942
FXAK67 PAJK 192326
AFDAJK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
326 PM AKDT Thu Sep 19 2024

.SHORT TERM...Current conditions across the panhandle remain
partly cloudy as satellite shows a band of precipitation headed
toward the panhandle. This is associated with a low in the gulf
that will bring rain and winds to the panhandle starting Friday
afternoon. The main impact will be increased wind seen across the
central and southern panhandle. As this low approaches, pressure
gradients tighten creating 30 to 40 kts along the coast and 25 to
30 kts across the southern inner channels.

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...The rest of today will continue to have prevailing VFR
conditions. As we get into the morning expect areas of fog to
develop that can limit visibilities to MVFR/IFR conditions.
Conditions will then start to deteriorate as a low brings rain and
winds across the panhandle, mainly impacting the southern panhandle.
Winds will start to increase late Friday morning as this low
approaches. Prevailing conditions will then change to MVFR.
Something to be aware of is potential for windshear across the
southern panhandle starting tomorrow early afternoon diminishing mid
Saturday.

&&

.MARINE...The first two impactful Autumn weather systems will
occur Friday and Sunday night. Both will feature pre-frontal
gales over the eastern Gulf of Alaska. The first system on Friday
night will also feature a wrap-around core of gale force
northeasterlies Friday evening in the northern quadrant of the
low. Marine winds associated with this first system will weaken
rapidly as the parent low weakens over land and winds over the
inner channels should be non-impactful Saturday and Saturday
night. Off the outer coast, northwesterly small craft winds
associated with a transient surface ridge will organize late
Saturday night but not amount to much as the ridge gets displaced
to the east by the next weather system. Winds over the eastern
Gulf will organize out of the southeast on Sunday and intensify to
gale force overnight Sunday. Multiple inner channels will likely
see gales again late Sunday night going into Monday but should
weaken rapidly in the post-frontal environment Monday afternoon.

&&

.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.

Friday 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 Friday afternoon for AKZ323.
     Strong Wind Friday afternoon for AKZ328.
MARINE...Gale Warning for PKZ036-641>644-661>664-671.
     Small Craft Advisory for PKZ022-032>035-651-652-672.

&&

$$

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

Visit us at http://www.weather.gov/Juneau