Small Craft Advisory 653, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
230 PM AKDT SUN OCT 23 2011

.SHORT TERM...UPPER TROF OVER THE GULF WILL MOVE EWD AND BE E OF
THE AREA MON. SFC TROF OVER THE ERN GULF WILL MOVE SLOWLY EWD AND
MOVE ONSHORE LATE TONIGHT. SFC RIDGE WILL BUILD OVER THE
PANHANDLE MON. AN OCCLUDED FRONT NEAR THE AKPEN WILL MOVE INTO
THE WRN GULF LATE TONIGHT...THEN REACH THE CENTRAL GULF BY LATE
MON AFTERNOON. THE FRONT WILL SLOWLY WEAKEN THROUGH THE PERIOD.
USED A BLEND OF THE 12Z NAM AND 00Z ECMWF FOR THE TONIGHT AND MON
PERIODS...MAINLY FOR THEIR HANDLING OF THE SFC TROF MOVING
ONSHORE AND RIDGE BUILDING IN BEHIND IT.

 MAIN FORECAST ISSUES WILL BE PRECIP POTENTIAL AND WINDS. RIGHT
NOW THERE ARE FAIRLY WIDESPREAD SHOWERS OVER THE ERN GULF AHEAD
OF THE DEEP LAYER TROF OVER THE CENTRAL GULF. EXPECT THE COVERAGE
TO REMAIN FAIRLY WIDESPREAD TONIGHT OVER MUCH OF THE
AREA...EXCEPT OVER THE FAR N WHERE DOWNSLOPE FLOW WILL LIMIT
SHOWER COVERAGE SOMEWHAT. SHOWER COVERAGE SHOULD DECREASE MON AS
SFC RIDGING BUILDS NWD OVER THE AREA...BUT LOWER LEVEL ONSHORE
FLOW WILL NOT ALLOW A COMPLETE DRYING OUT. PRECIP WILL INCREASE
OVER THE PAYA AND ADJACENT GULF AREAS MON AFTERNOON AS OCCLUDED
FRONT MOVES IN. THIS PRECIP SHOULD BE MORE STRATIFORM IN NATURE
HOWEVER.

 AS FOR WINDS...RIGHT NOW WINDS ARE GENERALLY 15-20 KT OVER THE
INNER CHANNELS...WITH A FEW EXPOSED AREAS NEAR SCA. WITH THE
GRADIENT EXPECTED TO SLOWLY DECREASE TONIGHT...WOULD EXPECT INNER
CHANNEL WINDS TO SLOWLY DROP OFF. HOWEVER...THEY WILL START TO
PICK UP AGAIN ESPECIALLY MON AFTERNOON AS GRADIENT INCREASES
BETWEEN RIDGE BUILDING IN FROM THE S AND FRONT MOVING INTO THE
CENTRAL GULF. AM EXPECTING SCA LEVEL WINDS OVER MAINLY THE
OFFSHORE WATERS AND NEARSHORE WATERS W ICY BAY MON AFTERNOON.
SEAS WILL REMAIN ON THE HIGH SIDE THOUGH SO WILL HAVE SCA FOR
SEAS GOING FOR REMAINING OUTSIDE WATERS. THERE MAY BE A SHORT
PERIOD OF SCA NW WINDS OVER THE FAR SERN GULF 12-18Z MON AS SFC
TROF MOVES INLAND AND RIDGE STARTS TO BUILD IN QUICKLY BEHIND IT.
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.LONG TERM...FORECAST PROBLEM OF THE DAY IS DEVELOPING LOW ALL THE
WAY OVER AT KAMCHATKA THIS AFTERNOON THAT WILL IMPACT THE GULF BY
12Z TUE. 23/12Z OPS MODELS BEGIN TO AGREE ON TRACK TO SOUTHERN END
OF SHELIKOF STRAIT. DEPTH FOR STORM WILL BE IN THE 960S WITH THE
12Z NAM BEING THE SLOWEST WITH LESS STRENGTH. WILL CONTINUE WITH
STORM FORCE FOR OUTSIDE WATERS FROM PREVIOUS SHIFT THEN CONTINUE
WITH HPC GUIDANCE DAYS 4 THROUGH 7. SYSTEM IS VERY MOIST DUE TO
TROPICAL CONNECTION EARLY IN ITS LIFE SO INDICATED HIGH QPF IN
GRIDS TUE AND WED. THICKNESS VALUES LOWER THU AND FRI NIGHTS BUT
KEPT MENTION OF SNOW OUT OF THE PUBLIC FORECASTS DUE TO SOUTHERLY
FLOW ALOFT BEGINNING AGAIN ON THU. WILL CONTINUE TO WATCH THICKNESS
AS WE GET CLOSER TO MIDWEEK. USED 23/12Z ECMWF AS CLOSEST MODEL FOR
THIS SET OF FORECASTS AND CONFIDENCE HIGH DAYS 2 THRU 4.

JC
.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...SMALL CRAFT ADVISORY PKZ012-041-052.
          SMALL CRAFT ADVISORY DUE TO SEAS PKZ042-043-051.

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