Small Craft Advisory 27, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
418 PM AKST TUE JAN 10 2012

.SHORT TERM...RATHER COMPLICATED FORECAST FOR TONIGHT AND
TOMORROW AS A FRONT COMES IN OFF THE GULF BRINGING PRECIP AND
WIND. LIGHT SNOW HAS ALREADY STARTED FALLING IN THE NORTHERN HALF
OF THE PANHANDLE TODAY AND YAKUTAT HAS SEEN THE HEAVIER SNOWFALL
RATES START UP IN THE LAST HOUR OR TWO. TEMPERATURES REMAIN BELOW
FREEZING IN MOST AREAS AT THE MOMENT. THE EXCEPTIONS ARE ALONG
THE SOUTHERN OUTER COAST AND EXTREME SOUTHERN PANHANDLE. WINDS
ARE ALSO STARTING TO PICK UP WITH GUSTS REACHING 20 KT IN PORT
ALEXANDER AND JUNEAU SO FAR.

THE MAIN FORECAST PROBLEM WILL BE HOW LONG THE SNOW WILL LAST
BEFORE THE WARM ADVECTION CHANGES IT OVER TO RAIN TONIGHT AND
TOMORROW AND HOW MUCH ACCUMULATION WILL WE GET. YAKUTAT LOOKS LIKE
IT WILL BE THE BIG WINNER WITH CHANGE OVER NOT OCCURRING TO LATER
TONIGHT. AS SUCH WITH THE HEAVIER SNOWFALL RATES ALREADY OCCURRING
I KEPT THE WINTER STORM WARNING UNCHANGED FROM THE PREVIOUS
FORECAST. OTHER AREAS ARE A BIT TRICKIER. THE WINTER STORM WARNING
FOR HAINES ALSO REMAINS BUT THE HIGHER ACCUMULATIONS WILL BE UP
THE HAINES HIGHWAY WHERE THE COLD AIR WILL BE HARDER TO DISLODGE.
HAINES ITSELF MAY SEE LESS AS OVERRUNNING EFFECTS MAY BE LESS
THERE. SKAGWAY WILL STAY SNOW BUT THE QPF MAY NOT MAKE IT THAT FAR
NORTH FOR ANY HIGH ACCUMULATIONS. JUNEAU, HOONAH, GUSTAVUS,
PETERSBURG AND PELICAN ARE THE HARD ONES AS THESE PLACES ARE VERY
CLOSE TO THE FREEZING POINT ALREADY AND HAVE THE POTENTIAL TO STAY
SNOW LONGER THEN AREAS FARTHER SOUTH. SHORT RANGE MODELS ARE AT
ODDS ON SNOW AMOUNTS WITH THE NAM BRINGING HIGH SNOW FALL AMOUNTS
AND THE GFS GOING FOR MUCH LOWER AMOUNTS. BASED ON EXPECTED QPF
AMOUNTS INLAND THE AMOUNT OF WARM ADVECTION AND MODEL TRENDS FOR
THIS SEASON SO FAR I AM TRENDING TOWARD THE LOWER AMOUNTS
ADVERTISED BY THE GFS. THAT WOULD MEAN AMOUNTS JUST BELOW ADVISORY
FOR JUNEAU AND ADVISORY FOR GUSTAVUS, HOONAH, AND PELICAN. FARTHER
SOUTH THE WARM ADVECTION WILL BRING THE CHANGE OVER TO RAIN FASTER
AND THE PRECIP WILL START LATER ENOUGH FOR ONLY LIGHT
ACCUMULATIONS.

WIND WILL BE THE OTHER PROBLEM. GALE FORCE WINDS ARE EXPECTED OUT
IN THE GULF THROUGH TOMORROW MORNING AND STRONG WIND HEADLINES ARE
UP FOR ELFIN COVE AND SITKA AREAS LATE TONIGHT. FARTHER SOUTH,
HYDABURG AND KETCHIKAN WILL JUST HAVE BREEZY CONDITIONS AS THE
FRONT WILL HAVE SHEARED APART ENOUGH FOR THE WINDS TO NOT BE AS
STRONG. THE INNER CHANNELS MAY ALSO SEE SOME BREEZY CONDITIONS AS
THE FRONT MOVES THROUGH.

