Small Craft Advisory 247, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
350 PM AKST THU MAR 10 2016

.SHORT TERM...RAIN AND SHOWERS ARE USUALLY GIVENS ACROSS MOST OF
SOUTHEAST. BUT OCCASIONALLY THERE COMES A TIME WHEN THE WINDOWS
OF OPPORTUNITY ARE SMALL. THE PLAYERS ARE FEW IN THIS SETUP. ONE,
WE HAVE A LOW MOVING RAPIDLY NORTHEAST ACROSS THE BC MOUNTAINS.
CLOUD COVER FROM THIS SYSTEM ADVANCED AS FAR AS JUNEAU MID-DAY
BUT LATELY HAS BEGUN RETREATING AS THE SYSTEM WEAKENS AND PUSHES
AWAY. THE RAIN FROM THIS SYSTEM HAD TROUBLE MOVING WEST OF HYDER
AND WRANGELL. TWO, WE ALSO HAVE A COMPLICATING RIDGE. HOW MUCH OF
A PLAYER WILL IT BE? WE THINK IT WILL HAVE A SAY IN KEEPING
THINGS DRY FOR AT LEAST THE EARLY EVENING FOR MOST LOCATIONS. BUT
AS THE SYSTEM TO THE EAST WEAKENS...ITS TRAILING RIDGE WILL AS
WELL. THE THIRD PLAYER IS AN AGING UPPER LOW OVER THE GULF OF
ALASKA SUPPORTING RAIN SHOWERS THAT APPEAR TO BE INCREASING IN
COVERAGE AND TRYING TO ADVANCE TOWARD OUR SHORES. THE SOUTHERLY
FLOW JUST WEST OF US IS WAITING FOR THE ONSHORE GATES TO OPEN,
AND THIS WILL HAPPEN ONCE THE COMPLICATING RIDGE MOVES
SUFFICIENTLY EAST. MID TO LOW LEVEL MOISTURE WILL BE RELEASED
INTO THE PANHANDLE OVERNIGHT AND WITH SOME HELP FROM OROGRAPHICS,
LIGHT RAIN SHOWERS WILL DEVELOP.

NOW FOR THURSDAY AND HOW THIS WINDOW BEGINS TO CLOSE. THIS OLD
UPPER LOW IN THE GULF WILL BEGIN DISSIPATING TONIGHT AS A NEW
SYSTEM SAPS ITS ENERGY WELL OUT INTO THE SOUTHWEST GULF. THIS NEW
SYSTEM WILL SEND A FRONT WELL OUT AHEAD INTO THE CENTRAL GULF,
BACKING WINDS SOUTHEAST ACROSS THE EASTERN GULF AND KEEPING
THINGS BRISK. FOR THE PANHANDLE INCREASING OFFSHORE WINDS AT THE
MID- LEVELS WILL HELP DRY THINGS OUT BY TOMORROW AFTERNOON AND
THUS WE NOW FORECAST THE SUN TO RE-EMERGE BY TOMORROW AFTERNOON
FROM JUNEAU-SITKA-KETCHIKAN EASTWARD. YAKUTAT MEANWHILE WILL STAY
SHOWERY FROM TONIGHT INTO FRIDAY AFTERNOON. LIKEWISE SHOWERS
ALONG THE COAST WILL BE THE LAST TO END.

GUIDANCE FROM THE HIGH RES SUPPORTED AN INCREASE IN WINDS
OVERNIGHT SO WE ADDED SOME SMALL CRAFT SOUTHERLIES IN ADVANCE OF
THE FRONT. WINDS BEGIN TO DIMINISH TOMORROW AND WILL TURN MORE
OFFSHORE BY THE AFTERNOON. OTHERWISE WE RELIED ON THE NAM AND
ECMWF FOR SMALL ADJUSTMENTS TO A FAIRLY SOLID FORECAST.
CONFIDENCE IS GOOD BUT IFFY ON SHOWER COVERAGE TONIGHT. TIMING
WAS DELIBERATELY LEFT BROAD DESCRIBING WHEN SHOWERS WILL ACTUALLY
DEVELOP.

