Small Craft Advisory 1, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
439 PM AKST SAT DEC 31 2011

.SHORT TERM...COMPLICATED WINTER WEATHER SCENARIO WITH BOTH
WINTER STORM AND HIGH WIND WARNINGS. A COMPLEX LOW SOUTH OF THE
GULF HAS A DEVELOPING WAVE ENTERING THE SOUTHERN GULF THIS
EVENING. THIS WAVE WILL DEVELOP INTO A SURFACE LOW OVERNIGHT.
HIGH PRESSURE OVER BRITISH COLUMBIA IN CONJUNCTION WITH LOW
PRESSURE OVER THE GULF IS ALREADY PRODUCING A STRONG EASTERLY
NEAR-SURFACE PRESSURE GRADIENT. ORIENTATION OF MID LEVEL
THICKNESS PATTERN AND VERY HIGH MID LEVEL MOISTURE VALUES SETTING
UP A SIGNIFICANT OVER RUNNING EVENT FOR SOUTHEAST ALASKA IN THE
SHORT TERM FORECAST PERIOD THAT WILL EXTEND INTO THE BEGINNING OF
THE LONG RANGE FORECAST PERIOD.

AS THE LOW APPROACHES TONIGHT, EXPECT THE OFFSHORE PRESSURE
GRADIENT TO INTENSIFY AND A SOUTHERLY PRESSURE GRADIENT OVER THE
FAR NORTHERN INNER CHANNELS WILL REVERSE. HIGH WIND WARNING IN
PLACE FOR ZONE 27 BEGINNING TOMORROW MORNING ASSOCIATED WITH A
PRE-FRONTAL TROUGH. HIGH WIND WARNING EXPANDS TO INCLUDE ZONES 23
AND 28 AS THE MAIN OCCLUDED FRONT APPROACHES LAND. THINK MOST OF
THE WIND FOR ZONE 23 WILL BE EXPERIENCED ALONG THE SOUTHEASTERN
PORTION OF BARANOF ISLAND. WINDY CONDITIONS WILL EXPAND NORTH AND
INLAND AS THE FRONT MOVES OVER LAND. WINDS GENERALLY EASTERLY OR
SOUTHEASTERLY SOUTH OF A LINE FROM CAPE SPENCER TO NEAR BERNERS
BAY. WINDS WILL BE NORTHERLY FOR POINTS NORTH OF HERE.
ADDITIONALLY, STRONG OUTFLOW GUSTS OUT OF THE NORTHEAST WILL OCCUR
OVER ZONE 17 WITH GUSTS TO 30 MPH IN YAKUTAT.

IN ADDITION TO HAZARDOUS WINDS, THIS SYSTEM WILL FEATURE HEAVY
SNOW. SURFACE TEMPS WILL SUPPORT SNOW AT THE START OF THIS EVENT
ACROSS ALL OF THE PANHANDLE AND SNOW WILL BEGIN LATE TONIGHT AND
SPREAD NORTH BEFORE THE ACTUAL WINTER STORM WARNING STARTS, SINCE
THE HEAVIEST SNOW IS NOT EXPECTED UNTIL TOMORROW AFTERNOON AND
CONTINUING THROUGH TOMORROW NIGHT FOR NORTHERN LOCATIONS. SOUTHERN
LOCATIONS WILL SEE 1 TO 2 INCHES OF SNOW BEFORE CHANGING OVER TO
RAIN, AS WILL YAKUTAT. SLIGHTLY HIGHER AMOUNTS ALONG THE OUTER
COAST BETWEEN CAPE SPENCER AND CAPE EDGECUMBE WITH 4 TO 8 INCHES
EXPECTED. LOCATIONS FROM SITKA SOUTH SHOULD SEE ONLY 1 TO 2 INCHES
BEFORE CHANGING OVER TO RAIN. CENTRAL PANHANDLE LOCATIONS EXPECTED
TO SEE HEAVIEST SNOW FROM THIS OVER RUNNING EVENT. WITH UP TO 12
INCHES CURRENTLY IN THE FORECAST FOR HAINES, GUSTAVUS, HOONAH, AND
JUNEAU. AM EXPECTING 8 TO 10 INCHES FOR KAKE, PETERSBURG, AND
WRANGELL. SNOW OVER THE WINTER STORM WARNING AREA WILL CONTINUE
INTO THE LONG RANGE FORECAST PERIOD WHICH BEGINS SUNDAY EVENING.

USED GFS FOR SHORT TERM FORECAST DUE TO SUPERIOR INITIALIZATION
OF DEVELOPING WAVE IN THE GULF AND PARENT LOW TO THE SOUTHWEST.
FORECAST CONFIDENCE IS ABOVE AVERAGE.

.LONG TERM...THE EVENTS IN THE SHORT RANGE SECTION ABOVE CONTINUE INTO
SUNDAY NIGHT WITH THE LANDFALLING FRONT PROVIDING WARM ADVECTION THAT
RAISES THE SNOW LEVELS IN A S TO NORTH SEQUENCE ALONG THE PANHANDLE.
SOME OF THE WINTER STORM WARNINGS LISTED BELOW ARE FOR HEAVY SNOW
THAT ENDS DUE TO THE WARMUP CHANGING SNOW TO RAIN OR AT LEAST MIXING
WITH RAIN. PLEASE READ THE WARNINGS FOR DETAILS.

MONDAY WILL HAVE LITTLE DIURNAL TEMPERATURE RISE WITH THE COLD AIRMASS
AFTER FROPA.

LARGE SCALE OF TWO MAJOR SYSTEMS, ONE ON EITHER SIDE OF THE DATELINE.
THE SECOND LARGE SYSTEM TWO BEGIN TO CROSS THE DATELINE AND HAS A
HIGHLY BAROCLINIC ENVIRONMENT WITH DEEP STRONG CYCLOGENESIS BEGINNING.
THE FORECAST CONFIDENCE FOR THE FIRST SYSTEM IS AVERAGE FOR THE
LONG RANGE SECTION.  THE FORECAST CONFIDENCE FOR THE SECOND MAJOR
SYSTEM IS BELOW AVERAGE.

MODELS: THROUGH 18Z MONDAY THE 31.12 GFS WAS EMPHASISED DUE TO A
GOOD INITIALIZATION OF A COMPLEX SYSTEM. THE SECOND MAJOR SYSTEM
IS STILL ISSUED USING BOTH THE GFS AND EC.

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...WINTER STORM WARNING FROM 2 AM TO 6 PM AKST SUNDAY FOR AKZ024-
     026.
         HIGH WIND WARNING FROM 6 AM TO 6 PM AKST SUNDAY FOR AKZ027.
         WINTER STORM WARNING FROM 9 AM SUNDAY TO 5 AM AKST MONDAY FOR
     AKZ019>021-025.
         WINTER WEATHER ADVISORY FROM 3 AM TO 3 PM AKST SUNDAY FOR AKZ022.
         HIGH WIND WARNING FROM 9 AM TO 6 PM AKST SUNDAY FOR AKZ023-028.
         STRONG WIND FROM MIDNIGHT AKST TONIGHT THROUGH SUNDAY AFTERNOON
     FOR AKZ029.
MARINE...STORM WARNING FOR PKZ022-036-041>043.
         GALE WARNING FOR PKZ011>013-021-031>035-051>053.

&&

ABJ/JBT