Area Forecast Discussion
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FXAK67 PAJK 152319
AFDAJK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
219 PM AKST Tue Jan 15 2019

.SHORT TERM.../Through Thursday night/ Weak upper ridge will
extend WNW across the northern panhandle through Thu night. Upper
trof will sink slowly S over NW Canada Wed night through Thu
night. At the sfc, high pressure will remain across much of NW
Canada through Thu night, with a low level ridge building SW
toward SE AK Wed through Thu night. A weak occluded front over the
eastern gulf will drift NW and be out of the forecast area by Wed
afternoon. Used 12z GFS/NAM blend to handle pressures through the
period.

Main forecast concerns will be fog and winds. Fairly warm temps in
the 850-925 mb layer will maintain a strong low level inversion
through Wed morning, then cold advection will cool this layer from
the NE beginning Wed afternoon. This will maintain fog over much
of the area tonight into at least Wed morning. Fog will be
thickest in wind sheltered locations, and locally dense fog is
expected to continue through Wed morning. Have kept dense fog
advisories going through 21z for much of the central and southern
inner channels. Do show the fog diminishing Wed afternoon, but
some areas away from the outflow regions of the Coast Mtns might
hang onto fog longer.

Strongest winds will be over the N inner channels through Thu
night. Expect some increasing winds over the N tonight and Wed
morning, but do not think they will get to previous forecast
levels as most of the gradient will still be on E side of the
Coast Mtns. Have limited winds to SCA levels through the daytime
hours Wed. Cold advection and low level ridging building into the
area will help increase outflow late Wed afternoon into Thu, and
some gale force winds will be likely over Lynn Canal and out of
the Coast Mtn passes by later Wed night. In the Juneau area,
conditions become increasingly favorable for a mtn wave to develop
Wed afternoon, so going with strong winds beginning late in the
afternoon for downtown Juneau and Douglas. Also have strong winds
developing in the Skagway area Wed night as NE pressure gradient
increases.

Otherwise, leftover precip with the occluded front will diminish
from the SE tonight into Wed morning. Could be a little freezing
rain in the Chilkat valley this evening, otherwise any lower
level precip will be mainly rain through Wed. Much of the central
and southern area will see partly cloudy or better conditions
through much of the period, although some bands of high clouds
will drift N across the area through Thu as weak shortwaves aloft
move through. Slow cooling trend will occur Wed night into Thu
night, and much of the N inner channels will be below freezing
during daytime Thu.

.LONG TERM.../Friday through Monday, as of 9 PM Monday/...The
extended forecast will carry a pattern change from cold, dry
northerly outflow late this week to a wet and warmer weekend.
Friday is best characterized with surface high pressure over
north central Canada and a surface low pressure system tracking
north over the eastern Pacific. This will induce a northeasterly
pressure gradient driving northerly outflow winds. However, with
this gradient orientation being more northeasterly stronger winds
will likely be observed in the east-west oriented channels rather
than the north-south oriented channels. Some areas to note would
be south of Douglas island, out of the Stikine River Valley and
the eastern portion of Icy Strait.

This pattern will come to an end this weekend as a likely gale
force low pushes north over the gulf. With cool temperatures in
place from prolonged outflow, precipitation looks to begin at snow
for most of the Panhandle including areas as far south as
Ketchikan. However, warming will occur with the frontal passage
which will limit snow totals, especially for the southern
Panhandle, as a rapid changeover to rain is expected. Note:
currently the forecast is carrying advisory level snow amounts for
portions the central Panhandle mainly around Juneau Saturday, but
these amounts and the timing are likely to change as forecast
confidence improves. Additionally, most ensembles carry the low
along the coastline and across the Gulf toward Kodiak; however, a
few ensembles and the operational 12Z ECMWF push the low to the SE
undercutting the Panhandle. In the latter case, a much cooler and
drier weekend would result for the northern Panhandle. Between
Sunday night and Monday expect another front to impact southeast
Alaska.

As a whole, only minor adjustments to the forecast were required.
Winds have been trended upward in anticipation of a gale force
front passing over the Gulf this weekend. Temperatures were also
allowed to warm more rapidly this weekend as the front passes.
Overall forecast confidence remains above average Thursday and
Friday, but drops to average for the weekend as timing and track
of the system remains uncertain.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...Dense Fog Advisory until noon AKST Wednesday for AKZ021-024>026-
     028.
     Dense Fog Advisory until noon AKST Wednesday for AKZ027.
     Strong Wind from Wednesday afternoon through late Wednesday
     night for AKZ025.
     Dense Fog Advisory from 6 PM this evening to noon AKST Wednesday
     for AKZ020.
     Strong Wind from Wednesday evening through late Wednesday night
     for AKZ018.
MARINE...Small Craft Advisory for PKZ012-013-022-031-041>043-051-052.
     Small Craft Advisory due to Seas for PKZ053.

&&

$$

RWT/JB

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