Gale Warning 246, NWS Juneau, AK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
307 PM AKST Tue Nov 3 2020

.SHORT TERM.../Through Thu night/ Showers and mostly cloudy to
cloudy skies are the rule of the day with onshore flow and a weak
low in the Northern Gulf. A band of heavier showers is moving
onshore on the NE gulf coast around 1 pm associated with a weak
trough that is rotating around the gulf low. Winter weather
advisories have been issued for the Yakutat, Elfin Cove, and
Pelican areas through the evening hours with anywhere from 3 to 6
inches of snow likely from these showers. Elfin Cove and Pelican
will likely see the lower snow totals as they will not see as many
showers as Yakutat and they are also starting out just above
freezing for temperatures so initial accumulation will not be much
until temperatures cool down a little more this afternoon and
evening.

Into Wed and Thu, two things will be happening at once. First the
cold air mass in the Yukon and interior Alaska will be
strengthening the surface high pressure there and along the Coast
Mountains. Second a strong storm system will be making its way
through the Dixon Entrance area late Wed. These two combined will
increase northerly outflow across the northern panhandle as the
pressure gradient between them increases. This will especially be
true for Wed night as winds in Lynn Canal reach well into gale
category and will likely make a run for storm force. With the cold
air some freezing spray will be possible as well.

Speaking of the Dixon Entrance low, that feature has trended
farther north in guidance over the last 24 hours. Consequently
the precip has also moved farther north past Sumner Strait and on
up to Frederick Sound. Now the concern becomes how much of that
precip on the northern side of it will fall as snow rather then
rain, and if snow how much. It is going to be tricky, as
temperatures around Petersburg, Wrangell, and Kake will be in the
mid to upper 30s when the precip starts up Wed afternoon, but will
cool through Wed evening. We may end up with a rain changing to
snow scenario, and the location of a deformation band will
determine how intense the precip will get. At the moment,
Petersburg is likely to receive the highest accumulations (around
4 to 6 inches) with other areas around Kake, Wrangell, and areas
from northern Prince of Wales Island over to Hyder seeing lesser
amounts. Forecast confidence is not that great, especially with
snowfall amounts, as any deviation in temperature or location of
the deformation band would result in higher or lower precip totals
and snow accumulation.

Overall changes mainly focused on the stronger outflow on Wed into
Wed night and on the precip forecasts for this evening and on Wed
night.

.LONG TERM.../Thursday through Tuesday night/...This extended
range forecast begins with a strong baroclinic low having
undercut the Panhandle and created an inverted trough that will
extend from the low itself, across the central panhandle and then
out to the eastern Gulf. Strong high pressure over the interior of
the state and the Yukon will act in conjunction with the
low/trough to create northerly gales over Lynn Canal. With the
Arctic front pressing down from the north, freezing spray is
expected in Lynn Canal as well as parts of Stephens Passage.
Outflow conditions will also result in clearing skies early on
Thursday. Residual showers from the low will clear the forecast
area in advance of the clearing skies early on Thursday. The break
from cloudy conditions and snow/rain will be brief, as the next
front will climb over the top of a large surface high situated
south of the Gulf. PoP for this front is somewhat low, since much
of the frontal energy will be dissipated getting over the top of
the surface high. Immediately after the passage of this front, a
ridge will rotate around the top of the surface high and produce
another dry and sunny day for Southeast Alaska on Saturday. Change
will occur soon thereafter, as a developing low and associated
front south of the Peninsula tracks rapidly over the northern Gulf
and displaces the surface high south and east. Current long range
models are indicating high QPF values with this system, so it
bear close watching.

A majority of the the effort tonight went into updating days three
and four to better represent the undercutting low discussed
above. Confidence through Thursday night is average to slightly
above average. Confidence thereafter is below average.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Winter Weather Advisory until midnight AKST tonight for AKZ022.
     Strong Wind Wednesday afternoon for AKZ019.
     Strong Wind Wednesday afternoon for AKZ018.
     Winter Weather Advisory until 5 AM AKST Wednesday for AKZ017.
MARINE...Gale Warning for PKZ012-041.
     Small Craft Advisory for PKZ013-031-033>036-042-043-051>053.

&&

EAL/Fritsch

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