Winter Storm in Alaska, March 26 to 27, 2018

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
559 AM AKDT Mon Mar 26 2018

.SHORT TERM.../Through Tuesday night/ Rather complex forecast in
the works for the next 24 hours. Another shot of cool dry air
from the Yukon was introduced to the northern panhandle overnight
cooling temperatures and dew points. A rather distinct arctic
boundary has developed across the central panhandle as a result
with noticeably cooler and drier air north of the boundary then
south of it. Northerly winds of 25 to 30 kt are still being
observed in the usual outflow areas this morning as a result.
These winds are expected to diminish through the day as the Yukon
high weakens in advance of the next gulf front.

A gale force front is expected to make land fall in the panhandle
today from the S and will interact with the arctic air mass that
is present across the northern panhandle. Guidance overnight has
not budged all that much on when the precip is expected to arrive
(Morning hours for the south, and afternoon for the north). The
tricky part is going to be ptype and snow amounts. The southern
panhandle will likely be too warm for much snow as the arctic
boundary only reached Sumner Strait this morning. North of Sumner
Strait, the interaction of the arctic boundary with the incoming
front is expected to cause overrunning precip with surface temps
being cold enough that snow will be the dominate ptype Mon night.
Warm air advection is rather weak with the east-west orientation
of the front so erosion of the arctic air mass will be slow at
best and will likely keep at least a mix for ptype into Tue for
most northern areas. As for snow amounts, the front will be
starting to shear apart Mon night across the northern panhandle
limiting total snow amounts to around 3 to 6 inches for many
areas. Amounts could become higher or lower depending on how far
north the rain/snow line gets pushed and when as well as if the
front holds together longer then currently expected.

A lingering surface trough remains draped across the northern gulf
and panhandle into tuesday in the wake of the front with SW flow
across much of the rest of the gulf and panhandle. Rain and snow
showers will be the order of the day with a cool, marine modified
air mass coming in from the SW and lingering pieces of upper level
energy embedded in the flow. The lingering surface trough may act
as a focus for showers Mon night into Tue night which could
result in training showers dropping locally higher amounts of snow
or rain in some areas of the northern panhandle. Winter weather
advisories remain up for much of the northern panhandle late this
afternoon into Mon night as a result.

As for winds, pre-frontal easterlies expected to reach gale force
in the northern gulf today with 25 to 30 kt winds elsewhere in
the gulf. Not much wind expected in the panhandle ahead of the
front due to unfavorable east to west orientation of the front.
Post front SW winds will kick up tonight with gale force winds
expected in the central gulf. Winds expected to gradually diminish
through Tue night.

.LONG TERM.../ Wednesday through Monday as of 10 pm Sunday /
Wednesday will see lingering showers from the frontal band that
had moved through on Tuesday. A weak high pressure ridge will be
moving northward over the panhandle and the gulf on Thursday.
The operational models are slightly similar with a low lifting
out out the central Pacific to the move into/just south of the
Gulf of Alaska on Thursday. With the continued model differences
that the morning and afternoon solutions were showing, stayed
closer to the WPC long range solution again. Did not end up with
large changes after that nudge.

One of the bigger changes was to bring a slightly stronger low
into the SE gulf Thursday evening that weakens as it moves east
over the southern panhandle Friday as it weakens. The one
consistency from the end of the week through the weekend is that
high pressure will continue over the interior of the state and
northwest Canada. Confidence in the mid to later periods of the
forecast are low to medium.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...Winter Weather Advisory from 1 PM this afternoon to 7 AM AKDT
     Tuesday for AKZ017-019>022-025.
MARINE...Gale Warning for PKZ012-022-043-051-052.
     Small Craft Advisory for PKZ013-021-031>033-035-036-041-042.
     Small Craft Advisory due to Seas for PKZ053.

&&

EAL/Bezenek

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