Small Craft Advisory 785, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
240 PM AKST TUE DEC 18 2012

.SHORT TERM...A STRONG GALE FORCE LOW OVER THE S-CENTRAL GULF
WILL DRIFT SE THROUGH WED. THE ASSOCIATED OCCLUDED FRONT WILL
MOVE INTO THE FAR SRN AREA TONIGHT...THEN REACH THE CENTRAL AREA
WED BUT GO ALOFT. USED A BLEND OF THE 12Z ECMWF AND NAM FOR THE
FORECAST THROUGH WED.

 MAIN FORECAST ISSUES WILL BE WINDS...PRECIP POTENTIAL AND
AMOUNTS...AND TEMPS. RIGHT NOW THE STRONGEST WINDS OVER THE INNER
CHANNELS ARE IN THE MORE E-W CHANNELS...WITH NEAR GALE TO GALE
FORCE WINDS IN THOSE AREAS. AS THE FRONT MOVES CLOSER TO THE AREA
TONIGHT...GRADIENT ORIENTATION WILL BECOME MORE FAVORABLE FOR THE
N-S CHANNELS THROUGH THE NIGHT...INCREASING WINDS IN THOSE AREAS
TO GALE FORCE IN MOST PLACES...EXCEPT TO STORM FORCE IN NRN LYNN
CANAL. WILL BE GOING WITH STRONG WIND HEADLINES FOR TONIGHT ALONG
THE SOUTHERN AND CENTRAL COAST...FOR THE PAJN AREA IN DOWNTOWN
JUNEAU AND DOUGLAS AND OTHER OUTFLOW AREAS FROM LATE EVENING INTO
WED...AND FOR PAHN/PAGY AREAS BEGINNING LATE TONIGHT...WITH THE
PAHN ZONE LIMITED TO ALONG LYNN CANAL.

 AS FAR AS PRECIP GOES...MOST OF IT WILL FALL OVER THE SOUTHERN
HALF OF THE AREA. THE HIGHEST AMOUNTS ARE LIKELY ALONG SOUTHERN
AND EASTERN BARANOF ISLAND. PTYPE SHOULD BE SNOW EXCEPT OVER THE
FAR S AREA WHERE PRECIP WILL LIKELY MIX WITH OR CHANGE TO RAIN.
AS FAR AS SNOWFALL AMOUNTS...SOUTHERN AND EASTERN BARANOF ISLAND
WILL LIKELY GET 2-4 INCHES TONIGHT AND 1-3 INCHES WED...WITH
1-3 INCHES ALONG THE SRN COAST AND SRN INNER CHANNELS TONIGHT AND
UP TO 1 INCH WED. HAVE CHANCE POPS AS FAR N AS PAOH/PAGN AREAS.
FURTHER N AND E THE OFFSHORE FLOW LOOKS TOO DEEP TO ALLOW ANY
SIGNIFICANT PRECIP...ALTHOUGH A FEW FLURRIES CANNOT BE RULED OUT
AROUND PAJN AND PAGS WED.

 AS FOR TEMPS...THE AIRMASS WILL BE SLOWLY MODERATING TONIGHT AND
EARLY WED. LOOKS LIKE TEMPS OVER THE N WILL BOTTOM OUT THIS
EVENING THEN SLOWLY WARM OVERNIGHT AS CLOUDS MOVE IN. OVER THE
S...TEMPS WILL LIKELY REMAIN NEARLY STEADY OR RISE A BIT TONIGHT
AS FRONT APPROACHES THE AREA. WED TEMPS SHOULD BE MILDER OVER THE
S WITH MOST AREAS GETTING ABOVE FREEZING OVER THE FAR S. LATER
WED COLD ADVECTION DEVELOPS OVER THE N WHICH WILL LIMIT TEMP
RISES ESPECIALLY IN THE AFTERNOON. WHITE PASS WILL BE COLD ENOUGH
AND HAVE ENOUGH WIND TO ISSUE A WIND CHILL ADVY BEGINNING THIS
EVENING...AND CONTINUING INTO WED.

