Small Craft Advisory 632, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
250 PM AKDT MON OCT 29 2012

.SHORT TERM...WEST OF SOUTHEAST ALASKA...OFFSHORE OF PRINCE
WILLIAM SOUND SURFACE WIND PATTERNS OF LATEST OBS THIS AFTERNOON
ARE CONFIRMING SIGNS OF A WEAK CIRCULATION. THIS DEVELOPING LOW
IN THE NORTHERN GULF OF ALASKA WILL STEADILY ORGANIZE THIS
EVENING AND STRENGTHEN TUESDAY AS A STRONG SHORTWAVE ALOFT HEADS
SOUTHEAST FROM SOUTHWEST ALASKA. SATELLITE IMAGERY SHOWS
INCREASING HIGH CLOUDS FROM THE NORTHWEST AND A STRATUS DECK
MOVING EASTWARD FROM THE WATERS OFFSHORE OF YAKUTAT.
YAKUTAT...COVERED BY A WINTER WEATHER ADVISORY THIS EVENING
THROUGH TUESDAY AFTERNOON...SHOULD RECEIVE THREE TO FIVE INCHES
OF SNOWFALL TONIGHT WITH THIS SYSTEM AND ANOTHER TWO TO THREE
INCHES TUESDAY MORNING BEFORE MIXING IN WITH RAIN BY TUESDAY
AFTERNOON. IN ADDITION...THE SPREADING MOISTURE SHOULD REACH LYNN
CANAL AND THE ICY STRAIT AREA LATE TOMORROW MORNING AND HENCE A
WINTER WEATHER ADVISORY HAS ALSO BEEN ISSUED FOR HAINES BEGINNING
LATE TUESDAY AFTERNOON. MORE ABOUT THAT OVERRUNNING EVENT IN THE
LONG TERM. LIGHT SNOW WILL LIKELY BEGIN IN JUNEAU LATE TUESDAY
AFTERNOON BUT ONLY MINOR ACCUMULATIONS ARE EXPECTED DURING THE
DAYTIME HOURS. FOR POINTS SOUTH...INCREASING CLOUDS WILL BE THE
RULE WITH ONLY A CHANCE OF PRECIPITATION SPREADING INTO ZONE
26 TUESDAY AFTERNOON.

 WITH HIGH PRESSURE EXITING EASTWARD DEEPER INTO CANADA...THE
PRESSURE GRADIENT SHOULD BECOME MORE PARALLEL TO LYNN CANAL THIS
EVENING SO WINDS HERE ARE EXPECTED TO DIMINISH BEFORE MIDNIGHT.
EVEN AS THE NORTHERN GULF LOW STRENGTHENS TUESDAY...THIS
ORIENTATION SHOULD REMAIN AND KEEP WINDS HERE RELATIVELY LIGHT
TUESDAY. OTHERWISE...MANY OF THE CENTRAL PANHANDLE INSIDE WATERS
SHOULD STRENGTHEN TO SMALL CRAFT ADVISORY LEVELS BY TUESDAY
AFTERNOON.

 VERY LITTLE CHANGES FOR THE NEW PACKAGE ASIDE FROM SOME
ADJUSTMENTS TO QPF TO HANDLE LATEST MODEL TRENDS WHICH MAY BE
DELAYING THE SNOW EVENT BY A FEW HOURS. NAM WAS USED FOR BOTH
TONIGHT AND TUESDAY WITH SOME RFC...GFS INCORPORATED IN FOR QPF
ESTIMATES. FORECAST CONFIDENCE IS AVERAGE.

&&

.LONG TERM...MODELS ARE IN GENERAL AGREEMENT THROUGH THE LONG
TERM PERIODS WITH AN UPPER LEVEL SHORTWAVE TROUGH DOMINATING GULF
OF ALASKA WITH EMBEDDED CLOSED UPPER LOW WEAKENING AND DRIFTING
SOUTHWESTWARD ALONG THE ALASKAN PENINSULA THROUGH THE MID WEEK.
THE CLOSED UPPER LOW THEN SWINGS BACK INTO THE SOUTHERN GULF BY
LATE THURSDAY AND TO THE NORTHERN GULF TOWARD THE WEEKEND. MODELS
ARE FAIRLY CONSISTENT THROUGH THURSDAY AND THE NAM AND ECMWF MADE
A GOOD CONSENSUS. BLENDED THE FORECAST PACKAGE WITH THE NAM AND
ECMWF THROUGH THURSDAY. AS THE UPPER LOW RETURNS TO THE SOUTHERN
GULF ON THURSDAY AND TO THE NORTHERN GULF TOWARD THE
WEEKEND...MODEL DIFFERENCES GROW A LITTLE BIGGER. LEANED OVER THE
HPC ENSEMBLE APPROACH OF ECMWF FOR THE REMAINING PERIODS.

 SURFACE LOW ACROSS THE NORTHERN GULF WILL WEAKEN THROUGH
WEDNESDAY AND DISSIPATE BY LATE WEDNESDAY NIGHT AS A DEVELOPING
LOW IN THE NORTH PACIFIC MOVES INTO THE SOUTHERN GULF. THE
NORTHERN GULF LOW WILL CONTINUE PRODUCE GOOD AMOUNT OF SNOW ACROSS
THE NORTHERN PANHANDLE THROUGH WEDNESDAY WITH ADVISORY LEVEL SNOW
ACCUMULATION FOR HAINES AREA DUE TO OVERRUNNING. SOUTHERN AREAS
WILL REMAIN GENERALLY DRY. THE NEXT SYSTEM COMING FROM THE
SOUTHWEST WILL BRING WARMER AIR MASS AND PRECIPITATION SHOULD BE
ALL RAIN...EXCEPT NORTHERN MOST PANHANDLE WHERE CHANCE SNOW CANNOT
BE RULED OUT COMPLETELY. AHEAD OF THE INCOMING SYSTEM...WINDS WILL
BEGIN PICKING UP ACROSS THE OUTER COASTAL WATERS TO GALE FORCE ON
THURSDAY AND WINDY CONDITIONS WILL BE FELT ALONG THE NORTHEASTERN
GULF COASTS BY FRIDAY. GALE FORCE WINDS WILL ALSO LIKELY AFFECT
THE NORTHERN INNER CHANNELS AND OCEAN ENTRANCES.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...WINTER WEATHER ADVISORY FROM 4 PM TUESDAY TO 7 AM AKDT WEDNESDAY
     FOR AKZ019.
         WINTER WEATHER ADVISORY FROM 7 PM THIS EVENING TO 4 PM AKDT
     TUESDAY FOR AKZ017.
MARINE...GALE WARNING FOR PKZ022-051.
         SMALL CRAFT ADVISORY FOR PKZ011-021-031>035-041>043-052.

&&

JWA/BEZENEK/AHN