FXAK67 PAJK 221529
Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
629 AM AKST Wed Nov 22 2017
.SHORT TERM...On a synoptic scale model agreement holds well
through Thursday. Weak low pressure over the northeastern Gulf is
the old news with the new low making headlines today as it moves
up from the N. Pacific to near Haida Gwaii. The low will continue
its northern progression into the central Panhandle tonight, then
make a right turn and go into British Columbia Thursday. Remember
the low up in the northeast gulf, well it is still residing in
the the northern gulf. The GFS and ECMWF both push it further to
the west, while the NAM keeps it between Yakutat and Cape Yakataga
by Thursday morning. By Thursday night all three main models
agree on the low moving to near the Kenai Peninsula, but
definitely do not agree on the strength or whether to dumbbell the
low with a secondary low before it starts its eastern solo trek
across the gulf Thursday night.
The snow forecast over the next few days is going to be a careful
dance between temperatures and precipitation. Confidence is good
in regards to the precipitation occurring where forecasted, but
as temperatures take more of the lead with the above freezing
temperatures bringing rain to the southern area and along the
outer coastal area mostly rain but could get a mix of snow, but
early this morning solid state precipitation in the form of snow
is still falling in Wrangell and northern stations. The warm air
is slowly advancing north and is expected to reach Hoonah daytime
on Thanksgiving and Juneau area by Thursday night. The snow
accumulations portion of the forecast has the lowest confidence
due to the temperature forecast and how wet the snow will be. The
interesting concern with regards to the impacts of the snow is
that as snow amounts go down due to warming temperatures and
possible mix with rain the snow will become heavier and thus be
more impactful than the light and fluffy snow of late. Winter
Weather Advisory in Juneau from 9 am to 9 pm was issued yesterday,
the area of the heaviest snow is showing a lean to the east and
may keep snow rates a bit lower.
Wind continues to be strong with the tight gradient to the north.
Strong wind in Skagway and SCA in Lynn Canal this morning and
diminishing through the afternoon. Winds increase again this
evening and then finally SCA flag will finally come down in
Northern Lynn Canal by early Thursday morning. Outflow winds will
be returning by late Thursday night, so the SCA flag will be
hoisted again with 25 to 30 kt winds for parts of the inside
waters, north-south oriented waterways will have the strongest
winds. Outer coastal areas around Cross Sound up to Yakutat will
have outflow winds of 20 to 30 kts late in the forecast period.
Made small mesoscale changes, with most of the efforts focused on
the winds. Other weather worthy news is there is some patchy fog
around Gustavus/Petersburg areas this morning and likely forming
overnight for Petersburg. It isn't in the current forecast but
will be looking at putting in some blowing snow near White Pass as
the snow starts to fly and then the winds increase. The one
weather element that has been a concern is freezing precipitation
with this slow warm up. Based on a conversation with the weather
observer at the Wrangell airport, have included a brief period of
freezing rain for portions of zone 26 early this morning.
.LONG TERM /Friday through Wednesday/...A weather front lying
across the Panhandle will support widespread precipitation Friday.
Temperatures across the central Panhandle will be marginally cold
enough for snow but confidence is only moderate. Even as warm air
lifts northward along the front, we think wet-bulb temperatures
should be lower than freezing. But given frontal orientation, we
are not considerate significant accumulations. Confidence is
higher for rain in the south. Very little changes were made in
winds during this time, as agreement continues to remain strong,
even as precipitation type is not as sure.
As the low pulls south, we are increasingly confident in a dry,
colder forecast. We lowered temperatures yet again for Saturday
and Sunday as outflow revs up again through the northern and
central Inner Channels. While currently we are only forecasting
gale force winds for northern Lynn Canal, it is conceivable these
may need to be expanded in coverage. We held back some of the
coldest air from some solutions as sky cover may continue to be
mainly cloudy due to a low to our southeast.
Leading into next week, we see some form of deeper onshore flow
returning along with a moderating temperature trend. This will
reintroduce precipitation type issues, but it is safe to say the
southern Panhandle and east and southeast gulf coast will return
to rain into the middle of the week while we forecasters continue
to debate and chase the ever impactful rain/snow line. As most
American students (and seasoned forecasters) will tell you, "When
in doubt, guess 'C.'" Our "C" stands for Wrangell to Peril
Strait, and this supplies a reasonable first guess. Forecast
during this time period continues to more strongly rely on
ensembles as evolution back to a wetter pattern highlights the
creative differences of our solutions. For all of these reasons,
forecast confidence drops next week.
PUBLIC...Winter Weather Advisory from 9 AM this morning to 9 PM AKST this
evening for AKZ025.
Strong Wind until noon AKST today for AKZ018.
MARINE...Small Craft Advisory for PKZ012-013-041-042.
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