NWS Juneau, AK wrote its last area forecast discussion before the first event at Jan 3, 5:32 AM AKST, 3 hours 28 minutes earlier.
Area forecast discussion, Jan 3, 5:32 AM AKST, 3 hours 28 minutes before
Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
532 AM AKST Wed Jan 3 2024
.SHORT TERM...A gale force front will enter the panhandle on
Wednesday, bringing with it snow, rain, and breezy conditions to
SE AK.
As of the time of writing, satellite imagery shows a gale force
cold front moving across the Gulf of AK, and towards the
panhandle. As the front arrives through the day, expect a surge of
winds and rain across the panhandle, At this time, small craft
conditions are expected for many of the inner channels, especially
through the latter half of the day and through Wednesday night,
with gale force conditions for the outer coastal waters and
Clarence Strait.
QPF totals with this system will largely remain seasonal, with a
period of heavier precipitation for Wednesday night through early
Thursday morning. Rain and snow showers will linger in the system's
wake, with cold air advection filtering in behind the front,
alongside a second wave which may move into the area through the
area on Thursday.
The big story for the northern panhandle will be snowfall.
Lingering cold air, alongside low dewpoints favoring snow melt
cooling, will contribute to an overrunning event for Haines,
Skagway, and their respective highways. The primary limiting
factor will be moisture, with the flow pattern looking sub-optimal
for moisture transport into these areas. Nevertheless, am
anticipating between 4 to 8 inches of snow - with the highest
totals for the Highways, between noon on Wednesday and noon on
Thursday.a Winter Weather Advisory has been issued for Haines,
Skagway, and the Haines and Klondike Highways through this time
period. As warm air associated with the warm conveyor belt of the
system attempts to work its way into the northern panhandle
beginning late tonight, it is possible that the town of Haines
could see a period of freezing rain. It remains an open question
if either Haines or Skagway will ultimately warm up enough to
convert to rain at all, given the lingering N winds and the
weakness of the system's associated warm air advection. This could
result in snow totals being higher, or lower, than anticipated,
depending on when - or if - warmer air does reach this area. The
heaviest snowfall rates will be between late Wednesday afternoon
and through Wednesday night.
.LONG TERM.../Thursday through Sunday/...Zonal flow with embedded
shortwave troughs and ridges will persist through Friday with
active but less impactful weather. Saturday sees a well defined
ridge set up over the gulf and into the interior of Alaska. By
Sunday, this ridge looks to be replaced by a longwave trough which
looks to spin up additional systems to impact the panhandle with
possibly a good amount of snow.
The post frontal environment of the frontal system on Wednesday
looks to have favorable conditions for some convective activity.
Lifting indexes of around -6 or less with modest surface CAPE and
vorticity aloft look to encourage some flashes of lightning along
the outer coast. These conditions look to only last during the day
as a clipper surface low looks to spin up and impacts the southern
panhandle Thursday evening into Friday morning. This low is expected
to generate at least up to 20 knot winds; however, the track and
strength of this system look less certain. Kept the winds associated
with this southern system fairly lax, but these may be increased
with increased confidence. As the low looks to spin up shortly
before impact, the overall moisture associated with this system is
expected to be less. Therefore, kept lower QPF amounts, but again,
these may be increased with more confidence.
As the aforementioned system passes south of the panhandle, high
pressure looks to build in the Yukon, encouraging more northerly
outflow winds and clearing skies for Saturday. In the gulf, a front
associated with a surface low near the Aleutians is expected to
traverse and impact the panhandle late weekend. Ahead of this front,
tightening pressure gradients will help the stable Yukon air be
pulled into the panhandle. The big question is how strong the cold
pool in the Yukon will be and how will the orientation of the
pressure field will set up with a front approaching from the west.
With a more north south facing pressure gradient, it stands to
reason that additional cold air will be pull from the Yukon.
Ultimately, this all leads to the late weekend system in which the
cold, stable air in place over the panhandle will result in an
overrunning snow event. With more stable, cold air in place over the
panhandle, the less likely it will be mixed out quickly and
potentially becoming decoupled. Furthermore, overall strength of the
front looks relatively weak when compared to climatological normal
during this time. With less strength comes less wind, meaning that
the boundary layer will mix out to rain more slowly. Ultimately, all
these factors will determine snow amount and snow composition. If a
shallow cold pool is pulled into the panhandle, then it is expected
that snow will be fairly wet and may last only a short while.
Regardless, this system late weekend will be monitored closely for
potential snow impacts.
&&
.AVIATION...Somewhat quiet morning aviation wise with mostly VFR
conditions and lighter winds prevailing. The exceptions are some
areas of the central inner channels with IFR conditions due to
some patchy fog/low clouds. There is also some gusty winds to 35
mph around Skagway this morning. Conditions are expected to
deteriorate through the day and into tonight as a new front comes
in from the W. Expect some breezy conditions by evening with some
MVFR vis and/or ceilings across most of the area due to precip and
clouds (Possibly IFR conditions around Haines and Skagway due to
snow). Turbulence and wind shear also possible as the front moves
through tonight. Improving conditions into Thursday as onshore
flow and showers take over (still possible for lower conditions
near heavier showers into Thursday).
&&
.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Winter Weather Advisory from noon today to noon AKST Thursday
for AKZ318-319.
MARINE...Gale Warning for PKZ036-642-643-652-661>664-671-672.
Small Craft Advisory for PKZ012-013-021-022-031>035-053-641-644-
651.
&&
SHORT TERM...GFS
LONG TERM....NC
AVIATION...EAL
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