Gale Warning 460, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
306 PM AKST SUN DEC 4 2011

.SHORT TERM...A LARGE FRONTAL SYSTEM ASSOCIATED WITH A LOW IN
THE BERING SEA WILL BE THE MAIN FEATURE THROUGH THE PERIOD.
CURRENTLY THE FRONT EXTENDS ACROSS GULF WITH A PLUME OF MOISTURE
COMING FROM THE TROPICAL PACIFIC ALONG THE UPPER LEVEL JET. A NEW
SURFACE LOW IS DEVELOPING IN THE LEFT EXIT REGION OF THE JET OVER
THE YUKON AND A RIDGE OF HIGH PRESSURE EXTENDS OVER THE
PANHANDLE. AS A RESULT THERE IS A TIGHT SOUTHERLY PRESSURE
GRADIENT OVER LYNN CANAL...WHERE THERE IS A GALE WARNING AND
STRONG WIND HEADLINES FOR HAINES AND SKAGWAY. THE FRONT IS
ALREADY BRINGING MODERATE TO HEAVY RAIN TO THE YAKUTAT AREA. THIS
RAIN WILL SPREAD INLAND TONIGHT AND THROUGH MONDAY
AFTERNOON...BECOMING HEAVY AT TIMES. SW FACING SLOPES CAN EXPECT
TO SEE THE GREATEST RAINFALL AMOUNTS. GUSTY WINDS AND HEAVY
RAINFALL MAY RESULT IN MUDSLIDES OR AVALANCHES.

 THIS IS A WARM SYSTEM SO EXPECT TO BE ALL RAIN...WITH EXCEPTION
OF SOME MIXING NEAR THE CANADIAN BORDERS. WITH WARM AIR ADVECTION
TEMPERATURES WILL BE NEARLY STEADY OVERNIGHT OR RISING.

 THIS SYSTEM HAS BEEN WELL FORECASTED OVER THE PAST SEVERAL
DAYS...KEEPING FORECASTER CONFIDENCE ABOVE AVERAGE. UPDATED THE
GOING FORECAST WITH THE ECMWF AND SREF AS THEY INITIALIZED THE
BEST.

 &&

 .LONG TERM...AT START OF THE LONG TERM FORECAST LOOKING AT A
SHIFT FROM THE MILD WET WEATHER OVER SE AK TO A COLD DRY SPELL.
MID LEVEL TROUGH AND SURFACE FRONT WILL EXIT TO THE SOUTHEAST
THOUGH EARLY MONDAY EVENING AS COLD AIR POURS IN FROM THE NORTH
OVERNIGHT. AS PRECIP SHOULD BE ENDING BEFORE THE PUSH OF COLD AIR
AND THERE WILL BE ENOUGH WARM AIR AT THE SURFACE TO KEEP PRECIP
AS RAIN WITH ONLY A MIX OF SNOW LATE. BY THEN THERE SHOULD BE NO
SIGNIFICANT SNOW ACCUMULATION. THE MAIN ISSUE TUESDAY MORNING
COULD BE BE ICY ROADS AND WALKWAYS SO CAUTION SHOULD BE TAKEN
DURING THE MORNING COMMUTE. THE COLD AND DRY CONDITIONS WILL LAST
THROUGH MID WEEK WITH MOSTLY SUNNY SKIES BEFORE THE NEXT FRONT
MOVES INTO THE WESTERN GULF THURSDAY. THE FRONT WILL BRING A
RETURN OF WARMER AIR TO THE PANHANDLE BY THE END OF THE WEEK AND
PRECIP WILL BE MORE OF A MIXED OF SNOW AND RAIN.

 BEHIND THE FRONT GALE FORCE WINDS ALONG BARRIER JET IN THE
NORTHWESTERN GULF WILL BEGIN TO WEAKEN. AT MID LEVELS 500MB
TROUGH DROPPING OVER THE N PANHANDLE AROUND 00Z TUE WITH 540 LINE
REACHING THE CENTRAL REGIONS. SEEING THE COLD AIR PUSH AS FAR
SOUTH AS FREDERICK SOUND WITH 850MB TEMPS AT -12C NEAR YAKUTAT TO
-6C NEAR ANNETTE. AT THE SURFACE AS LOW PRESSURE OVER THE YUKON
CONTINUES TO MOVE EAST AND HIGH PRESSURE RIDGE OVER THE SOUTHERN
PANHANDLE WEAKENS AND TRACKS EAST WINDS OVER THE REGION WILL
WEAKEN AND BEGIN TO SHIFT FROM SOUTH TO NORTH. SURFACE HIGH OVER
THE AK GULF WILL BEGIN TO PUSH EAST LATE WEDNESDAY INTO THURSDAY.
MODELS HAVE BEEN TENDING TO WEAKEN BLOCKING RIDGE AND MOVE IN
NEXT FRONT A BIT EARLY SO MAINLY LEFT PREVIOUS POP FIELD ALONE.
BY 00Z FRIDAY THERE IN GOOD CONSENSUS THAT A FRONT ASSOCIATED
WITH A LOW NEAR PRINCE WILLIAM SOUND WILL HAVE MOVED INTO THE
CENTRAL GULF WITH PRECIP MOVING OVER THE PANHANDLE BY THE END OF
THE WEEK INTO THE WEEKEND. WITH WARM AIR ADVECTION AHEAD OF THE
FRONT WILL START OF SEE A MIX OF PRECIP, BUT WILL NEED TO KEEP AN
EYE OUT IF COLD AIR BECOMES ENTRENCHED AND POSSIBLE OVER RUNNING
EVENT. THROUGH THE WEEKEND NEXT RIDGE OF HIGH PRESSURE MOVES INTO
THE CENTRAL AK GULF WITH ANOTHER PUSH OF COLD AIR.

 MODELS WERE IN GOOD AGREEMENT FOR THE START OF THE LONG TERM.
NAM WAS MORE OF AN OUTLIER WITH A WEAKER PRESSURE GRADIENT OVER
THE NORTHERN PANHANDLE AND DID NOT INITIALIZE AS WELL COMPARING
500-300MB RH TO WATER VAPOR IMAGERY. ECMWF AND GFS CONTINUED IN
FAIR AGREEMENT THROUGH THE END OF THE WEEK. RUN TO RUN
CONSISTENCY FOR THESE MODELS HAS ALSO BEEN GOOD. MAIN DIFFERENCES
START WITH POSITION AND STRENGTH OF A LOW MOVING FROM THE N
PACIFIC INTO THE BERING SEA BY THE WEEKEND. MODELS WERE A BIT
HIGH WITH SNOW LEVELS WITH THE COLD AIR MOVING IN SO DID LOWER
LEVELS A BIT. UPDATED GRIDS WITH AN EC/GFS BLEND THROUGH DAY
4 THEN TRANSITIONED TO NEW HPC GUID. MAIN CHANGES WERE AN
INCREASE IN GULF WINDS MONDAY NIGHT OTHERWISE CHANGES WERE MINOR.
FORECAST CONFIDENCE IS ABOUT AVERAGE.

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...STRONG WIND FROM MIDNIGHT AKST TONIGHT THROUGH LATE TONIGHT FOR
     AKZ019.
         STRONG WIND THROUGH LATE TONIGHT FOR AKZ018.
MARINE...GALE WARNING FOR PKZ012-036-052.
         SMALL CRAFT ADVISORY FOR PKZ011-013-021-022-031>035-041>043-051.

&&

HANNON/PRB