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FXAK67 PAJK 241423

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
523 AM AKST Fri Feb 24 2017

.SHORT TERM...Rather quiet yet cold morning across the panhandle.
Mostly clear skies and low winds have allowed temperatures to drop
into the teens and 20s overnight in most areas. Winds are
generally 15 kt or less across the panhandle with the highest
winds currently in the SE gulf where northerlies to 20 kt have
been observed.

Friday is looking to be another quiet day. Mostly clear skies
remain the norm for most areas with low winds. Temperatures are
expected to rebound back into the 30s (with some 40s for the
southern panhandle) this afternoon due to solar heating. The
exception to this is the northern gulf coast where increasing
clouds and increasing chances of precip will be working in this
afternoon as the next system begins to move in.

Friday night is looking to be somewhat active as a fast moving low
develops along the northern gulf coast and moves SE across the
panhandle spreading precip and some wind as it goes. Timing and
strength of the system looks to be well agreed upon. Yakutat will
be the first to see any precip (starting as early as this
afternoon). Northern half of the panhandle will start to see
precip this evening with the heaviest precip expected after
midnight. The Southern panhandle will have to wait until late
tonight before they start seeing any precip. In the meantime 25 to
30 kt winds will also be spreading across the gulf tonight.

The tricky part of this forecast is the ptype that various areas
will see. After the warm up this afternoon increasing cloud cover
over the northern panhandle will inhibit any substantial
radiational cooling Friday evening in that area. This combined
with some weak warm air advection ahead of the low will keep temps
hovering in the low to mid 30s. So ptype will likely be primarily
a rain/snow mix for the northern panhandle (more snow the farther
from the outer coast you get) with snow accumulations around 1
inch expected. The southern panhandle will have mostly clear
skies into Friday evening allowing for a longer period of
radiational cooling before clouds and precip move in. In that
area precip will likely start as snow in a few areas before the
warm air advection and cloud cover warms temps above freezing
again. Again snow accumulations will mainly be up to 1 inch for
areas that do see snow with areas farther from the outer coast
more likely to see snow rather then rain. Ptype and accumulations
will vary depending on how cold or warm an area does get tonight.

Mainly used GFS and Nam for guidance today.

.LONG TERM...Low pressure system tracking down the panhandle will
be over the southern region Saturday morning then over Haida
Gwaii by the late afternoon. Precip over the south will be a mix
of rain and snow early but with any lingering precip falling as
rain due to warming temps. As the low moves south an inverted
trough will extend over the panhandle with tightening pressure
gradient between it and a cold high over the Yukon. Biggest
weather change Saturday will be a quick shift from southerly to
northerly winds over the inner channels along with an increase in
wind speeds. Through Sunday the area of high pressure that
shifted to the western gulf will begin to move back over the
eastern gulf resulting in weakening gradient and decreasing
northerly winds over the panhandle. After the short warm up on
Saturday with the exiting low, the northerly flow will begin a
cooling trend that is expected last into next week. A weak wave
may drop down the less side of this ridge but for now it seems any
precip from this system will remain over the gulf.

Late Monday into Tuesday still the big question. Broad upper level
trough moves over the AK gulf from the north. A developing system
at the surface digs from the AK interior into the northern gulf
has the potential for an overrunning snow event due to cold air
in place. Significant differences in position of this low center
between models and from run to run, so avoided using operational
model runs and kept with WPC ensemble solution. Will continue to
monitor this situation, expect more fine tuning to the forecast
over the next few days.

Used a blend of NAM/ECMWF at the start of the long range to late
Sunday then kept with inherited WPC grids Monday onward. Forecast
confidence is above average initially then drops by Monday.


.AJK Watches/Warnings/Advisories...
MARINE...Small Craft Advisory for PKZ041>043-051-052.



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