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FXAK67 PAJK 212333
AFDAJK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
333 PM AKDT Thu Sep 21 2017

.SHORT TERM.../Thursday evening through Friday night/...Fog this
morning was less extensive than yesterday morning, but still
turned out to be dense and persistent in and around Kupreanof
Island and Mitkof Island. Dense fog advisory was in place until 1
pm this afternoon. No fog concerns for tonight as clouds have
moved in and will prevent any significant radiational cooling
tonight. A front is also moving across the gulf and moderate rain
has been falling in Yakutat since shortly after noon. Rain will
spread east and south this evening and through the overnight
hours, to encompass the entire panhandle by early tomorrow
morning. Rain will transition to showers very early tomorrow
morning with scattered to numerous showers across the panhandle
through Friday night. Exception will be a short wave feature that
will produce rain over the southern zones late Friday night.
Either way, it will remain wet across Southeast Alaska for the
duration of the short term forecast period.

Southeast small craft winds on the outer coast except for an
easterly barrier jet gale west of Icy Bay for tonight. Winds will
shift abruptly southwest with frontal passage and diminish to 15
kt late tonight. No significant winds over the eastern gulf for
the remainder of the short term. On the inside, pre-frontal
response vicinity Cross Sound only forecast to be 20 kts. Further
inland, southerly winds to 20 kt this evening over northern Lynn
Canal in response to an amplification to the surface ridge being
pressed up against the coast mountains by the approaching front.

Most aspects of the previous forecast remain unchanged. Did adjust
winds down for this evening over offshore zone 310. Updated QPF
with latest forecast blend provided by the RFC. Overall forecast
confidence is above average.

.LONG TERM...Saturday through Thursday...The upper level ridge of
high pressure, currently positioned over the gulf, will continue
to weaken and move east into Canada and the western CONUS, while
an upper level trough continues to dig into the the Alaska
mainland on Saturday. An upper level shortwave will develop out
of this parent trough and lift northeast across the northern gulf,
impacting portions of SE Alaska. This system and its associated
weather front will bring increased precipitation across the
panhandle, with increasing intensity beginning Sunday and
continuing into early Monday. A subtropical jet feature coupled
with this shortwave should advect large amounts of moisture,
mainly aimed for Haida Gwaii and western portions of British
Columbia, but we expect southern portions of the panhandle to see
some heavier precipitation with this setup. Models continue to
indicate anomalously high precipitable water amounts with this
event.

For adjustments to the forecast, we used a combination of the
ECMWF, Canadian, and the NAM during the weekend and into the early
part of next week, leaning more towards the EC. We trended
more towards WPC guidance after the Tuesday period. After the Day
6 timeframe, models have had a more difficult time agreeing on
the synoptic pattern, so a lot of uncertainty remains in our
forecast past the Tuesday/Wednesday period.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...None.
MARINE...Gale Warning for PKZ052.
     Small Craft Advisory for PKZ042-043-051.

&&

$$

Fritsch/Voveris

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