Small Craft Advisory 547, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
332 PM AKDT SAT SEP 17 2011

.SHORT TERM... A GALE FORCE LOW WILL MOVE INTO THE SOUTHEAST
GULF FROM THE NORTH PACIFIC THIS EVENING. THIS WILL INCREASE
WINDS ACROSS THE SOUTHERN MARINE AREAS THEN MOVE INTO THE LAND
AREAS OVERNIGHT. EXPECT 40-45KT SELY WINDS IN OUTSIDE WATERS WITH
GUSTS OF 55-60KT. FOR LAND AREAS WINDS WILL REACH 25-35MPH WITH
GUSTS OF 40-45MPH RESULTING IN A STRONG WIND HEADLINE. RAIN WITH
THIS SYSTEM WILL REACH THE PANHANDLE IN THE EVENING AND SPREAD
NORTH INTO THE CENTRAL PANHANDLE OVERNIGHT...BECOMING HEAVY AT
TIMES. THE HEAVY RAIN ALONG WITH THE STRONG SELY WINDS WILL LEAD
TO THE POTENTIAL OF MUDSLIDES. GREATEST RAINFALL AMOUNTS ARE
EXPECTED OVER THE KETCHIKAN AREA. THE LOW WILL WEAKEN TO AN OPEN
WAVE AS IT MOVES INTO THE CENTRAL PANHANDLE THROUGH SUNDAY. THIS
WILL ALLOW WINDS TO GRADUALLY EASE THROUGH THE DAY...ALTHOUGH
REMAINING STRONG THROUGH CLARENCE STRAIT THE LONGEST. OVERCAST
SKIES OVERNIGHT AND SUNDAY WILL LIMIT THE DIURNAL TEMPERATURE
SPREAD.

 FOR THE REST OF THE PANHANDLE...FROM ABOUT JUNEAU NORTH...THIS
LOW WILL HAVE THE OPPOSITE AFFECT. MID LEVEL WINDS WILL BE
OFFSHORE...RESULTING IN A DRYING CONDITIONS AND ALLOWING FOR
BREAKS IN THE CLOUD COVER. CLOUD COVER IS EXPECTED TO DECREASE
THROUGH SATURDAY NIGHT AS THE LOW MOVES EAST..ENHANCING THE
OFFSHORE FLOW. AFTER RAINFALL IN YAKUTAT TODAY AND CLEARING SKIES
INTO EARLY SUNDAY MORNING...EXPECT RADIATION FOG TO DEVELOP.
BREAKS IN THE CLOUD COVER TONIGHT WILL ALSO CAUSE THE MIN TEMPS
TO BE SLIGHTLY COOLER. PARTLY CLOUDY SKIES FOR THE FIRST PART OF
SUNDAY WILL ALLOW FOR SLIGHTLY WARMER HIGH TEMPERATURES. WITH THE
LOW TO THE SOUTH EXPECT WINDS THROUGH THE NORTHERN INSIDE WATERS
TO SHIFT OUT OF THE NORTH THIS EVENING THEN INCREASE.

 IN THE BROAD SCALE MODELS ARE IN GOOD AGREEMENT WITH THIS
LOW...HOWEVER SMALL DIFFERENCES IN LOW CENTER PLACEMENT AND
STRENGTH RESULT IN TIMING DIFFERENCES FOR WINDS THROUGH THE INNER
CHANNELS. THE NAM12 INITIALIZED THE BEST...SO UPDATED MOST GRIDS
WITH THAT. THE GFS/ECMWF ARE MUCH CLOSER TODAY AS WELL...ALLOWING
FOR ABOVE AVERAGE FORECASTER CONFIDENCE.

