Gale Warning 425, NWS Juneau, AK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
304 PM AKST THU DEC 6 2012

.SHORT TERM...SYNOPTIC SCALE BROAD LOW PRESSURE SYSTEM OVER THE
AK GULF WITH CIRCULATIONS IN THE WESTERN GULF AND A DEVELOPING
WAVE IN THE SOUTHEAST GULF WITH HIGH PRESSURE OVER THE YUKON.
SATELLITE IMAGERY SHOWED FIRST BAND OF SHOWERS THAT MOVED OVER
THE PANHANDLE THIS MORNING EXITING INTO BRITISH COLUMBIA WITH A
BAROCLINIC LEAF EXTENDING OVER THE EASTERN GULF FROM THE
DEVELOPING SE GULF LOW. THE SHOWERS TODAY REALLY SHOWED HOW
DIFFICULT THESE THINGS ARE TO TRACK. THERE WERE SOME WIDE
VARIATIONS IN SNOW FALL AMOUNTS OVER NIGHT...MOSTLY A BIT LOWER
THAN FORECAST FOR THE CENTRAL PANHANDLE. BY MID MORNING A STRONG
BAND MOVED ACROSS THE AREA WITH SNOW FALL AMOUNTS OF 2 INCHES OF
MORE IN LESS THAN 2 HOURS. THESE SHOWERS WERE MOVING FAIRLY
RAPIDLY AND BY THE AFTERNOON MANY AREAS WERE SEEING SOME SUNNY
BREAKS WITH ONLY SCATTERED SHOWERS REMAINING. THE NEXT BAND OF
PRECIP IS ASSOCIATED WITH THE DEVELOPING SE GULF LOW. THE
PROJECTED TRACK OF THIS LOW IS A BIT UNCERTAIN BUT FOR NOW IT
LOOKS TO TRACK CLOSER TO DION ENTRANCE. THE PRECIP BAND WILL BE
ORIENTED MORE ALONG THE WESTERN COAST AND SOUTHERN PANHANDLE. AS
THE LOW CONTINUES TO TRACK TOWARD BRITISH COLUMBIA PRECIP WILL
DIMINISH FROM NORTH TO SOUTH. FOR NOW EXPECTING SNOWFALL AMOUNTS
TO REMAIN IN THE 1 TO 3 INCH RANGE...BUT AS SEEN WITH RECENT
SHOWERS THERE WILL LIKELY BE LOCALLY VARIABLE AMOUNTS.

 ARCTIC FRONT STILL LOCATED SOUTH OF SUMNER STRAIT WHEN ANALYZING
DEW POINT TEMPERATURES. TEMPS ALONG THE WESTERN PANHANDLE COAST
SILL HIGH ENOUGH TO SEE A RAIN SNOW MIX OTHERWISE THERE LOOKS TO
BE A CLEAR LINE OF THE RAIN SNOW MIX TO THE SOUTH OF SUMNER WITH
ALL SNOW TO THE NORTH. THIS MIXING OF RAIN WILL HELP KEEP THOSE
AREAS THAT MAY RECEIVE HIGHER QPF AMOUNTS OVERNIGHT FROM
ACCUMULATING SIGNIFICANT SNOW. OVERNIGHT LOWS NOT EXPECTED TO
VARY MUCH FROM THE PREVIOUS DAYS WHILE THERE MAY BE SLIGHT
INCREASE FOR TOMORROWS HIGHS AS THE ARCTIC FRONT COULD PUSH A BIT
FURTHER NORTH.

 PRESSURE GRADIENT TODAY WAS ORIENTED MORE EAST-WEST WITH HIGHEST
WINDS ALONG CROSS SOUND AND ICY STRAIT. WITH THE LOW MOVING OVER
THE SOUTHERN PANHANDLE EXPECT THE SOUTHERN INNER CHANNEL WINDS TO
PICK UP TO SMALL CRAFT THIS EVENING. IN ADDITION THE NORTHERLY
PRESSURE GRADIENT SHOULD BECOME REESTABLISHED...SO HAVE WINDS
OVER N LYNN CANAL INCREASING TO GALE FORCE. SKAGWAY AS USUAL WAS
THE WINDY LAND AREA WITH GUSTS OF 40 MPH AT THE AIRPORT. GRADIENT
WILL WEAKEN AGAIN FRIDAY WITH THE WINDS OVER THE NORTHERN INNER
CHANNELS DROPPING OFF IN THE AFTERNOON.

