Small Craft Advisory 619, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
555 AM AKDT THU OCT 25 2012

.SHORT TERM...THE LONG DRY BREAK WILL CONTINUE THROUGH TONIGHT
AS AS THE ARCTIC AIRMASS COVERING NORTHWEST CANADA FLOWS THROUGH
SOUTHEAST ALASKA TO THE GULF OF ALASKA. HOWEVER, A CLOUDMASS FROM
A WEAK OCCLUSION IN THE NORTH PACIFIC WILL BE INCREASING THE
CLOUD COVER FOR THE SOUTHERN PANHANDLE WITHIN ABOUT 40 NM OF
DIXON ENTRANCE LATE TONIGHT. FOR MORE ABOUT THE PATTERN CHANGE
AND THE END OF OUR DRY BREAK PLEASE SEE THE LONG RANGE SECTION
BELOW.

 TWO STRONGEST SURFACE WIND EVENTS:  THE FIRST IS THE NORTHERLY
OUTFLOW DOWN LYNN CANAL THAT REMAINS A GALE BUT SHOULD WEAKEN TO
30 KT TONIGHT. THE SECOND IS FOR TAKU WINDS THAT WILL STOP AND
RESTART AS LEAST ONCE.

 THE SURFACE WIND AT SOUTH DOUGLAS WIND PROFILE SITE HAS HAD
GUSTS AT OR CLOSE TO 40 MPH SEVERAL TIMES OVERNIGHT, WITH THE
MOST RECENT OBSERVATIONS REPORTING GUSTS OF 37 MPH.

 THE MOST RECENT RUN OF THE NAM MODEL ARE CONSISTENT WITH A
MOUNTAIN WAVE IN THE VICINITY OF JUNEAU CONTINUING FOR DAY TIME
TODAY, WITH GUSTS IN DOUGLAS AND IN DOWNTOWN JUNEAU OF ABOUT
40 MPH. A COMPONENT  OF THE MOUNTAIN WAVE WILL PROBABLY FAIL LATE
THIS AFTERNOON AND THE MOUNTAIN WAVE WINDS WILL THEN REDEVELOP
OVERNIGHT. NOTE THE WIND SPEEDS ARE CALLED "STRONG WIND".  PLEASE
SEE THE LONG RANGE DISCUSSION  ABOUT A LATER HIGH WIND WATCH.

 THE NAM AND EC INITIALIZATIONS WERE BOTH GOOD EXCEPT FOR THE
OCCLUDED FRONT ALONG 50N SOUTH OF THE GULF, WHERE THE ECMWF HAS A
BETTER FIT. THE CHANGES TO THE FORECASTS DUE TO THE MODEL RUN
UPDATES ARE SMALL TO TRIVIAL THROUGH 15Z FRIDAY.

.LONG TERM...COMPLEX STREAM INTERACTION WILL BE THE ISSUE FOR
THE UPCOMING WEEKEND. MODELS DIFFER ON WHETHER THE NORTHERN OR
SOUTHERN STREAM ALOFT WILL BE DOMINANT AND THIS WILL HAVE AN
IMPACT AS FAR AS HOW FAR NORTH ANY PRECIP FROM A SOUTHERN STREAM
FRONT GETS. THE 00Z GFS SHOWED SOUTHERN STREAM DOMINATING THE MAIN
PART OF THE PANHANDLE AND ALLOW THE FRONT AND PRECIP TO GET ALL
THE WAY TO THE FAR NORTH SUN. THE 00Z ECMWF SHOWED THE NORTHERN
STREAM DOMINATING THE AREA AND KEEPING THE SOUTHERN STREAM FRONT
SOUTH OF THE AREA OVER THE WEEKEND. CURRENT FORECAST WAS IN
BETWEEN THOSE EXTREMES...AND ENDED UP LEAVING THE POPS OVER THE
WEEKEND ALONE AS IT WAS A GOOD COMPROMISE. ALSO PRETTY MUCH LEFT
NEXT WEEK AS IS ALSO DUE TO MODEL DIFFERENCES OUT THERE IN
HANDLING THE BREAKDOWN OF THE BLOCKING HIGH AND ALLOWING TROF TO
DEVELOP OVER THE GULF BY MIDWEEK.

 DID MAKE SOME CHANGES FOR FRI AND FRI EVENING OVER THE
SOUTH...AND  LOCALLY MADE CHANGES TO WINDS FRI INTO SUN MORNING.
BOTH THE GFS AND THE ECMWF ALLOW SOME PRECIP TO MAKE IT INTO THE
FAR SOUTHERN ZONES FRI BEFORE SHIFTING IT OFF TO THE EAST FRI
NIGHT. THIS IS DUE TO A WEAK FRONT MOVING TO JUST S OF THAT AREA
FRI BEFORE SHEARING APART FRI NIGHT AS UPPER SUPPORT MOVES
INLAND. HAVE BROUGHT IN CHANCE POPS TO THE FAR SOUTHERN ZONES FRI
THEN HAVE THOSE POPS SHIFT EAST OUT OF THE AREA DURING FRI NIGHT.
PTYPE SHOULD BE MAINLY RAIN ALTHOUGH A FEW SNOWFLAKES MAY MIX IN
ESPECIALLY FRI MORNING.

 LOCALLY AROUND JUNEAU...SET UP FOR A TAKU WIND EVENT IS LOOKING
MORE IMPRESSIVE FOR THE FRI NIGHT INTO SAT NIGHT TIME FRAME. THE
NAM SHOWS INCREASING CROSS BARRIER FLOW DURING THE FRI-SAT
MORNING PERIOD WITH AS MUCH AS 45 KT OF CROSS BARRIER FLOW BY
LATE SAT MORNING. THE INVERSION WILL REMAIN IN A GOOD
LOCATION...NEAR 850 MB...AS COLD AIR IS ADVECTED IN AT LOWER
LEVELS. MEANWHILE...UPPER TROF DIGGING SOUTH WILL TURN THE
MID-LEVEL FLOW AROUND 500 MB TO SW BY MIDDAY SAT...PLACING
CRITICAL LEVEL IN A GOOD LOCATION. BEFORE THAT THE MID-LEVEL FLOW
IS MORE NW FRI NIGHT...STILL PLACING A CRITICAL LEVEL IN A GOOD
SPOT. GIVEN THIS SET UP...HAVE ISSUED A HIGH WIND WATCH FOR FRI
EVENING THROUGH SUN MORNING FOR THE DOWNTOWN JUNEAU AND DOUGLAS
AREAS. WILL KEEP THE STRONG WIND HEADLINE GOING THROUGH THE DAY
FRI AS WELL AS IT WILL BE A LONG DURATION EVENT STARTING FROM
SHORT RANGE PERIOD.

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...STRONG WIND UNTIL 1 PM AKDT THIS AFTERNOON FOR AKZ025.
         STRONG WIND FROM LATE TONIGHT THROUGH FRIDAY EVENING FOR AKZ025.
         HIGH WIND WATCH FROM FRIDAY EVENING THROUGH SUNDAY MORNING FOR
     AKZ025.
MARINE...GALE WARNING FOR PKZ012.
         SMALL CRAFT ADVISORY FOR PKZ011-013-021-022-043-051-052.

&&

JBT/RWT