Heavy Snow in Alaska, January 7 to 8, 2020

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
645 AM AKST Tue Jan 7 2020

.SHORT TERM...Intense snow showers overnight brought a storm total
of 7.5 inches to Gustavus and likely high totals at Pelican along
the coast as well. Official numbers will be collected throughout
the morning as co-ops and spotters are contacted. Verification in
Juneau will depend on callers later on. Initial reports within
the Mendenhall Valley and the airport would not support the winter
storm warning. However, totals from last night and accounts of
downtown this morning suggest that the better orographics of
Downtown and Douglas Island possibly translated in higher snow
amounts.

An upper level trough over the gulf, a very unstable cold air
mass across the Panhandle, and southwesterly flow will continue
to cause snow showers to fall across much of the northern
Panhandle this morning and spread into the southern Panhandle
tonight. The greatest concerns today lie along an axis from
Pelican to Gustavus up to the Haines area. A convergence zone
between the southerlies of Lynn Canal and the northwesterlies
through the Chilkat Valley seem to support a convergence zone
straddling the region between Juneau's "Out the Road" areas and
Haines. Therefore, Mud Bay looks in line to possibly receive 4 to
7 inches of new snow today. And shower training into Gustavus and
Pelican closer to the coast as well as low visibilities by the
Gustavus ASOS suggest higher rates in these areas. Elsewhere, we
do expect light accumulations of 1 to 3 inches across the north,
with minor accumulations of less than an inch over the central
Panhandle.

Westerly and northwesterly flow aloft across the gulf will induce
low pressure over the gulf at the surface which in turn will
continue to support numerous to scattered snow showers across the
Panhandle through Wednesday. Meanwhile, a deeper trough swings
through the northeast gulf late Thursday. This one will begin to
prompt deeper cold air advection and induce stronger northerlies
through the northern Inner Channels. While there could still be a
chance of enhanced snow accumulations with convergence Wednesday
afternoon, the snow should begin to shift south Wednesday night as
drier air pushes through the north and ends precipitation. In
fact, the southern Panhandle could get advisory level snowfall of
2-4 inches on Wednesday night as a minor gulf low dashes to
Prince of Wales Island spreading snow showers ahead of it.
Finally, we do expect wind chills to approach 40 below zero by
Wednesday night for the Klondike Highway. Related to this, we have
heavy freezing spray late Wednesday for Lynn Canal accompanied by
40 kt northerlies.

Ensembles provided the bases for forecast changes, although QPF
was nudged upward above model for advised areas today to reflect
trends.

.LONG TERM.../Thursday through Monday/ As of 10pm Monday.
Weakening low pressure, tracking SE, will be over the southern
inner channels Thursday morning. Expect snow showers there to
become more isolated through mid morning. The rest of the
panhandle will have partly cloudy to mostly clear skies and
northerly outflow winds. As a result some freezing spray is
likely over the northern inside waters and cold wind chills to 35
below at White Pass.

A gale force low will track across the southern Gulf of Alaska on
Thursday. Nudged wind speeds up as models are coming into better
agreement on that idea, but there remains some differences on how
far north-south the low center and frontal band tracks. Latest
models are leaning toward a more southern track, which keeps
Juneau and the northern panhandle dry. The far southern panhandle
could see another round of advisory level snowfall from this low,
especially eastern POW Island. But may also see rain mixed in
under SE winds, which would limit accumulations near sea level.

The low passing through Dixon Entrance will tighten the northerly
pressure gradient across the northern inside waters. Gale force
winds are likely for Lynn Canal and Taku Mtn wave winds are
possible as well Thursday into Friday.

An arctic front quickly moves in behind the low Friday night with
continued dry northerly winds through the inner channels. Partly
cloudy to mostly clear skies and CAA will keep us below normal for
temperatures with many places seeing the teens to single digits
through the weekend.

&&

.AJK Watches/Warnings/Advisories...
PUBLIC...Winter Weather Advisory until 3 PM AKST this afternoon for
     AKZ020-022.
     Winter Weather Advisory until 6 PM AKST this evening for AKZ019.
MARINE...Small Craft Advisory for PKZ041>043-051.

&&

JWA/Ferrin

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