Small Craft Advisory 580, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
422 PM AKDT WED OCT 10 2012

.SHORT TERM...THE LAST REMNANTS OF THE RIDGE OF HIGH PRESSURE
FROM THE GULF OF ALASKA REMAINS AS WEAKENING FINGER OF HIGH
PRESSURE ALONG THE BRITISH COLUMBIA COAST AND ACROSS THE SOUTHERN
PORTION OF THE PANHANDLE AND THE IMMEDIATE COASTAL WATERS OF THE
PANHANDLE. THROUGH THE EARLY EVENING EXPECT WHAT REMAINS TO BE
SOUTH OF THE PANHANDLE LEAVING THE RIDGE OF HIGH PRESSURE FROM
THE ARCTIC SLOPE TO SOUTH OF THE GREAT SLAVE AND BEAR LAKES IN
NORTHWEST CANADA....AND EASTERN EDGE OF THE COMPLEX SYSTEM OF
LOWS MOVING INTO THE WESTERN PORTION OF THE GULF OF ALASKA.

THE FRONTAL BAND OF THE EASTERN MOST IS RUNNING EAST ALONG
ROUGHLY 54N SOUTH WEST OF KODIAK ISLAND TO ABOUT 145W THEN CURVES
SOUTHWARD. THIS FRONT IS SPREADING EAST FASTER THAN IT IS NORTH
AND EXPECT TO SEE CLOUDS AND SOME RAIN ASSOCIATED WITH THIS
FEATURE SPREADING INTO SOUTHERN PANHANDLE THURSDAY MORNING.

THE FORECAST ISSUE DURING THE AFTERNOON WAS THE STUBBORN AREA OF
MARINE STRATUS ACROSS THE SOUTHERN PORTION OF THE PANHANDLE AND
INTO THE NORTHERN GULF. IT IS RELUCTANT TO RELEASE ITS HOLD ACROSS
THE AREA...THOUGH THIS STARTING TO GIVE WAY THROUGH THE LATE
AFTERNOON. ESSENTIALLY JUST CHANCE OF RAIN THROUGH THURSDAY
AFTERNOON WITH A LIKELY JUST STARTING TO NUDGE IN FROM THE SOUTH.

ACROSS THE NORTHERN PORTIONS...THE WINDS ARE THE CONCERN...WE
EXPECTED THE GRADIENT IN A SLIGHTLY DIFFERENT LOCATION THAN WHERE
IT WAS. TRIED TO ACCOUNT FOR THAT FOR THE FORECAST TONIGHT SO HAVE
A SLIGHTLY RESTRAINED WIND FORECAST... ALTHOUGH IT DOES SEEM THAT
WINDS WILL BE PICKING UP FOR THE MORNING HOURS SO TRIED TO BRING
THE LYNN CANAL AREA BACK UP TO 30 KT AGAIN FOR THAT TIME FRAME.
OTHERWISE LIGHT WINDS. ALSO MENTIONED SOME LOCALLY GUSTY WINDS TO
25 MPH DOWNTOWN JUNEAU TONIGHT WITH A BRIEF PERIOD OF HIGHER WINDS
WORKING THEIR WAY OVER THE COAST MOUNTAINS DURING THE EARLY
MORNING HOURS.

.LONG TERM...THE TRANSITION FROM A RELATIVELY DRY PATTERN TO
MEASURABLE RAINFALL AND STRONGER WINDS WILL OCCUR DURING THE
NEXT 48 HOURS.  CONFIDENCE IS AVERAGE.

AT THIS TIME THE 500H RIDGE EXTENDS NW ALONG A LINE ABOUT 100 NM
W OF HAIDA GWAII AND OVER THE GULF OF ALASKA AND TO THE WNW
OVER KODIAK. THIS RIDGE IS WEAKEN AND DURING THU NIGHT AND
FRIDAY WILL BE REPLACED BY STRONG SW FLOW FOR MOST OF OUR AREA
OF RESPONSIBILITY.

GOES WV AND INITIALIZATION: GOOD MODEL CONSENSUS ON LEADING SIDE
OF CLOUD MASS ASSOCIATED WITH OCCLUDED FRONT 500 NM SW OF
PANHANDLE AT THIS TIME. THE GOES WV IS USED FOR THIS PURPOSE, AND
WAS COMPARED TO THE MODEL FIELDS OF 500-300 RH. THIS COMPARISON
ALSO INDICATES THE ECMWF AND GFS WILL BECOME FAVORED OVER THE NAM
AS THE LATER DOES NOT DEPICT THE LOCATION OF THE SW SIDE OF THE
OCCLUDED FRONTAL CLOUD MASS ABOUT 700 NM SW OF THE PANHANDLE.
USING THE SAME INITIALIZATION METHOD, THE ECMWF AND GFS HAVE ALSO
PROPERLY DEPICTED THE RAPID CYCLOGENESIS OCCURRING AT 43N/180.
THIS LATER SYSTEM IS CENTRAL TO THE LARGE SCALE PATTERN CHANGE
THAT HAS BEGUN TO OCCUR.

THE RIDGE ALOFT OVER THE GULF WILL BECOME REPLACED BY THE FIRST
OF A SERIES OF LOW PRESSURE SYSTEMS TRACKING NE INTO THE GULF
BEGINNING ABOUT 18Z FRI. SAT: GALE FORCE WINDS SHOULD OCCUR IN
EVERY ONE OF OUR MARINE ZONES IN THE OUTSIDE AND OFFSHORE WATERS,
EXCEPT FOR MARINE ZONE 52 WHICH SHOULD REACH GALE FORCE SUN. THE
GALES WILL EVEN EXTEND TO CLARENCE STRAIT SUN.

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...SMALL CRAFT ADVISORY FOR PKZ012-013-022-043-051-052.

&&

BEZENEK/JBT