Small Craft Advisory 600, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
557 AM AKDT WED OCT 17 2012

.SHORT TERM...MAIN FORECAST ISSUE IN THE SHORT RANGE IS WHETHER
OR NOT AN APPROACHING LOW WILL PRODUCE THE FIRST SIGNIFICANT
SNOWFALL FOR THE PANHANDLE SOUTH OF CAPE FAIRWEATHER. USUAL CUES
FOR SNOW VERSUS RAIN IN SOUTHEAST ALASKA ARE IN THE GREY ZONE
THAT COULD SUPPORT EITHER RAIN, SNOW, OR A RAIN SNOW MIX
DEPENDING ON MESOSCALE INFLUENCES. SPECIFICALLY, THE 1280H
1000-850 MB THICKNESS LINE LIES OVER THE FAR NORTHERN INNER
CHANNELS AS DEPICTED BY NAM, BUT IS FARTHER NORTH IN BOTH THE
ECMWF AND THE GFS. SIMILAR SITUATION FOR 850 MB TEMPERATURES WITH
THE -8 CENTIGRADE LINE OVER THE NORTHERN INNER CHANNELS AND THE
-4 LINE OVER THE FAR SOUTHERN INNER CHANNELS. 1000-500MB
THICKNESS VALUES SUPPORT RAIN OVER THE FAR SOUTHERN ZONES, SNOW
OVER THE FAR NORTHERN INNER CHANNELS AND YAKUTAT, AND A RAIN SNOW
MIX IN BETWEEN. NAM IS THE MOST CONSERVATIVE WITH THE LATE NIGHT
SURFACE FREEZING ISOTHERM AND KEEPS THE AREA SOUTH OF THE ICY
STRAIT AND WEST OF STEPHENS PASSAGE ABOVE FREEZING. USED THIS AS
A GUIDE FOR FORECAST SNOWFALL TONIGHT. HAVE UP TO AN INCH FOR
LOCATIONS NORTH OF ICY STRAIT AND ALSO IN THE MENDENHALL VALLEY.
ELSEWHERE INLAND FROM THE OUTER COAST AND NORTH OF SUMNER STRAIT
RAIN SHOWERS, POSSIBLY MIXED WITH SNOW SHOWERS AT TIMES, BUT NO
ACCUMULATION.

THE OTHER ISSUE FOR THE SHORT TERM FORECAST PERIOD WILL BE STRONG
WINDS ASSOCIATED WITH THE APPROACHING LOW. HAVE SOLID GALES FOR
THE SOUTHERN COASTAL MARINE WATERS AS WELL AS FOR CLARENCE STRAIT.
MAINTAINING THE STRONG WIND HEADLINES FOR TODAY AS ISSUED BY THE
TUESDAY DAY SHIFT AND ADDED SOME MORE FOR TONIGHT FOR ZONE 27. THE
LOW ITSELF IT QUITE COMPACT AND FAIRLY INTENSE. IT IS FORECAST TO
TRACK OVER THE FAR SOUTHERN PANHANDLE AND WINDS WILL SHIFT
DRAMATICALLY AS THIS HAPPENS. TRYING TO CAPTURE THAT IN GRIDS AND
WORDS HAS BEEN PARTICULARLY CHALLENGING.

PREFERRED ECMWF FOR POP BASED ON MID LEVEL MOISTURE
INITIALIZATION. FAVORED GFS FOR ADJUSTMENT TO TEMPS AND SNOW
LEVELS BASED ON SURFACE TEMPERATURE INITIALIZATION AND RECENT
MODEL PERFORMANCE. PREFERRED ECMWF FOR JET STRENGTH AND LOCATION.
OVERALL FORECAST CONFIDENCE IS AVERAGE.

&&

 .LONG TERM...EXPECTING AN UPPER LEVEL LOW TO SLOWLY MIGRATE FROM
THE NORTH CENTRAL GULF ON THURSDAY TO THE SOUTHEAST GULF ON
SATURDAY. A FAIRLY STRONG SURFACE HIGH IS FORECAST TO BUILD
ACROSS THE ALASKAN INTERIOR OVER THE WEEKEND AND THEN MOVE INTO
THE YUKON BY EARLY NEXT WEEK.

EXPECT SHOWER ACTIVITY TO DIMINISH FROM THE NORTHWEST THURSDAY
THROUGH SATURDAY AND THEN HAVE A DRY FORECAST BEYOND. SOME COLD
AIR ALOFT WITH THE UPPER LOW WILL KEEP A CHANCE THAT SHOWERS WILL
BE MIXED WITH SNOW BUT GENERALLY HAVE SNOW LEVELS 500 FEET OR
HIGHER.

WILL SEE INCREASING NORTHERLY WINDS FOR THE INNER CHANNELS
STARTING SATURDAY. CAA WITH THE NORTHERLY WILL BRING TEMPS DOWN BY
EARLY NEXT WEEK WITH HIGHS ONLY AT FREEZING FOR NORTHERN INNER
CHANNELS.

NO MAJOR DIFFERENCES BETWEEN MODELS OVER SOUTHEAST ALASKA. USED
NAM AND EC FOR THU AND FRI TRANSITIONING TO HPC GRIDS FOR LATER
PERIODS.

.AJK WATCHES/WARNINGS/ADVISORIES... PUBLIC...STRONG WIND FROM
1 PM AKDT THIS AFTERNOON THROUGH THIS EVENING      FOR
AKZ027-028.         STRONG WIND FROM THIS EVENING THROUGH LATE
TONIGHT FOR AKZ027. MARINE...GALE WARNING FOR PKZ036-041-043.
     SMALL CRAFT ADVISORY FOR PKZ021-022-033>035-042-051-052.

 &&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...STRONG WIND FROM 1 PM AKDT THIS AFTERNOON THROUGH THIS EVENING
     FOR AKZ027-028.
         STRONG WIND FROM THIS EVENING THROUGH LATE TONIGHT FOR AKZ027.
MARINE...GALE WARNING FOR PKZ036-041-043.
         SMALL CRAFT ADVISORY FOR PKZ021-022-033>035-042-051-052.

&&

FRITSCH/MM

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE JUNEAU AK
1234 PM AKDT WED OCT 17 2012

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1230 PM     SNOW             YAKUTAT                 59.54N 139.73W
10/17/2012  M6.9 INCH                           AK   NWS EMPLOYEE

            SNOWFALL ACCUMULATION FROM MIDNIGHT TO 1230 PM WEDNESDAY.

&&

RCL