Winter Storm in Alaska, March 21 to 23, 2022

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
1214 PM AKDT Mon Mar 21 2022

.UPDATE...Reports out of Skagway revealed 5 inches of snowfall had
fallen at White Pass in 4 hours time, which are incredible rates
for Southeast Alaska. Satellite indicates that the moisture
connection between the northern gulf low and the frontal system
arriving in the southeast gulf tonight has been made earlier than
expected. While we still think snow should ease this afternoon, we
feel that it should re-intensify late this evening with the
greatest rates from early Tuesday morning through the day on
Tuesday. We raised snow ratios to account for this, and the fact
that modeled snow levels should remain below 2000 feet for most of
the period. One other explanation for such impressive rates is
the approach of a weak front crawling northward up Lynn Canal.
While around 9 AM, stiff southerlies of 20 kt developed at Eldred
Rock, weak northerlies persisted through Taiya Inlet. All of this
likely contributed to a zone of convergence that certainly did its
part for warning snowfall rates to develop. From Tuesday morning
onward, we do expect the biggest contributer to heavy rates will
be the strong slug of moisture arriving from the south.

&&

.PREV DISCUSSION......ISSUED AT ...1119 AM AKDT Mon Mar 21 2022

UPDATE...Light northerlies with a sufficiently chilly and dry air
mass to allow snowmelt cooling processes to ensure snow at the
surface has plagued Upper Lynn Canal early. A spotter report of
just shy of 3 inches arrived around 8 AM from Haines. Given
visibility restrictions of less than one mile and light winds at
both Haines and Skagway, along with calm winds to the south at
Eldred, we felt strong enough to back start the winter weather
advisory to begin this morning, rather than waiting until 10 PM
this evening. New analysis offers potential paradigm shifts.
Questions we must answer this afternoon include: Will the warm
southerlies arrive at all today as forecast? Should they arrive,
will temperatures cool down again tonight such that precipitation
changes back to snow at sea level? Should southerlies not arrive,
we could get warning amounts out of this weak system. We will
likely have our hands full with adjustments to the forecast today.

PREV DISCUSSION......ISSUED AT ...556 AM AKDT Mon Mar 21 2022

SHORT TERM.../Through Mon night/ Short range forecast features
one front weakening across the northern panhandle and gulf this
morning while a new system takes aim at the panhandle for tonight.
Currently, the front that brought the rain and wind to the
southern panhandle yesterday is now over the northern panhandle
and noticeably weaker. Areas from Hoonah and Juneau northward
have been cold enough for a mix of rain and snow overnight, but
not cold enough for any notable accumulations.

That front and the parent low in the gulf will gradually weaken
away today. Guidance today was actually keeping the low in the
gulf around through the afternoon which resulted in some higher
winds lingering longer in the gulf near the low. The front on the
other hand will stall as it weakens over the northern panhandle
resulting in precipitation lingering there throughout the day.
Temperatures will warm however so most precip will be rain by
midday at the latest.

Focus then shifts to the next low that is coming up from the
south. This one is much stronger then the other lows we have seen
recently, but it is also much further out in the gulf. As such,
even though the incoming front for Mon night will bring gusty
winds to a wide area, the gusts to 40 mph or more will mainly be
for the southern panhandle (at least for tonight). The front will
also be bringing precipitation, however anyone hoping for snow
will largely be disappointed as warm air advection with the front
will make just about everywhere at sea level too warm for snow.
Only the higher elevations of the Haines and Klondike Highways are
expected to get any significant snowfall (both currently have
winter weather advisories out starting at 10 pm mon). The Haines
Highway will be tricky as temperatures will be hovering right
around freezing so a rain/snow mix is not out of the question
which could result in lower snow totals.

Overall changes mainly focused on winds around the lingering gulf
low today and on details for the front tonight. Model agreement
remains fairly good.

LONG TERM.../Tuesday onwards/...A relatively strong gale-force
storm with an associated plume of moisture moves into the
panhandle late Monday. A special weather statement was posted
about this system. Expect moderate precipitation rates and
widespread breezy conditions across the panhandle with the highest
rainfall totals (~2 inches) along the southern half of the
panhandle. Gusts to at least 40 mph are likely Tuesday across the
entire panhandle. Temperatures at night will become cold enough to
support snow in the northern panhandle with accumulation at
higher elevations including the Haines and Klondike highways.
Winter Weather advisories are posted for the highways from Monday
10 PM through Wednesday 6 AM. Minor accumulations are expected
elsewhere in the northern portion of the panhandle.

A quick break between systems is possible later Wednesday before
another storm Thursday evening, but there is lower confidence
with this system as there are considerable model differences.
Higher pressure over NW Canada and lower pressure over the Gulf is
forecasted for the weekend. Thus, expect a slow drying trend,
more so for the north than the south.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Strong Wind from 7 PM AKDT this evening through late tonight for
     AKZ027.
     Winter Weather Advisory until 6 AM AKDT Wednesday for AKZ019.
     Winter Storm Warning until 6 AM AKDT Wednesday for AKZ018.
MARINE...Gale Warning for PKZ036-041>043-051-052-310.
     Small Craft Advisory for PKZ012-013-021-022-031>035-053.

&&

JWA/EAL/KRT

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