SHORT RANGE FORECAST MODELS WERE IN DECENT AGREEMENT OVERALL BUT
THERE WERE SOME SMALL DIFFERENCES IN THE DETAILS. MAINLY WENT WITH
THE GFS AND NAM FOR FORECAST UPDATES. FORECAST CONFIDENCES IS
ABOUT AVERAGE DUE TO THE UNCERTAINLY IN THE PTYPE AND SNOW
AMOUNTS.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH TUESDAY/...LOW PRESSURE IN THE
GULF WILL CONTINUE RAIN AND SNOWFALL ACROSS THE REGION WED NIGHT
THROUGH THURSDAY. RAIN/SNOW LINE WILL BE FROM SITKA TO JUNEAU AND
ALONG THE COASTAL MOUNTAINS. EXPECT NORTHERN AREAS AND HYDER TO
REMAIN MAINLY SNOW. GREATEST QPF RATES WILL BE AS THE ASSOC TROUGH
PASSES MIDDAY THURS. PRECIP BECOMES MORE SCATTERED LATER THURSDAY
INTO FRIDAY.

THE LOW PRESSURE IN THE GULF WILL START TO SHIFT TO THE SE FRIDAY
AS A HIGH PRESSURE DEVELOPS OVER THE YUKON. THIS WILL SHIFT WINDS
TO THE NORTH AND MAKE THE SOUTHERN AREAS HAVE THE GREATEST
LIKELIHOOD OF RAIN AND SNOW MIX. WINDS WILL INCREASE OUT OF THE
NORTH THROUGH THE WEEKEND AS THE HIGH PRESSURE BUILDS BRINGING IN
A DRY ARCTIC AIRMASS FROM CANADA. EXPECT PARTLY CLOUDY TO MOSTLY
SUNNY SKIES AND TEMPERATURES IN THE TEENS TO SINGLE DIGITS ACROSS
THE NORTH. WIND CHILL VALUES LOOK TO BE IN THE NEGATIVE 20S AS A
RESULT. NUMERICAL MODELS HAVE MUCH COLDER TEMPERATURES THAN GOING
FORECAST...BUT LIMITED CHANGES TO ABOUT 5 DEGREES DUE TO
UNCERTAINTY THAT FAR OUT. THEREFORE WIND CHILLS COULD BE MORE
SIGNIFICANT AS WELL AS FREEZING SPRAY.

MODELS TEND TO DO WELL WITH WINDS DURING COLD AIR OUTBREAKS.
CONTINUED TO EMPHASIZE THE NORTHERLY GAP WINDS WITH THIS PACKAGE.
THE MODELS ALSO TEND TO OVERDUE COLD TEMPS IN THIS SITUATION SO
LIMITED CHANGES SOME. USED A BLEND OF THE ECMWF AND GFS FOR
PRESSURE WITH A NUDGE TOWARD THE GFS FOR WINDS AS IT SHOWED THE
GAP WINDS OFFSHORE. FORECASTER CONFIDENCE IS AVERAGE TO SLIGHTLY
ABOVE AVERAGE.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...STRONG WIND UNTIL MIDNIGHT AKST TONIGHT FOR AKZ025.
         WINTER WEATHER ADVISORY UNTIL 5 AM AKST WEDNESDAY FOR AKZ020>022.
         STRONG WIND THROUGH WEDNESDAY MORNING FOR AKZ023.
         WINTER STORM WARNING UNTIL 4 PM AKST WEDNESDAY FOR AKZ019.
         STRONG WIND UNTIL MIDNIGHT AKST TONIGHT FOR AKZ018.
         WINTER STORM WARNING UNTIL 5 AM AKST WEDNESDAY FOR AKZ017.
MARINE...GALE WARNING FOR PKZ036-041>043-051-052.
         SMALL CRAFT ADVISORY FOR PKZ011>013-021-022-031>035-053.

&&

EAL/HANNON

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