Gale Warning 485, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
559 AM AKST THU DEC 24 2015

.SHORT TERM...SERN AK WILL RESIDE BETWEEN AN INTENSIFYING STORM
SYSTEM OVER THE ALEUTIANS AND A BROADER AREA OF TROUGHING OVER
THE WRN CONUS/CANADA THU MORNING/AFTERNOON. AMPLIFYING UPPER RIDGE
WILL THEN SHIFT E AHEAD OF THE ALEUTIANS TROUGH TONIGHT...BECOMING
POSITIONED OVER THE PANHANDLE BY 12Z FRI.

A NW-SE ORIENTED BAND OF LOW/MID CLOUDS WAS POSITIONED FROM
ROUGHLY SITKA TO KLAWOCK AT 12Z/THU. HOWEVER...LARGE-SCALE
SUBSIDENCE OCCURRING WITH THE APPROACHING RIDGE...COMBINED WITH
DRY BOUNDARY LAYER AIR SPREADING S ACROSS THE PANHANDLE...IS
EXPECTED TO DISSIPATE SHOWER POTENTIAL WITH THE COASTAL CLOUD
BAND. IN FACT...THE ENVIRONMENT WILL BECOME INCREASINGLY HOSTILE
TO CLOUDS BY TONIGHT OVER THE CNTRL/SRN PANHANDLE...THOUGH HIGH-
LEVEL CIRRUS WILL INCREASE OVER AKZ017 AS THE UPPER RIDGE AXIS
SHIFTS E.

OTHERWISE...MODEST TEMPERATURE MODERATION THROUGH AFTERNOON WILL
GIVE WAY TO STRONG RADIATIONAL COOLING TONIGHT...RESULTING IN LOWS
IN THE TEENS OVER THE NRN PANHANDLE /AND HYDER/ TO THE 20S/LOW 30S
OVER SRN AREAS /WARMEST NEAR THE GULF COAST/.

TIGHT SURFACE PRESSURE GRADIENT IS FORECAST TO PERSIST OVER THE
SKAGWAY/LYNN CANAL REGION THROUGH MOST OF THE SHORT TERM PERIOD.
THIS WILL AID IN SMALL CRAFT TO GALE STRENGTH NLY WINDS OVER THE
CANAL...AND GUSTY WINDS AT SKAGWAY. MAGNITUDE OF THE GRADIENT
COMBINED WITH AN ARCTIC AIRMASS OVER THE YUKON WOULD SEEMINGLY
FAVOR STRONG WIND POTENTIAL AT SKAGWAY. HOWEVER...GUSTS HAVE
RESIDED WELL BELOW 40 MPH. THUS CURRENT FORECAST HAS BEEN WEIGHTED
TOWARD THE LOWER END GUSTS OBSERVED DURING THE PAST 24 HRS.

.LONG TERM...JUST AS AN ARCTIC AIR MASS IMPLANTS ITSELF OVER THE
PANHANDLE...ENOUGH RIDGING ATOP OUR REGION WILL HELP STRENGTHEN
THE COLD AIR DOME ATOP WITH MAXIMUM RADIATIONAL COOLING FROM
MAINLY CLEAR SKIES THURSDAY NIGHT INTO FRIDAY. THIS WILL BE KEY
IN THE EVENTS TO FOLLOW AS A GALE FORCE FRONT STEMMING FROM A
VIGOROUS SYSTEM WELL SOUTH OF THE ALEUTIANS IN THE NORTH PACIFIC
WILL SEND MOISTURE NORTHEASTWARD.

PRECIPITATION WILL BEGIN IN THE FORM OF SNOW FOR MOST ALL OF THE
PANHANDLE FRIDAY NIGHT. WINTER STORM WATCHES WERE CONSIDERED FOR
MUCH OF THE PANHANDLE AND WEIGHED AGAINST INHIBITING FACTORS. AT
THIS TIME...CONFIDENCE WAS JUDGED HIGHER FOR YAKUTAT, HAINES,
JUNEAU, PETERSBURG, KETCHIKAN, AND ESPECIALLY HYDER AND THEREFORE
WATCHES WERE ISSUED. WHILE OTHER AREAS WILL RECEIVE SNOW, THE
SPEED OF THE SYSTEM AND IN SOME CASES ALONG THE COAST BOTH
TEMPERATURE AND THE CHANGEOVER TO RAIN MAY CHECK SNOW AMOUNTS
SUFFICIENTLY TO QUESTION THE NEED FOR ANY WATCH AT THIS TIME.
THUS A SPECIAL WEATHER STATEMENT CONTINUES FOR THESE AREAS TO
CONTINUE ADVERTISING ACCUMULATIONS DURING THE HOLIDAY WEEKEND.
MODEL TRENDS WILL CONTINUE TO BE STUDIED SHOULD THIS CHANGE, AND
MORE WATCHES MAY NEED TO BE ISSUED TO COVER PORTIONS OF THESE
AREAS. EXPECT POSSIBLE SNOW ACCUMULATIONS OF 2 TO 6 INCHES OVER
AREAS OUTSIDE THE WATCH WITH 4 TO 10 INCHES FOR THE ZONES UNDER A
WATCH. ONE EXCEPTION IS HYDER WITH 1 TO 2 FEET POSSIBLE.

