Small Craft Advisory 586, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
333 PM AKDT FRI OCT 12 2012

.SHORT TERM...SNOW LEVEL AT 300 - 500 FEET IN THE INNER CHANNELS
NE OF A LINE FROM JUNEAU TO GUSTAVUS. GFS SHOWS SNOW LEVEL THAT
IS A NICE FIT. TROUGH NE ACROSS THE GULF OF ALASKA TO SITKA  WILL
MOVE N TO NORTH GULF COAST TONIGHT.

 TIMING OF FASTER TROUGH IS HARD TO GIVE A DETERMINISTIC POSITION
TO, BUT DATA HOLE OF SURFACE FEATURES LOWERS CONFIDENCE FOR THE
TRACK OF A FEATURE THIS IMPORTANT TO THE SHORT RANGE FORECAST
PACKAGE. BUT SMOOTHING THE LOCATION DUE TO LOW CONFIDENCE IN
POSITION.

 POST LANDFALL OF TROUGH WILL INCLUDE RAIN HEAVY AT TIMES, AND
FOR THE MARINE WILL INCLUDE BARRIER FLOW ON OUTER COAST.

.LONG TERM...LONG RANGE STARTS WITH A RATHER COMPLEX DEVELOPING
LOW MOVING NNE INTO THE GULF SAT NIGHT. MODELS HAVE BEEN
STRUGGLING HANDLING THE DETAILS WITH THIS SYSTEM BUT A GOOD
CONSENSUS DEVELOPED WITH THE 12Z ECMWF...UKMET AND GEM MODELS ON
IT. THEY SUGGEST ONE LOW WILL PROBABLY MOVE INTO THE FAR SE GULF
LATE SAT NIGHT THEN CURVING ALONG THE OUTER COAST SUN. ANOTHER
LOW CENTER SHOULD TRACK TOWARD THE S-CENTRAL GULF LATE SAT NIGHT
THEN SWING AROUND THE S SIDE OF THE FIRST LOW TOWARD THE CENTRAL
COAST SUN...THEN INLAND SUN NIGHT. MAY SEE ANOTHER LOW MOVE OUT
OF THE WESTERN GULF INTO THE NE GULF MON...ASSOCIATED WITH UPPER
LOW DIGGING SE INTO THE SW GULF THIS WEEKEND. USED THE 12Z ECMWF
FOR THE FORECAST PRESSURES AND WINDS FOR SAT NIGHT INTO MON
NIGHT.

 MAIN CONCERNS FOR THE SAT NIGHT INTO SUN TIME FRAME ARE THE
WINDS. THERE WILL LIKELY NEED TO BE SOME HEADLINES MAINLY FOR THE
SOUTHERN HALF OF THE AREA LATER SAT NIGHT AND SUN...BUT WHAT
LEVEL OF HEADLINE REMAINS TRICKY AS THAT WILL DEPEND ON EXACTLY
HOW STRONG THE TWO LOWS GET. AT THIS POINT THINK STRONG WIND
HEADLINES WILL SUFFICE. WILL HAVE GALES AND EVEN SOME STORM FORCE
WINDS OVER THE SERN HALF OF THE MARINE AREA DURING THIS TIME AS
WELL.

 ONCE THIS SYSTEM MOVES OUT LATER SUN NIGHT WILL PROBABLY SEE A
PERIOD OF MORE SHOWERY WEATHER BUT ARRIVAL OF NEXT LOW MON SHOULD
MEAN MORE STEADY PRECIP AGAIN. FOR FORECAST SIMPLICITY...HAVE
KEPT PRECIP CHARACTER AS STRATIFORM SUN NIGHT THROUGH MON NIGHT.

 DID NOT CHANGE ANYTHING BEYOND MON NIGHT DUE TO TIME CONSTRAINTS
AND WANTING TO FOCUS ON THE WEEKEND SYSTEMS. HPC USED A GFS
ENSEMBLE MEAN APPROACH TO THEIR GRIDS WHICH SOUNDS REASONABLE
GIVEN MODEL SPREAD LATER IN THE WEEK.

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE WARNING FOR PKZ043-051.
         SMALL CRAFT ADVISORY FOR PKZ012-013-021-022-031-033>036-041-042-
     052-053.

&&

JBT/RWT