Small Craft Advisory 538, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
150 PM AKDT FRI SEP 21 2012

.SHORT TERM...A HIGH PRESSURE RIDGE WILL WEAKEN OVER THE AREA
THROUGH TONIGHT. AN OCCLUDED FRONT OVER THE FAR SW GULF WILL MOVE
TO THE EASTERN GULF SAT. MODELS IN PRETTY GOOD AGREEMENT ON THE
LARGER SCALE FEATURES SO ENDED UP MAKING ONLY SMALL CHANGES TO
THE FORECAST WITH EXCEPTIONS NOTED BELOW.

 MAIN FORECAST ISSUES WILL BE FOG POTENTIAL...WINDS...AND PRECIP
TIMING. RIGHT NOW THE RADIATIVE FOG THAT DEVELOPED EARLY THIS
MORNING OVER MUCH OF THE AREA HAS BURNED OFF...BUT ADVECTION FOG
HAS SPREAD INTO THE FAR SRN AREA. THIS ADVECTION FOG EXTENDS ALL
THE WAY SE TO VANCOUVER ISLAND SO THE SRN AREA WILL BE IN IT FOR
QUITE A WHILE. WILL BE ISSUING DENSE FOG ADVY FOR ZONES 27 AND
28 FOR TONIGHT AND SAT MORNING AS VISIBILITIES IN THE FOG FURTHER
S ARE VERY LOW...AS LOW AS 1/8 OF A MILE. THIS FOG SHOULD
EVENTUALLY LIFT SLOWLY DURING SAT AS INCREASING LIFT AHEAD OF THE
APPROACHING FRONT RAISES THE INVERSION LEVEL. ELSEWHERE OVER THE
LAND AND INNER CHANNELS...PATCHY FOG SHOULD DEVELOP THIS EVENING
OVER MUCH OF THE AREA. WINDS JUST ABOVE THE SURFACE LOOK LIKE
THEY WILL BE A LITTLE STRONGER TONIGHT THAN THEY WERE FRI
MORNING...WHICH SHOULD LIMIT HOW MUCH FOG FORMS. LOOKS LIKE THE
FOG OVER THE CENTRAL AREA WILL BE LESS WIDESPREAD TONIGHT THAN IT
WAS FRI MORNING ...AND CHANCES FOR DENSE FOG THERE SHOULD BE
REDUCED. WILL KEEP IN MARINE FOG FOR THE GULF...WITH IT ERODING
AWAY FROM THE SW LATE TONIGHT AND SAT AS FRONT MOVES IN.

 AS FOR WINDS...A SLOW INCREASE IN E-SE WINDS SHOULD OCCUR FROM
THE SW TONIGHT AND SAT AHEAD OF THE OCCLUDED FRONT. WINDS SHOULD
REACH GALE FORCE W OF 142W BY LATE TONIGHT...THEN REACH THE REST
OF THE ERN GULF SAT. INNER CHANNEL WINDS WILL GENERALLY BE LESS
THAN 15 KT TONIGHT EXCEPT FOR CROSS SOUND WHERE 15-20 KT ELY
WINDS SHOULD PERSIST. WINDS SHOULD PICK UP TO 15-20 KT OVER MUCH
OF THE INNER CHANNELS SAT AS FRONT MOVES CLOSER TO THE AREA.

 PRECIP WISE...THERE MAY BE SPOTTY LIGHT PRECIP ALONG THE N GULF
COAST TONIGHT IN ONSHORE FLOW BUT WILL KEEP POPS LOW. RAIN SHOULD
MOVE IN FROM THE SW SAT...REACHING THE PAYA ZONE BY LATE MORNING
TO EARLY AFTERNOON...AND LIKELY REACHING THE CENTRAL COASTAL AREA
BY LATE AFTERNOON. WILL HAVE CHANCE POPS A LITTLE INLAND FROM THE
CENTRAL COAST BY LATE AFTERNOON AS WELL.

 OTHERWISE...WILL HAVE SOME LOW AND MID-LEVEL CLOUDS DRIFTING NWD
ACROSS THE AREA TONIGHT...THEN THE MORE NERN INNER CHANNELS MAY
SEE CLOUDS DIMINISH SAT AS OFFSHORE FLOW INCREASES. LOWERED MAX
TEMPS ESPECIALLY S AREA WHERE THEY WILL REMAIN IN MARINE CLOUDS
THROUGH THE DAY.

