Area Forecast Discussion
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000
FXAK67 PAJK 191407
AFDAJK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
607 AM AKDT Tue Sep 19 2017

.SHORT TERM.../Through Wednesday night/ Rather quiet short range
forecast today. Weak upper low in the central gulf is sliding SE
taking it`s showers with it. Meanwhile a couple of weak easterly
shortwaves are passing through the panhandle at the moment. The
first is currently over Yakutat at the moment and was what brought
the showers to the northern panhandle overnight. A second wave is
currently over the southern coast range and is trying to make its
way into the southern panhandle.

These shortwaves are not going to stick around very long. A
surface ridge will be building in the gulf today as the central
gulf low slides SE. The resulting strengthening NW flow will
clear out the remaining showers by this evening. After that point
the panhandle looks to remain dry at least through Wed night. The
NW flow will also help clear out some of the clouds with many
inner channel areas possibly seeing partly cloudy skies by late
Tue night. The clearing skies, low winds, and plenty of low level
moisture means that fog is possible for many areas Tue night so
have added patchy and areas of fog. The gulf is a different story
as marine layer clouds will likely keep skies mostly cloudy
through the period.

Winds remain mostly low through Wed night. Highest winds seen will
be around Cross Sound Tue and Wed evening as the NW flow forms a
tip jet off the southern side of the Fairweather Range. Expect 20
kt NW winds there Tue evening and up to 25 kt Wed evening. Other
then that winds will be 20 kt or less.

Few changes, other then local effects, were made over the previous
forecast. Model agreement was good. Used Nam for main guidance.

.LONG TERM.../Thursday through Monday as of 8 pm Monday/ The
extended forecast begins dry; however, it will quickly shift to a
wet pattern as a front approaches from the west. Increasing clouds
and rising PoP values are the trend for Thursday as the front
approaches. Yakutat remains the area that will see the earliest
onset of precipitation with rain likely by Thursday afternoon. The
rest of the panhandle may stay dry until Thursday evening.
Nonetheless, once precipitation begins, a wet period continues
through the long term. As the effects of this first front begin to
diminish, a low pressure system and its associated weather front
will begin to affect the panhandle Saturday. This will act to
increase rainfall across the panhandle once again. Little day to
day temperature variation is expected in the long term with highs
in the 50s across the panhandle through the extended.

A few significant changes were made in the long term. The front
approaching Thursday has trended slower, so its arrival was slowed
down. Also, there is enhanced model agreement that a surface low
develops over the pacific and tracks northeast into the gulf this
weekend. Operational models are in good agreement with this system
but diverge some from the WPC solution so some detail surrounding
the low was added with winds being increased to 20 kts over the
gulf; however, this may be trended upward as the event draws
closer. Precipitation associated with the low may be another
concern as models show tropical influence in the low`s
development. A blend of the NAM and ECMWF was used for Thursday
and more input from the ECWMF on Friday. The weekend low was
handled with a blend of the WPC, ECMWF, and GFS solutions;
however, before this timeframe the GFS is an outlier.

&&

.AVIATION...Diminishing showers combined with a light pressure
gradient and abundant low level moisture resulting in VLIFR to VFR
conditions early this morning. Periods of IMC CIGS and MVMC VSBY
expected through 16-18Z with VMC becoming prevailing by this
afternoon. Clearing sky cover combined with continued light
gradient makes conditions favorable for fog/stratus development
again overnight into Wed. Expect greater coverage of IMC
persisting through 17-20Z Wed morning.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...None.
MARINE...Small Craft Advisory due to Seas for PKZ041-042.

&&

$$

EAL/BC/Byrd

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