Small Craft Advisory 783, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
553 AM AKST MON DEC 17 2012

.SHORT TERM...THIS MORNING A 988MB LOW PERSISTS IN THE EASTERN
GULF AND HIGH PRESSURE OVER THE YUKON HAS BUILT INTO THE NORTHERN
PANHANDLE. THE LOW IS CAUSING SCATTERED SNOW SHOWERS OVER THE
SOUTHERN COASTAL AREAS WITH BARANOF ISLAND AND SITKA GETTING THE
BRUNT OF IT THIS MORNING. UP TO AN ADDITIONAL INCH OF
ACCUMULATION IS POSSIBLE THERE THIS MORNING. SHOWERS WILL BECOME
MORE ISOLATED THROUGH THE AFTERNOON AND DECREASE FROM NORTH TO
SOUTH AS THE LOW SHIFTS TO THE SOUTHEAST AND CONTINUES TO WEAKEN
TONIGHT. THE NORTHERN HALF OF THE PANHANDLE IS UNDER OFFSHORE
FLOW WITH DRY NORTH SURFACE WINDS...THUS HAVE NOT INCLUDED
MENTION OF SNOW. IF THERE WERE ANY IT WOULD BE A BRIEF FLURRY
WITH NO ACCUMULATION OR BLOWING SNOW.

 THE COMBINATION OF THE BUILDING HIGH TO THE NORTH AND THE LOW TO
THE SOUTH HAS CAUSED A STRONG NORTH PRESSURE GRADIENT OVER THE
NORTHERN INSIDE WATERS. A STORM WARNING IS IN EFFECT FOR NORTHERN
LYNN CANAL TODAY WHERE SUSTAINED WINDS OF 47KT HAVE BEEN RECORDED
AT ELDRED ROCK THIS MORNING WITH GUSTS IN THE MID 60S. THE NORTH
WIND AND CLEARING SKIES WILL CAUSE TEMPERATURES TO FALL THROUGH
THE DAY WITH THE HIGH BEING NEAR THE PRESENT TEMPERATURE AT 5AM
AND FALLING INTO THE SINGLE DIGITS IN HAINES AND SKAGWAY TONIGHT.
HEAVY FREEZING SPRAY WARNINGS ARE IN EFFECT FOR GLACIER BAY AND
NORTHERN LYNN CANAL DUE TO THE EXPECTED WINDS AND COLD
TEMPERATURES. FREEZING SPRAY IS ALSO EXPECTED IN SOUTHERN LYNN
CANAL AND YAKUTAT BAY THROUGH TONIGHT AND OUT OF INTERIOR PASSES
IN STEPHENS PASSAGE AND BETWEEN CAPE FAIRWEATHER AND ICY CAPE IN
THE GULF TONIGHT.

 WINDS ARE EXPECTED TO EASE SOME THIS EVENING AS THE LOW DEPARTS
TO THE SOUTH AND THE CANADIAN HIGH SHIFTS SLIGHTLY TO THE EAST.
STRONG AND COLD WINDS OUT OF INTERIOR PASSES WILL CONTINUE JUST
NOT QUITE AS STRONG AS DURING THE DAY. OVERNIGHT A NEW LOW WILL
MOVE INTO THE WESTERN GULF AND THIS WILL CAUSE THE EAST WINDS
THROUGH CROSS SOUND TO RISE AGAIN TO 30KT WITH HIGHER GUSTS.

 NUMERICAL MODELS HAVE HAD A GOOD HANDLE ON THE COLD AIR OUTBREAK
EXPECTED TODAY. USED THE NAM12 AS A BASE FOR UPDATES TODAY WITH
THE HIRES AND LOCAL WRF MODELS FOR MESOSCALE FEATURES AND OUTFLOW
WINDS. FORECASTER CONFIDENCE IT ABOVE AVERAGE.

 &&

 .LONG TERM...EXTENDED FORECAST IS LOOKING TO BE RATHER COLD FOR
THE NEXT FEW DAYS AS ANOTHER COLD ARCTIC HIGH CEMENTS ITS PLACE
IN THE YUKON. ALTHOUGH THE PRESENTS OF A DECENT STRENGTH LOW IN
THE GULF WILL HOLD OFF THE COLD AIR FOR A DAY OR TWO MID WEEK.
OVERALL MODEL AGREEMENT WAS GOOD THROUGH THE FIRST HALF OF THE
PERIOD BUT THEN SUFFERED INTO THE WEEKEND AND NEXT WEEK AS
DIFFERENCES HANDLING AN UPSTREAM UPPER RIDGE PLAYED HAVOC WITH
THE REST OF THE EXTENDED FORECAST. IN THE END DECIDED ON A
STAYING WITH THE NAM INTO FRI FOR THE DETAIL THAT IT PROVIDED ON
THE WIND AND PRESSURE GRADIENT OVER THE NORTHERN PANHANDLE. I
MADE VERY FEW CHANGES TO THE FORECAST FOR THE WEEKEND AND BEYOND
DUE TO THE LARGE DISCREPANCY BETWEEN MODELS THAT FAR OUT SO
DECIDED TO STAY THE COARSE FOR THE MOST PART. FORECAST CONFIDENCE
IS GOOD THROUGH FRI THEN DROPS TO BELOW AVERAGE INTO THE WEEKEND
AND BEYOND.

