Winter Storm Warning 28, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
1229 PM AKST THU DEC 17 2009

.SHORT TERM...SAT IMAGERY THIS MORNING SHOW RESIDUAL LOW
TRACKING N FROM PRINCE WILLIAM SOUND. COLD AIR MASS MOVED OVER
PAYA WITH INCREASE SNOW AMOUNTS AND A DELAY IN THE TRANSITION TO
RAIN. ISSUED A WINTER ADVY FOR PKZ17 TO NOON TO COVER THE
ADDITIONAL PRECIP. A 975 MB LOW TRACKING IN TO THE S AK GULF FROM
THE N PAC. FRONTAL BAND MOVING OVER THE PANHANDLE WITH RAIN
MOVING N OVER THE ENTIRE PANHANDLE...WITH SNOW OVER HIGHER
ELEVATIONS. WINDS OVER THE SOUTHERN ZONES HAVE INCREASED STEADILY
THIS MORNING WITH GUSTS NOW AT ADVY LVLS. EXPECT WINDS TO
CONTINUE THROUGH THE EVENING THEN DIMINISHING AS PRESSURE
GRADIENT SHIFTS FORM EAST WEST TO NORTH SOUTH. INSIDE WATERS WITH
GALES IN EAST WEST CHANNELS DIMINISHING TO SMALL CRAFT AS NORTH
SOUTH CHANNELS WILL SEE WINDS INCREASE SAT. TEMPERATURES WILL
DIMINISH OVER NIGHT AS COLD AIR MASS MOVES IN FORM THE WEST AND
CONTINUE TO DROP THROUGH THE DAY TOMORROW...HIGHEST TEMPS SHOULD
BE IN THE MORNING. THIS SAID PRECIP ASSOCIATED WITH THE FRONT
MOVING OVER THE AREA SHOULD STAY ALL RAIN FOR THE START OF THE
TONIGHT FORECAST THEN MIX WITH SNOW. AS TEMPS DROP BELOW FREEZING
PRECIP AMOUNTS WILL ALSO DIMINISH AS FORCING MECHANISMS WILL BE
MORE ONSHORE FLOW. SO...DO NOT EXPECT ANY SIGNIFICANT SNOW
AMOUNTS TONIGHT...EXPECT ALONG THE HAINES AND KLONDIKE HIGHWAYS
NEAR THE BORDERS. ISSUING WINTER ADVY FOR 4 TO 6 IN OF SNOW UNTIL
5 AM FOR THESE AREAS AFTER CONSULTING WITH CANADA. WILL ALSO SEE
SOME HIGHER GUSTS FOR ZONE 18 ANS 19. THE EAST WEST PRESSURE
GRADIENT WILL PRODUCE HIGHER GUSTS IN PKZ25...BUT FELT GUSTS
WOULD BE LOW OR INFREQUENT ENOUGH NOT TO WARRANT A WIND ADVY.
CONVECTIVE AIR MOVING ALONG WITH THE COLD AIR MASS WILL BRING
POSSIBILITY OF SOME ISOLATED THUNDER STORMS TO THE NORTH OUTSIDE
WATERS AND COASTAL AREAS.

 MODEL OF CHOICE AGAIN WAS THE GFS. CHANGES MADE WERE FAIRLY
MINOR TO EXISTING GRIDS AS OVERALL PATTERN DID NOT CHANGE MUCH.
CONFIDENCE WAS AVERAGE WITH QUESTIONS REGARDING PRECIPITATION
TYPE. IF TEMPERATURES DROP QUICKLY ENOUGH TONIGHT COULD SEE
HIGHER SNOW AMOUNTS ESPECIALLY WITH A TRANSITION TO A MORE
CONVECTIVE ENVIRONMENT.

&&

.LONG TERM...PRETTY GOOD SYNOPTIC AGREEMENT BETWEEN MODELS THROUGH
THE WEEKEND AS A BROAD MARITIME RIDGE BUILDS ACROSS NORTH PAC.
HAVE A LEAST 2 WEAK SHORT WAVES IN WESTERLY FLOW THAT MOVE TROUGH
RIDE WITH SOME TIMING DIFFERENCES. FOR MOST PART STUCK WITH GFS
THRU DAY 4 AND USED HPC GUIDANCE BEYOND.

SURFACE COLD FRONT THROUGH ALL OF PANHANDLE BY FRIDAY EVENING WITH
MDT CAA CONTINUING ACROSS SOUTHEAST ALASKA. ATMO ALREADY STARTING
TO STABILIZE A BIT AND SHOULD SEE SHOWERS BECOMING SCATTERED BY
SATURDAY AND ENDING FROM THE SOUTH ON SUNDAY. OVERALL QPF NOT TOO
IMPRESSIVE SO SNOW ACCUMS LIMITED TO A FEW INCHES DURING THIS
TIME. SINCE FLOW IS OFF THE GULF EXPECT TEMPS TO COOL SLOWLY UNTIL
CLOUDS BREAK UP SUNDAY NIGHT.

A MDT LOW PASSING WELL SOUTH OF THE AREA SUNDAY NIGHT AND MONDAY
WILL INCREASE EASTERLY DOWN SLOPE FLOW ACROSS SOUTHEAST ALASKA AND
EXPECT DRY WEATHER THROUGH MID WEEK. LOWS WILL CHILL INTO TEENS
MOST OF INNER CHANNELS WITH HIGHS IN THE UPPER 20S. OUTFLOW WINDS
WILL BE MAIN ISSUE AS SURFACE HIGH BUILDS INTO YUKON AND WILL BE
IN SMCR TO LCL GALE SCENARIO.

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...WIND ADVISORY UNTIL MIDNIGHT AKST TONIGHT FOR AKZ026.
         WIND ADVISORY UNTIL MIDNIGHT AKST TONIGHT FOR AKZ023-027>029.
         WINTER WEATHER ADVISORY FROM 4 PM THIS AFTERNOON TO 4 AM AKST
     FRIDAY FOR AKZ018-019.
MARINE...GALE WARNING FOR PKZ021-022-032>036-041>043-051-052.
         SMALL CRAFT ADVISORY FOR PKZ011>013-031.

&&

PRB/MM