 MODELS WERE NOT HANDLING THE LOW DEVELOPING IN THE SOUTHEAST
GULF WELL. NAM WAS MOST PROGRESSIVE WITH A TRACK FURTHEST TO THE
SOUTH. GFS WAS MOST INCONSISTENT COMPARED TO PREVIOUS DAYS AS THE
12Z RUN PUT A BROAD LOW NEAR SITKA WHILE YESTERDAY HAD A CLOSED
LOW NEAR DIXON ENTRANCE. OTHERWISE MOST MODELS KEPT AN OPEN WAVE
TROUGH IN THE SE GULF. LATEST SATELLITE SHOWS THE NAM MAY HAVE
THE IDEA OF THE SOUTHERN TRACK BUT WAS STILL MUCH TOO DEEP. WENT
WITH AN ENSEMBLE APPROACH FOR PRESSURE AND WINDS. AS THERE IS NOT
MUCH CONFIDENCE WITH THE SYNOPTIC PATTERN...EVEN IF IT IS FAIRLY
WEPUBLIC...THERE IS LOWER CONFIDENCE IN THE MESOSCALE FEATURES. MAIN
ISSUE WILL BE NORTHERLY AND EASTERLY EXTENT OF PRECIP WITH THE
BAROCLINIC ZONE FROM THE SE LOW AND SNOW FALL AMOUNTS WITH THE
PASSING SHOWERS.

 &&

 .LONG TERM...MAIN CONCERN IN THE LONG RANGE TODAY IS TRYING TO
FIGURE OUT WHAT GOING TO HAPPEN WITH THE GALE FORCE FRONT THAT
WILL BE MOVING THROUGH THE PANHANDLE OVER THE WEEKEND. SEVERAL
FACTORS ARE COMPLICATING THE FORECAST. FIRST IS THE PERSISTENT
COLD AIR THAT IS STILL PRESENT IN THE PANHANDLE. SECOND IS HOW
FAST THE FRONT WILL BE APPROACHING WHICH DETERMINES WHEN AREAS
START TO SEE SE WINDS. THIRD IS HOW MUCH PRECIP WILL THIS FRONT
DROP AND WHAT TYPE WILL IT FALL AS.

 AS IT STANDS NOW, THE FIRST SIGNS OF THIS FRONT WILL BE
APPEARING ON SAT AS SE WINDS START THEIR INCREASE TO GALE FORCE
OUT IN THE GULF. ON THE INSIDE CHANNELS MOST OF THE NORTHERN AND
CENTRAL INNER CHANNELS WILL STILL BE NORTH OR EAST WIND WITH COLD
AIR STILL IN PLACE. PRECIP WILL START UP OVER THE PANHANDLE ON
SAT WITH SNOW FROM ISENTROPIC LIFT DUE TO OVERRUNNING OF THE COLD
AIR IN THE INNER CHANNELS. PRECIP WILL STILL BE LIGHT BUT WILL
INCREASE IN INTENSITY SAT EVENING AS THE PRE-FRONTAL BANDS START
TO ENTER THE PANHANDLE. BY LATE SAT NIGHT SNOW WILL BE FALLING IN
MOST OF THE CENTRAL AND NORTHERN INNER CHANNELS WHILE THE SOUTH
WILL BE MOSTLY RAIN AS THE STRONG SE FLOW STARTS PICKING UP. BY
EARLY SUN, THE SE FLOW WILL HAVE MADE IT UP TO JUNEAU AND
GUSTAVUS, UP LYNN CANAL AND MAY HAVE MADE IT AS FAR NORTH AS
SKAGWAY AND HAINES. TEMPERATURES WILL START WARMING UP AND SNOW
WILL START CHANGING OVER TO OR MIXING WITH RAIN BY SUN AFTERNOON
WHICH WILL CONTINUE INTO SUN NIGHT. YAKUTAT WILL BE MUCH THE SAME
WITH EASTERLY FLOW AND SNOW MUCH OF SAT NIGHT BUT WILL SWITCH TO
MORE SE TO SW FLOW AND RAIN DURING THE DAY SUN. HIGHEST SNOW
ACCUMULATIONS ARE EXPECTED SAT NIGHT AND EARLY SUN BEFORE THE SE
FLOW WARMS UP TEMPERATURES AND CHANGE OVER OCCURS.

