Area Forecast Discussion
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000
FXAK67 PAJK 190008
AFDAJK

SOUTHEAST ALASKA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE JUNEAU AK
408 PM AKDT SAT OCT 18 2014

.SHORT TERM...UPPER TROUGH IS CENTERED OVER THE FAR SRN GULF THIS
AFTERNOON...WHILE AN EMBEDDED IMPULSE AND ASSOCIATED SURFACE FRONT
IS RAPIDLY LIFTING NWD INTO THE SRN/CNTRL PANHANDLE. SHIELD OF
STRATIFORM RAIN IS OCCURRING ALONG/AHEAD OF THE FRONT...WITH
MODERATE TO HEAVY RAINFALL RATES OBSERVED FROM HYDER TO KETCHIKAN
DURING MID-AFTERNOON. HI-RES MODEL GUIDANCE SHOWS THIS BAND OF
RAIN SPREADING N INTO THE JUNEAU/GUSTAVUS AREA BY LATE
AFTERNOON...HAINES AND SKAGWAY DURING EARLY EVENING...AND THEN
YAKUTAT BY LATE EVENING. MEANWHILE...COOL MIDLEVEL AIR /AROUND
-24C AT 500 MB/ WILL SPREAD NNE BEHIND THE FRONT. THIS WILL AID IN
DESTABILIZING THE ATMOSPHERE OVER THE GULF AND
SERN PUBLIC...RESULTING IN A TRANSITION TO A CONVECTIVE/SHOWER
REGIME. ISOLATED THUNDERSTORMS WILL ALSO BE POSSIBLE OVER THE
OUTSIDE WATERS AND FAR SRN PANHANDLE AS UPPER IMPULSES EMBEDDED
WITHIN THE PREVIOUSLY MENTIONED TROUGH INTERACT WITH THE WEAKLY
UNSTABLE ENVIRONMENT.

A 50+ KT LOW-LEVEL ESELY JET CURRENTLY RESIDES OVER THE SRN
PANHANDLE INTO THE CNTRL GULF...AND WILL SUPPORT WINDS FROM 20-30
KT OVER MOST OF THE INSIDE AND OUTER WATERS AS IT LIFTS N INTO
THE CNTRL PANHANDLE THIS EVENING...WITH WINDS UP TO GALE FORCE
POSSIBLE FOR CROSS SOUND AND MARINE ZONE 43. IN ADDITION...NLY
WINDS HAVE RECENTLY STRENGTHENED TO SMALL CRAFT OVER LYNN
CANAL...AND WILL LIKELY PERSIST THROUGH LATE EVENING.

GOING INTO SUN AFTERNOON...MODEL GUIDANCE SHOWS AN UPPER VORT LOBE
LIFTING N INTO THE PANHANDLE...WITH A WEAK REFLECTION DEVELOPING
AT THE SURFACE. THIS IS EXPECTED TO REINVIGORATE PRECIPITATION
RATES OVER THE CNTRL/SRN PANHANDLE WITH A CHANGE BACK TO A MORE
STABLE STRATIFORM REGIME. SURFACE WINDS WILL WEAKEN BRIEFLY DURING
THE AFTERNOON AS THE SURFACE WAVE ENTERS THE PANHANDLE...BEFORE
RESTRENGTHENING ONCE AGAIN GOING INTO THE LONG TERM PART OF THE
FORECAST PACKAGE.

PRESSURE GRIDS WERE NOT MODIFIED THROUGH 12Z SUN...THEN BLENDED IN
THE NAM/ECMWF IN ORDER TO ADD RESOLUTION TO THE SURFACE WAVE
LIFTING N OVER THE PANHANDLE. UTILIZED THE 3KM ARW AND NMM BLENDED
WITH COARSER RES GUIDANCE FOR POP AND QPF. FORECAST CONFIDENCE IS
AROUND AVERAGE.

