Gale Warning 291, NWS Juneau, AK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
308 PM AKST Mon Dec 4 2017

.SHORT TERM...Tonight through Wednesday...According to water
vapor satellite imagery, an upper level ridge currently extends
over the eastern gulf and western Canada, and a very deep upper
level trough, with multiple embedded shortwaves, extends into the
western gulf. One of the embedded shortwaves can be seen lifting
across the northern gulf into mainland Alaska and was associated
with some lightning strikes, which were observed via satellite
along the coastline near Yakutat this morning. Some shower
activity still lingers across the panhandle, but we have seen some
breaks in a few areas this afternoon. Patchy fog may be a
possibility this evening in areas that see additional clearing.
However, this should be shortlived this evening into tonight, as
another front will approach the panhandle beginning late tonight.

A stronger shortwave will continue to intensify tonight into
tomorrow, as the upper level ridge over Canada will remain in
place. This will actively tighten the gradient directly over the
eastern gulf, and act as a funnel for moisture advection,
especially over northern areas. Rain will begin to move in with
the front beginning late tonight, and the precip type should stay
as rain. 850 and 925 mb temperature analysis both show anomalously
high temperatures for this time of year, and model analysis
continues to show anomalously high precipitable water values with
this system. The only area we're expecting a precip type of snow
will be White Pass continuing through the Klondike Highway, where
we have also issued a Winter Storm Watch. Here, temperatures
should remain below freezing, and snow will likely be very wet and
heavy, as we may potentially see some dendritic snow growth with
lower snow ratios. In addition, due to the tight pressure gradient
that will develop at the surface between these two systems, wind
speeds should hover in and around gale force, especially along
the eastern gulf waters. Throughout the inner channels, we expect
generally Small Craft Advisory level winds.

Adjustments were made to the forecast using predominantly a
GFS/ECMWF blend. Most wind updates were made manually using
pressure analysis. Also, QPF was updated with a combination of Hi
Res ARW/NMM models and the GFS.

.LONG TERM...Wednesday through Monday as of 930 PM Sunday/ As the
front pushes through Tuesday night, the residual effects from this
system will be increased winds. Wind speeds might even push gale
force along the outer coast and Gulf. Areas of heavy rain are
expected to remain northward around the Yakutat area from the
overnight period Tuesday into Wednesday morning, showing QPF to be
2-3 standard deviations above normal.

More emphasis was placed on temperature trends and POP/QPF
amounts throughout the week. As the warm trend continues, model
spectrum spreads have suggested increasing temperatures into the
weekend. Temperatures at 500 mb (ranging from -18 C to -23 C)
imply that temperatures will remain moderate across the panhandle.
Minimum temperatures were also decreased during the early part of
the weekend due to partly cloudy skies. Previously, the 30-day
CPC outlook had predicted below normal temperatures for southeast
Alaska, but recent updates show that most locations across Alaska
will be above normal.

Extensive edits were made early on in the period due to border
issues (this was accomplished using a part GFS blend). An EC/GFS
blend was used for the early part of the timeframe and WPC blend
for the latter part. After about 12z on Thursday, model consensus
rapidly diminishes, as models are struggling with the placement of
a low in the Gulf. The low has deepened slightly since the last
model run and has progressed eastward. Only a few local edits were
made to wind grids late in the period. Due to uncertain placement
of the low at this point, some grids were left as is. Confidence
about the timing of the low remains mid-level confidence.

Chance of rain continues for most of the week with the next front
expected to push through Sunday night into Monday morning. This will
be more of a widespread rain event across the panhandle. Maximum
wind speeds along the inner channels are expected to coincide with
the the timing of maximum precipitation.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...Strong Wind until 3 PM AKST this afternoon for AKZ018.
     Winter Storm Watch from Tuesday morning through Tuesday
     afternoon for AKZ018.
MARINE...Gale Warning for PKZ012-022-043-051>053.
     Small Craft Advisory for PKZ011-013-021-031>036-041-042.

&&

Voveris/SS

Visit us at http://www.weather.gov/Juneau

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