Area Forecast Discussion
Issued by NWS Anchorage, AK

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FXAK68 PAFC 130103

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
503 PM AKDT Thu Sep 12 2019

The large low in the Bering Sea near Nunivak Island is vertically
stacked with a strong front extending out of it, though the Cook
Inlet region and into the northern Gulf of Alaska this afternoon.
The 250 mb jet is quite strong around the southwest flank of the
low where it moving around 160 kt. The depth of the moisture is
sufficient to mitigate some of the downsloping to the lee of the
Kenai and Chugach Mountains. This can be seen on radar as the
rain shadow is not as big as is often observed in this flow.


The model question from the past few days has been the structure
and track of the triple-point-low after it formed in Shelikof
Strait last night. It looks like the answer is that it is rather
elongated for a triple-point with a small center moving up the
Inlet and one heading toward Middleton Island.
The current model solutions look to have good agreement into the
weekend when the next Bering Sea low. The speed and track have
reasonable agreement to the Southwest Alaska coast, but the
question is how soon the triple-point will develop and move into
the northern Gulf of Alaska.


PANC...VFR conditions will persist. Some low level wind shear may
persist into the evening but should dissipate by midnight.


All of the fire areas should see wetting rains over the next day
in Southwest and Southcentral Alaska. The Tokaina fire will
potentially see enough downslope to not quite be a wetting rain,
but at this point it looks like enough moisture will be available
even there to reach the .1 inch wetting rain threshold. Most areas
around the region will see more than that.


The front associated with a vertically stacked low over the Bering
is oriented northwest to southeast, slowly tracking northward
past Kodiak Island towards the Kenai Peninsula/north Gulf Coast.
Gusty southeast winds have been observed along Turnagain Arm,
along with other mountain gaps in the Kenai and Chugach
Mountains. Coastal ridging ahead of the front will
support a gale force barrier jet tonight over the northern Gulf
Coast into Prince William Sound. As the front weakens and shifts
orientation to east-west, winds will diminish.

The parent low will shift southeastward into the Gulf Friday, and
a showery pattern will prevail over Southcentral and the Gulf,
with precipitation amounts in most places noticeably lower than
observed today. Ridging will build in over Southwest by Saturday,
and weather will turn warm, dry and relatively sunny over


A strong front is bisecting Southwest Alaska from the Kuskokwim
Mountains to around lake Iliamna. Behind the front along the
coast, the dryslot has moved in aloft, leaving showers and much
weaker onshore flow. The stacked upper/surface low will then
slowly move southeast and cross the AKPEN through tomorrow,
bringing an end to rain and showers with drying conditions Friday
night and Saturday. A subtropical warm front and broad southwest
flow will develop on Sunday evening with widespread heavy rain
moving across all of Southwest Alaska Sat night and Sunday.



Gales force winds and high seas continue to impact the Bering Sea
as a seasonably strong low moves inland across Southwest. The low
will cross the Alaska Peninsula and move into the Gulf of Alaska
Friday, bringing enhanced seas to the southern Alaska Peninsula
and Eastern Aleutians through Fri evening.

The next low moves into the Bering Sea Friday night as an
elongated weak gale force warm front. The low moves east and will
bring widespread rain to the Bering, but will not be nearly as
intense as the current low moving through.


.MARINE (Days 3 through 5/Sunday through Tuesday)...

Low pressure moving through the forecast area Sunday into Monday
will bring small craft advisory level winds and seas to the Bering
Sea and the Gulf of Alaska. The forecast for the strength of this
system has been on track for a couple days now, so we are confident
in this forecast. After the exit of this system, both the Bering
and the gulf remain quiet through Tuesday.


.LONG TERM FORECAST (Days 3 through 7/Sunday through Thursday)...

We can still expect low pressure to be moving through the
forecast area Sunday and Monday. Its frontal system will be
pushing through the northern gulf and Southcentral Alaska Sunday
into Monday. This will bring a good shot of rain, mainly to
coastal areas. Precipitation amounts are still being honed. Beyond
this system, it is very difficult to tell what the weather will
bring due to increased uncertainty in model guidance. Models were
coming together yesterday in the extended forecast, but seem to
have taken a step back today. At this time, we can at least say
the active fall pattern we are in looks to remain in place.
Therefore, expect partly to mostly cloudy skies and rain from
incoming weather systems every few days.





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