Heavy Snow in Alaska, March 14 to 15, 2022

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
631 AM AKDT Mon Mar 14 2022

.SHORT TERM...A weather front spreading precipitation northward
across the Alaska Panhandle today ahead of the strongest outflow
event we have seen in weeks provides our morning drama. Overnight,
strong winds to 40 mph blew through Downtown Juneau and northerly
gales rushed southward through Lynn Canal. Dewpoints tanked in
response, which has set up for a late season overrunning event for
the northern Panhandle as rain soaks the south.

Early on we decided to lower temperatures across Upper Lynn Canal
for tonight to keep them cold with northerly flow. This
substantially raised snowfall totals, enough to post a winter
weather advisory. We start the advisory a little earlier than the
bulk of the snow, but added wording that the greatest snowfall
rates would occur Monday night. MOS does hint at warming, but we
are not sold, as only the NAM introduces some southerlies up
there. With the main system still to the south and traveling
northwest, we do not feel the southerlies will emerge until this
low reaches the northern gulf (on Tuesday). This should warrant
more study should we believe the southerlies, and therefore the
rain changeover, arrives later than currently expected.

Snowfall has come in a little ahead of schedule and heavier for
Juneau this morning. Given a much drier boundary layer courtesy
of the strong cold air advection and downsloping from the
mountains, we even have cooled off as more precipitation fell.
While some high res models indicate a quicker turn to southeast
through Stephens Passage, thickness values still are low through
at least 21Z if not 00Z. We delayed the onset of rain while
keeping temperatures rising above freezing this afternoon. In
addition, model atmospheric soundings indicate the best chance for
lift in the snow growth zone occur this morning, which will make
it easier for temperatures to begin rising this afternoon. With
such a quick 1.3 inches in 3 hours between 1 AM and 4 AM, we upped
snow ratios above 15:1 and raised snowfall amounts to near
advisory totals. We did peruse the need to expand advisories for
communities west of Juneau, like Gustavus/Hoonah/Pelican/Elfin
Cove, but after making some adjustments, the original 1 to 3
inches still looked solid. We did up things to 1 to 4 just to be
sure.

Finally, we added a winter weather advisory for Yakutat to begin
at 4 PM today and continue through 6 AM Tuesday morning. While
confidence is low, there is a possibility of a warm nose
developing in the low levels that could give them the opportunity
for freezing rain, rather than snow at some point. Even NBM is
honing in on this with a high chance of freezing liquid. For this
reason, we elected to issue an advisory with potentially less than
4 inches of snow, but more importantly, a potential glaze of ice.

While the wind forecast has largely panned out, we were a little
soft for the gustiness across Prince of Wales Island. Once the low
approaches the southeast gulf today, we keep gustiness to 40 mph
on western Prince of Wales Island from this afternoon through
tonight. All in all, the wind forecast needed few changes.

.LONG TERM...This forecast period will feature wet weather
throughout. At the onset a low will be moving north and closing in
on the panhandle. This particular feature does not appear to be
particularly impactful in itself but it will turn the prevailing
flow around the region southerly and pave the way for yet another
frontal system on Wednesday. While the parent low look to remain
west of SEAK as it progresses north, an associated front will
usher in an enhanced round of precipitation and some gusty winds.
Right now the most noteworthy winds look to be along coastal
areas. Currently strongest forecast winds would only warrant small
craft advisories but will be monitoring trends in the forecast
guidance to determine if gales are more appropriate. While it is
expected to be wet more often than not through the week, early
Wednesday morning into the day will also be the period of the
heaviest precipitation. Some areas are forecast to be cold enough
during the night time hours this week to fall as snow. The main
areas of concern will be Yakutat and the higher elevations of the
Haines and Klondike Highways however sea level locations as far
south as the Icy Strait corridor could potentially see something
as well. After the Thursday system moves through some areas may
see a brief lull in the precip before yet another system moves
over the region on Friday. Forecast trends are that this will not
be as impactful as the Wednesday system.

/ Thursday to Saturday / By Thursday the Gulf of Alaska will have
broad general area of low pressure. Thursday a deeper low in the
general low will be south of Price William Sound. Friday to
Saturday will see another low tracking across the southern portion
of the gulf. Due to the broad low pressure staying in place
across the gulf and the south to southwest flow, most of the
precipitation in SEAK should fall as rain, although northern Lynn
Canal, Juneau area, parts of Glacier Bay and perhaps the NE gulf
coast my see a mix or periods of snow.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Strong Wind from 1 PM AKDT this afternoon through late tonight
     for AKZ027.
     Winter Weather Advisory until 4 PM AKDT this afternoon for
     AKZ025.
     Strong Wind until 6 AM AKDT early this morning for AKZ018-025.
     Winter Weather Advisory from 10 AM this morning to 6 AM AKDT
     Tuesday for AKZ018-019.
     Winter Weather Advisory from 4 PM this afternoon to 6 AM AKDT
     Tuesday for AKZ017.
MARINE...Gale Warning for PKZ013-043.
     Small Craft Advisory for PKZ011-012-021-022-031>033-035-036-041-
     042-051>053.

&&

JWA/JDR/JLC

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