Winter Storm Warning 27, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
126 PM AKST MON DEC 14 2009

.SHORT TERM...CLEAR SKIES THIS MORNING OVER THE SOUTHERN HALF OF
THE PANHANDLE WITH WHAT APPEARS TO BE A SMALL PATCH OF MARINE
STRATUS OVER SOUTHERN CHATHAM STRAIT. ELSEWHERE...OVERCAST. MID
HAD HIGH LEVEL CLOUDS ARE PUSHING SOUTH OVER THE INNER CHANNELS
DOWN TO NEAR FIVE FINGERS LIGHT BUT ARE FOR THE MOST PART
DISSIPATING NEAR FREDERICK SOUND. AN APPROACHING FRONTAL BOUNDARY
TO THE SOUTH WILL EVENTUALLY CLOUD UP THE SOUTHERN PANHANDLE
TONIGHT IN ADVANCE OF THE ASSOCIATED PRECIPITATION. AT THE SAME
TIME...AM EXPECTING PARTIAL CLEARING OVER THE NORTHERN PANHANDLE
THROUGH THE NIGHT TONIGHT.

 SNOW CONTINUES TO FALL IN YAKUTAT WITH 1 INCH ACCUMULATION
THROUGH THIS MORNING. A HEAVIER BAND OF SNOW ENTERED THE YAKUTAT
AREA AROUND 11 AM AND VISIBILITY WENT DOWN TO LESS THAN A MILE IN
MODERATE SNOW. WATCHING THE WINDS THERE CLOSELY FOR A SHIFT TO
THE SOUTH OF EAST WHICH SHOULD SIGNIFY A TRANSITION TO A
RAIN/SNOW MIX AND THEN FINALLY A CHANGE TO ALL RAIN. THIS SHOULD
HAPPEN AS A WEAK LOW NEAR PRINCE WILLIAM SOUND BECOMES A LITTLE
MORE ORGANIZED AND WHAT IS LEFT OF THE SURFACE RIDGE RE-ORIENTS
EAST-WEST. IF WINDS DO NOT SHIFT...YAKUTAT COULD EASILY REACH
ADVISORY LEVEL SNOWFALL LATER THIS AFTERNOON. CONFIDENCE IS HIGH
THAT WINDS WILL SHIFT MORE TO THE SOUTH LATER THIS AFTERNOON...SO
HAVE DECIDED TO NOT ISSUE A LATE BREAKING WINTER WEATHER
ADVISORY.

 GENERALLY...HAVE DECREASING POP IN THE WESTERN HALF OF ZONE
17 OVERNIGHT AND THROUGH TOMORROW. AT THE SAME TIME...POP IS ON
THE THE RISE OVER THE SOUTHERN THIRD OF THE PANHANDLE OVERNIGHT.
WENT FOR AROUND 1 INCH OVER ZONE 27 AND 1 TO 3 INCHES OVER ZONE
28 THROUGH TOMORROW MORNING BEFORE MIXING WITH OR CHANGING TO
RAIN IN THE AFTERNOON. FOR ZONE 29...WENT WITH A 1 TO 6 INCH
TOTAL ACCUMULATION DUE TO TEMPERATURES REMAINING BELOW FREEZING
ALL DAY BUT STILL NOT ENOUGH ACCUMULATION FOR A WINTER WEATHER
ADVISORY.

 DO HAVE A MARGINAL WIND ADVISORY IN PLACE FOR ZONE 29 TOMORROW
AS NORTHEAST OUTFLOW WIND IS EXPECTED TO STRENGTHEN OVERNIGHT
TONIGHT. ADVISORY LEVEL GUSTS WILL BE LARGELY CONFINED TO THOSE
LOCATIONS NEAR PORTLAND CANAL. PRESSURE GRADIENT ORIENTATION NOT
CORRECT TO GENERATE ADVISORY WINDS IN BEHM CANAL. LOCALLY WINDY
CONDITIONS IN HYDER...BUT THINK THEY WILL REMAIN JUST BELOW
ADVISORY LEVEL IN TOWN.

