Small Craft Advisory 543, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
346 PM AKDT THU SEP 15 2011

.SHORT TERM...SATELLITE IMAGERY REVEALS SOME SIGNIFICANT
CLEARING OVER THE SOUTHERN THIRD OF THE PANHANDLE THIS AFTERNOON
IN RESPONSE TO AN UPPER LEVEL TROUGH THAT PASSED OVER SOUTHEAST
ALASKA THIS MORNING. MUCH OF MISTY FJORDS IS STILL COVERED BY
CLOUDS, BUT CEILINGS HAVE RISEN AND SHOWERS OVER THE SOUTHERN
PANHANDLE HAVE ENDED. AS OF NOON THERE WAS A VERY SHARP BOUNDARY
IN THE CLOUD COVER EXTENDING FROM CAPE OMMANEY NORTH TO POINT
GARDINER, THEN NORTH AND EAST ALONG THE COAST OF ADMIRALTY
ISLAND. CLOUD COVER WILL CONTINUE TO INCREASE SOUTH AND EAST
THROUGH THE REMAINDER OF THE AFTERNOON. UNDERNEATH THIS
INCREASING CLOUD COVER AND SOUTH OF CAPE FAIRWEATHER, CONDITIONS
ARE BASICALLY DRY WITH ISOLATED SHOWER ACTIVITY AT BEST. HAVE NOT
SEEN ANY PRECIP REPORTED IN THIS SECTION OF THE PANHANDLE SINCE
9 AM. FARTHER NORTH, LIGHT RAIN HAS BEEN CONTINUOUS ALL MORNING
BUT THERE IS A CHANCE THAT LOCATIONS NORTH OF CAPE FAIRWEATHER
WEST TO CAPE SUCKLING MAY GET A BREAK BEFORE THE NEXT FRONT
ARRIVES.

A FRONT CURRENTLY LYING ACROSS THE CENTRAL GULF ORIENTED
NORTHWEST TO SOUTHEAST IS MAKING SLOW PROGRESS TO THE EAST. VERY
SHARP BOUNDARY BETWEEN THE BAROCLINIC CLOUD SHIELD AND COLDER AIR
BEHIND THE FRONT INDICATES GOOD JET SUPPORT AT THE MOMENT, BUT
THIS IS NOT EXPECTED TO LAST. THE JET WILL OUTRUN THE ADVANCING
FRONT OVER NIGHT TONIGHT AND BEGIN TO DIVE SOUTHEAST TOWARDS THE
WASHINGTON COAST. THE FRONT WILL CONTINUE TO TRACK ACROSS THE GULF
OVERNIGHT, BUT MID LEVEL VORTICITY WEAKENS SIGNIFICANTLY OVERNIGHT
IN RESPONSE TO FALTERING JET SUPPORT. DO NOT BELIEVE THIS FRONT
WILL PACK MUCH OF A PUNCH WHEN IT ARRIVES OVER SOUTHEAST ALASKA
TOMORROW. KEPT QPF VALUES ONE QUARTER OF AN INCH OR LESS EXCEPT
OVER HIGHER TERRAIN OVER BARANOF ISLAND AND WEST OF GLACIER BAY.

THIS FRONT IS CURRENTLY SOLID SMALL CRAFT WINDS IN ADVANCE OF THE
FRONT AND HAVE BUILT THIS INTO THE MARINE FORECAST FOR TONIGHT AND
TOMORROW. A CURRENT WEAK SOUTHERLY PRESSURE GRADIENT OVER THE
PANHANDLE WILL BECOME MORE OF AN OFFSHORE GRADIENT OVERNIGHT. HAVE
SMALL CRAFT ADVISORIES FOR CROSS SOUND AND ICY STRAIT AS A RESULT.
ALSO HAVE A SMALL CRAFT ADVISORY FOR SOUTHEASTERLY WINDS IN
SOUTHERN PORTIONS OF CHATHAM STRAIT. DO NOT EXPECT TO SEE MUCH
WIND OVER LAND SINCE THE 850MB JET BREAKS DOWN AS THE FRONT
ARRIVES ALONG THE OUTER COAST.