&&

 .LONG TERM...LONG WAVE TROUGH FROM ABOUT 180W TO 130W WILL BE
MAIN FEATURE FOR MOST OF THE LONG RANGE FORECAST. STRONG UPPER
LEVEL JET WITH MAX CORE WINDS AROUND 160 KTS WILL PROVIDE AMPLE
SUPPORT FOR THE SERIES OF STRONG LOW PRESSURE SYSTEMS MOVING INTO
THE GULF THROUGH THE WEEK. STRONGER WINDS OVER COASTAL MARINE
AREAS, EAST-WEST ORIENTED CHANNELS AND OVER THE SOUTHERN REGIONS
EXPECTED AGAIN ON MON INTO EARLY TUE. HEAVY RAIN WILL ACCOMPANY
PRECIP BANDS ASSOCIATED WITH THE LOWS MOVING OVER THE PANHANDLE

 REMNANTS OF GALE FORCE LOW WILL WEAKEN INTO AN OPEN WAVE TROUGH
SUN NIGHT THAT WILL MOVE OVER THE SOUTHERN PANHANDLE. WINDS WILL
BE IN A TRANSITION PERIOD THAT NIGHT WITH VARIABLE DIRECTION AND
DECREASING SPEEDS. A MID LEVEL HIGH PRESSURE RIDGE WILL FOLLOW
THE LOW PRESSURE REMNANTS MONDAY MOVING OVER THE PANHANDLE AND
QUICKLY TRACKING EAST BEFORE THE NEXT GALE FORCE LOW MOVES IN. THE
963 MB LOW WILL TRACK SOUTH OF THE ALEUTIAN ISLAND CHAIN SUNDAY
NIGHT WEAKENING TO 970 MB AS IT ENTERS THE WESTERN GULF. OCCLUDED
FRONT ASSOCIATED WITH THE GALE WILL TRACK ACROSS THE AK GULF
MONDAY INTO MONDAY NIGHT WITH WINDS INCREASING FROM NORTH TO
SOUTH. SOME FAIR MOISTURE CONNECTION WITH THE LOW AND EXPECTING
QPF VALUES UP TO ONE INCH REACHING THE COAST MONDAY NIGHT. A
SECOND SHORT WAVE WILL DEVELOP SOUTH OF THE MAIN GALE FORCE LOW
ROTATING INTO THE AK GULF WEDNESDAY. HIGH UNCERTAINTY REGARDING
THIS FEATURE WITH ITS STRENGTH, TIMING AND FINAL TRACK. ECMWF HAS
BEEN SLOWER WITH THE LOW AND GENERALLY KEEPING THE CENTER FURTHER
SOUTH COMPARED TO THE GFS. GFS HAS ALSO BEEN INCONSISTENT RUN TO
RUN WITH RESPECT TO THE LOW TRACK, BUT MORE CONSISTENT OVER ALL
COMPARED TO THE ECMWF. AS THIS SHORT WAVE MOVES OUT ANOTHER HIGH
PRESSURE RIDGE WILL BUILD OVER THE PANHANDLE FOLLOWED BY ANOTHER
GALE FORCE LOW TRACKING FROM THE NORTH PACIFIC INTO SOUTHEAST GULF
BY THE END OF THE WEEK.

 MODELS BEGAN IN GOOD AGREEMENT WITH SOME SLIGHT INITIALIZATION
DIFFERENCES. NEW MODELS RUNS HAD THE MON GALE LOW A BIT WEAKER BUT
THIS MADE LITTLE IMPACT ON THE SENSIBLE FORECAST. USED A BLEND OF
12Z NAM AND GFS WITH INHERITED GRIDS OUT TO 00Z WED. FROM THEN ON
UPDATED GRIDS WITH NEW HPC. AS THERE ARE LARGE INCONSISTENCIES
WITH THE WED SHORT WAVE MOVING INTO THE GULF HAVE KEPT GENERAL
PATTERN IN THE GRIDS SO FAR. IF NEWER RUN CONTINUE WITH THE
NORTHERLY LOW TRACK AS WITH THE 12Z GFS RUN DETAILS CAN BE ADDED.
FORECAST CONFIDENCE BEGINS ABOVE AVERAGE BUT FALLS SIGNIFICANTLY
BY MID WEEK.

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...GALE WARNING FOR PKZ033-036-041-042.
         SMALL CRAFT ADVISORY FOR PKZ012-013-022-031-032-034-035-043-052.
         SMALL CRAFT ADVISORY DUE TO SEAS FOR PKZ051.

&&

HANNON/PRB