 THE LOW THAT WILL BE AFFECTING THE FIRST PART OF THE EXTENDED
RANGE ENTERS THE GULF ON TUES BEFORE SLOWING ITS EASTWARD TREK
EARLY WED IN THE CENTRAL GULF. INTO WED THE SOUTHWARD EXPANSION
OF THE UPPER TROUGH SUPPORTING IT AS WELL AS THE SURFACE OUTFLOW
FROM THE HIGH IN THE YUKON WILL SEND THE LOW TO THE SE COMPLETELY
MISSING THE PANHANDLE. THE ASSOCIATED FRONT WILL STILL ADVANCE ON
THE PANHANDLE WITH GALES FORMING IN THE GULF AS IT COMES.
HOWEVER, ITS EASTWARD MOVEMENT WILL ALSO BE CHECKED WED AS THE
PARENT LOW'S SE MOVEMENT DRAGS THE FRONT ALONG WITH IT. AS A
RESULT, THE ASSOCIATED WIND AND PRECIP WILL NOT MAKE IT MUCH
FARTHER NORTH THEN THE CENTRAL INNER CHANNELS. STILL A FEW INCHES
OF SNOW AND SOME STRONG WINDS ARE NOT OUT OF THE QUESTION FOR THE
SOUTHERN OUTER COAST AND SOUTHERN INNER CHANNELS LATE TUES NIGHT
INTO WED NIGHT. FARTHER NORTH THINGS REMAIN MOSTLY DRY IN THE
NORTHERLY OUTFLOW THAT WILL DRY EVERYTHING OUT. TEMPS WILL BE A
BIT HIGHER THAN USUAL THOUGH DUE TO THE HIGH AND MID LEVEL CLOUD
COVER THAT THE SPREAD OVER THE AREA FROM THE FRONT.

 INTO FRI AND THE WEEKEND DRY CONDITIONS PREVAIL AS THE YUKON
HIGH ONCE AGAIN DOMINATES THE WEATHER OVER THE AREA, WITH THE
USUAL STRONG OUTFLOW AND TERRAIN INDUCED WINDS, AND COLDER
TEMPERATURES. FARTHER WEST A UPPER RIDGE IS BUILDING OVER THE
BERING AND WESTERN ALASKA. MODELS HAVE A DECENT HANDLE ON
BUILDING THE RIDGE INTO THE BERING, BUT THEN DIVERGE INTO
DIFFERENT WORLDS ON WHERE IT GOES FROM THERE. THE GFS FAVORS
FORMING THE RIDGE INTO A BRIEF REX BLOCK BUT THEN DESTROYING IT
WITH A SHOT OF VERY COLD AIR FROM THE ARCTIC PORING SOUTH OVER
THE YUKON SAT AND THEN WEST SAT NIGHT. THE ECMWF MOVES THE RIDGE
FARTHER EAST INTO CENTRAL ALASKA AND THEN FORMS A WEAK REX BLOCK.
THIS ONE HAS AN EVEN SHORTER LIFE SPAN AS IT QUICKLY DISSIPATES
AWAY BY SUN AFTERNOON. THE ECMWF ALSO DOES NOT HAVE THE
SUBSTANTIALLY COLD AIR FROM THE ARCTIC THAT THE GFS HAS, BUT THE
ECMWF IS MORE CONSISTENT RUN TO RUN THAN THE GFS. THIS WAS BACKED
UP BY YESTERDAY'S HPC RUN WHICH FAVORED THE EC ENSEMBLE MEANS.
THE WEATHER INTO EARLY NEXT WEEK REMAINS MOSTLY COLD WITH THE
CONTINUED PRESENTS OF THE YUKON HIGH THROUGH CONFIDENCES SUFFERS
FROM THE COMPLETE LACK OF AGREEMENT BETWEEN THE VARIOUS LONG
RANGE MODELS.

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...STRONG WIND THROUGH THIS EVENING FOR AKZ018-019.
         STRONG WIND THROUGH THIS AFTERNOON FOR AKZ017.
MARINE...HEAVY FREEZING SPRAY WARNING FOR PKZ011.
         HEAVY FREEZING SPRAY WARNING FOR PKZ012.
         STORM WARNING FOR PKZ012.
         GALE WARNING FOR PKZ011-013-022.
         SMALL CRAFT ADVISORY FOR PKZ021-031>033-043-051>053.
         SMALL CRAFT ADVISORY DUE TO SEAS FOR PKZ041-042.

&&

HANNON/EAL