Winter Storm in Alaska, February 8, 2021

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
251 PM AKST Sun Feb 7 2021

.SHORT TERM...Much of the same for today's forecast update. High
pressure has been building over the panhandle due to a surface
high over Canada that continues to strengthen. Much of the
panhandle has been high and dry Sunday as the extreme high
pressure builds from the east. Along the northeast gulf coast, a
surface low has developed increasing cloud cover for the northern
panhandle. This low is expected to move south along the coast
through Monday afternoon while strengthening slightly. With the
competing cold and dry continually air mass over the panhandle,
only a slight chance to chance of precipitation was added for
Yakutat and along the southern coastal areas. Any precipitation
that does fall will be snow, but less than one inch of
accumulation is expected. As the low moves south, associated cloud
cover will spread over the panhandle but will not last long as
clear skies take over the once again beginning Monday evening.
Precipitation chances then become non existent by Tuesday as
offshore flow increases drying out the panhandle into the weekend.

Pressure gradients will begin to increase as high pressure builds
along the coast mountains and the low develops offshore. Offshore
flow will begin increasing tonight leading to strong outflow
winds that last through Tuesday. Small craft (up to 37 mph) to
gale force (up to 54 mph) winds are expected along the coastal
waters and inner channels. Over land, strong wind headlines (gusts
40 to 59 mph) have been put in place throughout the central and
northern panhandle as outflow winds increase through the day on
Monday.

Cold temperatures are the big headline for this forecast period.
Temperatures across the panhandle have struggled to even reach
freezing today as a stable air mass keeps day time mixing to a
minimum. Strong cold air advection and clear skies, allowing for
radiative cooling, will cause overnight lows to plummet
beginning Monday night. With each passing day, temperatures
cool further with the coldest temperatures expected Tuesday
night. There is the possibility that some areas may be able to
break the strong inversion, if so, these areas will see a spike
in temperatures and an increase in gusty conditions. Knowing which
locations through the panhandle will accomplish this task, if
any, is the challenge and therefore confidence is lowest in this
part of the forecast. With combined winds and cold temperatures a
Wind Chill Advisory remains in place until midnight Monday night
for the Klondike Highway near White Pass. A Wind Chill Watch also
remains in effect through Tuesday morning as the potential for
wind chills as low as 55 below zero remains. There exists the
potential for additional Wind Chill Advisories Tuesday, in
particular areas surrounding Juneau and Hyder, as temperatures
reach below zero in some areas and wind speeds remain elevated.

.LONG TERM.../Tuesday through Sunday night/...Tuesday continues to
look like a particularly cold day across SE Alaska. In the upper
levels the descending NE flow along the flank of a broad ridge
going through the gulf and parts of interior Alaska will act as a
barrier to any storm systems of consequence. Closer to the
surface, an exceptionally strong area of high pressure will set up
over the Yukon. Operational runs and ensembles alike are both
indicating the high could approach or even eclipse 1060mb. This
will result in a sharp delineation of the pressure gradient
between the Coastal Mountains and the normally Pacific-moderated
Southeast Alaskan panhandle. Substantial northerly outflow winds
will result in gusty conditions across much of the area, with the
northern panhandle and Lynn Canal being especially impacted. The
northerly winds will also result in some of the coldest
temperatures experienced so far this winter for parts of the
area. A Wind Chill Watch is in effect Tuesday night for White
Pass and the Klondike Highway in particular, as there exists a
chance that the existing wind chill advisory may need to be
upgraded. Meanwhile, downtown Juneau is looking increasingly
likely to experience a Taku wind event. Though the event's
strength is still not set in stone conditions are looking
increasingly favorable with a critical level, an inversion, and
cross boundary flow all anticipated.

It is looking increasingly possible that the remainder of the
week could continue to enjoy some degree of outflow winds.
Although temperatures may not be as cold as early in the week,
ensembles are hinting that they could remain below normal for much
of SE Alaska. Another consequence of the outflow winds would be
continued reduced PoP chances across the area. Overall forecast
confidence remains average.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Strong Wind from midnight AKST tonight through late tonight for
     AKZ019.
     Wind Chill Watch from late Monday night through Tuesday morning
     for AKZ018.
     Wind Chill Advisory until midnight AKST Monday night for AKZ018.
MARINE...Heavy Freezing Spray Warning for PKZ011.
     Gale Warning for PKZ012-013.
     Small Craft Advisory for PKZ011-021-022-031>033-041>043-051>053.

&&

CC/GFS

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