Area Forecast Discussion
Issued by NWS Anchorage, AK

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000
FXAK68 PAFC 231253
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
453 AM AKDT Fri Jun 23 2017

.ANALYSIS AND UPPER LEVELS...
The semi-blocked pattern continues this morning as the upper level
dirty ridge slides toward the Canadian Yukon. A couple shortwave
troughs in the northern stream are facilitating this move as the
approach the southwestern mainland. The ridge is also getting
squeezed from the south as another shortwave rolls up on the east
side of a long wave trough. General high pressure sits over most
of the mainland at the surface with light winds. Convection over
the Copper River Basin and Canadian Yukon keeps plentiful cloud
cover under the ridge, while up-Inlet flow has brought low-level
clouds and even a little drizzle from Kenai northward up into the
Susitna Valley.

&&

.MODEL DISCUSSION...
The general synoptics of the upper pattern are well agreed upon.
However the evolution of the upper trough over the Gulf, and the
incoming shortwave have introduced some differences among
guidance. The OOZ and 06Z runs have come into better agreement
with this feature but it will have big ramifications on convection
in the Copper River Basin on Saturday.

&&

.AVIATION...
PANC...Marine layer stratus will linger around the Cook Inlet
region and slowly lift through the day. There is a chance for
lower IFR conditions to exist this morning, but they should be
transient and not widespread.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...

With the upper level ridge beginning to retreat to the East and a
low moving northward toward the Gulf of Alaska, the pattern is
beginning to slowly change. This should mean that today will be
the last for the persistent low stratus in the upper Cook Inlet
region with a possibility of marked improvement as early as this
evening. This will allow temperatures to rise back toward normal
for Saturday and above normal for Sunday when there will be a
break between systems.

There remains the possibility for a few thunderstorms over the
Talkeetna Mountains and into the Copper River Basin this afternoon
and evening as well as tomorrow, but there should not be anything
widespread.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2...Fri and Sat)...
The convergence zone hung up along the Kuskokwim Mountains lived
up to its billing. Light rain with some embedded convection was
apparent across the area through the night. It has also seemed to
cause just enough mixing to keep the dense fog from forming in the
Delta and Bristol Bay as it did Thu morning. We are still
expecting some patchy fog/marine stratus to move inland along the
coast, but it should not be nearly as dense as yesterday.

That boundary will not move much through the day, and in fact, it
will help to serve to focus some more isolated thunderstorms in
the region late this afternoon through the evening. Further to the
east, weak ridging will give way to more influence from a strong
low in the Gulf of AK later today into Sat. But first, another
round of isolated thunderstorms are expected along the northern
portion of the AK Range this afternoon-evening. These storms
should move to the west and could work in tandem with the aforementioned
boundary to make for a bit more widespread convection over the
Lower Kuskokwim Valley.

As the low in the Gulf works northward into Sat, it will allow
flow to switch to more northeasterly across Bristol Bay and the
Lower Kuskokwim Valley. This will result in warming temperatures
with more sunshine (after the patchy fog burns off) for these
areas. However, with the thermal trough still present, another
round of thunderstorms along the terrain is expected. Meanwhile,
across the Delta, onshore flow will persist and could lead to
another morning of marine stratus and fog, especially along the
coast. While skies should clear during the day with ridging
building in, temperatures will remain quite a bit cooler than the
rest of the SW Mainland.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2...Fri and
Sat)...
A broad area of low pressure will dominate the Bering as it pushes
weak high pressure to the east into the weekend. High pressure is
trying to hold on over the Eastern Bering for the next 48 hours.
Under it, there is fairly widespread marine stratus/patchy fog
with very light winds. But the big weather maker will be the low
currently near Shemya. This low will hold right on the northern
edge of the sub-tropical jet for the next several days. So as
pieces of energy ebb and flow along the jet axis, the low will
constantly undergo modifications to strength and location. But
overall, it will drift to the east. As it does so, it will bring
steady rain and sustained small craft winds to the Central
Aleutians. Conditions will be a bit more showery and gusty for the
far Western Aleutians as some cool air starts to wrap in behind it
by late Saturday.

&&

.LONG TERM FORECAST (Days 3 through 7)...
An amplifying longwave pattern looks to bring and end to the period
of nice weather over much of southern Alaska early next week. By
Tuesday, the upper level trough over the Bering Sea will dig
southward and begin tapping into some moist subtropical air while
advecting that air northward into the Gulf of Alaska. This looks to
set up a rather wet period for much of southern Alaska Tuesday
through Friday of next week as a series of systems move into the
Gulf of Alaska and north toward the gulf coast. There is pretty
remarkable model agreement with this change in weather pattern so
confidence continues to rise. However, it is to be expected that
there could be some breaks in the rain and clouds but overall, wet
and cloudy will be the theme for much of next week.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...NONE.
FIRE WEATHER...NONE.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...MTL
SOUTHCENTRAL ALASKA...EZ
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...MO
LONG TERM...MMC



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