Small Craft Advisory 602, NWS Juneau, AK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
711 PM AKST Sun Dec 5 2021

.SHORT TERM...Snow showers have continued across the panhandle
throughout the day on Sunday, with some areas picking up moderate
snow accumulations as a result. These showers are being generated
by weak impulses moving across the area. To the S, a system which
will pass over Haida Gwaii through the evening hours has brought
cloud cover back to much of the are, However, its impacts are
otherwise expected to be on the less impactful side.

As the system to the S departs, some areas, especially in the S
half of the panhandle, may see some clearing take place early on
Monday, before cloud cover rebuilds their ahead of the next major
system to impact the area.

This next system will bring snow back to much of the area. A
Winter Storm Warning for Yakutat will be in effect from Monday
morning through Tuesday morning. It will be joined by a Winter
Storm Warning for the Juneau area which takes effect late Monday
afternoon and goes through Tuesday morning. These warnings will be
complimented by Winter Weather Advisories for Gustavus, Haines,
Skagway, Petersburg, Wrangell, and Hyder. The bulk of the snow for
Juneau and Gustavus northward will likely fall in the late evening
and overnight hours. Petersburg and Wrangell will see snowfall
rates heaviest Tuesday morning, and Hyder will see snow fall from
Monday night through Tuesday night.

The Icy Strait Corridor, Juneau, and Yakutat will likely see snow
transition over to a more rain snow mix through the morning hours
on Tuesday, though the timing of this remains challenging to pin
down precisely. Precipitation will transition back to snow towards
the evening hours across these locations as the center of the low
transits to the S. Overall forecaster confidence is below average
with regards to exact timing, though confidence is high that much
of the Northern half of the panhandle will see snow accumulation.

.LONG TERM.../Tuesday afternoon through Friday/...The mid-range
forecast begins as the first impactful storm of the week
diminishes, leaving a brief period of rain and snow showers in
the forecast before the next system arrives Friday. The discussion
below focuses on this system.

Warm moist air from the coast of Japan will move towards the
peninsula of Alaska on Wednesday. The plume of moisture and the
forecasted 950 mb low will move overland resulting in a decrease
to the moist and IVT values, thus losing the general
characteristics of an atmospheric river as is approaches us in
Southeast Alaska. The surface low is forecasted to redevelop as a
triple-point low in the Gulf by Friday. High winds and heavy
precipitation are expected from this system, with most areas
starting out as snow and then changing over to a mix by Friday
mid-morning. Precipitation type and timing of changeover will be
difficult, but cold air is expected to wrap around the low,
changing the precipitation type back from a rain or rain/snow mix
to all snow. Alaska's River Forecasting Center is forecasting
heavy to moderate widespread precipitation Friday.

The Ocean Predication Center has hurricane-force winds up to 65
knots on the backside of the low before it reaches the peninsula,
thus storm-force winds are possible once it makes it to the Gulf.
High-end gale-force winds are likely for the Gulf of Alaska
closest to the panhandle. Wind forecast leaned heavily on the GFS
to get gales and the barrier jet in there. Manual edits included
increasing land winds trending towards strong winds in Sitka,
Hydaburg, and Ketchikan. One addition to note is the GFS has a
second smaller low off of the parent low that is forecasted
further south than the Canadian and EC. This means that Sumner
Sound and Wrangell could see stronger wind gusts, if the GFS is
correct.

PoP forecast for the system was blended to the ECMWF and QPF was
primarily RFC, with precipitation starting Thursday evening. The
snowfall forecast from this system will come out tomorrow, but
thoughts so far include snowfall from Wrangell north with the
highest snowfall amounts near Petersburg, Haines, and Yakutat
before the rainfall changeover. Once rain changes back to snowfall
with the cold air coming in on the back of this system, we will
want to keep an eye on Sitka for the potential of more snow.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Winter Weather Advisory from midnight Monday night to noon AKST
     Tuesday for AKZ026.
     Winter Storm Warning from 6 PM Monday to 9 AM AKST Tuesday for
     AKZ025.
     Winter Weather Advisory from 3 PM Monday to 9 AM AKST Tuesday
     for AKZ018>020.
     Winter Storm Warning from 6 AM Monday to 6 AM AKST Tuesday for
     AKZ017.
     Winter Weather Advisory from midnight Monday night to midnight
     AKST Tuesday night for AKZ029.
MARINE...Small Craft Advisory for PKZ041>043-051-052.

&&

GFS/KRT

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