Gale Warning 419, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
442 PM AKST WED DEC 16 2009

.SHORT TERM...SAT IMAGERY AT NOON SHOWS A COMPLEX FORECAST
PATTERN OVER THE AK GULF AND SE PANHANDLE. LOW 1 OVER PRINCE
WILLIAM SOUND WILL REMAIN THERE THROUGH THIS EVENING BEFORE
DISSIPATING N. THE FRONT FORM THIS SYSTEM HAS CONTINUED SNOW FALL
OVER PAYA THROUGH THE AFTERNOON. THE BIG QUESTIONS IS
TEMPERATURES OVER PKZ17. TEMPS HAVE BEEN AT OR BELOW FREEZING
THROUGH THE DAY WITH MODELS SHOWING WARMER TEMPS THIS AFTERNOON
BEFORE ANOTHER COLD POOL TRACKING IN. MODEL 850 TEMPS WARMING TO
-3 THIS EVENING THEN DROPPING TO -9. DECIDED TO KEEP THE AREAS
MORE SNOW WITH A MIX OF RAIN...THAT SAID SNOW AMOUNTS WERE
INCREASED SO HAVE EXTENDED THE WINTER WEATHER ADV OUT TO 5 AM
THU. WINDS OVER THE N OUTER COAST ARE AT GALE FORCE AND EXPECT
THEM TO CONTINUE THROUGH THIS EVENING BEFORE THE LOW DISSIPATED.
TIMING IS A BIT UNCERTAIN SO COULD SEE A DRAMATIC DROP OFF
EARLIER THAN EXPECTED. LOW2 OVER THE QUEEN CHARLOTTES HAS BEEN
TRACKING NE TOWARD BC. THIS HAS BEEN PROVIDING SOME LIGHT SNOW
OVER THE SRN ZONES THIS MORNING BUT HAS DISSIPATING. SNOW FALL
OVER HYDER FORM THIS LOW HAS BEEN LESS THAN ANTICIPATED SO HAD
ENDED THE WINTER WEATHER ADVISORY OVER PKZ29 EARLY. LOW 3 IS
MOVING UP FROM THE N PAC THU INTO FRI WITH GALE FORCE WINDS IN
COASTAL WATER WITH WIND ADVY GUSTS OVER THE SRN 3 ZONES. FINAL
TIMING OF THIS WILL DEPEND OF LONG TERM. A BIT OF UNCERTAINTY
WITH THE FINAL TRACK OF THIS LOW AS GFS HAD THE LOW DUMBBELL OVER
THE PANHANDLE FRI AFTERNOON.

 MODEL OF CHOICE WAS THE GFS BUT MADE FEW CHANGES TO PRESS AND
WINDS IN THE GRIDS. BIGGEST CHANGES WERE COOLING OFF TEMPS TO THE
N SLIGHTLY KEEPING SNOW LONGER IN THE FORECAST WITH HIGHER
AMOUNTS. CONFIDENCE IS BELOW AVERAGE. WHILE MODELS WERE IN FAIR
AGREEMENT AND INITIALIZED WELL THE TEMPERATURE RANGE SO CLOSE TO
A MIX OF SNOW AND RAIN CAN CAUSE SOME LARGE DIFFERENCES IN SNOW
FALL AMOUNTS.

&&

.LONG TERM...LONG RANGE MODELS REMAIN IN FAIR AGREEMENT THROUGH
WEEKEND BUT BEGIN TO DIVERGE BY THE BEGINNING OF NEXT WEEK. THE
COLD UPPER TROUGH IN THE GULF OF ALASKA TILTS SE TO NW AS IT
SWINGS THROUGH SE ALASKA BY SATURDAY. THEN A NEW TROUGH ALOFT IS
ESTABLISHED FURTHER WEST OVER THE BERING SEA THAT BUILDS A RIDGE
IN THE GULF BY MONDAY. MODELS DIFFER IN THE EASTERLY PROGRESSION
OF THE RIDGE. FOLLOWED HPC PREFERENCE OF STEEPING THE RIDGE BUT
KEEPING IT FIXED IN THE GULF RATHER THAN MOVING IT THROUGH
SOUTHEAST ALASKA. ENSEMBLES SHOW CONSIDERABLE SPREAD ON THE EAST
SIDE OF THE RIDGE SO THERE IS STILL A FAIR AMOUNT OF UNCERTAINTY
ABOUT WHETHER OR NOT THE WESTERLIES WILL BREAK THROUGH THE RIDGE.

FOR THE WEEKEND THE RAIN WILL ABRUPTLY CHANGE TO SNOW SHOWERS AS
VERY COLD AND STRONG WESTERLY FLOW FOLLOWS THE TROUGH THAT MOVES
INLAND INTO CANADA. THERE IS A POSSIBILITY OF THUNDER WITH THE
SHARP TEMPERATURE CONTRAST OVER FRI NIGHT. SHOWERS WILL DIMINISH
EARLY IN THE WEEK AS THE COLD ARE IS MODIFIED BY THE BUILDING
RIDGE.

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...WIND ADVISORY FROM NOON THURSDAY TO MIDNIGHT AKST THURSDAY NIGHT
     FOR AKZ027>029.
         WINTER STORM WARNING UNTIL 5 AM AKST THURSDAY FOR AKZ019.
         WINTER WEATHER ADVISORY UNTIL 5 AM AKST THURSDAY FOR AKZ017.
MARINE...GALE WARNING FOR PKZ011>013-022-033>036-041>043-051-052.
         SMALL CRAFT ADVISORY FOR PKZ021-031-032.

&&

PRB/CFD