Small Craft Advisory 816, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
539 AM AKST SAT DEC 29 2012

.SHORT TERM...A FRONTAL BOUNDARY OVER THE EASTERN GULF AS OF
EARLY THIS MORNING IS PRODUCING GALE FORCE WINDS OVER THE COASTAL
MARINE WATERS WEST OF ICY BAY. WIND OVER THE EASTERN GULF WILL
STEADILY INCREASE THROUGH THE DAY AND MOST OF TONIGHT AS THE
FIRST FRONT GOES ALOFT AND MOVES INLAND AND A SECOND FRONT
ASSOCIATED WITH A FAST MOVING STORM FORCE LOW ENTERS THE EASTERN
GULF. ASSOCIATED LOW WILL REMAIN WELL TO THE WEST, SO THE FRONT
WILL WEAKEN AS IT PUSHES INTO THE EASTERN GULF AND STORM FORCE
WINDS EAST OF ICY BAY WILL DIMINISH PRIOR TO SUNDAY MORNING. WILL
LIKELY SEE WIND GUSTS ALONG THE OUTER COAST TO 35 MPH BUT DID NOT
HAVE ENOUGH CONFIDENCE TO PUT STRONG WIND HEADLINES IN THE
MORNING FORECAST. STORM AND GALE WARNINGS ON THE OUTSIDE TODAY
AND TONIGHT. SMALL CRAFT ADVISORIES FOR MAINLY THE EAST-WEST
INNER CHANNELS AS WELL AS GLACIER BAY, CLARENCE STRAIT, AND
SOUTHERN CHATHAM STRAIT. ALSO HAVE A SMALL CRAFT OUT FOR YAKUTAT
BAY.

 WARM SECTOR AIR MASS WILL CAUSE A RISE IN TEMPS ACROSS THE
PANHANDLE TODAY THAT IS EXPECTED TO CONTINUE IN MANY LOCATIONS
THROUGH SATURDAY NIGHT WITH OTHER LOCATIONS SEEING LITTLE TO NO
DIURNAL VARIABILITY. ADJUSTED DAYTIME HIGHS AND OVERNIGHT LOWS
DOWN IN RESPONSE TO A SIGNIFICANT WARM BIAS IN RECENT FORECASTS,
BUT RESULTING SNOW LEVELS STILL SUPPORTING RAIN TONIGHT
EVERYWHERE EXCEPT ALONG THE HAINES AND KLONDIKE HIGHWAYS, NEAR
HYDER, AND EASTERN PORTIONS OF ZONE 26. NO SNOW ACCUMULATIONS
GREATER THAN ONE INCH IN THE SHORT TERM FORECAST. HIGHEST QPF
VALUES CONCENTRATED OVER CENTRAL ZONE 17 SLIGHTLY WEST OF YAKUTAT
BAY TONIGHT BUT STILL EXPECT TO SEE HEAVY RAIN TONIGHT IN THE
TOWN OF YAKUTAT.

 USED ECMWF FOR PRESSURE AND WIND DIRECTION. WIND SPEEDS BIASED
TOWARDS NAM. POP AND QPF BASED ON NAM. TEMPS ADJUSTED USING NAM
AND GFS40. FORECAST CONFIDENCE IS AVERAGE.

 &&

 .LONG TERM...ACTIVE LONG RANGE WEATHER PATTERN AS SERIES OF LOW
PRESSURE SYSTEMS MOVE UP FROM THE NORTH PACIFIC TOWARD THE
ALEUTIANS AND WESTERN GULF WITH ASSOCIATED WEATHER FRONTS MOVING
ACROSS THE AK GULF TOWARDS THE PANHANDLE. THIS STABLE PATTERN IS
DUE TO UPPER LEVEL TROUGH OVER THE BERING AND RIDGE OVER THE AK
GULF AND PANHANDLE. AS EACH FRONT TRACKS EASTWARD WILL INCREASE
WINDS OVER THE AK GULF TO GALE FORCE AND THE SOUTHERLY FLOW WILL
KEEP MOST OF THE REGION UNDER WARM AND WET CONDITIONS.

