Small Craft Advisory 80, NWS Juneau, AK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
220 PM AKST Tue Jan 30 2018

.SHORT TERM...As of 130 PM Tuesday, A surface low pressure system
is currently passing over the southern Panhandle. Snow and rain shower
activity remains ongoing as far northwest as southern Admiralty
Island. As the surface low moves east into Canada shower activity
will diminish from northwest to southeast. Localized snow
accumulations are possible where heavier snow showers occur. The
far southern Panhandle may continue to stay under scattered shower
activity through Wednesday night as a weak frontal feature tracks
north over the Southern Panhandle tomorrow. Then on Thursday a
weak short wave trough aloft will track east over the southern
gulf initiating a weak surface low; however, the track of this
system remains uncertain, which could lead to the southern
Panhandle drying out on Thursday, if it stays further south. A
more northern track would bring another round of precipitation
into the southern Panhandle on Thursday.

Some changes were made to the short term forecast. Shower
activity was increased over the southern Panhandle this evening
and pushed further north than originally forecast. Winds
associated with the northerly outflow pattern over the Panhandle
were increased as a whole. Primary guidance was the 12Z GFS with
some input from the NAMnest to handle the outflow winds.

.LONG TERM.../Friday through Monday/ Kept the cold trend going.
Models generally are showing a slightly cooler solutions going
into the weekend. Lowers temperatures a few degrees, less so in
the south where temperatures south of Sumner Strait will reach
into the mid to upper 30s by Sunday. Cold Wind Chill temperatures
will continue to be a concern for near White Pass.

The gradient will begin to loosen ever so slightly by Friday, with
the northern Panhandle hoisting a SCA for the the north-south
orientated inside passages. The winds will take a more serious
decline in speed Sunday night into Monday, as the high in the
Yukon moves east. The approaching low in the southwestern gulf
will not be of any concern, for now. Freezing spray will continue
to plague some of the northern inside passages with the stronger
winds.

Snow will start out over the Southern Panhandle up to around the
Elfin Cove-Juneau corridor through the weekend. Snowfall amounts
will be less than impressive, until we get into Friday night when
the southern Panhandle has potential for a few inches. Snow
amounts get a bit tricky with temperatures having a hand at
whether the snow will be wet and heavy or even more rain than
snow. Used the GFS for POP/QPF, with the ECMWF for snow level.
For the south, precipitation type will be a mix mainly becoming
snow overnight, and changing over to rain during the afternoon by
Friday. There are hints of heavier snowfall in the south on the
weekend and even potential for freezing rain, best potential is
the southwestern corner of Prince of Wales. For the north snow
will continue to be the precipitation type into Monday.

Models are still not in good agreement as to whether there will be
a low or a trof that moves across the gulf Thursday night into
Friday. Either way, either feature will enhance the weather across
the Panhandle with increased precipitation in the south and
stronger winds in the north. The GFS continues to be the most
aggressive with the low feature near Dixon Entrance Thursday
night/Friday. It is the only model with upper level support of a
closed low. An ensemble blend to nudge the current forecast was
the best a approach, with no large scale changes needing to be
done.

Forecast confidence is average, with a slight decrease in
confidence in regards to snow amounts in the south Friday night.

&&

.AVIATION...Expect periods of low visibilities associated with
ongoing snow showers spanning from the south central panhandle to
far southern Panhandle. (Near Ketchikan temperatures will be warm
enough to support rain showers this evening.) As the surface low
moves east into Canada shower activity will diminish from
northwest to southeast. However, showers may remain ongoing near
Ketchikan and Klawock airports as a weak frontal feature tracks
north tomorrow.

&&

.MARINE...Strong northerly outflow will continue through much of
the week. This will keep strong gale force to storm force winds
present in Lynn Canal. Freezing spray remains a concern as well
due to the cold northerly outflow that remains ongoing.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...Strong Wind through late tonight for AKZ018-025.
     Winter Weather Advisory until noon AKST Wednesday for AKZ018.
MARINE...Gale Warning for PKZ012-013-031.
     Small Craft Advisory for PKZ021-022-032>034-041-043-051-052.
     Small Craft Advisory due to Seas for PKZ042-053.

&&

JB/KV

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