Area Forecast Discussion
Issued by NWS Juneau, AK

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FXAK67 PAJK 250027 AAA
AFDAJK

Southeast Alaska Forecast Discussion...UPDATED
National Weather Service Juneau AK
327 PM AKST Wed Feb 24 2021

.SHORT TERM.../Through Friday/ Storm force low and its associated
front are churning through the eastern Gulf and Panhandle this
afternoon. Precip has already spread across most of the panhandle
and winds are picking up across the southern panhandle and outer
coast. High wind warnings remain up for Ketchikan, Metlakatla,
Prince of Wales Island, and southern Baranof with scattered gusts
of 50 to 60 mph already observed in some areas. As for Precip, 850
mb temps of -6C or colder as well as 1000-850 mb thicknesses of
1290 or less have allowed precip to change to all snow for many
areas as precip rates started to pick up earlier this afternoon.
Surface temps however are still sitting around 34 degrees F with
the strong southerly winds. The result is that while the precip
type is snow, accumulations have not been that substantial so
far. Spotter reports as well as webcams show around an inch or
two of accumulation in the central and southern inner channels
and the higher elevations of Prince of Wales Island as of 3 pm.

The tricky part of the forecast for tonight is figuring out when
the snow will change over to rain and how much snow areas will
get. The colder conditions aloft are forecast to move into the
northern panhandle as the low moves closer to the coast overnight
which should (combined with the still strong southerly surface
winds) change ptype over to rain. Highest snow accumulations will
be in the vicinity of Kupreanof Island where up to 5 inches could
accumulate before temperatures warm enough for rain to start
mixing in, or the precip diminishes. Lower accumulations expected
elsewhere as it will either be too warm (southern panhandle where
up to 3 to 4 inches could accumulate), or easterly flow will
curtail the amount of qpf received (Icy Strait area, Juneau, and
the Northern inner channels where around 1 to 3 inches could
accumulate). A winter weather advisory has been issued for zones
26, 27 and 28 until midnight for the accumulating snow. Uncertainly
remains however as very small changes in precip rate and/or
temperature could raise or lower how much accumulation an area
gets with maybe an isolated area getting up to 6 inches overnight
possible.

Thu into Fri will see a ridge building into the area behind the
strong low. This feature interacting with a still strong trough
over the western Canada will cause some rather strong W to NW flow
over the Gulf waters into Fri. Gale force winds are expected over
a large part of the gulf with wave heights reaching in excess of
20 ft. Strong wind gust will also likely be felt along the
southern outer coast during this time as well. Expect gusts to 40
or 45 mph in places like western Baranof and Prince of Wales
Island through early Fri. Otherwise weather turns quieter as
showers with the onshore flow will be the main feature of the
forecast into Fri aside from the higher winds.

Main changes for the short range forecast was the switch to more
snow for the panhandle for tonight and local effects for winds
and temperatures.

.LONG TERM.../Friday through Wednesday night/...An active weather
pattern continues into the long term with at least two systems
expected to impact Southeast Alaska through early next week.

The period begins with weak ridging building over the Gulf on
Friday leading to WNW flow over Southeast Alaska. Showers will be
diminishing in the morning becoming mainly dry for most of the
area by the afternoon. Drier air moving in aloft should even lead
to breaks in the clouds during the day. Unfortunately, the quiet
weather won`t last long as the next weather maker moves by
Saturday morning.

Precipitation moves back into the region as a low moves into the
NW gulf swinging a front into the Panhandle Saturday morning.
Good upper level dynamics will be associated with this front as a
SW-NE oriented jet pumps in subtropical moisture. The NAEFs and
EC Situational Awareness Tables already show IVT values and PW 2
to 3 standard deviations above normal for this time period. There
is potential for heavy rain across the region this weekend as
there are signals an atmospheric river will develop with this
front. P-type should be predominantly rain with the northerly
track of the low and persistent southerly flow into the Panhandle;
however precip may begin initially as snow before low level cold
air is scoured out. Snow levels will rise significantly as this
system pushes in with levels as high as 3,000 - 4000 ft across the
central and southern Panhandle on Saturday. Current thinking is
that a total of 1 - 2.5 inches of liquid will fall from Saturday
morning through Sunday evening. A brief break in the heavier
precipitation is expected Sunday night through Monday as the
system departs and a zonal onshore flow pattern sets up.

Models and ensembles continue the active weather pattern into
early next week as there is good agreement another system will
move into the northern gulf by Tuesday. This system may be very
similar to the previous one with good upper level dynamics and
subtropical connections. Details regarding these systems will be
fine tuned in the coming days. Overall confidence remains high in
an active pattern continuing across the region. Focused on the
weekend system for any changes to the forecast.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Winter Weather Advisory until midnight AKST tonight for
     AKZ026>028.
     Strong Wind until midnight AKST tonight for AKZ021-022-026.
     High Wind Warning until 6 PM AKST this evening for AKZ023-027.
     Strong Wind through late tonight for AKZ027.
     Strong Wind from Thursday morning through Thursday afternoon for
     AKZ023-027.
     Strong Wind until 9 PM AKST this evening for AKZ024.
     Strong Wind until 9 PM AKST this evening for AKZ025.
     Strong Wind until midnight AKST tonight for AKZ023.
     High Wind Warning until 9 PM AKST this evening for AKZ028.
     Strong Wind from 9 PM AKST this evening through late tonight for
     AKZ028.
MARINE...Storm Warning for PKZ041>043-051.
     Gale Warning for PKZ021-022-031>036-052.
     Small Craft Advisory for PKZ011>013-053.

&&

$$

EAL/CM

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