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FXAK67 PAJK 201323
AFDAJK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
523 AM AKDT Sat Jul 20 2024

.SHORT TERM...Diminishing chances of rain through the day on
Saturday will give way to mostly drier weather conditions on
Sunday, although lingering chances of some convective showers for
some locations in the northern panhandle may remain during the
latter half of the weekend.

Satellite and radar imagery as of the time of writing depict bands
of showers continuing to rotate around a vertically integrated low
over the central Gulf, with a weak wave currently moving up from
the SE and past Baranof Island, though expect it to stay largely
offshore of the area. Lingering onshore flow has continued to
provide moisture support for a cloud deck which has likewise
remained in place across much of the panhandle, though many areas
have nevertheless begun to experience increasing breaks in the
clouds as the pattern becomes increasing less favorable for
continued precip. These breaks have encouraged radiation cooling -
which has subsequently caused new low level stratus decks and fog
to form in many areas, especially across the southern half of the
panhandle.

Through the remainder of the morning, daytime heating will
contribute to the erosion of the fog and stratus while the wave
lifts off to the NW. In its wake, chances of rain will diminish
across the area, as the primary low in the gulf increasingly
steers any additional waves and most of the moisture support
orbiting around it further and further offshore. By the afternoon
and evening timeframe, significant breaks in the clouds are likely
across the panhandle, though a greater degree of cloud cover will
remain for the outer coast. The breaks in the cloud deck will
contribute to high temperatures reaching into the upper 60s and
even the 70s for some places. Sunday will largely be a dry day
across the panhandle through the morning, though a convective band
may try to reach parts of the area as it advances out of British
Columbia in the afternoon. For additional details, see the long
term forecast discussion.

Winds will largely remain on the lighter side, with the inner
channels largely staying between 5 to 15 kt. Some ocean effect
breezes are possible in the usual locations. Only minimal changes
were made to the forecast, primarily some minor adjustments to
winds as well as extending fog coverage across more of the inner
channels and some additional land-based areas for Saturday
morning. Forecaster confidence is average.

.LONG TERM...The long range forecast is broken up into two
distinct period, Sunday and Monday, marked by thunderstorms
attempting to cross into SE AK from Canada and largely failing,
and Tuesday, with a potent easterly wave bringing widespread
showers.

Sunday and Monday are expected to be the clearest day, for the
north on Sunday and for the south on Monday. A stacked low
feature parked in the southern gulf will bring in drier air from
Canada, while kicking up some clouds for the southern panhandle.
Naturally, due to the clearing in the north and in Canada, small
and large scale sea breezes will take effect, increasing winds in
Icy Straight, Lynn Canal, and the upper portion of Stephen`s
Passage up to 20 knots. During the afternoon period, there is the
small possibility of thunderstorms briefly passing over the White
Pass area as storm direction moves increasingly eastward.
Ultimately, any convection would need to line up with the
direction change in order to actually impact the White Pass area,
so naturally, confidence is lower on this solution.

The interesting situation is on Tuesday, where a rather potent
warm front from a low in British Columbia moves over SE AK from
the northeast. A somewhat unusual situation where a major moisture
source from continental air is overrunning entrenched drier,
cooler air to the south in SE AK. This will lead to light to moderate
rainfall for approximately 24 hours. Unfortunately, for this type
of system, confidence is relatively low. Due to model resolution
in the extended, and NE flow aloft moving over the Coast Mountains
could causing drying from downsloping winds. In addition, dry air
from the south will be drawn in via pressure gradient flow at the
surface. Therefore, actual rainfall is far less confident than any
one model would imply, being anywhere between 0.25 - 2.00 inches.
The EFI tables have tended to assert caution, with a majority of
the shift of tails over the eastern, mountainous portion of SE AK
and much less model consensus over even the far inner channels.

&&

.AVIATION...Early this morning, a wide range of aviation
conditions are being reported at surface stations and webcams
across SE AK. In the Northern Lynn Canal area, VFR conditions are
found. Along Icy Strait and south, IFR to low-end MVFR conditions
are being reported.

Going forward, conditions should improve quickly this morning to
high-end MVFR to VFR for today. Some evidence of conditions
decreasing again tonight, especially around Prince of Wales Island,
Ketchikan, Petersburg, and Wrangle. Hi-res models give these areas a
30 to 50% chance of MVFR conditions overnight. Much higher chance
(70 to 90%) for VFR conditions north of Frederick Sound tonight.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...None.

&&

$$

SHORT TERM...GFS
LONG TERM....NC
AVIATION...GJS

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