Winter Storm and Heavy Snow in Alaska, March 14 to 16, 2023

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
331 PM AKDT Tue Mar 14 2023

.SHORT TERM...Satellite imagery this afternoon showing two main
features impacting SE AK weather. A closed low centered over Haida
Gwaii moved in bands of snow showers with some mix of rain over
the southern regions today. This low will track to the north but
dissipate to an open wave trough as it crosses over the central
panhandle. The second is a banded front associated with a low
near Kodiak that will increase winds over the NE Gulf and bring
first round of precipitation to the panhandle coast this afternoon
through early Wednesday.

As we move through the day on Wednesday a deeper low moves into
the Western AK Gulf bringing in heavier bands of precip. Heaviest
amounts will be for the central and northern regions. Model QPF
amounts show highly localized differences likely trying to depict
terrain and banding areas. Felt these had a good depiction of
where some higher amounts would be located but with models having
different banding areas went with a generalized blend. The main
forecast issue will be when the shift from northerly to southerly
flow starts, how soon temperatures and dewpoints rise, and the
correspond precipitation type change. Expecting a non-diurnal
curve with temps steadily rising through Wednesday and remaining
steady overnight or continuing to rise into Thursday morning. In
addition for any place with snow, snow ratios would also be
impacted by this change in airmass. Areas south of Sumner Strait
have already started to see the switch with a mix of rain in with
snow showers. This mix will last overnight changing to all rain by
Wednesday morning. Central areas will remain snow longer
beginning to transition by the late afternoon and then overnight.
NE Gulf coast and far northern panhandle are expected to keep more
northerly flow and thus remain a snow. Highest accumulations will
be Haines and Skagway with around 7 to 14 inches of accumulation.
Central areas will get lower amounts, likely between 2 to 4
inches, with Juneau getting highest totals. Main issue with the
incoming weather isn't so much the snow accumulation but the
change over to rain which over an existing snow pack and many
locations with hard packed ice on roadways will make any travel
difficult to say the least. The warming temperatures along with
heavy rain on snow will cause ponding of water on roadways,
driveways, yards, and in already full culverts.

Had better alignment with the 12z NAM and Canadian. GFS started
well but was more of an outlier depicting what could be a triple
point low over the central gulf Wednesday night. Did a general
blend of QPF with NAM/Canadian and inherited grids. Good
confidence with the synoptic pattern. Timing of the precip type
change is more uncertain, and thus uncertain snow totals.

.LONG TERM...Heavy rain, warm temperatures, and strong winds will
be the main story Thursday as a plume of moisture and strong SW
flow directs themselves towards the panhandle. 48 hour rainfall
amounts of between 2-3 inches is likely across the central and
northern panhandle with around 1 inch favorable across the south.
These amounts are well above the normal for this time of year as
March is typically one of SEAK's driest months. There is the
potential that some communities could see daily record rainfall
amounts for this storm on Thursday. By Friday the main plume of
moisture pivots to the west over the northern Gulf Coast. At this
time, Yakutat should be cold enough to see heavy snow with
amounts between 5 to 9 inches possible. Strong winds will also be
associated with the strong SW flow Thursday into Friday. Strongest
winds are expected along the central Gulf Coast and through the
central inner channels, up to Gale Force winds are likely at
times.

Heading into the weekend, there is an increasing potential that
SEAK could turn cooler and drier once again. Models continue to
try and resolve a strong surface low moving into the central Gulf.
The forecast will vary drastically depending on how this low
develops and tracks. For now, it does look likely that this system
could develop far enough offshore that the Panhandle will remain
under offshore flow. That being said, confidence is low on at
this time until a better solution can be identified. By next week,
there is the potential that SEAK could start the week off on the
dryer side before precipitation is reintroduce back into the
forecast mid-late week.

&&

.AVIATION...Snow has moved in over the Panhandle and is progressing
from south to north. Snow will transition to rain in a similar
fashion. Rain will be heavy at times. Flight conditions will
deteriorate to IFR at times over the next 24 hours due to snow.
Low MVFR or possible IFR in heavy rain. In both cases, the lower
conditions will be due primarily to restricted visibility. LLWS
only expected at the opposite ends of Southeast alaska - Yakutat
and Ketchikan. Elsewhere wind shear not expected to be an issue.
Turbulence should be light and limited to the southern outer
coast Wednesday afternoon.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Winter Storm Watch from Thursday evening through Friday evening
     for AKZ317.
     Winter Storm Warning from 7 AM Wednesday to 10 AM AKDT Thursday
     for AKZ318-319.
     Small Craft Advisory from 10 AM to 1 PM AKDT Wednesday for
     AKZ322.
     Winter Weather Advisory from 4 AM Wednesday to 6 AM AKDT
     Thursday for AKZ325.
MARINE...Gale Warning for PKZ652-671-672.
     Small Craft Advisory for PKZ012-033-035-641>644-651-661>664.

&&

SHORT TERM...PRB
LONG TERM....CC
AVIATION...Fritsch

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Special Weather Statement
National Weather Service Juneau AK
256 PM AKDT Tue Mar 14 2023

AKZ320>324-326-327-151100-
Glacier Bay-Eastern Chichagof Island-
Cape Fairweather to Lisianski Strait-City and Borough of Sitka-
Admiralty Island-Petersburg Borough-
Western Kupreanof Island and Kuiu Island-
Including the cities of Gustavus, Hoonah, Tenakee Springs,
Elfin Cove, Pelican, Sitka, Angoon, Petersburg, Kake,
and Port Alexander
256 PM AKDT Tue Mar 14 2023

...HEAVY RAIN ON TOP OF FRESH SNOW AND ICE...

Heavy rain is expected to follow snow that is currently
progressing from south to north over the Panhandle. The transition
from snow to rain will follow that same pattern as warm air
behind the front moves in from the south. Rain will become heavy
at times on Wednesday and persist through Thursday night.

The primary concern is not snow totals, but rather heavy rain on
top of fresh snow and pre-existing snow and ice. With the ground
still frozen, runoff will become excessive, overloading storm
drains and culverts quickly. Additionally, ponding of water on
roadways will create hazardous driving conditions. Ponding of
water on airport runways will also impact aviation operations.

Daily rainfall totals will be well above normal for this time of
the year and may result in new daily precipitation records.