Small Craft Advisory 964, NWS Anchorage, AK

AREA FORECAST DISCUSSION
SOUTHCENTRAL AND SOUTHWEST ALASKA
1255 PM AKST THU DEC 4 2008

.ANALYSIS AND UPPER LEVELS...THERE ARE NOW TWO VERTICALLY STACKED
LOWS EMBEDDED WITHIN A HIGH AMPLITUDE TROUGH CENTERED OVER THE
BERING SEA/NORTH PACIFIC. ONE IS CENTERED SOUTH OF THE EASTERN
ALEUTIANS AND THE OTHER IS JUST NORTH OF THE PRIBILOF ISLANDS.
THERE IS VERY LITTLE MOVEMENT RIGHT NOW...BUT THESE LOWS WILL
BEGIN TO FUJIWARA WITH THE PACIFIC LOW TRACKING NORTHEASTWARD
AND THE BERING LOW DROPPING SOUTHWESTWARD. A HIGH AMPLITUDE RIDGE
EXTENDS ACROSS THE NORTHEAST PACIFIC UP TOWARD BRITISH COLUMBIA.
THE UPPER JET HAS NOW SLID EAST OF SOUTHCENTRAL AND IS POINTED
TOWARD SOUTHEAST ALASKA. WHAT IS LEFT BEHIND ARE WEAK UPPER WAVES
ROTATING AROUND THE WESTERN TROUGH NORTHWARD ACROSS MAINLAND ALASKA
AND THE EASTERN BERING SEA. ONE UPPER WAVE IS CURRENTLY EXITING THE
COPPER BASIN. SNOWFALL CONTINUES ACROSS MUCH OF THE BASIN...ENHANCED
BY UPSLOPE FLOW ALONG THE ALASKA RANGE. A WINTER WEATHER ADVISORY
FOR SNOW IS IN EFFECT FOR THIS AREA THROUGH 4 PM AND IT LOOKS LIKE
WE WILL BE ABLE TO LET THAT EXPIRE ON SCHEDULE. ALSO OF NOTE...THE
ARCTIC FRONT HAS PUSHED NORTHWEST ACROSS SOUTHWEST ALASKA TO THE
KUSKOKWIM MOUNTAINS. WARM AIR CONTINUES TO ADVECT NORTHWARD ACROSS
THE SOUTHERN MAINLAND. MOST COASTAL AREAS HAVE CHANGED TO ALL
RAIN...BUT INLAND LOCATIONS ARE STILL ALL SNOW. 00Z SOUNDING FROM
THIS AFTERNOON WILL BE KEY IN DETERMINING HOW MUCH THE ATMOSPHERE
HAS WARMED AND WHAT THE POTENTIAL FOR FREEZING RAIN WILL BE OVER
INLAND LOCATIONS. FINALLY...GALE TO STORM FORCE NORTHERLIES CONTINUE
WEST OF THE UPPER TROUGH OVER THE CENTRAL TO WESTERN BERING SEA.
AIR TEMPERATURES HAVE STEADILY DROPPED THE PAST 24 HOURS (BUOY 46035
IS DOWN TO 30 DEGREES) AND FREEZING SPRAY IS EXTENDING SOUTHWARD
ACROSS THE NORTHERN BERING SEA.

.MODEL DISCUSSION...12Z MODELS INITIALIZED WELL AND ARE IN VERY
GOOD AGREEMENT THROUGH THE SHORT-TERM PERIOD. WILL FINE-TUNE
CURRENT FORECAST WITH NO MAJOR CHANGES. GFS AND ECMWF HAVE ALSO
CONVERGED ON A SOLUTION WITH MAJOR LOW MOVING INTO GULF MONDAY...SO
WILL TREND TOWARD THAT SOLUTION.

.SHORT TERM FORECAST...

