High Wind in Alaska, January 31, 2015

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
358 PM AKST SAT JAN 31 2015

.SHORT TERM...ABOVE THIS BEAUTIFUL DAY, THERE IS A FASCINATING
COLLISION OF AIR MASSES ALOFT. WITNESS THE VISIBLE IMAGERY. A
MOIST AIR MASS FROM THE SOUTH IS PUSHING AHEAD OF AN APPROACHING
FRONT. THIS FRONT WILL AID IN THE DEVELOPMENT OF RAIN/SNOW ACROSS
OUR SOUTHERN ZONES TONIGHT INTO SUNDAY. WE FEEL THAT MOST OF THIS
WILL BE RAIN, BUT THE NORTHERN EDGES OF THE PRECIPITATION FIELD
MAY BECOME SNOW LATE...SO WATCH FOR UP TO 2 INCHES OF ACCUMULATION
HERE, UP TO 3 INCHES FOR HYDER. THIS WILL ALL BE SUB-ADVISORY.

TO THE NORTH, THE UNMISTAKABLE SNOW-PACKED PEAKS FROM THE CHUGACH
RUNNING EASTWARD ACROSS THE CANADIAN ROCKIES REVEAL NOTHING BUT
CLEAR AIR BETWEEN THE SATELLITE LENS AND THE GROUND. HERE A DRY
SHORT-WAVE IS PUSHING SOUTHEAST ACROSS THE PANHANDLE...USHERING IN
COLDER AND DRIER AIR FROM THE ALASKAN INTERIOR. TIGHT PRESSURE
GRADIENTS BETWEEN THE HIGH PRESSURE ACROSS CANADA AND THE LOW
PRESSURE IN THE SOUTHEAST GULF WILL KEEP STRONG WINDS FOR
SKAGWAY/HAINES TONIGHT AS WELL AS NORTHERLY STORM FORCE WINDS
THROUGH LYNN CANAL. COUPLED WITH SUBZERO TEMPERATURES AT WHITE
PASS, A WINTER WEATHER ADVISORY REPLACED THE WIND CHILL ADVISORY
FOR BOTH WIND CHILL AS LOW AS 40 BELOW ZERO AND BLOWING SNOW WITH
VISIBILITY ONE QUARTER MILE OR LESS. THIS ADVISORY WILL SPAN THE
SHORT-TERM AND EXTEND INTO THE LONG-TERM PERIOD.

THE CLOUDS ON THE NORTHERN BOUNDARY OF THE MOIST AIR MASS ARE
SHEARING APART EAST AND WEST AND WILL FIND IT DIFFICULT TO ADVANCE
MUCH FARTHER NORTHWARD OVERNIGHT, DUE TO THE ROBUST SHORT-WAVE
PLOWING SOUTHEAST. THIS WILL KEEP THE NORTHERN PANHANDLE CLEAR FOR THE
MOST PART WITH THE EXCEPTION OF A FEW OCCASIONAL STRIPS OF CIRRUS
OVERNIGHT.

THE SHORTWAVE WILL ALSO CONTRIBUTE TO A LAYER OF WIND DIRECTION
REVERSAL AROUND 450 MB...WHICH WILL ALLOW THE ENERGY FROM THE
SOLID NORTHEASTERLY WINDS AT MOUNTAINTOP LEVEL TO BOUNCE FROM
THIS LAYER DOWN TO THE SURFACE AS MOUNTAIN WAVE WINDS NEAR
DOWNTOWN JUNEAU TONIGHT. THEREFORE HIGH WIND GUSTS TO AROUND 60
MPH WILL BE POSSIBLE TONIGHT WITH THE LIKELIHOOD GROWING TOMORROW
AS YET ANOTHER SHORT-WAVE, STRONGER THAN THE FIRST DEEPENS THE
COLD AIR ON THE OTHER SIDE OF THE MOUNTAINS. THIS WILL ONCE AGAIN
OFFER ANOTHER CHANCE TO REFLECT THE ENERGY FROM THE RIDGETOP
LEVEL WINDS OFF THE CRITICAL LAYER TO THE SURFACE IN THE FORM OF
MOUNTAIN WAVES.

