Small Craft Advisory 571, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
156 PM AKDT SAT SEP 24 2011

.SHORT TERM...DIMINISHING SHOWER ACTIVITY IN A HIGHLY CONVECTIVE
ENVIRONMENT IS VISIBLE IN BOTH SATELLITE IMAGERY AS WELL AS RADAR
DATA TODAY. SO FAR TODAY, HAVE NOT DETECTED ANY LIGHTNING, BUT
HAVE INCLUDED ISOLATED THUNDERSTORMS IN THE NORTHERN COASTAL
MARINE ZONES FOR THIS EVENING. THE RIDGE OVER SOUTHEAST ALASKA
WILL BEGIN TO WEAKEN THIS AFTERNOON AS A LOW TRACKS TO THE NORTH
AND ENTERS BRITISH COLUMBIA WEST OF VANCOUVER ISLAND EARLY SUNDAY
MORNING. RESULTING SHIFT FROM LOW LEVEL ONSHORE WINDS TO MORE OF
AN OFFSHORE PATTERN WILL HELP TO CLEAR UP AND DRY OUT THE
PANHANDLE FOR SUNDAY. THE CLEARING SKIES TONIGHT WILL COMPLICATE
THE FORECAST IN TWO WAYS. FIRST, THERE IS THE SATURATED GROUND.
CLEARING SKIES TONIGHT WILL ALLOW TEMPERATURES TO FALL DOWN TO
THE DEWPOINT AND AREAS OF FOG ARE POSSIBLE. SECONDLY, IT IS THAT
TIME OF YEAR AGAIN TO THINK ABOUT FROST AND FREEZING TEMPERATURES
UNDER MOSTLY CLEAR NIGHT TIME SKIES. WORKING AGAINST BOTH THE FOG
AND FROST WILL BE DOWNSLOPING EASTERLY WINDS COMING OFF THE COAST
MOUNTAINS. WORKING AGAINST THE FROST IN PARTICULAR WILL BE THE
POTENTIAL FOR DEW TO FORM BEFORE OVERNIGHT LOWS GET COLD ENOUGH
FOR FROST TO DEVELOP. NEVERTHELESS, HAVE INCLUDED BOTH FOG AND
AREAS OF FROST IN THE AFTERNOON FORECAST FOR OVERNIGHT TONIGHT,
BUT BACKED OFF ON THE EXTENT OF BOTH FROM LAST NIGHT'S FORECAST.
BELIEVE THE HIGHEST LIKELIHOOD OF PATCHY FROST WILL BE IN LOW
LYING WIND SHELTERED AREAS AT HIGHER ELEVATIONS.

 OFFSHORE WINDS WITH CORRESPONDING DRY CONDITIONS AND MOSTLY
CLEAR SKIES SHOULD BE PREVALENT MOST OF THE DAY TOMORROW WITH THE
LOW LEVEL WIND TURNING ONSHORE AGAIN OVER THE SOUTHERN PANHANDLE
BY TOMORROW AFTERNOON. BY THAT TIME, BELIEVE IT WILL BE TOO LATE
IN THE DAY TO PUT A DAMPER ON WHAT LOOKS LIKE WILL BE AN REALLY
NICE OUTDOOR DAY. AM EXPECTING FAIRLY SEASONABLE DAYTIME HIGHS
RANGING FROM LOW TO MID 50S. THE ONLY EXPECTED WIND WILL BE OVER
LYNN CANAL, WHERE A SOUTHERLY 20 KT WIND THIS AFTERNOON WILL
BECOMING NORTHERLY TONIGHT AND INCREASE TO 25 KTS TOMORROW
MORNING. WILL ALSO PROBABLY SEE NORTHERLY WINDS OF 20 TO 25 KTS
OUT OF TAKU INLET AS WELL.

 USED ECMWF FOR PRESSURE AND NAM FOR WIND SPEEDS. BLENDED GFS,
NAM, AND GEM FOR POP. FORECAST CONFIDENCE IS ABOVE AVERAGE.

