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FXAK67 PAJK 211429

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
629 AM AKDT Sat Oct 21 2017

.SYNOPSIS...A storm force front will move northward into the
southeast gulf today and begin to weaken. Its parent low will
move into the southeast gulf and then slowly drift toward Baranof
Island through Sunday.


.SHORT TERM...A storm force front will lift north into the
southeast gulf this morning and steadily weaken as it continues
north and west across the eastern gulf. Rain bands, some moderate
will lift north across the southern Panhandle as well. There is
still some disagreement with how this complex system evolves. The
ECMWF has been stubborn with an impactful wave extending along the
far eastern flank of the front. While NAM and GFS MOS have reduced
wind speeds along the coast, given the strong possibility of this
wave from the ECMWF, we feel no reason to yank gusty winds of 40
to 45 mph from Sitka, Craig, and Hydaburg, and in fact, we have
added Ketchikan and Metlakatla as well for today.

Some scattered rain showers still persist across the Panhandle,
with some mix to snow reported around Yakutat and the Haines and
south Klondike. But no accumulation has been reported or is
expected at sea level. And only minor accumulations in the high
country along both roads.

As the low enters the southeast gulf this morning, confidence has
increased in it stalling today and very slowly beginning to move
to Baranof Island by Sunday. Therefore, we have delayed the onset
of southerlies across much of the northern and north-central
Panhandle until late Sunday. And while we are not expecting gusts
to 40 mph for tonight and Sunday, we do expect some gustiness to
25 or 30 mph to follow the system as it moves inland. At some
point late today, the system begins to occlude. This will allow
precipitation to become more showery tonight and remain such
through the weekend. As winds retreat to the far north Sunday
night, winds elsewhere lighten as an intervening ridge settles
across Southeast before the next significant system on Monday.

Finally, lightning detected along the front could potentially
spread into the southern portions of 310 later this morning, but
we think the stronger support for thunderstorms will arrive into
the southeast gulf this evening.

The 00Z Canadian NH and the 06Z NAM provided support for changes
made to the forecast, mainly for late Saturday night into Sunday
night. Forecast for today still holds. Confidence has improved for
Saturday night and Sunday. Moderate to high confidence still holds
for today.

.LONG TERM...Monday through Saturday...A very active and wet
pattern appears ready to set up through the next week. We`ll
start off with a shortwave developing Monday over the western
gulf out of a parent trough positioned over the Bering Sea and
western coast of mainland Alaska. Originally, there was quite a
bit of model uncertainty regarding the surface low that develops
with this feature. However, the GFS and Canadian runs from 00Z
this evening are agreeing more with the ECMWF solution, which has
also had more run to run consistency. According to the models, the
surface low will develop out of the south-central gulf and lift
northeast across the panhandle late Monday into Tuesday. An
associated weather front with this system will also lift north
beginning Monday, bringing some stronger winds and increased
precipitation across the panhandle. Due to a more southerly
origin with this low, we`ll expect it to be more subtropical in
nature, so we should see the snow level rise with the passing of
this system.

After Tuesday, models are still having a tough time agreeing on
the development of certain surface features, so we opted not to
change much of the forecast after this point, using mainly WPC
guidance for any consistency changes.

We`re also monitoring the extratropical transition of Typhoon Lan
over the course of the next week. Models currently hint at a very
wet event for our area late in the week, mainly Thursday into
Friday, but as far as who will get the more significant amounts of
precipitation is still to be determined.


.AVIATION...Most complex TAFs still are found in the southern
reaches of our area from Sitka southeast along the coast where
gusty winds and some MVMC conditions associated with
rain/visibility and ceilings along with gusty winds and wind shear
make for a complex 24 hours.


.AJK Watches/Warnings/Advisories...
PUBLIC...Strong Wind until 1 PM AKDT this afternoon for AKZ027.
     Strong Wind from 10 AM this morning to 4 PM AKDT this afternoon
     for AKZ023.
     Strong Wind until 4 PM AKDT this afternoon for AKZ028.
MARINE...Storm Warning for PKZ041.
     Gale Warning for PKZ035-036-042-043.
     Small Craft Advisory for PKZ021-022-031-033-034-051-052.




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