 EASTERLY OUTFLOW WINDS WILL ALSO RESULT IN SMALL CRAFT
CONDITIONS OVER THE SOUTHERN INNER CHANNELS LESS SOUTHERN CHATHAM
STRAIT THROUGH MUCH OF THE SHORT TERM FORECAST PERIOD AND FOR
STEPHENS PASSAGE IN THE VICINITY OF FIVE FINGERS LIGHT TOMORROW
MORNING. STRONG OUTFLOW WINDS NEAR TAKU INLET...THE STIKINE
RIVER...AND THE VARIOUS COASTAL MOUNTAIN PASSES THROUGHOUT THE
SHORT TERM FORECAST PERIOD.

&&

.LONG TERM...THE RELATIVELY DRY WEATHER IS COMING TO AN END AS A
WEAK WEATHER FRONT MAKES ITS WAY UP THE PANHANDLE TUE NIGHT. MAIN
CONCERN RIGHT NOW IS HOW MUCH SNOW IS IT GOING TO DROP BEFORE IT
CHANGES TO RAIN OR DIMINISHES. TEMPERATURES WILL BE WARMING UP
THROUGH THE NIGHT ESPECIALLY UP AT 850 MB WHERE TEMPERATURES WILL
BE ABOUT -4C OVER JUNEAU BY WED MORNING. CURRENT THINKING IS THAT
MOST INNER CHANNEL LOCATIONS WILL POSSIBLY SEE ADVISORY CRITERIA
FOR SNOW TUE NIGHT WITH NORTHERN LOCATIONS SEEING THE HIGHER
AMOUNTS BEFORE SNOW STARTS MIXING WITH RAIN.

PAST THU, MODELS STARTS HAVING SOME DISAGREEMENTS IN DETAILS OF
THE NEXT SYSTEM. OF THEM, THE GFS APPEARS TO BE THE MAIN OUTLIER
FOR THE SYSTEM ON FRI. THE GFS HAS A 980 MB LOW MAKING LANDFALL IN
THE SOUTHERN PANHANDLE FRIDAY MORNING. THE REST OF THE MODELS
SUPPORT A MORE WESTWARD TRACK THAT KEEPS THE LOW OUT OVER THE GULF
AND MAKING LANDFALL NEAR YAKUTAT. ELECTED TO STAY WITH THE EC AS
IT KEEPS THE LOW OUT OVER THE GULF LIKE MOST OF THE ENSEMBLES
SHOW. WITH THIS SYSTEM MOST PRECIP WILL BE A MIX TO ALL RAIN AS
THERE WILL STILL BE A VERY WARM PUSH THROUGH THE PANHANDLE AT THAT
TIME.

BY THE END OF THE WEEKEND MODEL AGREEMENT BECOMES EVEN WORSE WITH
THE GFS KEEPING ONSHORE FLOW OVER THE AREA THROUGH EARLY NEXT WEEK
WHILE THE EC BUILDS ANOTHER STRONG HIGH OVER THE GULF AND INTERIOR
OF CANADA. WAS NOT TOO KEEN ON THE EC OUT THIS FAR AS THE STRONG
HIGH IN THE GULF WAS NOT SUPPORTED BY ANY OTHER MODEL INCLUDING
THE VARIOUS ENSEMBLES. THE FORECAST OUT HERE IS MAINLY HPC
GUIDANCE WHICH KEEPS MORE ONSHORE TO ALONG SHORE FLOW OVER THE
AREA INTO EARLY NEXT WEEK.

FORECAST CONFIDENCE IS AVERAGE AND GRADUALLY DIMINISHES TO BELOW
AVERAGE AS SIGNIFICANT DIFFERENCES STILL EXIST BETWEEN THE VARIOUS
MODELS.

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...WIND ADVISORY FROM 6 AM TO 9 PM AKST TUESDAY FOR AKZ029.
MARINE...SMALL CRAFT ADVISORY FOR PKZ022-031-034>036-041.
         SMALL CRAFT ADVISORY DUE TO SEAS FOR PKZ042-043-051-052.

&&

FRITSCH/EAL