741
FXAK67 PAJK 181304
AFDAJK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
504 AM AKDT Wed Sep 18 2024

.SHORT TERM...Windy and wet conditions are beginning to move into
the panhandle as a front associated with a parent low near the
northern gulf moves eastward. Minor changes to the overall
forecast package mainly for marine. For an excellent description
of QPF and winds that holds true for this forecasting package,
refer to the prior short term AFD. Still expecting 20-25 knot
winds in the inner channels as the front progresses eastward, but
increased areal extent of 25-30 knot winds in the gulf for the
post frontal period. Mid to upper level cold air advection will
provide a punch of westerly winds behind the front. Current ASCAT
passes show 25-30 knot W-SWerlies around the central gulf, which
further supports this idea. Additionally, due to the stout
westerly component to the winds behind the front, winds in the
inner channels will likely take an increasingly SW direction with
the frontal passage.


Finally, while not enough confidence to force a change to the PoP
forecast, mid level drying along the southern panhandle in the
post frontal environment may lead to only periods of rain, with
breaks in between. Regardless much of the southern panhandle is
still expecting rain, at least measurable amounts every three
hours.


.LONG TERM...The long-term forecast is characterized by a
plethora of storms moving across the Gulf into the Panhandle
bringing wind and rain concerns from Thursday into the weekend.
Touching on rain, an atmospheric river will impact Queen Charlotte
Sound, with the southern Panhandle on the northern edge of the
higher moisture, potentially limiting more significant impacts.
For mariners operating in our area, especially in the inner
channels, expect changes on wind speeds in some inner channels as
guidance shows better agreement through the week.

More details:
At 500mb, a longwave trough will eject into Canada Thursday, with
the accompanying surface low in the Gulf beginning to weaken as
it loses support aloft, allowing surface winds speeds and rainfall
to diminish. Thursday afternoon into early Friday are now looking
like the only window for a break past the weekend. Early Friday
ensembles highlight another system moving into the southeast Gulf,
deterministic runs show decent divergence from the mean, with the
GFS and ECMWF trending towards gale force southerly winds for
Clarence. Furthermore, the trends of both deterministic are moving
the low further north with a drop in surface pressure and agree
in location. For now, the forecast reflects near-gale force
southerly winds impacting the southern coast, Dixon, and Clarence
Strait by Friday, with elevated easterly outflow winds shooting
east out of Cross Sound, and north winds in Lynn Canal. For now,
the highest winds Friday to Saturday look to impact the central
and southern Panhandle. By late Sunday or Monday, a broad low is
expected in the Gulf.

Switching to rainfall, the jet will begin to push a moderate
atmospheric river into Haida Gwaii and Queen Charlotte Sound with
the southern Panhandle on the northern edge of the AR. Expect
rainfall through the weekend into next week, resulting in about 1
to 2 inches per day, heaviest rainfall in the southern Panhandle.
With that said long range guidance is struggling with the
location, magnitude, and extent of the atmospheric river which
could swing more rainfall than anticipated further north.

&&

.AVIATION...Conditions are starting to deteriorate across the
northern panhandle this morning. Yakutat is already seeing IFR
ceilings down to 600 ft. Rain is beginning in the rest of the
northern panhandle and outer coast early this morning, but VFR
conditions are still hanging on. Expect ceilings and vis to drop
into MVFR or lower criteria through the morning with the southern
panhandle getting in on the act by afternoon. Ceilings will likely
stay low into Wed night, but vis may improve as rain starts to
diminish late.

Winds are the other issue with gusty winds in northern Lynn Canal
already this morning. The rest of the northern panhandle will see
some increased winds as well by midday though the strongest will
be around Skagway. Some light turbulence and low level wind shear
are possible mainly today with frontal passage.


&&

.MARINE...The next front is moving in from the west, causing wind
speeds to increase. 20 to 30 knots in the outer coastal waters
with 20 to 25 knots in the inner channels. Northern Lynn Canal
will be the highlight of this system, with winds increasing to 30
knots this morning and continuing to remain elevated through
Wednesday night.

Seas will get up to 3 to 5 feet in the inner channels with gulf
seas getting up to 10 to 16 feet for this morning and begin
diminishing in the evening.


&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Strong Wind until 10 AM AKDT this morning for AKZ318.
MARINE...Small Craft Advisory for PKZ012-013-022-031>033-053-641>644-651-
     652-661>664-671-672.

&&

$$

SHORT TERM/MARINE...NTC
LONG TERM....AP
AVIATION...EAL

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