Winter Weather Advisory 39, NWS Juneau, AK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
308 PM AKST Mon Nov 15 2021

.SHORT TERM...Isolated showers over the southern half of the
panhandle have been winding down today as the assoc surface low
weakens and moves off to the south across Dixon Entrance. A
stationary boundary between the departing low and ridging over
the central gulf can be seen on satellite imagery. This is assoc
with an upper level band of vorticity which will track eastward
across the panhandle through the evening. All models show this
band of snow showers lingering over the panhandle into Tuesday
morning, even becoming enhanced Tuesday morning ahead of an
approaching low pressure system. As a result, many across the
north will wake up to snow accumulations of around 1-2 inches.

A gale force low pressure system tracks E to NE across the Gulf of
Alaska through Tuesday. This will have a warm sector, causing the
snow showers Tuesday morning to transition to rain. However, the
track of the low will keep northerly winds and thus colder
temperatures entrenched over Yakutat, Haines, Skagway, and Hyder
with snow continuing and becoming moderate to heavy at times Tuesday
afternoon/evening. The wind shifts to the south for those locations
as well Tuesday night, causing a mix near sea level around midnight
then an eventual change to all rain by Wednesday morning.

Strong wind (gusts to 40mph) is likely as winds shift to the W-SW
Tuesday afternoon/evening, especially for the central outer coast.
After this wind shift and FROPA, CAA will begin and the rain will
become more showery. By Wednesday afternoon some showers may even
start mixing with snow again.

Preferred the more west track for the low pressure system which was
the consensus of the GFS, ECMWF, and Canadian models. Therefore a
blend of those were used for most updates to the forecast, including
the GFS for the timing of temperature warm up.

.LONG TERM.../Wednesday Afternoon through Friday night as of 3PM
Monday/...The front that has prompted the Winter Storm Warnings
for the far northern Panhandle will have pushed through southeast
Alaska around the beginning of the long-term forecast period.
Therefore, mainly convective showery activity will be present
throughout the Panhandle behind the front through the remainder
of the period. Generally lighter snow amounts are anticipated
through the rest of the period. Sky-cover will become more broken
to scattered in nature, particularly in northern areas as we
approach the end of the period.

Some fairly strong northerly outflow winds look to be possible
for the northern Panhandle for Thursday through the end of the
period as the weakening low associated with the cold front that
passed through drifts southeastward while weakening while a strong
area of high pressure stays poised over the Yukon region of
Canada, creating a tight pressure gradient over the northern
third of the Panhandle. Areas like northern Lynn Canal look to
have sustained winds near Gale-force around the Thursday evening
through Friday night timeframe, which is the time when the
pressure gradient looks to be the tightest, causing the outflow to
be the strongest. Windchills could be unpleasant. Be sure to
dress warmly and limit time outdoors if possible.

Speaking of temperatures, MOS guidance, ensembles, model forecast
850mb temperature advection, and thicknesses indicate a rather
potent cool down is in store for the region for the weekend. High
and low temperatures will remain near or below freezing from
Thursday, onward, for the northern 2/3 of the Panhandle. Low
temperatures will be much colder. Therefore, the most of the
precipitation received will remain snow throughout the majority of
Southeast Alaska.

Forecast confidence is above average for the long-term forecast
period as the models were generally in good agreement. A
GFS/CMC/ECMWF model blend was used to create the forecast.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Strong Wind Tuesday afternoon for AKZ023-026.
     Winter Storm Warning from 9 AM Tuesday to 8 AM AKST Wednesday
     for AKZ019.
     Winter Storm Warning from 9 AM Tuesday to noon AKST Wednesday
     for AKZ018.
     Winter Storm Warning from 6 AM Tuesday to midnight AKST Tuesday
     night for AKZ017.
     Winter Weather Advisory from noon Tuesday to 8 AM AKST Wednesday
     for AKZ029.
MARINE...Gale Warning for PKZ031-033-041>043-310.
     Small Craft Advisory for PKZ013-021-022-032-034>036-051-052.

&&

Ferrin/JLC

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