Brisk Wind Advisory 22, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
400 PM AKST SUN FEB 8 2009

.ANALYSIS AND UPPER LEVELS...A COLD UPPER VORTEX OVER THE ARCTIC IS
SINKING SOUTHWARD TOWARD NORTHERN ALASKA WITH A POSITIVELY TILTED
TROUGH OVER THE CHUKCHI SEA SWINGING SOUTHEASTWARD TOWARD NORTHWEST
ALASKA. ANOTHER TROUGH EXTENDING FROM THE SOUTHERN MAINLAND
SOUTHEASTWARD ACROSS THE GULF IS PROGRESSING EASTWARD TOWARD CANADA.
COLD ADVECTION ALONG THE BACK SIDE OF THIS TROUGH CONTINUES TO
PRODUCE STRONG WINDS THROUGH GAPS IN THE ALASKA PENINSULA AND OUT
ACROSS THE WESTERN GULF. QUIKSCAT IMAGERY FROM 15Z SHOWS A SOLID
BAND OF 45 KT SOUTH OF KODIAK ISLAND WITH ANOTHER BAND OF SLIGHTLY
WEAKER WINDS IN THE BARREN ISLANDS REGION NORTH OF KODIAK ISLAND.
THERE ARE A FEW AREAS OF LIGHT SNOW OR FLURRIES OVER THE SOUTHERN
MAINLAND DUE TO COLD ADVECTION AND WEAK UPPER LOWS EMBEDDED IN THE
TROUGH. OTHERWISE...STRATUS AND PATCHY FOG HAVE SETTLED IN OVER
LIGHT WIND AREAS.

A HIGH AMPLITUDE LOW WAVELENGTH RIDGE EXTENDS FROM THE SOUTHERN
ALASKA PENINSULA NORTHWESTWARD TO SIBERIA. WEST OF THIS RIDGE IS
A LONG-WAVE TROUGH WHICH EXTENDS ALL THE WAY ACROSS ASIA. A
PERSISTENT STRONG JET (150 KT PLUS) EXTENDS OUT OF ASIA INTO THE
WEST PACIFIC WHERE LOWS CONTINUE TO DEVELOP IN QUICK SUCCESSION
AND TRACK TOWARD THE WESTERN ALEUTIANS. SATELLITE IMAGERY SHOWS
THE MOST RECENT OF THESE LOWS NOW STATIONARY JUST EAST OF KAMCHATKA
(CENTRAL PRESSURE IN THE 960S) WITH A STRONG FRONT PUSHING NORTH
AND EAST ACROSS THE BERING AND ALEUTIANS. THE SOUTHERN PORTION OF
THE FRONT SOUTH OF THE ALEUTIANS IS MOVING QUICKLY EASTWARD CAUSING
ELONGATION AND SLOWING OF THE FRONT BACK OVER THE BERING SEA. ASIDE
FROM STRONG WINDS THE MAIN THREAT ASSOCIATED WITH THIS FRONT IS
SNOW AND BLOWING SNOW. A BLIZZARD WARNING REMAINS IN EFFECT FOR
THE PRIBILOFS WHERE CONDITIONS ARE DETERIORATING QUICKLY THIS
MORNING. TEMPERATURES ALONG THE EASTERN ALEUTIANS AND SOUTHERN
ALASKA PENINSULA WILL WARM TO NEAR FREEZING...SO BLIZZARD
CONDITIONS ARE NOT EXPECTED...BUT PRECIPITATION WILL STAY ALL SNOW
SO VISIBILITY WILL STILL BE QUITE LOW AT TIMES.

.MODEL DISCUSSION...THE POSITION AND STRENGTH OF CURRENT LOW EAST
OF KAMCHATKA AS WELL AS NEXT LOW MOVING UP TOWARD THE ALEUTIANS
DIFFERS AMONG THE DIFFERENT MODELS...BUT NOT ENOUGH TO CAUSE ANY
MAJOR PROBLEMS...AND THE MOVEMENT AND STRENGTH OF FRONTS IS VERY
SIMILAR. THERE ARE ALSO DIFFERENCES IN THE DEVELOPMENT OF A TRIPLE
POINT LOW NEAR THE SOUTHERN ALASKA PENINSULA TONIGHT. PREFER THE
MORE CONSISTENT NAM/GFS POSITION. OVERALL...NEW GUIDANCE SHOWS
DECENT RUN-TO-RUN CONSISTENCY THROUGH TUESDAY SO ONLY MINOR
ADJUSTMENTS WILL MADE TO CURRENT FORECAST.

BEYOND TUESDAY MODEL CONSISTENCY HAS BEEN POOR. PREFER THE SLIGHTLY
MORE CONSISTENT ECMWF. SINCE CURRENT FORECAST ARE BASED OFF OF VERY
OLD MODEL GUIDANCE PLAN ON UPDATING MID TO LATE WEEK FORECAST WITH A
HEAVY BLEND TOWARD THE LATEST ECMWF. IN PARTICULAR...ECMWF AND GFS
BOTH INDICATE ANOTHER SIGNIFICANT LOW DEVELOPING OVER THE WEST
PACIFIC MONDAY AND TUESDAY AND TRACKING TO THE BERING SEA WEDNESDAY.
THERE IS NOT ENOUGH CONFIDENCE YET TO GO AS STRONG AS MODELS INDICATE
(CENTRAL PRESSURE 940S TO 950S)...BUT ENOUGH CONFIDENCE TO HEAD IN
THAT DIRECTION.

