Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 01/27/22

Southeast Alaska Forecast Discussion

National Weather Service Juneau AK

 356 PM AKST Wed Jan 26 2022

.SHORT TERM.../Through Saturday morning/ Another period of active
weather is in the forecast for Southeast Alaska as multiple
fronts and waves rotate around a parent low in the western Gulf.

The short term starts out with low clouds and fog blanketing much
of Southeast Alaska. MDCRS Soundings Wednesday afternoon from
both PAKT and PAJN show a strong inversion around 1,800 feet;
which has been responsible for keeping the low clouds and fog
around. Weak shortwaves moving overhead have also provided just
enough lift to squeeze out some drizzle across the area so have
added that to the forecast for this evening. Not expecting dense
fog like last night; but patchy fog should remain around the
region through tonight.

The main weather maker for the rest of the week approaches very
early Thursday morning. Current satellite imagery shows the low
approaching the SW gulf with a warm front extending NE towards SE
AK and a cold front stretching southward into the N Pacific.
Guidance suggests the low will move northward into the NW Gulf
then occlude and remain around that region through at least
Saturday morning. As the low sits and spins, multiple fronts and
waves will rotate into the Panhandle increasing rainfall rates and
coverage.

For Thursday, expect the warm front to weaken and dissipate as
the cold front to the west occludes and overruns it. The occluding
gale force front approaches the Outer Coast by Thursday afternoon
and pushes through by Thursday night. Expect low end Gales along
the Outer Coast and small craft conditions to develop through the
Inner Channels as the front pushes through. Steadier, heavier
rain arrives from west to east on Thursday then becomes more
showery in nature behind the front. There is a slight chance
precipitation could start as a brief period of snow for Yakutat
and Upper Lynn Canal before a changeover to rain. Expect snow for
the highways before snow levels rise near or above pass levels on
Friday. Overall, nothing out of the ordinary for this time of
year.

The second, stronger wave moves northward through the eastern
gulf Friday afternoon through Saturday morning increasing winds
and rainfall rates once again. Gale force conditions redevelop for
the eastern Gulf and move up the coast Friday night. Depending on
how close this wave tracks to the coast, strong wind gusts and
Gales may need to be added to the Inner Channels and SE Gulf
Coastal communities. Heaviest rain will spread from S to N across
the area during this time frame. Expect 48 hour rainfall totals
from Thursday afternoon to Saturday afternoon around 2 to 4 inches
for much of Southeast Alaska with the highest totals along the NE
Gulf Coast and along steep terrain. These totals agree well with
what ensemble guidance has for the area, so confidence is high
regarding the rainfall threat in the short term.

.LONG TERM.../Saturday into Monday morning/...Precipitation will
slowly and progressively dissipate and move out of the region from
north to south through the period as the aforementioned Gale-
force low and associated front continue to weaken and drift
southeastward, remaining just off the Outer Coast.

Temperatures will cool starting on Saturday night as a ridge of
high pressure presents its influence behind the frontal system,
which will give way to a more northerly/continental flow over the
area. This is indicated via model forecast 850mb Cold Air
Advection and MOS guidance. Overall, temperatures should not dip
very much below seasonal averages for the area.

As for the winds, for Saturday morning, as the front passes, Gales
look to be over Dixon Entrance and near the ocean entrance of
Clarence Strait with small craft winds all the way up the strait.
Also, for Saturday morning, Small Craft winds look to be
around/near ocean entrances up the Panhandle and just off the
Outer Coast. After that, winds will progressively subside through
the period as the front and low continue to weaken and move past
the area. For Sunday afternoon, onward, a tightening north to
south pressure gradient, caused by a high pressure center poised
over the Canadian Yukon, looks to cause Small Craft winds over
the Lynn Canal area.

Forecast confidence is generally average until mid Sunday morning,
which is when operational models began to diverge on the strength
and track of the aforementioned low/front as it begins to dip
southeastward. Therefore, for that point, onward, we blended
toward the NBM/WPC.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Gale Warning for PKZ042-043-051-052.
     Small Craft Advisory for PKZ022-032>036-041-053.

&&

$$

CM/JLC

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