IN REALITY, THIS NOW LOOKS TO BE A BORDERLINE WARNING CASE OVER
MUCH OF THE NORTH. ONE REASON IS THAT BOTH NAM AND ECWMF ARE
SUGGESTING SOME SORT OF WAVE DEVELOPMENT ALONG THE FRONT AS IT
APPROACHES THE COAST. IF A WAVE FORMS FARTHER NORTH...THE NORTHERN
PANHANDLE MAY RECEIVE GREATER SNOW AMOUNTS. SHOULD THE WAVE FORM
SOUTH...SNOW TOTALS WILL FALL SHORT OF CURRENTLY FORECASTED. THE
SPOT WITH THE MOST CONFIDENCE CONTINUES TO BE HYDER WHERE SNOW
WILL LIKELY BE MEASURED IN FEET RATHER THAN INCHES. THE SOUTHERN
INNER CHANNELS WILL PROVIDE AN INTERESTING TEST CASE. SHOULD WINDS
BE MORE EASTERLY THAN SOUTHERLY...WARNING CRITERIA IS POSSIBLE
LATE FRIDAY NIGHT INTO SATURDAY MORNING. GUIDANCE IS FUZZY ON
TEMPERATURES WITH SOME DISAGREEMENT. BUT GIVEN THE POSSIBILITY OF
IMPRESSIVE SNOWFALL TOTALS, THAT ADVISORY CRITERIA IS JUDGED BY A
LOWER THRESHOLD, AND THAT THE HOLIDAY WEEKEND CARRIES CHALLENGES
FOR PLANNING, WE DECIDED TO PLACE THIS AREA UNDER A WATCH AS WELL.
SNOW WILL BEGIN TO CHANGEOVER TO OR MIX WITH RAIN ACROSS THE COAST
AND CENTRAL AND SOUTHERN ZONES SATURDAY AFTERNOON. THIS WILL
SIGNAL AN END TO HEAVIER SNOW ACCUMULATIONS.

GALE FORCE WINDS WILL APPROACH THE COAST FRIDAY AND WINDS RISE
ACROSS THE PANHANDLE FRIDAY NIGHT. WINDS WILL LIKELY BE STRONG
ALONG THE CENTRAL AND SOUTHEAST GULF COAST. WINDS WERE GENERALLY
LIGHTENED ACROSS THE INTERIOR PANHANDLE IN THE MID-RANGE.

CHANGES TO THE EXTENDED FORECAST WERE RESERVED FOR THE
SIGNIFICANT SNOW EVENT FRIDAY NIGHT/SATURDAY...THUS VERY LITTLE
WORK WAS COMMITTED TO THE EXTENDED FORECAST. SNOW AND SNOW/RAIN
SHOWERS WILL SLOWLY DISSIPATE SATURDAY NIGHT INTO MONDAY NIGHT FOR
THE PANHANDLE AS THE NEXT FRONT ENTERS THE GULF FROM THE
SOUTHWEST. THIS SYSTEM LOOKS INCREASINGLY WET AND A LITTLE WARMER.
TRENDS SEEM TO BE SIGNALING A WARMER PATTERN INTO NEXT WEEK WITH
THE POTENTIAL FOR RISING SNOW LEVELS AND MORE RAIN MENTIONED AT
SEA LEVEL THAN CURRENT PACKAGE. SNOW LOVERS, THIS WEEKEND IS FOR
YOU TO ENJOY. DO NOT COUNT ON NEXT WEEK TO BE AS NICE. RAIN
LOVERS, YOUR TIME IS ON ITS WAY.

FORECAST CONFIDENCE NOT WHERE WE WOULD LIKE. BUT WE MUST HEDGE
WITH A POTENTIALLY IMPACTFUL FORECAST ON A HOLIDAY WEEKEND. USED
NAM AND ECMWF FOR UPDATES TO THE MID-RANGE. NUDGED WINDS TOWARD
WPC IN THE LONG-TERM.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...WINTER STORM WATCH FROM LATE FRIDAY NIGHT THROUGH SATURDAY
     MORNING FOR AKZ026-028.
         WINTER STORM WATCH FROM FRIDAY EVENING THROUGH SATURDAY MORNING
     FOR AKZ019-025.
         WINTER STORM WATCH FROM FRIDAY EVENING THROUGH SATURDAY MORNING
     FOR AKZ017.
         WINTER STORM WATCH FROM LATE FRIDAY NIGHT THROUGH SATURDAY
     AFTERNOON FOR AKZ029.
MARINE...GALE WARNING FOR PKZ012.
         SMALL CRAFT ADVISORY FOR PKZ013-031-041-042.
         SMALL CRAFT ADVISORY DUE TO SEAS FOR PKZ043-051-052.

&&

GARNER/ADKINS

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