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FXAK67 PAJK 182325
AFDAJK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
325 PM AKDT Wed Sep 18 2024

.SHORT TERM.../Through Thursday night/...Post frontal showers will
prevail through this short term forecast period. As the remnants
of the front cross into Canada, gusty winds over the northern
inner channels will ease, but low level onshore flow will persist
through the period before backing to the southeast in advance of
the next front. Overnight lows through Thursday night will be
getting down to the lower 40s, so no frost concerned yet. With
the growing season behind us now, no frost or freeze warnings will
be issued, so pay attention to overnight lows lest your late
season outdoor plants get inadvertently damaged. Near White Pass,
overnight lows tonight and tomorrow should be getting low enough
that a mix of rain and snow is possible, though no accumulation is
expected. Daytime highs in the mid to upper 50s forecast for
tomorrow.

.LONG TERM...

Key Points:
Multiple lows impact the Panhandle through next week bringing wind
and rain. Most rainfall expected in the far southern region.
Potential break in rain Sunday.

For rainfall details see Hydrology section.

Early Friday a long wave trough will be departing the Panhandle
moving into western Canada, shutting off support to the surface
low positioned in the Gulf. With the loss of reinforcing dynamics,
expect the pressure gradient to weaken, allowing winds and rain
to diminish into Friday afternoon. This break will be short lived
as an extensive jet drops south of our region allowing multiple
embedded shortwave troughs to rapidly move into the Panhandle.
Current forecasts reflect a surface low associated with each of
these features, bringing elevated wind Friday into Saturday and
potentially Sunday. Snow levels are dropping but no impacts
expected at this time.

While the Panhandle is impacted by these lows this weekend, a
broad open long wave trough will begin to move into the Gulf.
Associated with this feature will be a 980 to 985mb surface low.
While the low takes residence near Cook Inlet Sunday the pressure
gradient will tighten over the Panhandle with winds increasing out
of the south again.

&&

.AVIATION...Flying conditions for the panhandle today have varied
depending on location. Some places continue to report IFR
conditions while other locations have improved to VFR while others
are still experiencing MVFR CIGs. CIGs are expected to improve
during the evening and overnight hours as showers continue to
dissipate. There is the potential though that fog could develop
during the overnight hours with the clearing skies. So that is
something to be mindful of as we head into the overnight hours.

&&

.HYDROLOGY...Multiple rounds of heavy rainfall through the next 7
days. SPS issued for Friday into Saturday in the south.

First round, Friday into Saturday: Long range guidance is still
flip-flopping on location, extent, and magnitude of an Atmospheric
River (AR) that will be carried by the jet stream for this
weekend. Current ensemble prognosis indicates a weak AR event with
some outliers reaching moderate. With that said, guidance the
ECMWF extreme forecast index continues to shift this first AR
north a touch from Hecate Strait/Haida Gwaii; simply put, heavier
rainfall is becoming more of a reality in the southern Panhandle,
potentially breaking some record 24 hour values with rivers
responding region wide. No flooding is anticipated at this time.


Second round Monday into Tuesday: As a broad longwave trough
positions itself in the western Gulf Monday and Tuesday, the jet
axis will become positive, which will steer a more potent
atmospheric river into the Panhandle. Guidance is showing some
agreement that this could be a moderate to strong AR with most
rainfall expected in the central and south. ECWMF EFIs are
highlighting a significant shift from climate normal over most of
the Panhandle with further trend analysis required over the next
few days. Simply put we could see a more significant rainfall event
Monday and Tuesday.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Strong Wind until 10 PM AKDT this evening for Akz018-319.
MARINE...Small Craft Advisory for
PCs-013-022-031-053-641>644-651-652- 661>664-671-672.

&&

$$

SHORT TERM...Fritsch
LONG TERM....AP
AVIATION...SF
HYDROLOGY...AP

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