205
FXAK67 PAJK 201313
AFDAJK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
513 AM AKDT Fri Sep 20 2024

.SHORT TERM...Next gale force system is on the panhandle`s
doorstep, with winds increasing through the morning hours and
staying elevated through tonight. Gales to strong gales will
extend from Cape Spencer down the Dixon Entrance this morning
before being replaced by strong breeze westerlies behind the
front. Unfortunately, a good amount of uncertainty on low track
even this close to the event remains present. If the low center
rides south along the coastline with upper energy pushing inland,
then it will quickly shear apart with elevated winds extending up
until Point Couverden and Grave Point. However, if the low center
pushes inland and into northern British Columbia, then elevated
winds tonight could extend all the way up Lynn Canal. Regardless
of outcome, increased winds to gale for the Five Finger portion of
Stephen`s Passage and Frederick Sound.

As for 24 hour rain amounts, the southern half of the panhandle
can expect 2 to 4 inches with the northern half getting less at 1
to 2 inches. This first impactful Autumn storm will dissipate
through Saturday before the next system arrives Sunday.

.LONG TERM...

For rain details, see hydrology. Over the next
several days a series of shortwave troughs will impact the
Panhandle along with multiple atmospheric rivers. While most of
the next week will feature active weather, the most concerning
time frames in the long-range discussion continue to be Saturday
and then Sunday night into Tuesday.

Saturday winds will remain elevated but diminishing from the gale
force winds some areas experienced Friday. A secondary low late
Saturday has the potential to increase winds to small craft
criteria along the southern coast, Dixon, and into Clarence
Strait, something to watch.

Moving onto Sunday an extensive 980mb low, perhaps deeper, will
set up in the western Gulf, with the pressure gradient tightening
across the region. 35 to 40 knots of easterly wind are expected
along the northern coast with fresh seas reaching 15ft, at least.
There is a potential to see gusts reach storm force, but for now
the current forecast reflects gusts in the low 40s. For the inner
channels, 25 to 30 knots of southerly wind will be the norm, with
isolated areas like northern Lynn, Grand Island seeing gusts near
30 to 40 knots.

&&

.AVIATION...

LIFR to VFR flight conditions across this panhandle this morning
with isolated fog and lowered CIGS, anticipating patchy fog to
dissipate mid morning through 14-18z. Big story through TAF period
will be a strong low pushing into the eastern Gulf of Alaska
through the afternoon. Anticipate prevailing MVFR or worse flight
conditions with CIGS AoB 3000 to 5000ft and intermittent vsbys
down to 4SM or less developing through 00z this afternoon and into
the evening. Winds increase across the panhandle through mid
afternoon with sustained winds up to 15 to 20kts and gusts up to
30kts, lasting into the late evening. Mechanical turbulence and
LLWS increase through the afternoon along the southeast Gulf
Coast, spreading northeastward through Friday evening. Strongest
LLWS and mechanical turbulence expected across the southern
panhandle 21z to 06z before decreasing by 09-12z Saturday morning.


&&

.HYDROLOGY...

Key points. Two Atmospheric rivers will impact the region: Friday
into Sunday. Monday into Wednesday.

The trends and divergences of different models over the last week
in the placement, magnitude, and extent of multiple atmospheric
rivers have been a challenge to pinpoint impacts, with guidance
still struggling to show some agreement 72 hours out. For now, we
can say that two atmospheric rivers will impact the Panhandle:
the first Friday into Sunday and the second, Monday into
Wednesday.

Today into Sunday. A weak AR-1 will slide into the southern
region Friday bringing heavy rainfall into Saturday, buy-and-
large, expect 2 to 4 inches of rain in 24 hours, with the most in
the south. Sunday is the big unknown, with the GFS continuing to
be the outlier suggesting a longer duration event into later
Sunday. For now, trending with the ECMWF solution. In simple
terms, expect rainfall to continue Sunday, but at lighter rates,
with the north likely seeing rain come to an end for a few hours.


Early Monday into Wednesday. A moderate to potentially strong
atmospheric river will move in, with trends bringing more
moisture further north for a longer time frame. While 24 hour
amounts are a bit far to say with any single value certainty, we
have confidence there will be moderate to heavy rain for 24 hours,
along with elevated winds from the extensive low in the western
Gulf. Ranges from long range guidance give about 4 to 7 inches
from Monday into Wednesday. To put this range into perspective, 8
inches of rainfall in a 3 day period for Ketchikan is classified
by return intervals as a 1 year event. A very wet fall storm with
wind concerns but 24 hour rainfall values remain separate from a
more extreme event.

For this weekend, significant river rise is expected in the south but
flooding is not anticipated. Some flooding for the start of the
week is starting to look more likely but will ultimately depend on
how much rain we receive through Sunday and the placement of our
next AR.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Strong Wind this evening for AKZ322-326-329.
     Strong Wind from 4 PM AKDT this afternoon through this evening
     for AKZ323.
     Strong Wind from this evening through late tonight for AKZ327.
MARINE...Gale Warning for PKZ022-031-034>036-641>644-661>664.
     Small Craft Advisory for PKZ021-032-033-053-651-652-671-672.

&&

$$

SHORT TERM...NC
LONG TERM....AP
AVIATION...NM

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