SOUTHERN MAINLAND/ALASKA PENINSULA...WEAK WAVES WILL CONTINUE TO
ROTATE ACROSS THE SOUTHERN MAINLAND...ALASKA PENINSULA...AND
EASTERN BERING TONIGHT INTO FRIDAY. CHARACTER OF PRECIPITATION
WILL PREDOMINANTLY BE SHOWERY. HOWEVER...UPSLOPE AREAS AND INLAND
VALLEYS WHERE OVERRUNNING DOMINATES WILL SEE STEADIER PRECIPITATION
AS THESE WAVES MOVE THROUGH. PRECIPITATION WILL GENERALLY BE LIGHT
AND SHORT-LIVED. HOWEVER...AS MENTIONED ABOVE THERE IS A THREAT FOR
FREEZING RAIN ACROSS MUCH OF INTERIOR SOUTHERN ALASKA THIS AFTERNOON
THROUGH TONIGHT. WILL NEED TO LOOK AT 00Z SOUNDINGS BEFORE MAKING
A FINAL DECISION...BUT FOR NOW SINCE DONT EXPECT WIDESPREAD OR
STEADY PRECIPITATION PLAN TO DOWNPLAY THE THREAT AND FORECAST A
CHANCE OF FREEZING RAIN OR ISOLATED AREAS OF FREEZING RAIN. AS
THE LOW SOUTH OF THE ALEUTIANS (AND UPPER TROUGH AXIS) MOVE TOWARD
KODIAK ISLAND FRIDAY AND SATURDAY...STEADIER PRECIPITATION WILL
SPREAD NORTHWARD ACROSS THE GULF AND THEN DIMINISH AS IT MOVES
INLAND OVER SOUTHCENTRAL AND SOUTHWEST ALASKA. THIS LOW WILL
QUICKLY WEAKEN OVER THE GULF SUNDAY WHILE A RIDGE BUILDS FROM
THE WESTERN BERING TOWARD NORTHWEST ALASKA...HELPING TO GRADUALLY
END PRECIPITATION AND ADVECT COLDER AIR BACK ACROSS THE REGION
SATURDAY NIGHT THROUGH SUNDAY NIGHT.

BERING SEA/ALEUTIANS...AS THE LOW NEAR THE PRIBILOF ISLANDS DROPS
SOUTHWARD TONIGHT THROUGH FRIDAY NIGHT AN ALREADY TIGHT PRESSURE
GRADIENT WILL TIGHTEN FURTHER ON THE WEST SIDE OF THE LOW.
THEREFORE...EXPECT SOLID STORM FORCE WINDS CAN BE EXPECTED FROM
THE NORTH CENTRAL BERING SOUTHWARD TO THE VICINITY OF ADAK.
TEMPERATURES WILL CONTINUE TO COOL ACROSS THE CENTRAL TO WESTERN
BERING AND FREEZING SPRAY WILL SPREAD SOUTHWARD. AFTER THIS LOW
DROPS SOUTH OF THE ALEUTIAN CHAIN FRIDAY NIGHT WINDS WILL GRADUALLY
DIMINISH THROUGH SATURDAY NIGHT. A GALE FORCE FRONT WILL MOVE INTO
THE WESTERN ALEUTIANS SUNDAY AND THEN WEAKEN AS IT TRACKS EASTWARD.
ALL IN ALL ITS LOOKING LIKE A FAIRLY CALM PERIOD ACROSS THE BERING
SEA AND ALEUTIANS.

.LONG TERM FORECAST...CONFIDENCE IS SLOWLY BUILDING FOR THE EXTENDED
FORECAST PERIOD. A MEAN RIDGE WILL SET UP FROM THE WESTERN BERING TO
NORTHERN ALASKA WITH A MEAN TROUGH OVER THE GULF. THUS...ITS LOOKING
LIKE AN EXTENDED CALM PERIOD OVER THE BERING SEA/ALEUTIANS AND MAINLY
DRY AND COLD OVER MAINLAND ALASKA WITH PERHAPS SOME PRECIPITATION
ALONG THE GULF COAST. MODELS ARE NOW INDICATING A BLOCKING RIDGE
SETTING UP OVER THE BERING THE END OF NEXT WEEK...WHICH WOULD RESULT
IN STRONG COLD ADVECTION ACROSS MAINLAND ALASKA ALONG WITH STRONG
NORTHERLY WINDS IN THE USUAL LOCATIONS.

.AER/ALU...WATCH/WARNING SUMMARY
PUBLIC...NONE.
MARINE...STORM WARNING...172 175.
         GALE WARNING...176 185.
         HEAVY FREEZING SPRAY WARNING...185.
FIRE WEATHER...NONE.

SEB DEC 08