICH IN TURN IS PUSHING LOW LEVEL ARCTIC
AIR SOUTHWARD ACROSS THE GULF...RESULTING IN GALE FORCE WINDS.
OTHERWISE...CONDITIONS ARE CLEAR AND CALM ACROSS MOST OF THE
SOUTHERN MAINLAND.

.MODEL DISCUSSION...MODELS CONTINUE TO DIVERGE WITH HANDLING OF
STRONG PACIFIC LOW AS IT TRACKS ACROSS THE WESTERN ALEUTIANS AND
BERING SEA ON WEDNESDAY. ECMWF/UKMET ARE STRONGER AND SLOWER THAN
GFS/NAM. GFS ENSEMBLE MEAN MATCHES UP WELL WITH NAM POSITION (WHICH
IS SLOWER THAN GFS OPERATIONAL RUN). PLAN TO USE NAM POSITION AND
GFS STRENGTH AND MAKE MINOR CHANGES TO CURRENT FORECAST INSTEAD OF
GOING WITH ECMWF/UKMET WHICH WOULD RESULT IN LARGE CHANGES WITH LOW
CONFIDENCE. HANDLING OF BUILDING RIDGE OVER THE REST OF ALASKA IS
HANDLED SIMILARLY BY ALL MODELS AND FORECAST CONFIDENCE IS HIGH.

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...BERING SEA RIDGE WILL BECOME HIGHLY AMPLIFIED
THE NEXT COUPLE DAYS. THIS WILL INITIALLY FORCE A SHORT-WAVE OVER
INTERIOR ALASKA SOUTHWARD ACROSS SOUTHCENTRAL. DO NOT EXPECT ANY
PRECIPITATION WITH THIS WAVE...WITH THE EXCEPTION OF OVER THE
MOUNTAINS. ARCTIC AIR WILL CONTINUE TO ADVECT ACROSS SOUTHCENTRAL
ALASKA AND THE GULF. MEANWHILE...THE SURFACE HIGH WILL STRENGTHEN
AND BUILD OVER INTERIOR ALASKA SETTING UP A TIGHT PRESSURE GRADIENT
BETWEEN THE INTERIOR AND THE GULF. WHEN YOU PUT ALL OF THE FACTORS
TOGETHER YOU END UP WITH A CLASSIC WIND EVENT ALONG THE GULF COAST.

AT THIS POINT IT DOES NOT LOOK LIKE WARNING LEVEL WIND THRESHOLDS
WILL BE MET. HOWEVER...WITH THE PRESENCE OF THE STRONG UPPER JET
THOMPSON PASS MAY HAVE A SHOT AT COMING CLOSE. THE GREATER THREAT
FOR THOMPSON PASS IS BLIZZARD CONDITIONS. REPORTS INDICATE THAT
THERE IS STILL ENOUGH LOOSE DRY SNOW AVAILABLE TO BLOW AROUND.
THEREFORE...WILL CONSIDER ISSUING A BLIZZARD WATCH WITH THE
AFTERNOON FORECAST PACKAGE. THE UPPER RIDGE WILL BUILD EASTWARD
ACROSS THE MAINLAND BY WEDNESDAY BRINGING AN END TO THE WIND EVENT.
NON-COASTAL LOCATIONS OF SOUTHCENTRAL WILL SEE LITTLE IN THE WAY
OF WIND AND WILL THUS REMAIN COLD AND DRY FOR THE NEXT FEW DAYS.

SOUTHWEST ALASKA...HIGH PRESSURE WILL BUILD OVER SOUTHWEST ALASKA
TONIGHT PROVIDING FAVORABLE CONDITIONS FOR FOG FORMATION. THE
SURFACE HIGH WILL SLIDE OFF TO INTERIOR ALASKA MONDAY NIGTH AND
TUESDAY SO COASTAL AREAS WILL BEGIN TO SEE SOME WIND ON THE WEST
SIDE OF THE HIGH WHILE FOG WILL REMAIN A THREAT FOR INLAND AREAS.
THE UPPER RIDGE WILL REMAIN OVERHEAD THROUGH MID WEEK ENSURING DRY
AND COLD CONDITIONS CONTINUE ACROSS THE REGION.

BERING SEA/ALEUTIANS...AS UPPER RIDGE BECOMES AMPLIFIED THE STORM
TRACK WILL SET UP ALONG ITS WESTERN EDGE WITH STORMS MOVING FROM
SOUTH TO NORTH ACROSS THE WESTERN ALEUTIANS AND WESTERN BERING SEA.
THE FIRST COUPLE LOWS TRACKING ALONG THIS CORRIDOR LOOK FAIRLY WEAK.
A MUCH STRONGER LOW IS EXPECTED TO DEVELOP TUESDAY OVER THE NORTH
PACIFIC AND MOVE UP ACROSS THE ALEUTIANS. WITH LARGE DIVERGENCE IN
MODEL SOLUTIONS CONFIDENCE IN THE STRENGTH AND SPEED OF THIS SYSTEM
IS LOW. THERE IS HIGHER CONFIDENCE IN THE EVENTUAL TRACK OF THE
LOW UP TOWARD EASTERN RUSSIA. THE FRONT ASSOCIATED WITH THIS LOW
GRADUALLY TRACK EASTWARD ACROSS THE BERING MID TO LATE WEEK AS
THE UPPER RIDGE MOVES OVER MAINLAND ALASKA.

.LONG TERM FORECAST...A STRONG FRONT OVER THE CENTRAL BERING MID
WEEK WILL SLOWLY WEAKEN AS IT MOVES TO SOUTHWEST ALASKA LATE IN
THE WEEK. THE REMNANTS OF THE FRONT WILL THEN MOVE OVER SOUTHCENTRAL
LATE FRIDAY INTO THE WEEKEND. MODELS INDICATE SOME UPPER SUPPORT
WITH A SHORT-WAVE MOVING THROUGH. SO EVEN WITH A WEAKENING FRONT
THERE IS A GOOD SHOT AT PRECIP AS THE FRONT MOVES THROUGH. IT LOOKS
LIKE ANOTHER RIDGE WILL BUILD IN BEHIND THE FRONT OVER THE BERING
SEA FRIDAY AND THEN BACK TO MAINLAND ALASKA BY THE END OF THE
WEEKEND.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...STORM WARNING...175 176.
         GALE WARNING...120 127 128 129 172 179 180 185.
         HEAVY FREEZING SPRAY...121 129 126 127 128.
FIRE WEATHER...NONE.

SEB FEB 11