.LONG TERM...UPPER LEVEL LOW PRESSURE WILL DOMINATE THE GULF OF
ALASKA THROUGH TUESDAY MORNING. AT THAT TIME, AN UPPER LEVEL
RIDGE WILL BUILD IN FROM THE SOUTH AND BE CENTERED OVER THE
EASTERN GULF AND SOUTHEAST ALASKA. THE RIDGE WILL BECOME MORE
AMPLIFIED TOWARDS THE END OF THE WEEK AS IT IS IMPINGED UPON BY
ANOTHER UPPER LOW THAT MOVES IN FROM THE WEST. MODELS DIVERGE ON
THE TRACK OF THIS SECOND LOW, AND THE RESULTANT DISPOSITION OF THE
UPPER RIDGE. ECMWF DEPICTS A STRONG NEGATIVE TILT DEVELOPING WITH
THE UPPER LOW RIDING UP THE WESTERN SIDE OF THE RIDGE. GFS TIPS
THE RIDGE NEGATIVELY EVEN MORE SO AND UNDERCUTS THE FEATURE WITH
THE UPPER LOW WEST OF OREGON.

AT THE SURFACE, THE UPPER PATTERN SUPPORTS A SURFACE LOW REMAINING
OVER THE SOUTHEASTERN GULF AND ROTATING SHOWERS NORTH OVER THE
PANHANDLE UNTIL IT FINALLY WEAKENS TUESDAY MORNING. MODE AGREEMENT
ON THIS FEATURE IS GOOD UNTIL IT BEGINS TO WEAKEN. GFS AND THE
CANADIAN NH TAKE IT EAST INTO CANADIAN COASTLINE SOUTH OF HAIDA
GWAII WHEREAS DRIFTS IT NORTH AND INLAND AS A DYING LOW OVER THE
CENTRAL OUTER COAST. AT THIS POINT, ECMWF DIVERGES FROM BOTH GFS
AND THE CANADIAN NH, WHICH BOTH TRACK YET ANOTHER SURFACE LOW
INTO THE SOUTHEASTERN GULF BY WEDNESDAY MORNING. FARTHER SOUTH AND
WEST, MODES ARE IN GOOD AGREEMENT ON A MUCH STRONGER LOW
APPROACHING THE GULF FROM THE SOUTH BY THURSDAY MORNING. GFS KEEPS
THE SURFACE FEATURE SOUTH OF 50N AND TRACKS IT SLOWLY TO THE EAST
THROUGH NEXT SUNDAY MORNING. ECMWF TRACKS IT NORTH AND THEN
NORTHWEST INTO THE WESTERN GULF. THE TREATMENT OF THIS FEATURE AT
THE SURFACE IS CONSISTENT WITH EACH MODELS' UPPER LEVEL PATTERNS.
PREFER THE GFS SOLUTION AT THIS TIME DUE TO THE UPPER LEVEL
UNDERCUTTING THE RIDGE VICE RIDING UP THE VERY NEGATIVELY TILTED
RIDGE AS DEPICTED BY ECMWF.

EITHER WAY, THE EXTENDED RANGE FORECAST FEATURES SEVERAL DRY DAYS
FOR THE NORTHERN HALF OF THE PANHANDLE WITH ONLY CHANCE POPS
EXTENDING AS FAR NORTH AS SITKA ON THE OUTSIDE AND ACROSS THE
SOUTHERN ZONES SATURDAY EVENING. PERIODS OF PARTLY CLOUDY SKIES
WILL PUNCTUATE MOSTLY CLOUDY AND DRY DAYS AND NIGHTS FOR MUCH OF
THE COMING WEEK. BREAKS IN THE CLOUDS WILL ALLOW TEMPS TO FALL TO
NEAR FREEZING OR BELOW THROUGH NEXT MONDAY. DAYTIME HIGHS WILL BE
IN THE MID TO UPPER 40S. STRONG NORTHEASTERLY PRESSURE GRADIENT
WILL KEEP MARINE WINDS OVER THE INNER CHANNELS AT 20 TO 25 KTS
THROUGH SATURDAY NIGHT AND 15 KTS OR SO THROUGH SUNDAY NIGHT.
STRONG WINDS LIKELY IN SKAGWAY ON SATURDAY.

CHANGES TO THE EXTENDED RANGE FORECAST LIMITED TO MONDAY AND
ONWARD, WHERE THE LATEST WPC WAS USED FOR PRESSURE AND WIND. TEMPS
ADJUSTED USING BIAS CORRECTED GFS AND SREF AS WELL AS GFS ENSEMBLE
MOS. QPF FROM CANADIAN NH AND ECMWF. OVERALL FORECAST CONFIDENCE
IS AVERAGE.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE WARNING FOR PKZ041>043-052.
     SMALL CRAFT ADVISORY FOR PKZ011-013-022-031-033-035-036-051-053.
&&

JWA/FRITSCH

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