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FXAK67 PAJK 251443

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
543 AM AKST Sat Feb 25 2017

.SHORT TERM...Fast moving short wave tracking across the panhandle
this morning is bringing precip to many areas. Ptype has been a
mixed bag across the area overnight. The precip started as
freezing rain/drizzle in Yakutat and Juneau overnight before
higher precip rates and more saturated conditions aloft changed
it over to either rain or snow around midnight. Since then around
3 inches of snow has fallen at the Juneau forecast office as of 4
am. Snow has also been observed from Angoon northward so far this
morning. South of that area, the precipitation is just starting up
as of 5 am as the short wave continues to move to the SE.

Winds have mainly been a marine concern so far. Wide spread 25 to
30 kt winds have been observed across the gulf and some tip jet
effects gave rise to a brief period of gale force westerly winds
at Cape Spencer and Cape Decision overnight ahead of the surface

The next 24 hours sees the rapid departure of the current system
to the SE. The northern 2/3rds of the panhandle will be precip
free and start to see some significant breaks in the cloud cover
by early Sat afternoon due to increasing northerly outflow. The
southern panhandle will hang on to the precip and clouds a little
longer but by Sat evening even they should be starting to clear
out. Clouds will again enter the northern panhandle late tonight
as a weak area of vorticity moves into the area from the west. The
period of clearer skies will allow temps to warm back up into the
mid to upper 30s in many places this afternoon before they drop
into the 20s and teens overnight due to radiational cooling
particularly in wind sheltered areas.

Helping to clear out the panhandle are some strong northerly
winds in the wake of this system. An area of high pressure
building in behind the system is increasing pressure gradients to
the point that northerly winds will increase to 25 to 30 kt in
many of the inner channels today. Min gale force winds are also
likely in northern Lynn Canal today. No strong cold air mass
accompanies this northerly push so no strong wind gusts are
expected in areas like Skagway and downtown Juneau this time.
Winds are expected to diminish Sat night as the rapidly retreating
short wave weakens pressure gradients.

Changes to the forecast mainly revolved around local changes for
wind and ptype as the system moves through. Used mainly Nam for
guidance this morning.

.LONG TERM...Upper level ridge remains over the AK gulf until a
northern stream trough drops down from the AK interior late
Monday into Tuesday where it will form a closed low over the
northern gulf. This upper low will remain over the gulf, with some
shifting, but then weaken toward the end of the week. Light
northerly flow lasts until Monday then increases in magnitude with
developing surface low. Dry weather continues until the Monday
wave. The cold northerly flow will drop overnight temps over the
region into the low 20s. Past model runs have shown wide spread
due to difficulty dealing with phasing of northern and southern
streams, but now starting to see some alignment. While some
earlier runs moved the low center down to the southeast gulf
indications the surface low will remain more over the northern
gulf before retrograding to the west. However still not fully
confident on this solution until models stabilize. Still large
amount of spread on timing of when the associated front will cross
over the panhandle and when next round of precip will start. Due
to the colder air becoming established over the panhandle this
system is setting up for an overrunning snow event. Precipitable
water standardized anomalies are low however getting snow
estimates ranging from 3 to 6 inches. Model soundings show deep
layer moisture over the cold air and good dendritic grown zone
which could bump up those snow estimates.

Only minor changes made to the forecast as either the new model
runs were still close to inherited forecast or spread was too
large to make use of operational models worthwhile. Initially
NAM/ECMWF were in line then NAM becomes more of an outlier by day
3. Forecast confidence is low due to uncertainty in details of
next weeks system.


.AJK Watches/Warnings/Advisories...
MARINE...Gale Warning for PKZ012-041-042.
     Small Craft Advisory for PKZ011-013-021-022-031>036-043-051>053.



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