Small Craft Advisory 595, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
210 PM AKDT MON OCT 15 2012

.SHORT TERM...A LOW OVER THE WESTERN GULF WILL DRIFT NNE TO THE
NORTHERN GULF BY TUE AFTERNOON. A LOW PRESSURE AREA OVER SOUTHERN
HAIDA GWAII WILL MOVE NE AND INLAND ALONG THE CENTRAL BC COAST
THIS EVENING. A TROF OVER THE EASTERN GULF WILL MOVE NE ACROSS
THE AREA TONIGHT. ENDED UP USING A BLEND OF THE 00Z AND 12Z ECMWF
FOR THE SHORT TERM PERIOD...WITH SOME ADJUSTMENTS FOR LOCAL
EFFECTS.

 MAIN FORECAST ISSUES WILL BE PRECIP POTENTIAL...CHANCES FOR ANY
TSTMS...AND WINDS. RIGHT NOW...A FAIRLY LARGE AREA OF RAIN IS
OVER MUCH OF THE MAIN PANHANDLE AREA AHEAD OF THE TROF OVER THE
EASTERN GULF. THIS RAIN AREA WILL SHIFT NE AS THE TROF MOVES
ONSHORE TONIGHT...WITH THE LAST PART OF THIS RAIN AREA OUT OF THE
FAR EASTERN AREAS BY LATE TONIGHT. THERE MAY BE A SMALL BREAK IN
THE PRECIP UNTIL SHOWERS MOVE IN FROM THE SW LATE TONIGHT AND TUE
MORNING. GIVEN ONSHORE FLOW...SEVERAL VORT LOBES...AND FAIRLY
UNSTABLE AIRMASS...EXPECT SHOWERS OVER MOST OF THE AREA TUE.
EXCEPTION TO THE HIGH POPS FOR TUE IS THE FAR NORTHERN INNER
CHANNELS WHERE THE MOUNTAINS SHOULD INTERCEPT MOST OF THE SHOWERS
BEFORE GETTING THERE SO AM KEEPING THE POPS LOWER IN THE
PAHN/PAGY AREAS. LOOKS LIKE ENOUGH INSTABILITY AND DEEP LAYER
LIFTING AHEAD OF A COUPLE OF STRONG VORT LOBES FOR ISOLATED TSTMS
OVER THE NORTHERN GULF TONIGHT...SO WILL INCLUDE THOSE FOR THAT
AREA.

 AS FOR WINDS...RIGHT NOW STRONGEST WINDS ARE OVER THE SOUTHERN
AREA. AM EXPECTING THOSE TO DECREASE LATER THIS AFTERNOON AS THE
LOW TO THE SOUTH TURNS AND WEAKENS THE PRESSURE GRADIENT THERE.
ONCE LOW MOVES INLAND THIS EVENING WINDS SHOULD FLIP AROUND TO NW
AND PICK UP AGAIN...BUT THEY WILL LIKELY REMAIN BELOW SCA LEVELS
OVER THE SOUTHERN INNER CHANNELS. THEN WINDS SHOULD COME BACK TO
SE TUE MORNING OVER THE SOUTHERN INNER CHANNELS AND SCA LEVEL
WINDS ARE LIKELY BY TUE AFTERNOON. ELSEWHERE...THERE WILL BE SCA
LEVEL E WINDS OVER THE FAR N GULF TONIGHT INTO TUE MORNING...THEN
WIND SHOULD SHIFT TO S-SW WITH STRONGER WINDS FURTHER OFFSHORE. A
LARGER AREA OF SCA TO GALE FORCE W-SW WINDS ARE EXPECTED OVER THE
SOUTHERN GULF TONIGHT THEN REACH THE CENTRAL INTO MOST OF THE
NORTHERN AND EASTERN GULF TUE IN THE STRONG COLD ADVECTION S OF
THE GULF LOW. THIS WILL KICK UP SOME FAIRLY LARGE SEAS AS
WELL...WITH 20+ FT SEAS LIKELY OVER THE SOUTH-CENTRAL GULF LATER
TONIGHT AND THE SOUTHEAST GULF TUE.

