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FXAK67 PAJK 231352

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
552 AM AKDT Fri Mar 23 2018

.SHORT TERM.../Through Sat night/ Outflow winds have significantly
decreased overnight with the highest winds still reported in Lynn
Canal. Eldred Rock and Little Island are still showing sustained
gale force winds this morning while 20 to 30 kt winds are common
in many of the other northern inner channels. As for land areas,
gusts have diminish at Skagway, Juneau, and Tenakee Springs, but
some lingering gusts to 40 mph are still being observed at Douglas
and downtown Juneau this morning.

Outflow is expected to continue into Sat night, but at a much
diminished state then what was observed yesterday. Highest winds
are expected this morning before the weakening Yukon high lowers
pressure gradients enough that by this afternoon only Lynn Canal
should be seeing small craft winds. After this point, the Yukon
high will try to re-strengthen two separate times (Fri night and
Sat night) in response to two weak upper troughs dropping
southward and slightly reinforcing the cool air mass. Neither
surge is very strong and will mainly result in 20 to 30 kt
northerly winds continuing in Lynn Canal through at least Sat
morning with a second weaker wind max Sat night. Otherwise, once
the winds diminish today most areas should only see winds of 20 kt
or less through Sat night.

Meanwhile, a persistent band of showers lingers over the southern
half of the panhandle as a result of a surface convergence zone
(between the northerly outflow and the SE winds around the low
near Haida Gwaii) and upper level vorticity. These showers have
been rather light and some snow has mixed in for areas that have
become just cold enough this morning. This band is expected to
linger over the southern panhandle today as overall steering flow
remains parallel to the band. This changes tonight as steering
flow turns NW and begins to push the band S with it exiting the
panhandle by Sat morning. Rest of the panhandle expected to remain
dry through Sat before a weak trough brings the chance of rain
back into the forecast for the south Sat night.

Overall model guidance was in decent agreement with local effects
changes to winds and some increase in pops where the band of
showers lingers today being the main modifications to the forecast
in the near term. The trough that develops over the gulf Sat into
Sat night was shifted slightly southward per guidance trends but
other changes were minor. Preferred guidance was Namnest,
particularly with winds.

.LONG TERM.../Sunday through Thursday as of 10 PM Thursday/The
long term forecast continues to look wet. The primary concern in
the extended forecast remains a weather front that will track east
across the gulf Sunday. Precipitation still looks to begin as
snow or a rain and snow mix with this system before transitioning
to rain as warm air advection occurs. The far northern Panhandle,
specifically, the Haines and Klondike Highways may stay all snow
with this system. However, the bulk of heavier precipitation looks
to set up over the Southern Panhandle where it will fall as rain,
so snow accumulations remains low as a whole with about 1 inch
forecasted over the northern Panhandle. This system continues to
look quite wet with precipitatible water values in excess of 2
standard deviations above normal. Models have trended the heavier
precipitation further south so the largest rainfall totals are
expected south of Fredrick Sound currently. A brief break in
precipitation may occur after this front moves out, before
another low and its associated front move north over the gulf
toward the middle of the week.

Model agreement is average with poor run to run consistency
leading to lower forecast confidence. Not much change was made in
the extended forecast Sunday and Monday. Models are still
struggling with the timing of the system and precipitation totals;
however, they were diminished slightly and models have trended
precip totals downward with the exception of the GFS which
continues to be the wettest model. Primary guidance was a blend of
the ECMWF and Canadian to handle minor changes to the Sunday and
Monday timeframe with newest WPC being used beyond that timeframe
to add the midweek low to the extended forecast.


.AJK Watches/Warnings/Advisories...
PUBLIC...Strong Wind until 10 AM AKDT this morning for AKZ025.
MARINE...Gale Warning for PKZ012-013-043.
     Small Craft Advisory for PKZ021-022-031-032-034-042-051.




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