ALTHOUGH SOME LOWER CLOUDS LINGERED IN GUSTAVUS THIS MORNING,
WE THINK THAT A DRYING BOUNDARY LAYER WILL KEEP FOG FROM BEING SO
WIDESPREAD TO MENTION IN THE ZONES TONIGHT. TEMPERATURES HAVE NOT
BEEN OUR BEST FORECASTING COMPONENT AS OF LATE. WE COOLED
TEMPERATURES IN THE FAR NORTH, ESPECIALLY AT WHITE PASS/HAINES
CUSTOMS AND WARMED THEM A TAD OVER THE NORTH CENTRAL ZONES, MAINLY
BECAUSE OF ATMOSPHERIC MIXING. ONLY SMALL CHANGES WERE RESERVED
FOR THE SOUTH.

MAINLY USED NAM FOR UPDATES WITH SOME HELP FROM SREF AND ECMWF.
FORECAST CONFIDENCE GOOD SIDE OF AVERAGE.

.LONG TERM...THE ARCTIC HIGH OVER INTERIOR ALASKA AND FAR
NORTHWEST CANADA CONTINUES TO SLIDE SOUTHEAST BY MONDAY NIGHT AS A
LOW MOVES ACROSS THE ARCTIC SLOPE. THE OFFSHORE GRADIENT WILL
REMAIN BRISK THROUGH MONDAY PRIMARILY BECAUSE OF THE STRONG LOW
SOUTH OF KODIAK ISLAND ABOUT 600 NM PERSISTS INTO EARLY NEXT
WEEK. A TROUGH EXTENDS EASTWARD TOWARDS THE BRITISH COLUMBIA COAST
AS THE REMAINS OF THE OLD STALL FRONTAL BOUNDARY THAT COULDN'T
FORCE ITS WAY NORTH PAST DIXON ENTRANCE.

THE AREA OF LOW PRESSURE WILL BECOME MORE COMPLEX AS AT WILL
ATTRACT A LOW OUT OF THE PACIFIC AND ONE MOVING EAST ACROSS THE
NORTH PACIFIC. FURTHER NORTH A HIGH OUT OF SIBERIA REGION OF
RUSSIA WILL BE HEADED TO NORTHWEST ALASKA COAST TUESDAY NIGHT.
WINDS LATER ON TUESDAY TO WEDNESDAY ACROSS THE PANHANDLE ARE
LIGHTER.

THE EXTENDED FORECAST FOR END OF THE WEEK IS A LITTLE CONFUSED AS
MODELS HAVE SOME TRACKING ISSUES. THE GUIDANCE I USED WAS A BLEND
OF ENSEMBLES THAT RESEMBLED THE ECMWF BUT WAS NOT AS STRONG. ONLY
MADE SOME MINOR CHANGES TO THE EXTENDED PORTION OF THE FORECAST.
CONFIDENCE IS ABOVE AVERAGE THROUGH TUESDAY AND THEN LOWERS
BEYOND THAT.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...HIGH WIND WARNING UNTIL 6 AM AKST MONDAY FOR AKZ025.
         STRONG WIND THROUGH LATE SUNDAY NIGHT FOR AKZ019.
         STRONG WIND UNTIL 4 PM AKST THIS AFTERNOON FOR AKZ018.
         WINTER WEATHER ADVISORY UNTIL 6 AM AKST MONDAY FOR AKZ018.
         STRONG WIND FROM 6 PM AKST THIS EVENING THROUGH LATE TONIGHT FOR
     AKZ029.
MARINE...STORM WARNING FOR PKZ012.
         GALE WARNING FOR PKZ011-013-021-022-031-032-034-035-041-043-051.
         SMALL CRAFT ADVISORY FOR PKZ033-042-053.
         SMALL CRAFT ADVISORY DUE TO SEAS FOR PKZ052.

&&

JWA/BEZENEK

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