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FXAK67 PAJK 232337

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
237 PM AKST Tue Jan 23 2018

.SHORT TERM.../Through Thursday night/ Main story of the short
range today is the return of outflow winds followed by another
shot of snow for mid week. Large upper level trough over the gulf
and Alaska is directing a new cold air mass south out of the
arctic. Most of the cold air will miss us to the west but enough
should pile up in the southern Yukon to have strong outflow resume
across the northern panhandle tonight. Gale force winds expected
in Lynn Canal along with gusts to 40 mph for Skagway, Haines near
Lynn Canal, and in downtown Juneau due to a moderate Taku wind
developing. Winds expected to continue into Wed afternoon before
an approaching front causes those winds to diminish. Few changes
made here as outflow was generally well represented by guidance today.

Focus then turns to the weak front moving north through the
panhandle tonight into Wed night. It appears to be a series of two
weak fronts, the first is moving into the southern panhandle this
afternoon before it nearly stalls briefly over Frederick Sound
Wed. The second comes north Wed afternoon and merges with the
first over the central panhandle before rapidly moving north Wed
night. Both fronts are rather weak and lacking moisture so only
light precip and low winds are expected. Cold air will still be in
place for the northern and central panhandle so snow is the main
expected ptype from Sumner Strait northward. Highest snow amounts
are expected over the central panhandle around Frederick Sound as
the first front sort of stalls briefly Wed. However, the general
lack of moisture with these systems and its general fast movement
will mainly result in less then 4 inches of accumulation in any 12
hour period for Wed into Wed night so no winter weather advisory
have been issued at this time. Nam and Canadian used for updates
to pop and qpf to narrow down the timing and structure of the
precip bands.

.LONG TERM.../Thursday through Tuesday/...Long range period
begins with an upper low south and east of the Gulf of Alaska
close to the Washington coast. Another upper low located over the
northern interior will be dropping into the north gulf vicinity
Kenai Peninsula late Thursday night. Upstream, an Omega block will
have formed over the Bering Sea and extreme eastern Russia. The
upper low will slowly track south and dominate the western gulf
by Friday morning with an upper trough extending southeast across
the eastern gulf. A short wave will develop along the upper jet
stream and the associated surface reflection will move into the
southeastern gulf by Saturday morning. Models are trying to
undercut the Omega block with a strongly negatively tilted upper
trough late in the weekend. At this same time, models are digging
a shortwave to the southwest along the southern coast. Have
doubts about these two events happening so will keep a close
watch on how follow-on model runs treat these features. Near-
surface cold air rotating around the upper low(s) has made its way
into the Gulf and colder surface temperatures are already being
observed. A warmer low-level airmass will not arrive until at
least mid-week next week, so true Southeast Winter temperatures
will persist through the coming week. Precipitation through at
least mid weekend will be convective in nature, so expect snow
showers with occasional rain showers over southern zones.
Additionally, no low level warm air advection to scour out the
cold surface air should allow the snow that does fall to stick
around for a while without getting excessively rained on. Models
are indicating the possibility of a front late in the next
weekend. If that in fact does happen, the rain-snow line may push
farther north - into the central panhandle - but that is still a
long way off.

Changes to pressure and wind limited to Thursday and Thursday
night using a blend of GFS and ECMWF. PoP and QPF primarily from
NAM for the same time frame with little change for the remainder
of the long range forecast. Temps unchanged. Overall forecast
confidence is average.


.AJK Watches/Warnings/Advisories...
PUBLIC...Strong Wind from 6 PM AKST this evening through Wednesday
     afternoon for AKZ025.
     Strong Wind from 9 PM AKST this evening through Wednesday
     afternoon for AKZ018-019.
MARINE...Gale Warning for PKZ012-013-022-041.
     Small Craft Advisory for PKZ011-021-031>033-035-036-042-043-051.
     Small Craft Advisory due to Seas for PKZ052.




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