.SHORT TERM FORECAST...

SOUTHERN MAINLAND...WINDS WILL DIE DOWN QUICKLY TONIGHT AS THE
UPPER TROUGH EXITS TO THE EAST. LEFT IN ITS WAKE WILL BE LOTS OF
LOW LEVEL MOISTURE IN THE FORM OF STRATUS AND FOG. THE FRONT MOVING
EASTWARD ACROSS THE ALEUTIANS WILL MAKE IT TO THE SOUTHER ALASKA
PENINSULA...PERHAPS SPREADING SNOW AS FAR NORTH AS PORT HEIDEN...BUT
THIS FRONT AND TRIPLE POINT LOW THAT DEVELOPS NEAR THE SOUTHERN
ALASKA PENINSULA WILL BE SHUNTED SOUTHWARD BY THE TROUGH SWINGING
DOWN ACROSS MAINLAND ALASKA. THIS TROUGH WILL SWING ALL THE WAY
ACROSS THE SOUTHERN MAINLAND MONDAY NIGHT AND TUESDAY. IT IS A
SHARP ENOUGH TROUGH THAT SOME CLOUDS WILL DEVELOP AHEAD OF THE
TROUGH AND MAY SEE A FEW AREAS OF LIGHT SNOW OR FLURRIES...BUT
NOTHING OF ANY SIGNIFICANCE. ALSO EXPECT A WEAK LOW TO DEVELOP
OVER THE NORTHERN GULF AND PRODUCE A FEW SNOW SHOWERS ALONG THE
COAST...BUT THIS WILL QUICKLY BE PUSHED EASTWARD WITH THE TROUGH.
THE TROUGH DOESNT DROP FAR ENOUGH SOUTH TO ALLOW FOR A GOOD PUSH
OF ARCTIC AIR SOUTHWARD ACROSS THE REGION. MARGINALLY COLDER AIR
WILL ACCOMPANY THE TROUGH...BUT WILL QUICKLY EXIT TO THE EAST ON
TUESDAY AS A SHORT-WAVE TROUGH MOVES ACROSS THE EASTERN BERING AND
SURFACE FRONT MOVES TO THE SOUTHWEST COAST. THERE IS UNCERTAINTY
IN THE DETAILS AFTER THIS POINT...BUT WITH A VERY PROGRESSIVE
PATTERN THERE IS CONFIDENCE THAT THIS SHORT-WAVE WILL CROSS THE
SOUTHERN MAINLAND MID TO LATE WEEK BRINGING A SHOT OF SNOW.

BERING SEA/ALEUTIANS...THE NORTHWARD PROGRESSION OF THE FRONT WILL
COME TO A HALT THIS AFTERNOON AND EVENING DUE TO TROUGH DROPPING
DOWN FROM THE NORTH. THE FRONT WILL THEN REMAIN GRADUALLY SHEAR
APART TONIGHT AND MONDAY. BLIZZARD CONDITIONS WILL PERSIST ON THE
PRIBILOFS THROUGH THE EVENING HOURS AND THEN IMPROVE OVERNIGHT AS
WINDS AND SNOW DIMINISH. THE NEXT SYSTEM WILL TAKE A VERY SIMILAR
TRACK TO THE CURRENT ONE. WINDS WILL BE A LITTLE WEAKER...BUT STORM
FORCE WINDS ARE STILL EXPECTED ALONG THE FRONT. THE OTHER DIFFERENCE
IS THAT THE UPPER TROUGH WILL TAKE A MORE NORTHERN TRACK TO MAINLAND
ALASKA...SO THE SURFACE FRONT WILL PUSH ALL THE WAY ACROSS THE BERING
SEA TO SOUTHWEST ALASKA. BLIZZARD CONDITIONS WILL AGAIN BE POSSIBLE
ON THE PRIBILOF ISLANDS...BUT WOULD BE SHORT-LIVED DUE TO THE
PROGRESSIVENESS OF THE FRONT. ANOTHER MAJOR LOW IS EXPECTED TO
APPROACH THE WESTERN ALEUTIANS MID WEEK...BUT IT IS TOO EARLY TO
NAIL DOWN THE DETAILS.

.LONG TERM FORECAST...THE PATTERN WILL REMAIN VERY PROGRESSIVE
THROUGH THE EXTENDED FORECAST PERIOD. THEREFORE...EXPECT STORMS
TO QUICKLY TRACK FROM WEST TO EAST ACROSS THE FORECAST AREA. THE
AMPLITUDE OF THE UPPER PATTERN WILL BE LOW...SO WARM AIR WILL
REMAIN DOWN OVER THE PACIFIC AND PREDOMINANT PRECIPITATION TYPE
WILL BE SNOW.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...BLIZZARD WARNING 195.
MARINE...GALE WARNING...155 165 172 175 176 179 185.
         HEAVY FREEZING SPRAY WARNING...121 129 150 160 165 179.
FIRE WEATHER...NONE.

SEB FEB 09