952
FXAK67 PAJK 082310
AFDAJK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
310 PM AKDT Tue Oct 8 2024

.SHORT TERM...Diminishing low pressure off the coast of Baranof
Island will give way to onshore flow tonight and tomorrow. A
front will push northward along with the parent low through
tonight, bringing increased marine winds and some rain showers. Continued
widespread showers throughout the panhandle with a few
thunderstorms in the southern panhandle. While there is a modest
amount of drying aloft allowing for CAPE values near 200 J/kg,
available shear to keep these thunderstorms alive simply is not
present. Therefore, any thunderstorms that do develop will quickly
diminish. Continued cloud cover for most of the panhandle will
moderate temperatures overnight and tomorrow to a maximum of 10
degree diurnal trend. Finally, while a low chance, it is possible
to see some snow at upper elevations on the Klondike Highway with
snow levels dropping to 2500-3000 ft. Any snow that falls is
unlikely to accumulate due to warm  temperatures near the
surface, however.

For chances, reduced the strength of the diminishing low and
associated wave moving northward tonight due to current
observations. Still expecting fresh breezes to the southeast with
the frontal push. Keeping Lynn Canal as light air ahead of the
front and extended the duration of the moderate to fresh breeze
due to westerly to southwesterly flow aloft causing lee side
troughing.


.LONG TERM...Thursday southwest flow continues aloft as a
multitude of shortwave troughs set up along south-central Alaska
and also slide underneath the gulf. For impacts, light rain
showers continue across the Panhandle. Meanwhile, high pressure
builds across British Columbia east of the Boundary Ranges,
bringing a dry period Friday for the Panhandle. Overall minimal
concerns for wind and precip into early Friday morning.

As our communities enjoy the fall weather through the week, an
open longwave trough will move off the Kamchatka Peninsula
Wednesday morning, interacting with an area of high baroclinic
instability near the Aleutians. Through the afternoon, upper level
dynamics will engage with the underlying surface feature,
resulting in intense cyclogenesis. Current ensemble systems are
show a range of surface pressures near 950mb to 960mb associated
with the developing extratropical cyclone as it ejects southeast
across the Aleutians by early Friday morning. As this storm
reaches maturity, a front will begin to move across the gulf
Friday afternoon, featuring sustained southeasterly storm force
winds along the coast, with gusts reaching hurricane force. Our
current forecast reflects gale force by the afternoon, with peak
storm force winds occurring overnight Friday into Saturday.
Strongest winds along the coast south of Cape Suckling and Cape
Fairweather, especially out of Icy Strait into Cross Sound.
Through the weekend into the start of next week the storm will
weaken as it stagnates in the western gulf, bringing stout
southwest swell along the coastal waters with 20 to 30 knot winds
continuing.


&&

.AVIATION.../Through Wednesday afternoon/...CIGs 3000ft or better
with no change expected. VSBY better than 5sm with no change there
either. Above bases, layered clouds well up into the flight levels
with attendant icing concerns between 5k and 13k ft in clouds.
Expected thunderstorm activity over the eastern Gulf and outer
coast has yet to develop, which comes as a surprise given
observed and modeled atmospheric instability. Forecast instability
parameters for tomorrow are equally as strong as today, but am
skeptical based on the lack of thunderstorms today. Only one mode
is predicting any meaningful LLWS and have not seen any reports of
it or turbulence in PIREPS, so will hit that very lightly if at
all in afternoon TAFs.


&&

.MARINE...The simple message is this, for mariners operating in
the gulf Friday and over the weekend a significant storm will
bring storm force winds and 30 to 35 southeast seas Friday night;
highest seas south of Cape Suckling. Expect a transition to 20 to
25ft swell from the south- southwest by Saturday evening. For the
inner channels, Yakutat Bay, and Dixon Entrance, expect gales
Friday night into Saturday afternoon with windy conditions into
Monday. For the inner channels there will likely be a resurgence
of high winds as a disturbance moves into the Panhandle Monday.
Stay tuned.


&&

.HYDROLOGY...
No significant threats through early Friday. Associated with the
mature cyclone over the weekend will be an atmospheric river with
deep moisture through the troposphere; current ensemble players
show a quick hit of moderate AR conditions, rapidly transitioning
to weak AR conditions. In plain English, heavy rain will move over
the northern coast late Friday, pushing east and south through
Saturday, with much lighter rainfall rates by late Sunday. Digging
into impacts, we expect 1.5 to 3 inches in 24 hours for most sea
level communities through Sunday. Rise in small streams and creeks
are expected but no flooding is anticipated at this time. Rain
continues at lighter rates into next week.

Late Sunday into Monday there is a potential for heavier rain
associated with a disturbance in the southern Panhandle, stay
tuned.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Small Craft Advisory for PKZ641>644-661>664-671.

&&

$$

SHORT TERM...NC
LONG TERM....AP
AVIATION...Fritsch

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