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FXAK67 PAJK 181441
AFDAJK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
541 AM AKST THU DEC 18 2014

.SHORT TERM...STRONG WEATHER FRONT MOVING NORTH WILL SPREAD STORM
FORCE WINDS THURSDAY ACROSS MUCH OF THE EASTERN GULF WATERS AND
HIGH WINDS GUSTING TO AROUND 60 MPH FOR WESTERN PRINCE OF WALES
ISLAND. LOWER PRESSURES REPORTED BY BUOYS TO THE SOUTH OVERNIGHT
SUGGEST A STRONGER SYSTEM THAN WHAT MODELS HAVE INDICATED. THUS
PREFERRED THE SLOWER PROGRESSION OF THE ECMWF AND THE GFS. WHILE
THE NAM WAS EVEN SLOWER, IT WAS ALSO MUCH WEAKER WITH THE TRIPLE
POINT LOW/WAVE, AND THUS WAS DISCOUNTED EARLY.

A MUCH WEAKER FRONT BROUGHT SOME VERY LIGHT RAIN TO THE
SOUTHERN/CENTRAL PANHANDLE OVERNIGHT, AND ITS APPROACH FROM THE
SOUTH HELPED FLIP WINDS ACROSS THE NORTH YESTERDAY AFTERNOON. WITH
PARALLEL FLOW ACROSS THE JUNEAU AREA, LIGHT WINDS, AND A NIGHTTIME
INVERSION, FOG BECAME DENSE YESTERDAY EVENING. HOWEVER, SOME MIXING
ASSOCIATED WITH THE WEAK FRONT MOVING NORTHWARD WILL HELP CONTINUE
TO THIN OUT THE FOG THROUGH THE MORNING.

GUSTY WINDS HAVE ALREADY DEVELOPED ACROSS MUCH OF THE PANHANDLE,
BOTH PRE-FRONTAL IN THE SOUTHERN PANHANDLE AND RESPONSIVE OUTFLOW
WINDS IN THE NORTH. WE STILL EXPECT GALES OVER NORTHERN LYNN
CANAL AND CROSS SOUND LATER THIS MORNING. SOME OUTFLOW WINDS ARE
POSSIBLE FOR DOWNTOWN JUNEAU, BUT NOT COMPLETELY SOLD ON IT.
HIGHER RESOLUTION NAM12 HAS A WEAK SHORT-WAVE LIFTING NORTHWARD
THIS MORNING THAT MAY UNLEASH SOME MOUNTAIN WAVE ACTIVITY THIS
AFTERNOON. IN ADDITION HIGH RES NMM AND ARW BOTH CALLING FOR SOME
HIGHER WIND SPEEDS IN VICINITY OF SALISBURY RIDGE PEAKING THIS
AFTERNOON AND DIMINISHING THIS EVENING. COVERED THIS WITH GUSTS OF
35 MPH THIS AFTERNOON DIMINISHING IN THE EVENING.

MOVING DOWN SOUTH...A LOW LEVEL 925 MB JET OF 65 KT ASSOCIATED
WITH THE PASSING STORM SHOULD BE ENOUGH TO GENERATE STORM FORCE
WINDS THAT WILL LIFT NORTHWARD FROM 41 THIS MORNING INTO 42, 43,
AND 310 THROUGH THE DAY. WHILE WINDS WILL BE STRONG WITH GUSTS TO
AROUND 50 MPH FOR THE SOUTHERN INNER CHANNELS AND BARANOF ISLAND,
WESTERN PRINCE OF WALES WILL BE MOST EXPOSED TO THESE FRONTAL
WINDS. AT THIS POINT, WINDS SHOULD RISE THROUGH THE EARLY MORNING
HOURS, PEAKING TO AROUND 60 MPH AROUND MIDDAY BEFORE DIMINISHING
LATE IN THE AFTERNOON. ALL MODELS ARE SUGGESTING A THIRD TRIPLE
POINT FORMING SOUTH OF THE STORM FORCE LOW THAT WILL FOLLOW
THURSDAY NIGHT. HOWEVER, THE NAM SEEMS TO TAKE IT MUCH FARTHER
WEST...AKA AROUND DIXON ENTRANCE WHILE THE ECMWF AND GFS SWING IT
MUCH FARTHER EAST INTO HECATE STRAIT SAFELY AWAY FROM THE SOUTHERN
PANHANDLE. IF NAM IS CREDIBLE, THEN WINDS MAY LAST LATE INTO THE
AFTERNOON FOR ZONE 27, AND THUS THE WARNING EXPIRATION TIME
OF 6 PM IS GOOD GIVEN SLIGHT UNCERTAINTY. IN THE SYSTEM`S LEE,
THERE WILL BE HARDLY A BREAK AS A NEW FRONT APPROACHES FROM THE
SOUTH LATE THURSDAY NIGHT KEEPING GALES BLOWING ACROSS MUCH OF THE
OUTSIDE WATERS.

