Small Craft Advisory 757, NWS Juneau, AK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
353 PM AKST Fri Dec 2 2016

.SHORT TERM...A storm force low will make landfall very soon near
Lituya Bay late this afternoon. High winds to around 60 mph were
recorded along the coast around Cape Decision, Port Alexander,
Klawock, and Hydaburg overnight into the this morning. Because of
changes to the forecast track of the low (see below), we cancelled
the High Wind Warning for Juneau earlier this morning as the
strongest winds would remain to the south. Rain showers have been
moderate at times across the Panhandle, with all locations near
sea level reporting rain. This will change in the next 24 hours as
a much colder marine air mass begins to move in tonight and
Saturday.

The models all have shifted the low's track farther south to
where it crosses Lynn Canal later this evening. The track will
effectively become a frontal boundary separating gusty southerly
winds to the south and the northerly winds to the north.
Therefore, most of the changes in this forecast have centered
around these zones. We have lightened winds near Skagway and
Haines as they will also remain northerly. Strong southerly winds
will continue this evening just behind the system from Craig north
to Juneau and west to Elfin Cove this evening. Winds and gusts
will slowly diminish overnight.

Also due to the track and the fact that the Klondike Highway has
barely reported any precipitation today, we cancelled the Winter
Storm Warnings for the highways today. Haines Customs received 4
inches from 7 AM this morning to 2 PM, but this was not a rate of
snowfall sufficient for a warning.

Snow levels will begin to fall dramatically tomorrow as the
warmest temperatures of the day will be reached during the
morning. By afternoon, many areas around the central Panhandle
may see accumulating snows of up to 2 inches in showers. Drying
will begin from the north as a more continental air mass amasses
near the border.

We used NAM and ECMWF for edits today. Forecast confidence is
good.

.LONG TERM...On Saturday evening, CAA will be ongoing across much
of the area with 850 mb temperatures falling to between -10 to
-12 C. Ongoing shower activity will have transitioned to snow
showers across the northern half of the area. A general
accumulation of 1-3 inches is anticipated from Sitka northward
Saturday night. There are some concerning factors that some of the
snow showers could be heavy at times and lead to locally higher
amounts than currently forecast. Onshore flow will provide ample
moisture into the area with steep lapse rates due to the CAA
aloft. The NAM has also been consistent indicating a convergence
zone setting up along the Icy Strait corridor from Elfin
Cove/Pelican over to Juneau. This would focus snow shower activity
and promote training snow showers. However, confidence in this
scenario is not high at this point. Later shifts will monitor
model trends and make the necessary adjustments if needed.
Precipitation will diminish from north to south on Sunday as the
northerly pressure gradient strengthens with more cold air
spilling in from the north. Very cold air will reside over the
panhandle through at least the middle part of next week. Single
digit low temperatures are expected over portions of the northern
panhandle with highs struggling to make it out of the teens. The
southern panhandle can expect lows around 20 degrees and highs
around freezing. Small craft to gale force northerlies are also
anticipated. The threat of freezing spray will begin Sunday night
through early next week in the northern inner channels.

Latest model guidance has trended toward a drier scenario through
much of next week. Cold air and a strong northerly gradient will
likely suppress the storm track into the far southern gulf.

Used the 18z NAM for updates through 84 hours then the latest WPC
from day 4 onward.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...Strong Wind until 6 PM AKST this evening for AKZ021-026.
     Strong Wind until 9 PM AKST this evening for AKZ022>025-027.
MARINE...Storm Warning for PKZ042.
     Gale Warning for PKZ022-031>036-041-043.
     Small Craft Advisory for PKZ011-013-021-051-052.
     Small Craft Advisory due to Seas for PKZ053.
&&

JWA/TPS

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