Gale Warning 273, NWS Juneau, AK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
241 PM AKST Sun Nov 26 2017

.SHORT TERM.../Sunday night through Monday night/...Satellite
imagery shows a well defined front over the western and central
gulf progressing to the east. Associated hurricane force low
located over the bering Sea will remain well to the west and only
marginal gale force winds are forecast to affect the eastern gulf
late tonight through mid day monday. Post frontal wind shift to
the southwest over the gulf will persist through Monday afternoon
and aide in setting up a long period southwesterly swell that
will build to 18 feet by late Monday night. On Monday night, a
surface low will enter the extreme southeastern gulf and undercut
the panhandle. At the same time the hurricane force low currently
in the Bering Sea will have weakened significantly as it crosses
the Alaskan Peninsula. This will induce a very weak surface ridge
over the eastern gulf with small craft northerlies over the
southern outer coast and southerly to southeasterly winds 20 to 25
kts over the central gulf and along the coast west of Icy Bay for
Monday night. On the inside, there is evidence of the strong
northeasterly pressure gradient beginning to relax. This is in
response to a synoptic scale shove to the east by the approaching
front. Winds in Skagway are still gusting regularly to 40 mph or
greater, but conditions in Haines and over northern Lynn Canal
have begun to relax slightly. look for this trend to continue
through the short term forecast period. Even as this happens,
easterly winds over Icy Strait and Cross Sound will increase as
the front draws near, followed by southeasterlies over Clarence
Strait. Monday afternoon and Monday night will feature the
lightest winds the far northern inner channels have seen in many
days, but winds over Lynn Canal will begin increasing again late
Monday night as the northerly pressure gradient builds back in
briefly.

Precipitation from the front is expected to arrive along the outer
coast around midnight tonight. PoP gradients in the forecast are
fairly broad owing to model disagreement, but precip will
definitely affect the entire panhandle on Monday. The snow line
will be moving slowly north in response to low level warm air
advection from the south ahead of the front, and this will limit
the amount of snow that locations south of the Icy Strait corridor
will experience from this next front. 24 hour snow totals between 2
and 3 inches from Angoon north are expected through Monday night.
Snow ratios will be slowly but steadily falling, so by the end of
this event, what accumulates on the grounds will be the wet and
heavy variety.

Used a blend of NAM and GFS with a little help from the Canadian
for updates to pressure. Used NAM as a foundation for updates to
winds. PoP and QPF primarily from ECMWF with some help from hi
resolution models early on. Overall forecast confidence is
average.

.LONG TERM.../ Tuesday to Sunday / The new model solutions are
still in fair agreement regarding the lows and frontal features
over the eastern half of the gulf into the panhandle. A wound up
low moving past southern tip of Haida Gwaii with its front into
the BC coast early Tuesday morning. Over the northern gulf and
into the northeast gulf coast a trough will push inland Tuesday
morning, but another front with a low forming from south of Kodiak
Island will sweep across the gulf late Tuesday. There should be a
large warm sector and a good warm air push northward ahead of the
front. Think Yakutat could see some rain out this and north to
southern Glacier Bay and to the Juneau area potentially.

Minor cooling behind the front to prevent a complete warm up
however expect the rain snow line to be hung up across the
northern/central panhandle and play havoc with precipitation type
forecasting from midweek to the end of the week.

From Friday onward model agreement gets shaky again looking at
the operational runs Saturday evening. The blocking feature has
been moved east leading to a more quick zonal type flow pattern.
Short waves and lows, which either develop or do not, can impact
down stream weather.

Some work was done for the Tuesday to Wednesday forecast features,
which included increasing frontal winds and an increase in PoPs.
With a touch warmer temperatures we made some minor weather type
changes from snow to rain or a mix. After those, only small
changes were made to later time frame of the forecast. Used a
blend with an emphasis on GFS for the wind pattern and Pops where
nudged slightly towards the SREF. During later time frames the
WPC solution was preferred.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...Strong Wind until 9 PM AKST this evening for AKZ018.
MARINE...Gale Warning for PKZ012-022-043-052.
     Small Craft Advisory for PKZ011-013-021-031-032-034>036-041-042-
     051-053.

&&

Fritsch/Bezenek

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