Gale Warning 191, NWS Juneau, AK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
129 PM AKST Thu Nov 7 2019

.SHORT TERM...Main forecast concerns over the next 24 to 48 hours
will initially be low ceiling and visiblities impacting aviation,
transitioning to a modestly strong outflow pattern by Friday
evening.

A warm front will be lifting north into the southern Panhandle
this afternoon before. A weak surface low will track along the
front, across the far southern Panhandle into western Canada
tonight. A second surface low will track northeast along the
boundary into the SE Gulf on Friday evening. Models remain in some
disagreement as to the eventual track of the surface low, but the
consensus is to keep it south of Sumner Strait as it slides slowly
eastward Saturday.

To the north of the warm front, saturated ground, light winds,
and a general reduction in mid to high cloud cover will lead to
the existing low ceilings and visibility likely getting lower
overnight. Dense fog advisory has been issued in advance of this
system for Gustavus and Yakutat and this area may need to be
expanded in coverage as the night goes on. Over the southern
Panhandle, roughly south of Sumner Strait, deep layer WAA and
moisture transport will lead to moderate rainfall overnight.
Rainfall amounts of 1 to 3 inches are likely in the Prince of
Wales Island to Ketchikan areas tonight through Friday.

At the same time, a cold 1040mb arctic high pressure system will
be sliding southward through the Yukon. Cold air advection will
commence in earnest by Friday evening over the northern Panhandle
from Frederick Sound northward. The surface gradient will be
impressive between the weak low to the south and strong high
pressure to the north. Thus expect northerly gales to 40 kt or so
in Lynn Canal, out of Taku Inlet and Cross Sound Friday night into
Saturday. Cross barrier flow will increase dramatically Friday
night over Salisbury Ridge. Forecast profiles look supportive of
at least modest mountain wave activity with a solid inversion
between 2 and 3 kft and a flow reversal aloft near 500mb. Thus
decided to go with a High Wind Watch for the Taku Wind areas of
downtown Juneau and Douglas for Friday night through Saturday. The
track of the surface low may be the key in exactly how this event
unfolds. Should it track across the far southern Panhandle, the
gradient orientation may be too northerly (as opposed to
northeasterly) for mtn wave development.

Snow potential looks limited especially over the northern
Panhandle through Saturday as offshore flow will dry out the low
levels, preventing any substantial precipitation. Some concern
further south near the Petersburg area depending on the exact
track of the surface low that moisture and cold air may be
superimposed enough for snow accumulations there on Saturday.
Later shifts will need to monitor the evolution and track of this
system.

.LONG TERM.../Saturday through Wednesday/...As of 10 PM Wednesday
night. With a bit more consistency between operational forecast
models, it appears the weekend is more likely to be trending
drier, especially across the northern panhandle. This break from
the wet weather will not likely last long as precipitation is
expected to return by Monday. But the complex split flow pattern
continues to cause large variations in model solutions.

By Saturday, the upper level high will be positioned over the
northern interior of Alaska and will likely move SE into the
Yukon. At the same time an upper low in the SW gulf will remain
rather stationary before slowly drifting north. Across the
panhandle will see the interaction between jet streaks associated
with the synoptic pattern aloft. Latest models suggest the
northerly stream will be more dominant suppressing the southern
stream further south. If the surface low is able to reach the
southern panhandle early Saturday, anticipate the system will be
sheared out, keeping chances of precipitation very low from
spreading northward. It is becoming more likely that outflow
winds will increase as surface high pressure builds across NW
Canada. There are still significant differences between model
details on how strong the wind event could be this weekend.
Northerly gale force winds will be likely through Lynn Canal
Saturday along with the possibility of a mountain wave event near
downtown Juneau. Do anticipate colder temperatures to accompany
the outflow winds Saturday and Sunday, but chances of snow
becoming less probable because of the lack of moisture.

The next system is currently anticipated to move north from the
NPAC Sunday into the southern gulf by early Monday. This will be
another system that will be somewhat difficult to pin down timing
as well as precipitation type across the northern panhandle.
Models and ensembles are in fair agreement that Monday will see
the return of wet weather but timing is still a low confidence
issue. The GFS has consistently been more aggressive while the
Euro and Canadian are somewhat slower moving the system north and
keeping the cooler air ahead of the front. For now keeping a
rain/snow mix along the Icy Strait corridor with rain south and
snow possible along the northern highways. Warmer air advection
will likely follow the system Monday warming temperatures above
freezing. Expect onshore flow to continue with rain likely through
the first part of next week. WPC and NBM guidance were used
Sunday through early next week. Overall forecast confidence
remains average to below average through the long range.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...High Wind Watch from Friday evening through Saturday afternoon
     for AKZ025.
     Strong Wind Friday afternoon for AKZ025.
     Dense Fog Advisory from 9 PM this evening to noon AKST Friday
     for AKZ017-020.
MARINE...Small Craft Advisory for PKZ012-013-035-036-041-042-051-052.

&&

DEL/DDH

Visit us at http://www.weather.gov/Juneau