&&

 .LONG TERM...RATHER ACTIVE LONG RANGE FORECAST IN THE WORKS AS
WE HAVE THREE SEPARATE SYSTEMS TO WORRY ABOUT OVER THE NEXT WEEK.
SYSTEM NUMBER ONE SHOWS UP ON SAT NIGHT INTO EARLY SUN AND WILL
BRING AN END TO THE NICE WEATHER WE HAVE BEEN HAVING RECENTLY.
MUCH OF THE GULF WILL BE EXPERIENCING SE TO E WINDS OF 25 KT TO
30 KT SAT NIGHT AND SUN WITH MIN GALE FORCE WINDS SAT EVENING IN
THE NORTHERN GULF DUE TO THE USUAL BARRIER JET THAT WILL SET UP
ALONG THE NORTHERN GULF COAST. THE WIND DO NOT MAKE IT VERY FAR
INLAND AS THE CURRENT RIDGE WILL STILL BE HANGING STRONG OVER THE
AREA AND THE DISTANCE OF THE FRONT FROM ITS PARENT LOW WILL CAUSE
IT TO WEAKEN AS IT MAKES THE OUTER COAST. SO I AM MAINLY
EXPECTING BREEZY CONDITIONS ALONG THE OUTER COAST EARLY SUN AND
LESS WIND INLAND. RAIN WILL ALSO BE FORTHCOMING WITH THIS FRONT,
BUT WILL NOT BE THE SOAKER THAT ANCHORAGE HAS BEEN GETTING OVER
THE LAST FEW DAYS. MOISTURE PLUME WILL BE WEAKENING ALONG WITH
THE FRONT AS IT MOVE ONSHORE. THAT AND THE FRONT WILL BE MOVING
AT A DECENT CLIP SO ANY HEAVY RAIN WILL NOT STAY OVER ONE PLACE
FOR VERY LONG. TOTAL RAINFALL AMOUNTS ARE EXPECTED TO BE FROM A
QUARTER INCH TO HALF AN INCH OVER THE PANHANDLE WITH MAYBE UP TO
1 INCH NEAR YAKUTAT.

 FOLLOWING THIS IS A TWO DAY STRETCH OF RELATIVELY DECENT WEATHER
WHERE THEIR MAY EVEN BE SOME FOG IN AREAS OF THE PANHANDLE MON
AND TUES MORNING. THEN SYSTEM NUMBER TWO ARRIVES FOR TUES NIGHT.
THIS ONE LOOKS TO BE ABOUT THE SAME STRENGTH AS THE WEEKEND
SYSTEM BUT MAY BE A BIT STRONGER IN THE WIND DEPARTMENT MAINLY
DUE TO A WEAK WAVE DEVELOPING ALONG THE FRONT IN THE CENTRAL
GULF. LOOKING AT POSSIBLY GALES ALONG THE NORTHERN GULF WITH SOME
GUSTY WINDS POSSIBLE ALONG THE OUTER COAST TUES NIGHT. MODELS ARE
IN FAIRLY GOOD AGREEMENT ON THE FRONT BUT THE STRUCTURE OF THE
PARENT LOW OVER THE ALASKA PENINSULA LEAVES SOMETHING TO BE
DESIRED. DECIDED ON A EC/GFS BLEND TO EVEN THINGS OUT FOR LATE
MON INTO TUES.

 FOR MID WEEK AND BEYOND MODELS ARE STARTING TO INDICATE THAT
THEIR MAY BE A STRONGER SYSTEM IN THE WORKS FOR WED NIGHT INTO
THURS AS A FAIRLY STRONG SHORTWAVE ROUNDS THE BASE OF THE ALASKA
PENINSULA LOW AND MAKES ITS WAY INTO THE GULF. WHERE AND HOW
STRONG ARE BEING FIERCELY DEBATED BY THE MODELS BUT MOST AGREE ON
SOMETHING BEING IN THE GULF BY EARLY THURS. THE OPERATIONAL ECMWF
HAS THE GREATEST SPREAD ON STRENGTH WITH THE NEW AND OLD 12Z RUNS
NOT HAVING MUCH OF A LOW THERE (AROUND 998 MB) WHILE THE 0Z RUN
HAD A 956 MB LOW IN THE SAME PLACE. OPERATIONAL GFS HAS BEEN THE
MOST CONSISTENT WITH AROUND A 968 MB LOW IN THE CENTRAL GULF.
VARIOUS OTHER SUPPORT COMES FROM THE LATEST RUNS OF THE LONG
RANGE UKMET (964 MB), THE GEM GLOBAL (956 MB), AND THE GFS
ENSEMBLE MEAN (975 MB). OPTED FOR THE HPC GUIDANCE THAT WENT FOR
A 973 MB LOW TRAVELING NORTH THROUGH THE WESTERN AND CENTRAL GULF
ON THURS AS THAT SEEMED LIKE A DECENT MIDDLE GROUND TO WORK WITH
FOR THE MOMENT. WILL HAVE TO KEEP AN EYE ON WHAT FUTURE RUNS DO
WITH THIS AS IT COULD HAVE THE POTENTIAL TO BEING SOME RATHER
STRONG WINDS TO THE AREA.

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...DENSE FOG ADVISORY FROM 6 PM THIS EVENING TO 10 AM AKDT SATURDAY
     FOR AKZ027-028.
MARINE...GALE WARNING FOR PKZ041>043-051-052.

&&

RWT/EAL