 FOR SUNDAY THE STORM FORCE LOW NEAR KODIAK WILL WEAKEN AS IT
MOVES TO THE NORTHWEST. WINDS IN THE NORTHERN GULF WILL DIMINISH
AS THE BARRIER JET WEAKENS WITH THE EXITING LOW. THE ASSOCIATED
FRONT WILL BEGIN TO SHEAR APART AS IT MOVES TO THE EAST. BEFORE
THIS FRONT SHEARS APART THE LONG FETCH OF MOISTURE WILL KEEP HIGH
QPF VALUES THROUGH THE DAY. THE HEAVIER RAINFALL FROM THIS
ATMOSPHERIC RIVER COULD PRODUCE ADVISORY LEVEL SNOWFALL AMOUNTS
AT HIGHER ELEVATION ALONG THE NORTHERN PANHANDLE HIGHWAYS..BUT AS
OF NOW HAVE KEPT SNOW AMOUNTS BETWEEN 1 TO 3 INCHES FOR THESE
AREAS. THERE ARE INDICATIONS OF A SHORT WAVE MOVING UP FROM THE
PACIFIC INTO THE SOUTHERN AK GULF BY SUNDAY AFTERNOON BUT THERE
IS A FAIR AMOUNT OF SPREAD AMONG THE MODELS REGARDING THIS
FEATURE. PREVIOUS RUNS HAD A CLOSED LOW FORMING BUT NEWER RUNS
NOW INDICATE A MUCH WEAKER SYSTEM OR AN OPEN WAVE TROUGH. MAIN
DIFFERENCES WOULD BE WIND MAGNITUDE ALONG THE SOUTHERN AK GULF
AND PANHANDLE COAST.

 BY MONDAY REPEATING THIS PATTERN OF A GALE FORCE LOW MOVING FROM
THE NORTH PACIFIC TOWARD THE ALEUTIANS WITH WEATHER FRONT MOVING
ACROSS THE GULF. SEEING SIMILAR ATMOSPHERIC RIVER MOVING IN
SIGNIFICANT MOISTURE AND A DEVELOPING LOW MOVING INTO THE
SOUTHERN PANHANDLE BY TUESDAY EVENING AS THE MAIN LOW TRACKS
NORTH TOWARDS THE BERING SEA. BY MID WEEK WHILE THERE IS NOT MUCH
CHANGE TO THE PATTERN BUT MODEL SPREAD WITH RESPECT TO SURFACE
DETAILS INCREASES. MAY SEE TEMPERATURES DROPPING SLIGHTLY LATER
IN THE WEEK BUT OVERALL WITH SOUTHERLY FLOW THE REGION WILL
REMAIN ABOVE FREEZING WITH MAJORITY OF PRECIPITATION FALLING AS
RAIN.

 WHILE MODELS WERE NOT IN GOOD AGREEMENT FOR SUNDAY FOR THE
DEVELOPING LOW MOVING INTO THE SOUTHERN GULF THEY FALL BACK IN
LINE WITH THE NEXT WESTERN GULF SYSTEM BY MONDAY. UPDATED
FORECAST WITH GFS ON SUNDAY THEN TRANSITIONED TO A GFS/ECMWF
BLEND. KEPT THE HPC ENSEMBLE SOLUTION FOR DAY 4 ONWARD DUE TO THE
LARGER MODEL SPREAD. FORECAST CONFIDENCE IS AVERAGE FOR THE
GENERAL WARM AND WET SYNOPTIC PATTERN BUT BELOW AVERAGE WITH
SURFACE DETAILS AND SYSTEM TIMING.

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...STORM WARNING FOR PKZ051-052.
         GALE WARNING FOR PKZ041>043.
         SMALL CRAFT ADVISORY FOR PKZ011-021-022-033>036-053.

&&

FRITSCH/PRB