Heavy Snow in Alaska, March 5 to 7, 2024

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
220 PM AKST Tue Mar 5 2024

.SHORT TERM...Next front comes rolling into the panhandle tonight
and will impact the majority of the panhandle through Wednesday.
With cold air in place, in particular the low dewpoints, most
areas will see accumulating snow.

To begin with marine concerns, the low system currently in the
gulf will intensify before becoming vertically stacked and
diminished. Before diminishing, it will generate moderate gales
along the NE gulf coast down to Cape Decision before loosing steam
as the front crosses over land. Prolonged 40 to 45 knot winds in
the NE gulf coast will churn up seas to heights of around 20 to 25
ft early Wednesday morning. In the inner channels, wind speeds
have slightly increased to 25-30 knot winds in N-S facing channels
as the front passes. In addition to these inner channel winds,
most likely will see gale force gusts accompanying these winds.

When it comes to snow for this system, changeover to rain
continues to be problematic to say the least. Problem areas
include the outer coast and southern panhandle. In terms of
moisture, a bulk of the QPF will fall Wednesday morning along the
coast before sliding south. The bulls eye of highest rates appear
to be around the Ketchikan, which lends itself to the uncertainty
regarding this front. If rates are high enough, with current
conditions, precipitation could stay as snow for longer than
expected. This scenario becomes increasingly likely if winds do
not come in as strong as anticipated. All of this culminates into
a very broad range of snowfall amounts, with Ketchikan having the
potential, albeit low (15%), of getting over 8 inches in a 6 hour
period.

In terms of moisture, it does indeed appear that moisture will not
be pushing in to the inner channels as much as anticipated, with
the exception of the northern panhandle. Due to the orientation of
the low level moisture transport roughly parallel to Lynn and
Chatham, more moisture than previously anticipated will impact
Haines and Skagway. Due to current dry and cold conditions and
lifting mechanisms being in the prime dendritic growth zone, the
determining factor for how much snow falls is how much moisture
ends up making its way northward. Furthermore, how much of this
moisture will end up reaching the ground due to very dry
conditions currently present. These areas will be watched
carefully in the coming hours.

.LONG TERM.../Thursday through Tuesday/...Gale force low and
associated front tracks into the SE Gulf Thursday morning. The low
will push the front along with increasing precip, winds, and
temperatures northward into Friday. The low center will reach the NE
Gulf Friday night while weakening. As of now another low looks to
track toward Haida Gwaii late Saturday into Sunday. For next week
ensembles depict a broad low over the Gulf while operational models
show increased spread as more lows move in from the west. Models
started to fall more in line with the GFS for the Thursday gale
force front but GFS is still fastest and strongest, so did not blend
in fully. The main impacts for the end of the week are the
increasing temperatures and heavy precip (especially for the south,)
which due to the increasing temperatures is expected to fall mostly
as rain. 24 hour rainfall amounts of 1 to 2 inches for the event
will cause issues due to current frozen ground and remaining snow
pack. This includes more run off and ponding of water along with
packed snow becoming icy due to the rain. Model snow levels not
fully reflecting the MOS temperature guidance for the central
panhandle so lower confidence if the Icy Strait corridor will get
accumulating snow with 24 hour amounts above 4 inches. For now think
snow accumulations will be in the 1 to 3 inch range. The far north
will be colder but get lower QPF. Grand ensemble probability of 24
snow above 6 inches is in the low teens. Overall after a cold start
to the month more seasonable weather expected for the mid and long
range.

&&

.AVIATION...The quiet aviation weather looks to come to an end
tonight. A gale force front will approach the gulf coast tonight,
bringing enhanced precipitation and LLWS to the outer coast. Snow
showers already impacting the coast and the Icy Strait area will
spread eastward through the evening hours. Conditions around the
panhandle will continue to deteriorate into the night as CIGs lower
ahead of the approaching front with VIS dropping quickly quickly
with snowfall. LLWS out of the SSE along with general turbulence can
be expected to pick up along the NE gulf coast Tuesday night.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Gale Warning until 6 PM AKST this evening for AKZ317.
     Small Craft Advisory until 6 PM AKST this evening for AKZ322.
     Winter Weather Advisory from 3 AM Wednesday to 3 AM AKST
     Thursday for AKZ318-319.
     Winter Weather Advisory from 6 AM to 6 PM AKST Wednesday for
     AKZ322-328-330.
     Strong Wind from late tonight through Wednesday morning for
     AKZ323.
MARINE...Gale Warning for PKZ642>644-651-652-662>664-671-672.
     Small Craft Advisory for PKZ021-022-031>036-053-641-661.

&&

SHORT TERM...NC
LONG TERM....PRB
AVIATION...GJS

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