.LONG TERM...NORTHWARD MOVING IMPULSES OVER SOUTHEAST ALASKA WILL
CONTINUE MONDAY NIGHT ON THE EAST SIDE OF THE DEEPENING LONGWAVE
LOW IN THE VICINITY OF DILLINGHAM. BROAD SURFACE LOW WILL HEAD OFF
NORTHWEST INTO PRINCE WILLIAM SOUND BY MONDAY MORNING. A RELATED
WEATHER FRONT WILL REACH THE FAR SOUTHERN PANHANDLE BY MONDAY
EVENING. THIS FRONT MAY STALL A BIT AS IT MOVES NORTH. PRE-FRONTAL
WINDS WILL NOT BE THAT STRONG THOUGH. IN FACT...ABOUT ALL THINGS
WILL MUSTER IN THE CENTRAL PANHANDLE WILL BE A FLIP TO THE
SOUTH...MAYBE TO 20 KT FOR STEPHENS/NORTHERN CHATHAM. SMALL CRAFTS
WILL REACH FREDERICK SOUND AND CHANNELS SOUTHWARD. SAW NO REASON
TO GO WITH GALE FOR CLARENCE, BUT BOOSTED THEM TO 30 KT AS SOME
LOW LEVEL JET WINDS WITH THE FRONT MAY TRANSFER A LITTLE MORE
EFFICIENTLY DOWN TO THE SURFACE.

TRULY, MODELS AS THEY ALWAYS DO ARE HAVING DIFFICULT TIMES
RESOLVING FRONTAL PASSAGES THROUGH THE PANHANDLE WITH THIS KIND OF
PATTERN WITH A BROAD AREA OF LOW PRESSURE BASICALLY STUCK IN THE
GULF. TO GENERALIZE...FRONTS AND A SEMI-CONSTANT LOW LEVEL JET
OVER THE SOUTHERN/CENTRAL PANHANDLE WILL KEEP WINDS SOUTHERLY,
WHILE NOT ON THE PARTICULARLY STRONG SIDE THROUGH MONDAY.

MONDAY NIGHT/TUESDAY YET ANOTHER FRONT WILL HERALD A PATTERN CHANGE FOR
MOST OF THE PANHANDLE. SHOWERS WILL BEGIN DIMINISHING ACROSS THE
COAST RANGE AS A PERIOD OF MORE OFFSHORE FLOW SETS UP IN THE UPPER
LEVELS AND EVENTUALLY AT THE SURFACE. ROUNDING THE BASE OF THE
DILLINGHAM UPPER LOW IN THE ZONE OF STRONG BAROCLINICITY WILL
DEVELOP A LOW THAT WILL STALL IN THE SOUTHEAST GULF. WHILE RAIN
WILL REMAIN LIKELY OVER THE SOUTH...CHANCES WILL DIMINISH OVER THE
NORTH AS OFFSHORE WINDS SET IN. NOT PARTICULARLY COLD OFFSHORE
WINDS WITH THIS PATTERN IN THE MID-WEEK, BUT POSSIBILITY THAT THE
ATMOSPHERE COOLS OFF ENOUGH OVER THE NORTH TOWARD THE WEEKEND WITH
SOME SNOW MIXING IN AT NIGHT OVER THE FAR NORTHERN ZONES.

FORECAST CONFIDENCE AVERAGE FOR PERIOD. USED ECMWF/NAM SUNDAY
NIGHT/MONDAY WITH ECMWF TRANSITIONING TO WPC MONDAY NIGHT INTO
MID-WEEK.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...STRONG WIND UNTIL 4 PM AKDT THIS AFTERNOON FOR AKZ027.
MARINE...GALE WARNING FOR PKZ022-036-041>043.
         SMALL CRAFT ADVISORY FOR PKZ012-013-021-033>035-051>053.

&&

$$

GARNER/JWA

VISIT US AT HTTP://WWW.WEATHER.GOV/JUNEAU








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