Small Craft Advisory 529, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
556 AM AKDT SUN SEP 16 2012

.SHORT TERM...THE WEATHER OVER THE PANHANDLE THIS MORNING
REMAINS QUIET BUT THAT WILL NOT LAST LONG AS AN APPROACHING FRONT
BRINGS RAIN AND WIND FOR TONIGHT. CURRENTLY THE MAIN CONCERN
ACROSS THE AREA IS DENSE FOG IN THE SOUTHERN AND CENTRAL
PANHANDLE. DENSE FOG ADVISORIES ARE UP FOR ZONES 26 AND 27 THIS
MORNING AS FOG WITH VISIBILITIES OF A QUARTER MILE OR LESS HAVE
BEEN CONSISTENTLY OBSERVED AT OBSERVATIONS SITES AND ON VARIOUS
WEB CAMS AT PETERSBURG, WRANGELL, CRAIG, AND KLAWOCK. THAT FOG
SHOULD DISSIPATE AFTER SUNRISE THIS MORNING. LYNN CANAL AND
SKAGWAY CONTINUE TO HAVE BREEZY CONDITIONS WITH 25 KT SOUTH WINDS
AT ELDRED ROCK AND BREEZY CONDITIONS AT SKAGWAY. ELSEWHERE SKIES
RANGE FROM PARTLY CLOUDY IN THE SOUTH TO CLOUDY IN THE NORTH WITH
WINDY CONDITIONS BEGINNING TO DEVELOP IN THE NORTHERN GULF AND
OFFSHORE ZONES WEST OF 140W WHERE THE CAPE SUCKLING BUOY IS
ALREADY REPORTING GUSTS AS HIGH AS 47 KT AND SEAS UP TO 12 FT.

THOSE WINDS AND HIGH SEAS WILL SPREAD EAST THROUGH TODAY AND
TONIGHT AS THE FRONT MOVES ITS WAY TOWARD THE PANHANDLE. A STORM
WARNING IS UP FOR THE AREA AROUND CAPE SUCKLING DUE TO THE USUAL
BARRIER JET THAT HAS SET UP THERE TODAY. GALES WILL BE SPREADING
ACROSS THE NORTHERN GULF TODAY AND YAKUTAT HAS A STRONG WIND
HEADLINE UP FOR THIS AFTERNOON AND EARLY THIS EVENING FOR GUSTS TO
40 MPH. BY TONIGHT THE WINDS WILL HAVE REACHED THE REST OF THE
PANHANDLE BUT BY THAT TIME IT WILL BE LOSING SOME OF ITS PUNCH.
THE FRONT WILL BE RATHER FAR FROM ITS PARENT LOW BY THIS POINT AND
UPPER LEVEL SUPPORT IS WEAKENING SO THE FRONT WILL BE STARTING TO
SHEAR APART. STILL IT WILL HAVE ENOUGH STRENGTH TO BRING BREEZY TO
WINDY CONDITIONS TO THE INNER CHANNELS SUN NIGHT. FORECAST
CONDITIONS ARE BORDER LINE ON WHETHER A STRONG WIND HEADLINE WOULD
BE NEEDED FOR JUNEAU, SKAGWAY, AND MAYBE HAINES FOR TONIGHT.
DECIDED ON NOT ISSUING AS INDICATIONS LOOKED LIKE WINDS WOULD FALL
JUST BELOW THE CRITERIA FOR THAT BASED ON PRESSURE GRADIENT AND
MESOSCALE MODEL WIND FORECASTS. STILL DECIDED TO PUT GUSTS TO 35
MPH FOR JUNEAU AND SKAGWAY FOR TONIGHT.

