Area Forecast Discussion
Issued by NWS Anchorage, AK

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FXAK68 PAFC 260043

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
443 PM AKDT Tue Jul 25 2017

A strong dominant ridge remains centered just south of the Western
Aleutians, with widespread fog and stratus well established across
the Bering Sea and Aleutians region. A series of troughs are
affecting the southern mainland of Alaska; a very weak one
crossing Southcentral, a much stronger one moving through
Southwest Alaska, and an upper level low along the west coast of
Alaska diving southward toward Southwest Alaska. All of these
together are producing widespread clouds, cool temperatures and
areas of rain and fog.


Models are in good agreement with large scale features over the
next couple days. There are some differences in northern extent
of steady rain in Cook Inlet region tonight through Wednesday
which creates uncertainty in whether the rain will make it into
Anchorage. With such a moist environment it won`t take much
forcing to produce some light rain, so will largely stick with
rain likely for Anchorage and vicinity.


PANC...Weak flow in a moist environment combined with weak forcing
for rain means there won`t be a whole lot of change in ceilings
or visibility through Wednesday afternoon. Expect MVFR conditions
to prevail, but periods of IFR conditions are likely. It will be
very difficult to nail down exact timing for these lower conditions.
A shift in flow late Wednesday may be just enough to improve
ceilings a bit, perhaps up to VFR.


A weak deformation zone over Southcentral Alaska combined with
above average moisture for this time of year (1.13" of PW over
Anchorage) is currently leading to areas of showers extending from
the southern Kenai Peninsula north to the middle Susitna
Valley. Rain will taper off through the evening today before a
stronger shortwave moves into the area, embedded within an upper
level low pressure system diving south across western Alaska
tonight and tomorrow morning. Rain associated with this feature
will spread east across the Alaska Range and into Southcentral by
early tomorrow morning, with heavier amounts expected in the
southern half of the Kenai Peninsula. Rain is also expected to
push north into the Anchorage Bowl and Mat-Su. As the main upper
level low continues to move south, rain will begin to taper off
north to south by tomorrow evening. One caveat to this is in the
Anchorage Bowl and Mat-Su, where a weak easterly wave rotating
around the main parent low will push in over the area tomorrow
evening, which could lead to showers persisting through the night.

Showers should diminish over most of the area by Thursday.  The
exception to this will be in the Copper River Basin, where a weak
surface low will move southwest bringing rain spreading across the
Wrangell Mountains into the Prince William Sound by Thursday



A shortwave that developed over Bristol Bay this morning, along
with an associated surface trough, reinvigorated precipitation
today behind the decaying front. This wave will move east over the
Alaska Range tonight. The next feature of interest to affect the
area will be an upper-level Arctic low currently digging
southeastward over the Bering Strait. Models previously struggled
with the track of this feature, however consensus is building in
latest runs that this low will track through the Kuskokwim Delta
tonight and move to the Alaska Peninsula tomorrow afternoon. This
low will bring yet more precipitation to the area through
tomorrow. Behind the low, a brief ridge will build in to the
Kuskokwim Delta Thursday morning allowing for a drier morning. The
next front will quickly move in Thursday afternoon however,
bringing precipitation back to the area.

The fog and low stratus that has plagued the Southwest Coast
should move inland again tonight. Tomorrow night however, enough
offshore flow will setup over the Bristol Bay area to keep the
marine layer mainly offshore.



The ridge over the western Bering will amplify tomorrow, keeping
the Bering under westerly and northwesterly flow through
Thursday. An upper-level disturbance rounding the top of the
ridge tonight will bring some rain to the central Bering and
support some accelerated winds squeezing through bays and passes
in the central Aleutians through Wednesday. Wednesday night, a
front will quickly move through the central Bering and approach
the western Alaska coast by Thursday afternoon. The main sensible
weather effect of this front will be another line of rain that
will move through the Bering. A strengthening low over eastern
Siberia Wednesday night will flatten the ridge over the Bering
Thursday. A swath of small craft advisory winds will develop over
the western Bering as the gradient between the eastern Siberian
low and the high south of the western Aleutians increases.


.LONG TERM FORECAST (Days 3 through 7)...
While the guidance is still having some struggles with the long
term there is decent agreement for three of the main features. One
is a ridge extending from the North Pacific into the Bering.
There is also another ridge extending over mainland Alaska from
the east and the third is a low over the Gulf. While all of these
features will have some movement there is good agreement that
they will stay in relatively similar locations from the weekend
into the middle of next week. This pattern would keep light
showers over the southern mainland that will be enhanced
occasionally by shortwaves rotating around the Gulf low. This type
of pattern is also favorable for fog over the Bering.




LONG TERM...DK is the U.S. government's official web portal to all federal, state and local government web resources and services.