Gale Warning 70, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
105 PM AKST WED JAN 20 2010

.ANALYSIS AND UPPER LEVELS...TODAY IS THE BEGINNING OF A TRANSITION
IN THE LONG-WAVE PATTERN. A RIDGE IS BEGINNING TO BUILD OVER THE
WESTERN TO CENTRAL BERING AHEAD OF A DEEP AND COLD TROUGH SWINGING
OUT OF ASIA. THIS RIDGE WILL BRING AN END TO COLD ADVECTION ACROSS
THE CENTRAL TO EASTERN BERING...AND THIS IS BEING REFLECTED IN THE
OBSERVED TREND OF DIMINISHING NORTHERLIES AND SNOW SHOWERS. THE
LOW WHICH HAS BEEN NEARLY STATIONARY SOUTH OF KODIAK ISLAND IS
BEING PUSHED OFF TO THE SOUTHEAST AS A TROUGH OVER THE EASTERN
BERING PROGRESSES EASTWARD. ONE LAST SHORT-WAVE IS ROTATING
WESTWARD ACROSS KODIAK ISLAND AND BRISTOL BAY THIS AFTERNOON...AND
WILL HEAD SOUTHWARD TONIGHT AS THE TROUGH OVER THE EASTERN BERING
MOVES EASTWARD. A DEVELOPING SURFACE LOW IS MOVING NORTHWARD OFF
THE BRITISH COLUMBIA COAST TOWARD THE EASTERN GULF AND WILL PLAY
A MAJOR PART IN THE GULF FORECAST THE NEXT COUPLE DAYS. LASTLY...A
RIDGE OVER CANADA IS BUILDING WESTWARD OVER THE EASTERN
MAINLAND...WHICH HAS LED TO CLEARING ACROSS MUCH OF THE REGION.

.MODEL DISCUSSION...MODELS INITIALIZED WELL AND ARE IN FAIR
AGREEMENT THROUGH THE SHORT-TERM. THE ECMWF SOLUTION WITH LOW
MOVING INTO THE GULF NOW MATCHES WHAT THE GFS/NAM HAVE BEEN
ADVERTISING AND IS CLOSE TO CURRENT FORECAST. THUS WILL GO
HEAVILY WITH WHAT IS NOW A MODEL CONSENSUS. OUT WEST DIFFERENCES
HAVE POPPED UP IN THE MODELS REGARDING SURFACE WAVES MOVING UP
THE MAJOR FRONT MOVING ACROSS THE BERING AND ALEUTIANS. TOO EARLY
TO PICK OUT A PREFERRED SOLUTION AT THIS POINT AND WILL GO WITH A
WASHED OUT REPRESENTATION OF THESE WAVES. ALL MODELS HAVE ALSO
TRENDED SLOWER WITH THE FRONT WHICH SEEMS REASONABLE CONSIDERING
THE AMPLITUDE OF THE RIDGE BUILDING OUT AHEAD OF IT.

.SHORT TERM FORECAST...

SOUTHCENTRAL ALASKA...MOISTURE EXTENDS OUT AHEAD OF SURFACE
LOW OFF THE BRITISH COLUMBIA COAST...SO EXPECT THIS TO MOVE INTO
THE EASTERN COPPER BASIN AND EASTERN PRINCE WILLIAM SOUND AREAS
TONIGHT. AS THE LOW TAKES A MORE WESTERLY TRACK ON THURSDAY THE
WESTWARD PROGRESSION OF THIS MOISTURE WILL COME TO A HALT. ALSO...THE
TIGHTENING PRESSURE GRADIENT BETWEEN INTERIOR ALASKA AND THE
GULF WILL TIGHTEN AND OFFSHORE FLOW WILL INCREASE. THIS WILL
MAINTAIN A SUPPLY OF DRY LOW LEVEL AIR SO THAT PRECIP ALONG THE
COAST WILL BE LIGHT. MEANWHILE...UPPER TROUGH OVER THE BERING WILL
DIG SOUTHEASTWARD ACROSS SOUTHWEST ALASKA TONIGHT AND THURSDAY AND
THEN STALL AND WEAKEN AS IT RUNS INTO ENERGY MOVING FROM THE EAST.
ARCTIC AIR ACCOMPANYING THIS TROUGH WILL ADVECT ACROSS THE ALASKA
PENINSULA AND PRODUCE THE USUAL STRONG GAP WINDS ACROSS THE KODIAK
ISLAND WATERS. HIGH PRESSURE WILL STRENGTHEN INLAND OVER THE
WEEKEND...PRODUCING COLD AND DRY CONDITIONS. ANY PRECIP THAT DOES
FALL WILL BE CONFINED TO THE GULF.

SOUTHWEST ALASKA...SNOW WILL COME TO AN END ACROSS SOUTHWEST ALASKA
TONIGHT AS THE EASTERN BERING TROUGH PROGRESSES EASTWARD. A SECOND
TROUGH WILL CATCH UP TO THE FIRST AND ADVECT ARCTIC AIR SOUTHWARD
ACROSS THE REGION THURSDAY AND THURSDAY NIGHT...WITH THE MAIN IMPACT
BEING STRONG GUSTY WINDS ALONG THE ALASKA PENINSULA. HIGH PRESSURE
WILL THEN BUILD IN FRIDAY AND REMAIN OVERHEAD THROUGH THE
WEEKEND...RESULTING IN DRY AND COLD CONDITIONS.

BERING SEA/ALEUTIANS...COLD ADVECTION SNOW SHOWERS AND STRONG
NORTHERLIES WILL DIMINISH ACROSS THE EASTERN BERING TONIGHT
INTO THURSDAY AS STRENGTHENING RIDGE BUILDS IN FROM THE WEST.
STORM FORCE FRONT WILL BE THE MAIN FEATURE IN THE SHORT-TERM
AS IT PROGRESSES EASTWARD ACROSS THE BERING AND ALEUTIANS AT
A VERY SLOW PACE.

.LONG TERM FORECAST...ALTHOUGH THERE IS DEFINITELY MODEL
INCONSISTENCY IN THE EXTENDED PERIOD...IT LOOKS LIKELY THAT HIGH
PRESSURE WILL HOLD OVER MUCH OF MAINLAND ALASKA THROUGH AT LEAST
THE MIDDLE OF NEXT WEEK. THEREFORE...ACTIVE WEATHER SHOULD BE
CONFINED TO THE GULF AND ALONG THE ALEUTIANS.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...STORM WARNING...176.
         GALE WARNING...127 130 132 150 155 160 170 175 185.
         HEAVY FREEZING SPRAY WARNING...150 155 160 170.
FIRE WEATHER...NONE.

SEB JAN 10