.LONG TERM...THE MODELS ARE IN FAIR AGREEMENT WITH THE NEXT BIG
LOW MOVING OUT OF THE NORTH PACIFIC INTO THE SE GULF MON BUT THERE
IS STILL SOME DIFFERENCES WITH THE TRACK OF THE LOW. DID NOT
CHANGE THE MORE EASTWARD TRACK FROM THE PREVIOUS FORECAST AS THE
EC CONTINUES ON THE SAME TRACK AND THERE IS SOME AGREEMENT WITH
THE NAM. SO WITH THAT SAID THE STRONGEST WINDS WILL BE OVER THE
FAR SOUTHERN ZONES OF THE PANHANDLE. THROUGH THE REST OF THE WEEK
THERE IS GOOD AGREEMENT WITH THE OVERALL WEATHER PATTERN WITH THE
MEAN UPPER TROF REMAINING OVER THE GULF BUT THERE IS DIFFERENCES
IN THE TACK AND DETAILS OF WEATHER SYSTEMS DRIFTING OUT OF THE
NORTH PACIFIC INTO THE GULF. SO FROM WED THROUGH NEXT WEEKEND WENT
WITH THE LATEST HPC FORECAST WHICH HEAVILY LEANED ON ENSEMBLE
MEANS. SO THIS WILL KEEP A CHANCE TO LIKELY RAIN POPS THROUGH THE
END OF THE WEEK.

AT THE START OF THE LONG TERM PERIOD THERE WILL BE DRY CONDITIONS
SUN NIGHT ACROSS THE FORECAST AREA WITH INCREASING OFFSHORE FLOW
FROM THE APPROACHING LOW. CLOUDS WILL INCREASE OVER THE SOUTHERN
AREAS THROUGH SUN WITH INCREASING ONSHORE FLOW BUT THE NORTHERN
AREAS WILL SEE PARTLY CLOUDY SKIES AND DRY CONDITIONS WITH
OFFSHORE FLOW THROUGH MONDAY AFTERNOON. THE NORTHERN AREAS SUN
NIGHT WILL SEE LARGE BREAKS IN THE CLOUD COVER AND PRODUCE A GOOD
CHANCE OF PATCHY FROST.

SUN NIGHT THE REMNANTS OF AN OLD TYPHOON WILL BE DEVELOPING OVER
THE NORTH PACIFIC AND BEGIN TO DRIFT NE AROUND THE LARGE UPPER LOW
OVER THE GULF. THIS LOW WILL DEEPEN TO 970MB BY MONDAY MORNING AND
BE SW OF HAIDA GWAII. THIS FEATURE WILL INCREASE THE WINDS OVER
THE SE GULF ALONG WITH THE SOUTHERN THIRD OF THE PANHANDLE THROUGH
MONDAY AS IT DRIFTS NE. MAX GALES WILL DEVELOP OVER THE MARINE
WATERS WITH STRONG WINDS OVER LAND FROM FREDRICK SOUND SOUTHWARD
MON MORNING AND AFTERNOON. SEAS HEIGHTS WILL BUILD TO BE NEAR 20
FT OVER THE SE GULF THROUGH MON WITH MUCH LOWER HEIGHTS OVER THE
NE GULF. THE SEAS WILL SLOWLY SUBSIDE THROUGH WED. THE STRONG
WINDS OVER THE SOUTHERN AREAS WILL PERSIST INTO TUE AS THE LOW
LIFTS INTO CANADA AND STRONG PRESSURE RISES DEVELOP OVER THE INNER
CHANNELS AS A SURFACE RIDGE BUILDS BEHIND THE LOW. FURTHER NORTH
THE WINDS WILL INCREASE TO SMALL CRAFT LEVELS FROM THE NORTH
THROUGH MON AND THEN BACK AROUND TO THE SOUTH THROUGH TUE WITH THE
RIDGE BUILDING OVER THE FORECAST AREA.

AS THE FRONT DRIFTS NORTH A CHANCE OF RAIN WILL INCREASE OVER THE
NORTH CENTRAL AREAS THROUGH MON NIGHT. THE FAR NORTHERN INNER
CHANNELS AND GULF COAST WILL REMAIN MOSTLY DRY THROUGH TUESDAY BUT
WITH A UPPER TROF MOVE ACROSS THE GULF THIS WILL INCREASE A CHANCE
OF SHOWERS TUE NIGHT.

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...SMALL CRAFT ADVISORY FOR PKZ012-052.
         SMALL CRAFT ADVISORY DUE TO SEAS FOR PKZ041>043.

&&

FRITSCH/ABJ