VERY LITTLE TEMPERATURE CONTRAST ON THE BACK SIDE OF THE FRONT,
SO NO MAJOR CHANGES TO OVERNIGHT LOWS OR DAYTIME HIGHS. NOT A VERY
THOROUGH DRYING DAY TODAY IN SPITE OF THE BREAKS IN THE CLOUD
COVER, SO DID INCLUDE AREAS OF FOG AGAIN FOR TONIGHT, BUT NOT
QUITE AS MUCH AS LAST NIGHT.

USED NAM AND ECMWF FOR PRESSURE AND WIND. BLENDED NAM AND A
LITTLE SREF TO EXISTING POP FIELDS. FORECAST CONFIDENCE IS ABOVE
AVERAGE.

&&

.LONG TERM /FRIDAY NIGHT THRU THURSDAY/...A FRONTAL TROUGH OVER
THE PANHANDLE WILL CONTINUE RAINFALL ACROSS THE AREA BUT BEGIN TO WEAKEN
THROUGH FRIDAY NIGHT. RAIN WILL TURN TO MORE INTERMITTENT SHOWERS
BY SATURDAY AS A RIDGE BUILDS BACK OVER THE PANHANDLE. A LOW
PRESSURE SYSTEM MOVING INTO THE SOUTHEASTERN GULF WILL CAUSE
MIDLEVEL WINDS TO TURN OFFSHORE...ALLOWING SHOWER ACTIVITY TO
DIMINISH AND SOME BREAKS IN THE CLOUD COVER OVER THE NORTHERN HALF
OF THE AREA SATURDAY NIGHT AND SUNDAY. RAIN ASSOC WITH THIS LOW
WILL MOVE INTO THE SOUTHERN MOST AREAS SATURDAY NIGHT. WINDS WILL
INCREASE TO GALE FORCE AHEAD OF THE LOW FOR THE SOUTHERN OUTSIDE
WATERS AND INTO CLARENCE STRAIT. FOR OTHER INSIDE WATERS THE WIND
WILL TURN OUT OF THE NORTH INTO THE LOW AND INCREASE. THERE ARE
STILL DIFFERENCES BETWEEN THE NUMERICAL MODELS IN PLACEMENT AND
STRENGTH OF THIS LOW. ECMWF CONTINUES TO BE THE FASTEST/STRONGEST
AND MOVE THE LOW UP THE PANHANDLE...THIS SOLUTION WOULD CAUSE AN
INCREASED CHANCE OF RAIN FOR SUNDAY OVER THE NORTHERN AREAS. THE
GFS REMAINS WEAKER AND FURTHER SOUTH. THE NAM IS CLOSER TO THE GFS
TODAY AND OTHER MODELS ARE MORE IN THE MIDDLE...NAMELY SOUTH OF
THE ECMWF SOLUTION. HAVE GONE WITH A CONSENSUS SOLUTION...KEEPING
THE LOW CENTER OVER THE SOUTHERN PANHANDLE AND DISSIPATING THERE
AS AN OPEN WAVE BEFORE THE NEXT SYSTEM APPROACHES. WITH MODELS IN
SLIGHTLY BETTER AGREEMENT FORECASTER CONFIDENCE FOR THE WEEKEND
HAS INCREASED TO AVERAGE.

THE NEXT LOW PRESSURE SYSTEM MOVES INTO THE GULF LATER SUNDAY INTO
MONDAY WITH WINDS INCREASING GALE FORCE OFFSHORE THEN REACHING THE
OUTSIDE WATERS MONDAY AFTERNOON. RAIN WITH THIS SYSTEM WILL MOVE
INTO THE PANHANDLE MONDAY MORNING...BECOMING WIDESPREAD AND OCCNLY
HEAVY. THE LOW WILL BECOME NEARLY STATIONARY IN THE CENTRAL GULF
THROUGH MIDWEEK CONTINUING TO BRING RAIN TO THE AREA AS UPPER-
LEVEL SHORTWAVES PASS.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE WARNING FOR PKZ052.
         SMALL CRAFT ADVISORY FOR PKZ021-022-033-041>043-051.

&&

FRITSCH/HANNON