&&

.LONG TERM...MODELS ARE IN GENERAL AGREEMENT THROUGH FRIDAY NIGHT
WITH AN UPPER LEVEL CLOSED LOW OVER THE FAR SOUTHEASTERN GULF
SLOWLY FILLS AS A HIGH AMPLITUDE UPPER RIDGE CONTINUES BUILDING
ACROSS THE WESTERN GULF NORTH OVER ALASKAN INTERIOR. A SURFACE
FRONTAL PASSAGE ASSOCIATED WITH THE CLOSED UPPER LOW WILL CONTINUE
TO AFFECT THE SOUTHERN SOUTHEAST ALASKA THROUGH THURSDAY.
REFRESHED THE INHERITED FORECAST PACKAGE WITH THE ECMWF THROUGH
LATE THURSDAY TO MAKE A SMOOTH TRANSITION FROM THE SHORT TERM
FORECAST AND MAINTAIN A MAXIMUM CONSISTENCY FOR THE EARLIER
PORTIONS OF THE LONG TERM PACKAGE.

 AS THE LOW PRESSURE SYSTEM GRADUALLY WEAKENS OVER THE FAR
SOUTHEASTERN GULF...EXPECT NO SIGNIFICANT WINDS ACROSS THE
SOUTHERN PANHANDLE BUT SNOW WILL CONTINUE WITH POSSIBLE 1 TO 3
INCHES OF ACCUMULATION THROUGH LATE WEDNESDAY NIGHT. DRY COLD
WEATHER WILL PREVAIL ACROSS THE NORTHERN AND CENTRAL PANHANDLE
WITH LOCALLY WINDY CONDITIONS NEAR INTERIOR PASSES EAST OF
YAKUTAT...NORTHERN MOST PANHANDLE AND DOWNTOWN JUNEAU. STRONG
OUTFLOW WILL CONTINUE ACROSS NEAR OCEAN ENTRANCES OF INNER
CHANNELS. SOME INLAND WIND PROTECTED LOCATIONS WILL LIKELY SEE
SINGLE DIGIT OVERNIGHT MERCURY READINGS.

 THE LOW OVER THE FAR SOUTHEASTERN GULF WILL GRADUALLY SLIDE
FARTHER SOUTH AND OFFSHORE LOW LEVEL FLOW WILL CONTINUE TO ENHANCE
ACROSS SOUTHEAST ALASKA. HAVE DECIDED TO PUT STRONG WIND HEADLINE
FOR SKAGWAY...HAINES AND JUNEAU ZONES INITIALLY THROUGH THURSDAY
NIGHT. MODEL DIFFERENCES BECOME LARGER TOWARD THE WEEKEND AND THUS
LEANED OVER THE HPC ENSEMBLE APPROACH OF HEAVIER WEIGHTING ON
ECMWF FOR THE REMAINING LONG TERM PERIODS. EXPECT THE HIGH
CONTINUES MARCHING NORTH INTO THE ARCTIC OCEAN THROUGH THE
WEEKEND. THIS WILL OPEN A DOOR TO GREET A DEVELOPING STORM OVER
THE NORTH PACIFIC INTO THE GULF OF ALASKA BEFORE CHRISTMAS DAY.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...STRONG WIND FROM 6 PM AKST THIS EVENING THROUGH LATE TONIGHT FOR
     AKZ027.
         STRONG WIND FROM 9 PM AKST THIS EVENING THROUGH LATE THURSDAY
     NIGHT FOR AKZ025.
         STRONG WIND FROM 9 PM AKST THIS EVENING THROUGH LATE TONIGHT FOR
     AKZ023.
         STRONG WIND FROM LATE TONIGHT THROUGH LATE THURSDAY NIGHT FOR
     AKZ018-019.
         WIND CHILL ADVISORY FROM 9 PM THIS EVENING TO 6 PM AKST
     WEDNESDAY FOR AKZ018.
MARINE...HEAVY FREEZING SPRAY WARNING FOR PKZ012.
         STORM WARNING FOR PKZ012.
         GALE WARNING FOR PKZ011-013-021-022-031>036-041>043-051-052.
         SMALL CRAFT ADVISORY FOR PKZ053.

&&

RWT/AHN