Small Craft Advisory 658, NWS Juneau, AK

Southeast Alaska Forecast Discussion...UPDATED
National Weather Service Juneau AK
204 AM AKST Fri Dec 31 2021

.UPDATE...

Through the overnight hours, snow has begun falling a few hours
earlier than anticipated in Yakutat as warm air overrunning has
resulted in an earlier onset of precipitation. This earlier
beginning to precipitation will encourage greater snowfall rates
in some areas of the region, notably parts of the southern
panhandle. As a result, the Winter Weather Advisory for Ketchikan
and eastern Prince of Wales Island has been upgraded to a Winter
Storm Warning. Snowfall totals of between 3 to 9 inches of snow
are anticipated, though snowfall totals will be highly dependent
on local topographic influences as the anticipated warm air push
with this system will attempt to scour out the entrenched cold air
across the region.

GFS

&&

.SHORT TERM.../Through Saturday Night/ The blocked pattern that
we've been stuck in breaks down over the next 24hrs as the upper
level ridge that has been over the state shifts east. With the
ridge axis past, upper level jet stream flow will turn SWLY, a
direction we haven't seen in quite some time. The fairly long
fetch of moisture directed at the panhandle does look to be
progressive however, starting over the northern gulf Friday
morning then shifting SE through Friday night.

Expect snow to begin early Friday morning in Yakutat as a surface
low moves into the northern Gulf. An occluded front then spreads
the snow over the rest of the panhandle through mid day. A triple
point looks to form around the Sitka area with a warm sector
spreading over Baranof, Prince of Wales and Ketchikan region
through Friday night causing a change over to mainly rain as snow
levels rise as high as 2kft. The plume of moisture will cause
greatest snowfall along the Coast Mountains with over a foot
expected for Juneau to Wrangell and nearing 2 feet for Hyder when
all is said and done. Winter Storm Watches that were in effect
have been upgraded to either Warnings or changed to Advisories,
please see the latest statement or the point forecast for your
area for details.

As for wind, expect the gales of 35kt over the outside waters
during the day Friday. Then the front pushes through the inside
waters Friday night with 20-30kt winds and some land areas seeing
gusts of 30-40mph. A wind shift to the SW late Friday night will
coincide with FROPA and the warming temperatures across the south
as noted above. As this happens, precip across the north in
particular will become convective and we may start to see some
breaks in the snow by Saturday morning.

On Saturday the surface low will slowly track south across the
gulf, causing winds through the northern inner channels to
increase out of the north and increase. Expect cold air to advect
in with the northerlies and change some places back to snow
showers. Up to 2 additional inches of snow could be expected with
these showers.

.LONG TERM...Sunday through Wednesday/ The long term forecast period begins with
some lingering showers from the weekend storm system still hanging
around the panhandle. As the low pushes off to the south, high
pressure builds in over the Yukon and will become the biggest player
during the forecast period. Therefore, aside from those lingering
showers on Sunday, precip does not appear to be an issue for the
duration of the week. After the brief (relative) warmup from the
weekend low, outflow winds around the high will push a surge of
arctic air over the panhandle. The potential does exist for some
daily min temp records to fall in the coming week. A very strong
pressure gradient will also become established over at least the
northern portion of the region which should introduce some pretty
strong winds. At the moment the most impacted areas look to be
through some of the typical locations such as Lynn Canal, Cape
Spencer and out in the Gulf. Guidance is also hinting at the
potential for a Taku Wind event on Sunday and will need to continue
to be monitored for just how long conditions will be suitable to
sustain such winds. Aside from just the wind itself causing troubles
for marine interests, but the extremely cold temps also raises the
flag for potential heavy freezing spray.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Winter Storm Warning from 9 AM this morning to noon AKST
     Saturday for AKZ025-026.
     Winter Weather Advisory from 9 AM this morning to midnight AKST
     tonight for AKZ027.
     Winter Storm Warning from 6 AM this morning to 9 AM AKST
     Saturday for AKZ018>022-024.
     Winter Weather Advisory from 6 AM this morning to 4 PM AKST this
     afternoon for AKZ023.
     Winter Storm Warning from 9 AM this morning to midnight AKST
     tonight for AKZ028.
     Winter Storm Warning from noon today to 3 PM AKST Saturday for
     AKZ029.
     Winter Storm Warning until 6 AM AKST Saturday for AKZ017.
MARINE...Gale Warning for PKZ041>043-051-052.
     Small Craft Advisory for PKZ022-031-034>036-053.

&&

Ferrin/JDR

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