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FXAK67 PAJK 240011

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
311 PM AKST Thu Nov 23 2017

.SHORT TERM.../Through Friday night/ An occluded front over the
eastern gulf will move slowly NE across SE AK tonight and Fri
morning. Parent low will move into the far S gulf by late
tonight, then wobble around the SE gulf through Fri night. Used
the 12z NAM to handle main system movement, with the main low
track adjusted to the NE some from previous forecast.

Main concern will be snowfall amounts. Still looking like a decent
snowfall event across the N tonight and Fri morning as front moves
in. Decided to start the Winter Wx Advy for zones 20 and 25 at
00z this afternoon as snow has been falling all day and should
continue on and off until main snow band with the front comes
through later tonight and Fri morning. Went for 4 to 8 inches by
late Fri morning in the advisory areas. Elsewhere over the
N...looking like a 2 to 4 inch snowfall tonight and 1 to 3 more
inches Fri. Areas along S side of Icy Strait corridor will likely
see some rain mix in by early this snowfall in those
areas will be limited to 1 to 3 inches tonight. More shortwaves
moving around the main low center will bring snow showers to the N
third of the area Fri afternoon into late Fri night at least, and
these could produce several more inches of snow, but models
differ on placement of the heavier snow bands so no headlines will
be issued for this time frame attm.

Elsewhere, rain with snow mixed in at times over the more E areas
will continue into Fri morning before transitioning to showers.
Colder air will try to filter slowly S Fri night, which could
cause more of the central panhandle to become snow showers.

Expect a band of gale force winds ahead of the front in the
eastern gulf tonight, and some of these could get into Clarence
Strait for a short period late tonight as front moves through
them. Did drop the strong wind headlines though as stronger flow
aloft will coincide with warm advection so not expecting much
momentum transfer downward. Northerly winds will slowly increase
over the N tonight through Fri night, and winds should reach gale
force in Lynn Canal Fri and continue Fri night.

.LONG TERM.../Saturday through Thursday/ Active weather pattern
continues through the long range. Uncertainty is still the word
for the weekend forecast. While there is some agreement at mid and
upper level patterns the details with surface features are
causing large variability. What is expected after the weekend is a
shift from the cold arctic air in place over the central and
northern panhandle to a warming trend. Needless to say forecast
confidence is low.

High amplitude pattern at mid levels on Saturday with upper level
trough over the eastern AK gulf dropping almost down to S
California with a sharp ridge to the west extending from the N
Pacific and all the way into the Chukchi Sea. The trough/ridge
will start to shift to the east and flatten through Sunday as
another low drops from the Bering Sea over the Aleutians and over
the western gulf Monday. As this low moves east will have a
repeating pattern of ridge following the low, followed by another
low tracking across the Aleutians and into the western gulf. The
weekend surface feature is causing the most difficulty. Low
pressure over the gulf on Friday was originally shown to move
quickly to the east but now indications that this feature will
become quasi stationary into Sunday before weakening and moving to
the south. If the GFS/NAM are correct the more southerly
positions of the low pushes more warm air over the panhandle,
raising temps and snow levels but would be drier. The ECMWF keeps
the low further north, keeps precip in longer but keeps northerly
flow and thus lower temps and snow levels. ECMWF has shown more
run to run variability for the weekend system but is more
consistent for the systems next week. The Monday low looks like a
typical SE AK system moving a low center into the western gulf
with frontal boundary moving across the eastern gulf then over the
panhandle Monday night into Tuesday. While models differ on the
position and strength of the low center, they are in general
agreement on southerly flow which would once again raise temps and
snow levels. Began the process of increasing temps and for now
have more mix of rain/snow for areas north of Frederick Sound, but
could be switching this to all rain at lower elevations. In
addition to the precip and warming temps each low will bring in
another round of stronger gulf winds, with gales likely but
potential for stronger winds by Tuesday over the gulf. Not seeing
any real change to this warmer/wetter pattern for the rest of the

Initially models for Saturday had enough spread that changes
seemed undesired from the previous ensemble type forecast. Latest
check now shows, at least until 12z Sunday, more agreement on
rotating the low center counterclockwise over the southcentral AK
gulf before dissipating. Best agreement between the newest
GFS/NAM but held off on using that blend until more detail for the
Friday system could be established. For the rest of the time
frame utilized latest WPC, which was pretty much in line with
previous WPC resulting in some minor adjustments to wind speeds.


.AJK Watches/Warnings/Advisories...
PUBLIC...Winter Weather Advisory until 9 AM AKST Friday for AKZ020-025.
MARINE...Gale Warning for PKZ012-022-041>043-051>053.
     Small Craft Advisory for PKZ011-013-021-031>036.




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