Small Craft Advisory 629, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
419 PM AKDT SUN OCT 28 2012

.SHORT TERM...AFTERNOON SATELLITE LOOP REVEALS A WEAK LOW
DEVELOPS IN THE NORTHEASTERN GULF...JUST OFF YAKUTAT BAY. HIGH
PRESSURE OVER THE YUKON SLOWLY DRIFTS SOUTHWARD ACROSS THE YUKON
AND BRITISH COLUMBIA BORDER. ANOTHER DEVELOPING LOW IN THE FAR
SOUTHEASTERN GULF SLOWLY MOVES NORTHEASTWARD HEADING TO HAIDA
GWAII. OFFSHORE FLOW CONTINUES WITH SMALL CRAFT WINDS PREVAIL
OVER NORTHERN LYNN CANAL AND NEAR SHORE OF THE CENTRAL OUTSIDE
WATERS. GUSTY OUTFLOW CONTINUES NEAR INTERIOR PASSES. SOME MID
CLOUDS INCREASE ACROSS THE NORTHERN MOST AREA AS THE HIGH OVER
THE YUKON SLIDES SOUTHWARD. THE LOW HEADING TOWARDS HAIDA GWAII
PUSHES MID TO HIGH CLOUDS OVER DIXON ENTRANCE AND SOUTHERN
PANHANDLE AREAS.

 MODELS REMAIN FAIRLY PERSISTENT WITH THE HIGH PRESSURE OVER THE
YUKON CONTINUES TO DRIFT SOUTHWARD INTO NORTHERN BRITISH COLUMBIA
THROUGH LATE MONDAY. THE WEAK LOW OVER HAIDA GWAII TONIGHT WILL
FURTHER WEAKEN AND DRIFT EASTWARD INTO CANADA BY MONDAY NIGHT.
REFRESHED THE INHERITED FORECAST PACKAGE WITH THE 12Z RUN NAM FOR
ITS BEST INITIALIZATION. AFTERNOON OBSERVATIONS HINT A
DEVELOPMENT OF LOW PRESSURE OVER KENAI PENINSULA. AS THIS LOW
DEVELOPS...THE WEAK LOW ROTATING IN THE NORTHEASTERN GULF WILL
SLOWLY DRIFT SOUTH AND DISSIPATE EARLY THIS EVENING. AN UPPER
LEVEL SHORTWAVE TROUGH WILL CONTINUE TO SHARPEN OVER SOUTHEAST
ALASKA THROUGH MONDAY MORNING THEN MOVES TO THE EAST AWAY FROM
THE AREA AS A WEAK UPPER RIDGE MOVES INTO THE NORTHERN AREAS.

 THE SHARPENING UPPER TROUGH WILL ENHANCE THE LOW OVER HAIDA
GWAII A LITTLE TONIGHT AND BRING A CHANCE POP OF RAIN AND SNOW.
OFFSHORE FLOW WILL CONTINUE THROUGH MONDAY MORNING AND THE
ALASKAN PANHANDLE WILL ENTER A TRANSITION PERIOD FROM OFFSHORE
FLOW TO ONSHORE FLOW. THE TRANSITION WILL BEGIN LATE MONDAY
MORNING FROM THE NORTHWEST AND CONTINUE THROUGH MONDAY AFTERNOON
OVER THE NORTHERN PANHANDLE. CLOUDS WILL GRADUALLY INCREASE OVER
YAKUTAT AREA WITH A CHANCE SNOW BEGINS WEST OF ICY BAY IN THE
AFTERNOON. SMALL CRAFT WINDS OVER THE OUTSIDE WATERS WILL EAST
DOWN IN THE MORNING AND THE WINDS ACROSS NORTHERN AND CENTRAL
INNER CHANNELS WILL DIMINISH TO BELOW SMALL CRAFT CRITERIA EARLY
IN THE AFTERNOON. ROUGH SMALL CRAFT SEAS WILL REMAIN ACROSS THE
CENTRAL OUTER WATERS THROUGH THE AFTERNOON HOWEVER.

.LONG TERM...MONDAY NIGHT'S DEVELOPMENT OF THE NORTHERN GULF OF
ALASKA LOW IS ON SCHEDULE. GFS HAS BACKED OFF THE STRENGTH OF IT
SOMEWHAT...FALLING BETTER IN LINE WITH NAM AND ECMWF. STILL
DISCOUNTED ECMWF BECAUSE IT SHEARS APART FASTER ON WEDNESDAY.
YAKUTAT SHOULD RECEIVE ONE TO THREE INCHES OF SNOW MONDAY NIGHT
WITH POSSIBLY ONE OR TWO MORE TUESDAY MORNING BEFORE IT CHANGES TO
RAIN. THIS IS BELIEVABLE DUE TO THE COLD AIR COMING SOUTHEAST FROM
THE BERING STRAIT INTERACTING WITH THE WARMER WATERS OF THE GULF...
SO IT SHOULD BE A CASE OF QUICK CYCLOGENESIS. THE PRECIPITATION
SPREADS EASTWARD TUESDAY AS THE MOIST ONSHORE FLOW OVERRUNS THE
ARCTIC AIR MASS IN PLACE OVER THE NORTHERN PANHANDLE. WET BULB
TEMPERATURES WILL BE LOW SO THERE IS THE POTENTIAL FOR A FEW
INCHES IN NORTHERN LYNN CANAL AND GLACIER BAY WHERE COLD AIR HAS A
TENDENCY TO SCOUR OUT LAST. JUNEAU ALSO LOOKS A STRONG CANDIDATE TO
SEE ITS FIRST ACCUMULATION OF THE SEASON.

WINDS FOR THIS SYSTEM ARE ALSO ON SCHEDULE TO DEVELOP WITH SMALL
CRAFT SOUTHEASTERLIES SPREADING SOUTHWARD ACROSS THE OUTSIDE
WATERS MONDAY NIGHT INTO TUESDAY WHILE SOLID WESTERLIES ARISE
OFFSHORE. DUE TO THE ORIENTATION OF THE PRESSURE GRADIENT BECOMING
PARALLEL TO MANY OF THE NORTHERN INSIDE CHANNELS...DECIDED TO
FLIP DIRECTIONS MONDAY NIGHT AND TUESDAY TO SOUTH IN SOME KEY AREAS.

MASSIVE LONG WAVE TROUGH EXTENDING SOUTHWEST FROM MAINLAND ALASKA
WILL DIG DEEPER MIDWEEK TO SPAWN A NEW LOW IN THE NORTH PACIFIC
WHICH WILL ARRIVE IN THE SOUTHWEST GULF THURSDAY. THE NEW LOW WILL
QUICKLY DEPRIVE THE NORTHERN GULF LOW OF ENERGY AND THE BIG STORY
FOR SOUTHEAST WILL BE WARMING TEMPERATURES AND RAIN FOR LATE IN
THE WORK WEEK SPREADING INTO NEXT WEEKEND.

GFS/NAM MIX WAS USED FOR NEAR SHORT-TERM WITH GFS BLENDING INTO
SUN 00Z HPC FOR EXTENDED. CONFIDENCE IN LONG TERM FORECAST
AVERAGE.

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...SMALL CRAFT ADVISORY FOR PKZ011>013-022-031-035-042-043.
         SMALL CRAFT ADVISORY DUE TO SEAS FOR PKZ051.

&&

AHN/JWA