Gale Warning 26, NWS Juneau, AK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
626 AM AKST Fri Jan 12 2018

.SHORT TERM...
...SNOW TODAY, RAIN SATURDAY...
Light snow has moved into the outer coast and Icy Strait this
morning associated with a pre-frontal trough. The main part of the
front will merge with this trough and help to increase the
snowfall rates as it moves inland this afternoon. An upper level
wave will track north across the panhandle this evening and cause
another increase in precip rates. Behind the wave NVA (negative
vorticity advection) will cause precip to diminish or end all
together. Greatest snowfall amounts are expected to be from
Pelican to Petersburg, northward. Did not make any adjustments to
the warning/advisory times, but snowfall amounts were adjusted
slightly based on temperature. Places along the outer coast
should warm enough to see a mix in the afternoon and some places
like Kake/Angoon/Elfin Cove will likely see a change over to rain
in the evening. Sitka has already warmed into the upper 30s with
rain reported. Please use the point and click map to see specific
amounts and timing for where you live.

The front will have moved north of the area by Saturday morning
with some breaks in the clouds possible. This will be somewhat of
a tease, but should be a long enough of a break to get out and
shovel the snow before the rain starts. The next frontal system to
move northward into the gulf looks to be a true frontal system
with an occlusion and triple point. WAA will dominate and an
atmospheric river will become directed at the panhandle, thus
expect nearly all precipitation to fall as rain. The rain will
begin over the southern panhandle Saturday morning, then spread
northward, reaching Juneau/Haines in the late afternoon. Most
locations will even see a period of moderate to heavy rain through
Saturday night. At this time the area with the greatest rainfall
expected looks to be the outer coast between Yakutat and Sitka.

As for winds, the gulf will feature gale force winds for most of
the next 48 hours as the series of fronts move through. The
panhandle will be spared some of this as the fronts will be weaker
the farther east you get. Still, we are looking at 40 mph gusts
expected along the southern outer coast as some of these front
come in and many inner channel areas will see 25 to 30 kt winds
particularly Sat into Sun. Main changes to winds were to refine
frontal timing and a general increase in winds in the inner
channels for the Sat night into Sun front. Favored GFS/Nam for
these updates.

.LONG TERM.../Sunday through Thursday/The early part of the
extended period will remain warm and wet, as heavy rain and strong
winds will lead this transition. Currently, we can see hints of
the ridge over western Canada losing definition and the low
shearing out.

Models hint at a potential low tracking through the Gulf late
Sunday, which was the focus of long-term edits for tonight. Models
were all over the spectrum as far as positioning of this low.
Current pressure grids were blended with the NAM/GFS early on, as
these two models suggested the presence of this low without
changing pressures substantially. The ECMWF has altered track
from previous model runs, although it is the model that varies to
a greater extent for individual details. Winds were adjusted in
the Gulf accordingly. There is also another possible low tracking
northward from Haida Gwaii Thursday into Friday. However, much
uncertainty remains for the tracking, timing, and latitudinal
extent of this system.

Both maximum and minimum temperatures were mostly within model
spectrum spreads, with the exception of Tuesday's max temps
increased and decreasing min temps for days 6 and 7. Temperatures
will peak on Sunday, before beginning another downward trend.
POP's were blended with the SREF early on and with current WPC
guidance during the later part of the period. Previous model runs
had the precipitation moving westward of Yakutat by Monday, but
new guidance suggests this next low will keep precipitation over
the panhandle during the latter part of the weekend. The southern
panhandle, however, will remain drier. QPF adjustments were made
as a blend of NAM, GFS, NBM, and WPC, which might keep amounts on
the lower end of the spectrum. The CPC outlook for the next 10-14
days shows the probability of below normal temperatures and below
normal precipitation. Latest model guidance has provided some
stability, but forecast confidence remains low to moderate at best
for the next few systems.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...Winter Weather Advisory from noon today to midnight AKST tonight
     for AKZ024-026.
     Strong Wind from 3 PM AKST this afternoon through late tonight
     for AKZ027.
     Winter Storm Warning from noon today to 5 AM AKST Saturday for
     AKZ019-025.
     Winter Weather Advisory from 9 AM this morning to midnight AKST
     tonight for AKZ021-022.
     Strong Wind this evening for AKZ023.
     Winter Storm Warning from 9 AM this morning to 5 AM AKST
     Saturday for AKZ020.
     Winter Weather Advisory from 3 PM this afternoon to 5 AM AKST
     Saturday for AKZ029.
     Strong Wind until 9 AM AKST this morning for AKZ018.
MARINE...Gale Warning for PKZ022-041>043-051-052.
     Small Craft Advisory for PKZ021-031>036.
     Small Craft Advisory due to Seas for PKZ053.

&&

Ferrin/EAL/SS

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