 &&

 .LONG TERM...MODEL AGREEMENT HAS GOTTEN BETTER FOR THE MID WEEK
LOW OVER THE PAST 24 HOURS. THEY ARE NOW CONVERGING ON A TRACK
THAT TAKES THE LOW THROUGH NORTHERN HAIDA GWAII OR DIXON ENTRANCE
WED EVENING. THERE IS STILL SOME SPREAD ON STRENGTH HOWEVER.
MODELS RANGE FROM A 990 MB LOW IN THE ECMWF TO A 1001 MB LOW IN
THE UK AND GEM. DECIDED ON A BLEND SOME WHERE IN THE MIDDLE WITH
A 995 MB LOW COMING IN NEAR DIXON ENTRANCE WED EVENING. AS FAR AS
WHAT THE WEATHER WILL BE DOING, WINDS IN THE SOUTHERN PANHANDLE
WILL BE INCREASING AS EARLY AS WED MORNING AS A TROUGH OUT AHEAD
OF THE LOW PASSES THROUGH THE PANHANDLE. CURRENT THINKING IS THAT
STRONG WIND HEADLINES FOR THE SOUTHERN PUBLIC ZONES AND A GALE
WARNING FOR CLARENCE STRAIT MAY BE NEEDED WED INTO WED NIGHT AS
THIS LOW PULLS THROUGH. WIND WARNINGS SHOULD NOT BE NEEDED AS
850 MB WINDS ONLY GET TO 50 KT OVER THE SOUTHERN PANHANDLE. THIS
FEATURE WILL ALSO BRING A BAND OF MORE FREQUENT PERIODS OF RAIN
TO THE MAIN PANHANDLE SOUTH OF YAKUTAT WED BEFORE THE PRECIP
ASSOCIATED WITH THE LOW GETS TO THE SOUTHERN PANHANDLE LATER IN
THE DAY.

 COMPLICATING THINGS FURTHER IS THE COLD AIR ADVECTION COMING IN
FROM THE WEST TUES NIGHT THROUGH WED NIGHT. SOME AREAS FROM ICE
STRAIT NORTHWARD MAY SEE SNOW EARLY WED AND EARLY THURS AS THE
-6C 850 MB TEMPERATURE LINE DROPS AS FAR SOUTH AS SUMNER STRAIT
WED MORNING. ANY ACCUMULATIONS SHOULD LIGHT AND MOSTLY BE
CONFINED TO NORTH OF THE ICE STRAIT CORRIDOR AS AIR AND GROUND
TEMPS ARE STILL A BIT WARM.

 FOLLOWING THE MID WEEK SYSTEM PRECIP CHANCES START TO DIMINISH
LATE WEEK AS THE UPPER TROUGH STARTS TO SLOWLY DRIFT EAST. THE
WEAK SURFACE REFLECTION OF IT THAT HAS BEEN SITTING IN THE
NORTHERN GULF FOR THE PAST FEW DAYS WILL SLOW DRIFT TO THE SE
WITH IT. AS IT DOES SO THE SW ONSHORE FLOW WILL DIMINISH AND
THINGS START TO DRY OUT AGAIN FOR THE WEEKEND AS THE RETREATING
LOW TURNS INTO AN INVERTED TROUGH OVER THE AREA. ADDING TO THE
OFFSHORE FLOW THAT THIS PRODUCES IS A DEVELOPING COLD STRONG HIGH
IN THE ALASKA INTERIOR THAT WILL BE PUSHING INTO THE YUKON EARLY
NEXT WEEK.

 OVERALL LONG RANGE MODELS ARE IN DECENT AGREEMENT THROUGH THE
PERIOD. DECIDED ON A BLEND OF THE ECMWF AND THE GFS WITH HPC
TAKING OVER IN THE FAR EXTENDED. FORECAST CONFIDENCE IS ABOUT
AVERAGE.

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE WARNING FOR PKZ041-043.
         SMALL CRAFT ADVISORY FOR PKZ012-022-036-042-051-052.

&&

RWT/EAL