High Wind in Alaska, December 26, 2018

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
202 PM AKST Tue Dec 25 2018

.SHORT TERM.../Through Wednesday night/ Did not make any
significant changes to the forecast as models still waffling a bit
on low track Wed into Wed night. Latest model runs have shifted
the low further SE, which would diminish the precip threat some
over the N. However, with the inconsistencies with the models on
low track, felt staying the course was best idea attm.

As low and occluded front move N tonight, winds will increase over
the eastern gulf and much of SE AK. Still expect a storm force
band of wind with occluded front tonight. Have out several strong
wind headlines as well, mainly along the southern and coastal
areas. Also kept in strong wind for downtown Juneau area tonight
as weak mtn wave event is likely. Did also mention strong winds
for zone 17 for outflow out of interior passes tonight. It is
possible for isolated wind gusts to 60 mph over the S tonight, but
not enough occurrence for high wind warning. Winds should drop
some after front passes by, but another round of stronger wind is
expected over the SE gulf and central to southern outer coast Wed
with second wrap of front moving into that area. Low should
weaken rapidly Wed afternoon and evening as it pushes inland, with
winds generally diminishing over the S Wed night.

Still expect much of the precip with the occluded front to be
over the S half, as offshore flow over the N will be fairly
strong. Most precip over the N will be localized to areas that
favor E-NE flow such as eastern sides of Chichagof and Admiralty
islands. As low moves onshore Wed evening, precip will increase
over the central and possibly northern areas. Decided to keep the
winter storm watch for zone 25 beginning Wed night, but if latest
model trends on the low track hold true, there will be much less
precip in the Juneau area Wed night than currently forecasted.

.LONG TERM.../Thursday through Monday/...Models are converging on
the storm force low described above being severely weakened by
the inevitable anticyclonic force of a broad ridge building over
the gulf Wednesday night and Thursday. While there are differences
in the details on how the surface low tracks into the central
Panhandle, northerly winds within the northern Inner Channels
quickly flip back to south as the system eventually ejects into
Canada. Aside from fine-tuning winds, we also lowered
temperatures and hence snow levels southward Thursday morning.
There will likely be light accumulations all day over the far
northern Panhandle and at least in the morning across much of the
central Panhandle. South and south central areas should be all
rain however. We can already see as the rain/snow line will
be particularly challenging during this time. Just as shower
activity begins to die across the Panhandle with this exiting low,
another shortwave directs a front across the gulf Thursday
afternoon and pops rise again Panhandle wide Thursday night. Ptype
with this front may lean slightly more liquid with this front
but again chance of snow will persist across the north.

Southwest but cool maritime flow will leave more precipitation in
the forecast on Friday as a longwave trough deepens over the
western gulf. This long-wave trough looks scheduled to push into
the North American West Coast somewhere on Saturday. Strength of
this system and impacts are debated by solutions as the ECMWF
carries most of the precipitation into the Canadian coast Saturday
while the GFS spreads impacts for the entire coast including
Southeast Alaska. Our current solution reasonably accounts for
these differences, so we kept it.

From Sunday beyond, there is far greater differences in what could
happen. Currently we entertain GFS theories for our weather next
week, which leaves us wet and seasonal. However, both Canadian and
ECMWF build a much stronger ridge late in the weekend into early
next week. Should this occur, instead of cloudy, wet, and
seasonally cool with rain over the south and a mix/snow over the
north, we could have an extended period of lighter winds and
widespread potentially impactful fog. Those with planned holiday
travel early next week should check back as weather could affect
transportation of all sorts.

Changes Thursday and Thursday night were led with GFS/NAM/ECMWF
ensemble. We committed virtual no changes Friday onward as the
early weekend consensus looks good with current forecast. Wide
disparity in what could happen from Sunday prevented change next
week.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...Strong Wind from 6 PM this evening to midnight AKST tonight for
     AKZ026.
     Strong Wind until midnight AKST tonight for AKZ027.
     Strong Wind from Wednesday morning through Wednesday afternoon
     for AKZ024.
     Strong Wind through late tonight for AKZ025.
     Winter Storm Watch from Wednesday evening through Thursday
     morning for AKZ025.
     Strong Wind from 9 PM AKST this evening through Wednesday
     afternoon for AKZ022.
     Strong Wind through Wednesday afternoon for AKZ023.
     Strong Wind from 6 PM AKST this evening through Wednesday
     afternoon for AKZ021.
     Strong Wind from 6 PM AKST this evening through late tonight for
     AKZ028.
     Strong Wind from late tonight through Wednesday morning for
     AKZ017.
MARINE...Storm Warning for PKZ042-043.
     Gale Warning for PKZ022-033-036-041-051-052.
     Small Craft Advisory for PKZ012-013-021-031-032-034-035-053.

&&

RWT/JWA

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