Area Forecast Discussion
Issued by NWS Anchorage, AK

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FXAK68 PAFC 051305

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
505 AM AKDT Tue Jul 5 2022


Overall a persistence weather pattern continues with a few key
features to note. Over the far western Bering Sea, a vertically
stacked low pressure system continues to linger over the general
area and a large shroud of cloud cover extends across the entire
Bering Sea. Some rainfall is likely falling over the western
Aleutians. Low visibility from fog is being reported in the
Pribilofs. Over the eastern Bering, an upper level ridge is
beginning to amplify as a longwave trough cuts through Southwest
Alaska and stretches through the Barren Islands into the Gulf.
Southerly flow across Southcentral is bringing a few, isolated
convective showers northward through the southern Kenai Peninsula
and the Susitna Valley. Over eastern Alaska and the Yukon
Territory, high pressure is bringing mostly clear skies tonight
over the Copper River Basin, although a few lightning strikes from
a thunderstorm occurred near Mentasta Lake and along the Alaska
Range for some time after midnight. Low stratus along the northern
Gulf coast is beginning to slowly move up the Copper River and
very slow starting to fill in at the edge of the Prince William



Model guidance is in overall agreement with the evolution of the
pattern over the next couple days. The deep upper level low and
trough sitting over the northwestern Bering Sea will track to
Bristol Bay Thursday and then into the Gulf of Alaska, reforming a
low near Kodiak Island after that. Differences become a little
more noticeable late Wednesday onwards as the low nears Bristol
Bay. There are some differences with strength and track of
shortwaves rotating around the upper level low, which will affect
timing and location of heaviest rain. While the details of these
features will need to be worked out, there is increasing
confidence in an overall synoptic pattern shift for southern
Alaska and the Gulf of Alaska later this week.


PANC...VFR conditions and light winds will persist.



Southcentral: The main focus is again on the Copper River Basin
where temperatures will once again be in the 80 today and tomorrow
with RH values in the 20s with a few areas in the upper teens.
The Highest temperatures and lowest RH values will once again be
in the area running from Glennallen to Chitina to McCarthy.

Thunderstorm activity will kick off again today along the Alaska
Range and Talkeetna Mountains. Most intense thunderstorm activity
will be in the northern Copper River Basin.

Wednesday will see southerly winds along the Copper River
increase in the late afternoon through evening hours. Gusts may
reach 15 mph during that timeframe.

Thursday will see some lower temperatures and higher RH values
with increased moisture coming from the Gulf of Alaska.

Southwest: Fire weather concerns will continue to be low this
week as the general pattern remains cool and cloudy with showers.
A large Bering Sea low will move eastward towards Bristol Bay for
the next couple days. Although there is minor uncertainty in the
timing and track of the low, chances for wetting rains are
expected to increase over portions of Southwest, especially
Wednesday night into Thursday. As the low reforms near Kodiak
Island, gusty southeasterly winds will increase through Kachemak
gap into the interior Bristol Bay Thursday and shift a little more
easterly by Friday morning. Precipitation chances may continue
through Friday.


Tuesday through Thursday)...

Today will once again be very similar to yesterday for most of
Southcentral as the remnants of the upper level trough remain
over the southern Kenai Peninsula to the Gulf of Alaska. The main
difference will be that Kodiak Island will be out of the rain and
should see some sunny periods today. The Anchorage and Mat-SU
regions will also see slightly less cloud cover as some increased
clearing has moved in from the east. Expect thunderstorm formation
again this afternoon and evening in the northern Copper River
Basin and near the Talkeetna Mountains.

The stratus is once again pushing into the Gulf coastal areas
though it is expected to retreat away from the coast by late this
morning. Actually, tomorrow will also be similar to today except
for some increased winds in the afternoon and evening through the
typical breezy gaps such as Turnagain Arm, Knik River, and along
the Copper River.

The bigger change will occur on Thursday as we do get more of a
pattern change with a stronger upper level low cutting south of
Kodiak Island and bringing a front to the north Gulf coast. This
system has more moisture associated with it and that will bring
in more cloud cover to Southcentral in conjunction with some
cooler temperatures.


The longwave trough is over the Bering this morning. Shortwave
energy will get ejected from an upper low and into western Alaska.
The longwave trough will move eastward over western Alaska. Expect
mild weather this forecast period. Cool and wet conditions will
continue through Thursday across Southwest Alaska. Areas of fog
and low stratus are possible. A surface low in the western
Bering Sea and its associated surface low will track into the
Eastern Bering. There remains uncertainty with the timing of the
low and the leading edge of the precipitation shield. However,
much of Southwest will likely receive rain as this system moves



With the longwave trough in place expect an active pattern over
the Bering and the Northwest Pacific. On satellite imagery there
is a mature low over the Bering with a frontal boundary extending
into the northwest Pacific that eventually marries up with the
moisture fetch from Tropical Depression Aere which is east of
Japan. The first surface low is north of Attu and it will be near
Nunivak on Wednesday. Expect a weak transitory ridge in the wake
of the frontal passage and then there will be a new surface low
south of Attu on Wednesday afternoon. The models are pinging into
negative height anomalies at 500 mb across the region.


.MARINE (Days 3 through 5: Thursday through Saturday)...

Expect winds less than 35 kts and seas less than 20 ft for the
Day 3 through 5 period.


.LONG TERM FORECAST (Days 4 through 7: Friday through Monday)...

Looking ahead into the extended forecast, the latest operational
model runs are in good agreement with the evolution and
progression of the synoptic scale features, but diverge in the
specific details towards the end of the period. An active weather
pattern change remains on track as an upper ridge from western
Canada to the eastern interior Alaska breaks down as a longwave
trough and closed upper low moves into the eastern Bering Sea. By
Friday, the trough axis extends from the western Mainland through
the Gulf of Alaska. Model guidance has trended this northwest to
southeast orientation to bring increased moisture and appreciable
rain for the entire Southwest Alaska. At the surface, a triple
point low with an attendant front progresses northward from the
Alaska Peninsula and into Southcentral Friday and into the weekend.
Much of the coastal areas and portions of interior Alaska can
expect widespread wetting rain along with some moderate to locally
terrain enhancing precipitation as increasing southerly flow
draws deep Gulf moisture. Moreover, there is the potential for
significant rain for the Gulf coasts, including Prince William
Sound and along the eastern Kenai Peninsula. The Kenai River is
currently running high due to warmer temperatures and snow melt.
With the pattern change anticipated, any coastal rain could push
the river into flood stage.

Temperatures are also expected to trend back toward normal as
lower heights and thicknesses brings in a cooler air mass
spreading eastward across the state. Ensemble means are decently
clustered with the pattern evolution aloft through the medium
range period as subsequent shortwaves rounding the southern edge
of the trough brings continued rain chances and possible gusty
winds along the north Gulf coast. Uncertainty emerges, however,
as individual model solutions vary significantly with embedded
systems and interactions over time. Meanwhile, periodic wet
conditions continue for the Bering Sea and Aleutians as the
aforementioned trough shifts to the southeast beginning on
Saturday. By Sunday, quiet conditions return with low stratus and
fog to persist as a ridge of high pressure builds over the Western
Bering and slowly moves eastward.





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