RAIN WILL BE THE OTHER CONCERN FOR THIS SYSTEM. THERE IS A
SUBSTANTIAL MOISTURE PLUME ASSOCIATED WITH THIS FRONT THAT IS VERY
CLEARLY EVIDENT ON SATELLITE TOTAL PRECIP WATER RETRIEVALS. THE
PLUME EXTENDS ALL THE WAY DOWN TO JUST NW OF HAWAII. IT IS
CURRENTLY AIMED AT SOUTH CENTRAL ALASKA BUT WILL BE MOVING EAST
WITH THE FRONT THROUGH TONIGHT. YAKUTAT WILL BARE THE BRUNT OF THE
RAIN WITH 6 HOUR RAINFALL AMOUNTS POTENTIALLY REACHING UP TO 1
INCH OR MORE THROUGH THIS EVENING. THE AXIS OF HIGH ATMOSPHERIC
MOISTURE DOES NOT STAY STATIONARY FORTUNATELY. IT WILL BE MOVING
EAST WITH THE FRONT THROUGH TONIGHT AND WITH THE WEAKENING FRONT
AND UPPER SUPPORT SO TOO WILL THIS MOISTURE PLUME WEAKEN IN
STRENGTH BY THE TIME IT GETS TO THE REST OF THE PANHANDLE. STILL
ENOUGH STRENGTH REMAINS THAT PERIODS OF POTENTIALLY HEAVY RAIN MAY
STILL BE OBSERVED IN THE REST OF THE PANHANDLE AS THE FRONT MAKES
ITS WAY THROUGH TONIGHT BUT WITH LESS 6 HOUR RAINFALL AMOUNTS
EXPECTED. SMALLER STREAMS AND RIVERS ACROSS THE AREA MAY SEE
SPIKES IN WATER LEVEL AS THE PRECIP MOVES THROUGH BUT IT SHOULD
NOT BE AS EXTREME AS WHAT WAS OBSERVED LAST WEEK SINCE THE PRECIP
WILL NOT BE AS LONG LASTING.

SHORT RANGE MODELS WERE IN GOOD AGREEMENT THROUGH THE PERIOD WITH
ONLY A FEW DIFFERENCES NOTED. THE 0Z EC HAD THE BEST
INITIALIZATION OUT OF THE BUNCH WITH THE NAM NOT TOO FAR BEHIND.
DECIDED ON A BLEND OF THE EC AND NAM WITH SOME EDITING FOR THE
INNER CHANNEL WINDS DURING FRONTAL PASSAGE TONIGHT. FORECAST
CONFIDENCE IS A LITTLE ABOVE AVERAGE.

&&

.LONG TERM...THE FRONT WILL CONTINUE TO MOVE SOUTHEAST ACROSS
SOUTHEAST ALASKA AND WEAKEN ON MONDAY. RIDGE REBUILDS INTO THE
GULF MONDAY AND SHIFTS EAST OVER SOUTHEAST ALASKA TUESDAY WHERE IT
STAYS THROUGH THE END OF THE WEEK. A STRONG AND WARM UPPER HIGH
CENTER OVER THE NORTH CENTRAL PACIFIC STARTS OUT FLAT BUT SHARPENS
UP WED-THU WITH AXIS ACROSS SOUTHERN SOUTHEAST ALASKA. UPPER HIGH
IS EXPECTED TO CAP A MARINE LAYER OVER THE GULF.

RAIN DIMINISHES ACROSS NORTHERN AREAS MONDAY MORNING AND ACROSS
SOUTHERN ZONES DURING THE AFTERNOON AND EARLY EVENING. WITH THE
SOUTHERLY JET STREAK WEAKENING EXPECT RAIN AMOUNTS TO DIMINISH AS
THE FRONT PUSHES FARTHER SOUTH. WILL HAVE A SE SMCR MONDAY MORNING
FOR CLARENCE BUT THIS DIMINISHES THROUGH THE DAY AND WILL SEE WINDS
SHIFT TO THE NORTH BEHIND THE FRONT.

AS RIDGE BUILDS OVER THE GULF EXPECT A MARINE LAYER TO DEVELOP
UNDER A RATHER WARM AIR MASS THAT CAPS OFF THE INVERSION. THE
NORTHERN PANHANDLE WILL CONTINUE TO SEE ONSHORE FLOW UNTIL RIDGE
SHARPENS UP AND EXPECT CLOUDY SKIES FOR NORTHERN HALF OF
SOUTHEAST ALASKA. FOR NOW POPS REMAIN LOW WITH PAYA ZONE HAVING
BEST CHANCES FOR PRECIP BUT DO HAVE A FAIRLY FAST WSW JET WITH
SMALL DISTURBANCES EMBEDDED. HAVE PARTIAL CLEARING FOR SOUTHERN ZONES SOUTH
OF THE RIDGE AXIS LATER IN WEEK.

CONCENTRATED ON MON AND TUESDAY IN GRIDS. USED MAINLY NAM FOR PRES
AND WIND BUT INCLUDED GFS AND EC FOR POPS AND QPF. MAD ONLY SMALL
CHANGES IN LATER PERIODS.

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...DENSE FOG ADVISORY UNTIL 10 AM AKDT THIS MORNING FOR AKZ026-027.
         STRONG WIND FROM 1 PM AKDT THIS AFTERNOON THROUGH THIS EVENING
     FOR AKZ017.
MARINE...STORM WARNING FOR PKZ052.
         GALE WARNING FOR PKZ012-043-051-053.
         SMALL CRAFT ADVISORY FOR PKZ013-021-022-031>033-041-042.

&&

EAL/MM