Area Forecast Discussion
Issued by NWS
FXAK67 PAJK 280126
Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
426 PM AKST Mon Feb 27 2017
.SHORT TERM...Upper trough seen on water vapor imagery emerging
into the northern Gulf late this afternoon. This trough deepens
and shifts eastward late tonight and Tuesday setting up an
overrunning snow event for much of the panhandle. Confidence is
high that areas along the eastern Gulf coast and the inner
channels roughly south of a line from Pelican to Tenakee to Angoon
will see significant snow accumulations into Tuesday. Low level
thickness values are briefly marginal for snow over Prince of
Wales Island late tonight, but feel that heavier precipitation
rates will be able to overcome any boundary layer warming.
A second area of concern is the Icy Strait corridor including the
Juneau area. Currently have a Winter Weather Advisory in these
areas but there is some disagreement as to how far south the best
overrunning will set up. 18Z NAM indicates this may happen farther
south which would allow more easterly downslope flow to
significantly decrease snow amounts in these areas.
Leaned primarily on the EC solution for the short term as it has
been the most consistent model over the past few days. Confidence
is high for the outer coast and central/southern zones, but much
less in snow amounts for the northern panhandle.
.LONG TERM...With the stalwart positioning of the ECMWF`s
northeast gulf low and now the 18Z GFS`s late decision to lean
towards this solution, our confidence is increasing for a band of
potentially heavy snow once again setting up ahead of a surface
trough across the central Panhandle. This setup will overrun
moisture across the central and portions of the northern
Panhandle Wednesday into Thursday. Were it not for the event
tonight into Tuesday, we may have considered prolonged winter
storm watches. We even discussed extending the winter storm
warnings for the southern Panhandle, but the rates look to lighten
in an intervening time between a deformation band setup Wednesday
lifting northward and the initial wave causing tonight/Tuesday`s
snow. The main message aside from the impacts of this storm, is
that it will likely remain snowing across much of the area into
Tuesday night and perhaps intensify Wednesday into Thursday. Keep
your shovels handy. Ironically, in this scenario, some of snowier
spots like Yakutat and Haines will see much less.
Wednesday a deeper trough digs in over Kodiak and taps deeper
moisture and warmer air from a system in the North Pacific. This
wave will then push across the Gulf and lift a surge of warmer air
and very moist air into the Panhandle. This will likely break the
cold air over the south and begin turning the snow to at least a
mix Wednesday night into Thursday. But for the central and
northern Panhandle, it looks increasingly likely for heavy snow to
persist. Beyond Thursday the forecast has virtually been
unchanged due to dynamic shifts in the short to mid-range. But
temperatures will chill even further across the Panhandle leading
into the weekend.
Winds were unchanged, as the main impacts will be with snow.
PUBLIC...Winter Storm Warning from 9 PM this evening to noon AKST Tuesday
Winter Weather Advisory from midnight tonight to noon AKST
Tuesday for AKZ025.
Winter Weather Advisory from 9 PM this evening to noon AKST
Tuesday for AKZ020-021.
Winter Weather Advisory from 9 PM this evening to 9 AM AKST
Tuesday for AKZ017.
Winter Weather Advisory from 6 AM Tuesday to 6 AM AKST Wednesday
MARINE...Small Craft Advisory for PKZ012-022-041>043-051-053.
Small Craft Advisory due to Seas for PKZ052.
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