RAIN WILL INCREASE ACROSS THE SOUTH WITH THE APPROACH OF THE STORM
FORCE FRONT. GIVEN OUTFLOW WINDS IN THE NORTH, REDUCED THE
LIKELIHOOD OF SNOW FOR JUNEAU AND POINTS NORTH. IN THE WAKE OF THE
FRONT, WINDS WILL TURN A LITTLE MORE SOUTHERLY AND ALLOW FOR MORE
MOISTURE TO EXTEND NORTHWARD. THIS SHOULD TRANSLATE INTO AN INCH
OF SNOW POSSIBLE FOR GUSTAVUS, HOONAH, AND JUNEAU TONIGHT. QPF
WILL BE LIGHT, AND IN SOME LOCATIONS THIS MAY BE OVERKILL. IN ANY
EVENT, RAIN WILL INTENSIFY FOR AREAS SOUTH OF FREDERICK SOUND
THURSDAY NIGHT.

ECMWF AND GFS WERE PREFERRED MODELS. FORECAST CONFIDENCE GOOD.

.LONG TERM...UPPER LEVEL LOW ASSOC WITH THE THURS SYSTEM WILL
WEAKEN BY FRIDAY MORNING AS IT RETROGRADES TO THE WESTERN GULF.
DESPITE THIS FLOW WILL REMAIN ONSHORE AND DIFFLUENT ALOFT...MEANING
STAYING WET FOR MUCH OF THE EXTENDED FORECAST.

OUR WEATHER WILL BE DICTATED BY WAVES OF VORTICITY AND TROUGHS
ROTATING AROUND THE PARENT LOW IN THE WESTERN GULF UNDER THIS ACTIVE
ONSHORE PATTERN. AS MENTIONED ABOVE...A FRONTAL TROUGH WILL MOVE
INTO THE SE GULF FRIDAY MORNING WITH GALE FORCE WINDS. THE TROUGH
AXIS HAS SHARPENED IN THE LATEST MODEL OUTPUT WHICH MEANS THAT
WINDS ON THE NORTH SIDE OF THE TROUGH WILL BE OFFSHORE WITH NORTH
WINDS THROUGH THE INSIDE WATERS AND OUT OF INTERIOR PASSES. THE
NORTH WINDS WILL KEEP TEMPERATURES LOWER FOR SNOW...HOWEVER THE
OFFSHORE FLOW WILL CAUSE DOWNSLOPING/SHADOWING AND LIMIT POP/QPF.
DESPITE THIS HAVE KEPT LIKELY POPS IN FOR FRIDAY OVER THE NORTH
BUT SNOWFALL AMOUNTS LOOK TO BE LESS THAN 1 INCH DURING THE DAY.
THE SOUTHERN OUTER COASTAL AREAS WILL SEE RAIN AND TEMPERATURES IN
THE LOW 40S. FRIDAY NIGHT AND SATURDAY POPS ARE A LITTLE HIGHER
AND SNOWFALL AMOUNTS COULD BE 1-2" EVERY 12HRS FOR
HAINES/SKAGWAY/JUNEAU VALLEY NORTH/HYDER. HOWEVER THIS FLOW
PATTERN WILL CONTINUALLY BRING IN WARM/MOIST AIR FROM THE GULF
WHICH WILL COMPLICATE THE P-TYPE FORECAST. GENERALLY EXPECTING ALL
RAIN SOUTH OF HOONAH WITH THE EXCEPTION OF HYDER. HAVE A LOT OF
RAIN AND SNOW MIXED IN THE FORECAST TEXT FOR THE NORTH/CENTRAL
AREAS. THIS IS IN PART DUE TO THE ZONES HAVING COLDER INTERIOR
AREAS AT SLIGHTLY HIGHER ELEVATION WHERE SNOW IS MORE LIKELY TO
OCCUR. OTHERWISE THINK THAT THE PRECIP IS MORE LIKELY TO BE RAIN
WITH SNOW MIXED IN AT TIMES AND WITH LITTLE TO NO ACCUMULATION IN
THE MAIN POPULATIONS AREAS.

TOWARD THE MIDDLE OF NEXT WEEK THE UPPER LEVEL PATTERN LOOKS TO
CHANGE AS A RIDGE OF HIGH PRESSURE MOVES INTO THE GULF. THIS WOULD
SHIFT FLOW TO A MORE DRY NWLY DIRECTION. HARD TO CALL THIS A PATTERN
CHANGE SINCE THE RIDGE LOOKS BE PROGRESSIVE MOVING TO THE EAST
MAKING OUR "DRY" PERIOD SHORT-LIVED. TIMING OF THIS WILL LIKELY BE
ADJUSTED SOME AS TIME GETS CLOSER.

USED AN ENSEMBLE APPROACH FOR PRESSURE WITH AN EMPHASIS ON THE
ECMWF. MAIN CHANGES WERE TO INCREASE WIND SPEEDS THROUGH THE INSIDE
WATERS WITH THE FRONTAL TROUGH IN THE SHORT/MID RANGE. THEN KEPT
THE EXTENDED FORECAST LARGELY IN TACT.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...HIGH WIND WARNING UNTIL 6 PM AKST THIS EVENING FOR AKZ027.
         STRONG WIND THROUGH THIS AFTERNOON FOR AKZ023-028.
MARINE...STORM WARNING FOR PKZ041>043.
         GALE WARNING FOR PKZ012-022-033-036-051-052.
         SMALL CRAFT ADVISORY FOR PKZ011-013-021-031-032-034-035.
         SMALL CRAFT ADVISORY DUE TO SEAS FOR PKZ053.

&&

$$

JWA/FERRIN

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