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Southcentral and southwest Alaska forecast discussion 
National Weather Service Anchorage Alaska
500 am akdt Sat Jul 30 2016

Analysis and upper levels...

Two large scale weather systems bear watching this morning near
southern Alaska. An upper level low centered south of the Alaska
Peninsula is pushing eastward and is not expected to be a
significant factor in the weather directly. The reason it's
mentioned however is that it will move the upper level ridge out
of the way to aid in the progression of the other weather system
rapidly encroaching on the area.

The other system is a front and associated upper level low pushing
towards the area through northern Alaska. Its satellite presence
is as a band of clouds stretching northeast to southwest from
interior central Alaska across the central Bering and western
Aleutians. Extensive cloud cover associated with the front is over
most areas north from the coasts of the Gulf and Bristol Bay. This
will be the next rain-maker for all of southern Alaska over the
next several days. More on this below.

The cloud cover and a tightening pressure gradient ahead of the
front are helping keep temperatures quite mild this morning. Mid
to upper 50s are common over nearly all of southern Mainland
Alaska as west to southwest breezes transport moisture inland.


Model discussion...

The models are in excellent agreement through day 2. This lends
above average confidence to the forecast. The latest trends in the
models however have been for all of them to shift slower with the
progress of the aforementioned front and an associated low
expected to develop along the front Saturday night near the
Kuskokwim Delta. Thus, without consistent run-to-run continuity
in any of the models, there remains an associated bit of
uncertainty particularly with precipitation timing and placement
over the weekend.


Short term forecast southcentral Alaska (days 1 and 2)...

Although weak ridging has established over the southern Mainland,
an upper level trough with a weak surface reflection is dropping
into southwest Alaska over the next couple of days. The resulting
tighter pressure gradient across the southern Mainland is fueling
the stronger south and southwest wind up Cook Inlet. This pattern
will persist through Saturday night before the trough over the
North Slope sags south Sunday. A surface low will drop over
southwest Alaska Sunday night as the Gulf of Alaska ridge holds
into Prince William Sound establishing a broad southwest flow
across Kodiak Island into the Susitna Valley. This will bring rain
and clouds back over south central Alaska beginning Sunday. Since
the surface low looks to be further west than previous model runs
indicated, we have backed off slightly on the probability of rain
and showers in the northern Cook Inlet region to Prince William
Sound and the Copper River basin Sunday and Sunday night.


Short term forecast southwest Alaska (days 1 and 2)...

The closed upper level low remains positioned near Barrow with an
associated trough extending southwestward into the northern to
central Bering Sea. This feature is resulting in deep southwesterly
flow with the scatterometer winds depicting this through the
Bering this morning. Therefore, as the surface low associated
with the aforementioned upper level dynamics tracks into the y-k
Delta Region there will be widespread wetting rains developing in
the southwest Alaska today. This precipitation will move from
west to east across the aor through the weekend. By Sunday
afternoon the upper level low will bring colder air aloft
resulting in unstable conditions. Look for isolated thunderstorms
over the waters along the southwest Alaska coastlines. Due to the
southwesterly storm motion these isolated thunderstorms will track
into the Kuskokwim Delta, and the Bristol Bay inland areas. The
precipitation will transition from a stratiform nature to a
showery weather regime heading into Monday.


Short term forecast Bering Sea/Aleutians (days 1 and 2)...

The bulk of the Bering Sea, the Aleutians will remain under the
influence of the trough as it tracks from the west to east across
the region. As this feature moves eastward an upper level closed
low develops just south of Nunivak Island by Sunday morning.
This synoptic feature becomes almost stationary over the lower
Kuskokwim Bay to the Bristol Bay region heading into Monday. This
will result in rain/stratus for the eastern Bering through the
weekend. Meanwhile, high pressure builds into the region as the
trough exits the region. The Bering will see the typical marine
layer stratus/fog developing the next several days.


Long term forecast (days 3 through 7)...

Monday through Wednesday a closed low is progged to track from
the southwest Mainland to the eastern Gulf with a ridge building
across the Bering. Models are in good agreement with the synoptic
change which stays progressive through the end of next week. The
next upper low develops east of the Kamchatka peninsula mid week
and picks up an easterly pace on Friday. There are some differences
between model solutions on this system...the less aggressive European model (ecmwf)
and it's mean was used to update the extended range.


Afc watches/warnings/advisories...
Fire weather...none.



Synopsis and model discussion...jw
southcentral Alaska...surface observation
southwest Alaska/Bering Sea/Aleutians...period

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