 AS FOR WINDS, THE STRONGEST ARE EXPECTED IN THE GULF AND ALONG
THE OUTER COAST AND SOUTHERN PANHANDLE SAT NIGHT INTO SUN. GALE
FORCE WINDS ARE EXPECTED IN THE GULF AND CLARENCE STRAIT. AS FOR
THE LAND AREAS. BREEZY CONDITIONS ARE EXPECTED WITH LOW END
STRONG WIND CONDITIONS POSSIBLE FOR THE KETCHIKAN, ANNETTE,
HYDABURG, AND SOUTHERN BARANOF ISLAND AREAS SAT NIGHT. THE FRONT
IS TOO FAR AWAY FROM ITS PARENT LOW AND PRESSURE GRADIENTS IN THE
PRE-FRONTAL ENVIRONMENT ARE TOO WEAK TO SUPPORT ANY HIGHER WINDS.
THE FRONT WILL BE MOVING THROUGH THE PANHANDLE DURING THE DAY SUN
AND WINDS IN MOST AREAS, ESPECIALLY ALONG THE OUTER COAST, WILL
SWITCH TO SW AND INCREASE TO BREEZY CONDITIONS. SHOWERS WILL ALSO
BE THE RULE OF THE DAY FOR SUN NIGHT INTO MON.

 FOR THE REST OF THE LONG RANGE, MODEL CONSISTENCY IS NOT THAT
GOOD. THERE IS THE HINT OF SOME WEAK SYSTEM COMING THROUGH THE
GULF AND PANHANDLE ON MON NIGHT AND TUES BUT WHERE AND HOW STRONG
ARE UP FOR DEBATE. FOLLOWING THAT IS A WEAK COLD AIR OUTBREAK
MAINLY IN THE YUKON. MODELS VARY ON STRENGTH BUT GENERALLY AGREE
ON IT NOT STICKING AROUND FOR MORE THAN A DAY.

 LONG RANGE MODELS WERE FINALLY IN FAIR AGREEMENT FOR THE WEEKEND
SYSTEM WITH THE NAM BEING A SLIGHT OUTLIER AS FAR AS FRONTAL
SPEED (IT WAS A BIT TOO FAST COMPARED TO THE OTHER MODELS).
DECIDED ON A BLEND OF THE EC AND GFS THROUGH THE WEEKEND. FOR MON
AND BEYOND DECIDED TO STICK MORE TOWARD THE HPC (FOR ITS
INCLUSION OF THE ENSEMBLE MEAN SOLUTIONS) AND THE EC (WHICH WAS
MORE CONSISTENT WITH ITS SOLUTIONS IN THE LONG RANGE). FORECAST
CONFIDENCE IS ABOUT AVERAGE THROUGH THE WEEKEND THEN FALLS TO
BELOW AVERAGE FOR MON AND BEYOND.

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...STRONG WIND THROUGH FRIDAY MORNING FOR AKZ018.
MARINE...HEAVY FREEZING SPRAY WARNING FOR PKZ012.
         GALE WARNING FOR PKZ012.
         SMALL CRAFT ADVISORY FOR PKZ011-013-021-022-033>036-041-042.
         SMALL CRAFT ADVISORY DUE TO SEAS FOR PKZ043-051-052.

&&

PRB/EAL