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Southcentral and southwest Alaska forecast discussion 
National Weather Service Anchorage Alaska
432 am akdt Thursday Jul 2 2015

Analysis and upper levels...
an easterly wave associated with an upper level low near Yakutat
is bringing a broad area of widespread stratiform rain from the
eastern interior...through Denali park...and into the Susitna
Valley. This wave set up a further to the west than the models had
indicated...which has allowed most of southcentral to remain dry
from this feature into the early morning hours. This wave will
drift east and weaken this morning as the upper low moves inland
over northwest Canada...which should allow for a short period of
light rain around southcentral later this morning. Over the
northwest coast another upper low is beginning to enter the
western Mainland. This trough will move very slowly through the
western interior just to the north of the aor over the next few
days. Persistent ridging that has existed over the eastern Bering
continues to hold even as an Aleutian low continues to spin near
Adak. This ridge is expected to hold through the work week...while
the Aleutian low will remain nearly stationary over the central
Aleutians.

&&

Model discussion...
the models remain in very good synoptic agreement into the
weekend...with most of the main issues being placement of a
complex low over the Aleutians Friday night-Saturday. There
remains uncertainty however in the placement of the upper level
wave producing rainfall over southcentral this morning. In general
though...the higher resolution NAM and Gem regional have
initialized the best with this rainfall...and are both in good
agreement of a short lived period of rain over southcentral this
morning. Over the Bering Sea the models have come into better
agreement with the progression of a complex low that will stretch
from the Aleutians into the northwest Pacific into this
weekend...therefore forecast confidence is increasing wtih this
system through Saturday.

&&

Fire weather...
southcentral...rainfall from the wave currently stretching from
Susitna Valley into Cook Inlet will drift eastward and weaken later
this morning as the associated upper level troughs moves inland
near Yakutat. As a result...areas of southcentral that have
remained largely dry so far for the event will likely see a
period of light rain later this morning...but chances of wetting
rains will be minimal outside of the Susitna Valley. After this
wave dissipates over the Copper River basin this
evening...southerly flow will keep cloudy and moist conditions in
the area with a chance of rain showers into Saturday. The thermal
trough will also retreat into western Canada on Friday...limiting any
thunderstorm activity will be limited to the Alaska Range and
Talkeetna Mountains on Friday with limited coverage.

Southwest...the upper level trough over the western interior will
keep cloudy and moist conditions over much of the area through
Friday. There is a chance that this trough may produce convective
showers this afternoon...however with minimal instability
thunderstorms are not expected throughout the work week. Further
to the south over Bristol Bay...ridging from the Bering will keep
conditions generally moist with light onshore flow today. This
ridging will then move overhead on Friday...allowing for warmer
and drier conditions over interior Bristol Bay...however with min
relative humidity values only in the middle 30s critical fire weather conditions are
not expected.

&&

Short term forecast southcentral Alaska (days 1 and 2)...
an upper wave currently stretching south across the Susitna
Valley to southern Cook Inlet moves east into the Copper River
basin this afternoon. Rain associated with this feature should
clear areas west of the Copper River basin by afternoon the slowly
diminish over the Copper River basin tonight. The main area of
wetting rain will be the Susitna Valley and to a lesser extent
portions of the Copper River basin. Showers are expected on the
backside of this feature and will likely continue as a threat
through Friday night as minor short waves embedded in the developing
southwesterly flow aloft move across the region. Brisk west to
north West Gap flows are expected across the eastern Kenai
through early this afternoon.

A weather front moving north across the North Pacific brings rains
and brisk easterly winds to the western and southern Gulf Friday
afternoon/eve.

&&

Short term forecast southwest Alaska (days 1 and 2)...
drier conditions can be expected over the region through Friday
night as high pressure will move into southwest Alaska. Scattered
showers are expected along the Alaska/Aleutian Range today with
isolated showers developing over mainly the Kuskokwim valley
tonight and Friday night. As the high moves into the
region...afternoon highs will warm slightly with partly cloudy
skies expected. Areas of smoke will continue through Friday night
with the worst conditions during overnight/morning inversions.

&&

Short term forecast Bering Sea/Aleutians (days 1 and 2)...
winds will remain just below gale force through Friday night along
the front now starting to move into the central Aleutians. As the
front migrates northward and elongates from east to west...expect
the core of the winds to push northward into the north-central
Bering Sea by Friday evening. Rainfall can be expected along most
of the front today and tonight from Unalaska eastward. Rainfall
will spread westward into the western Bering Sea Friday night as
the front elongates. Expect the heaviest rainfall today in the
eastern Aleutians as the flow becomes southerly over the
area...bringing moisture directly over the region. Most of the
heaviest precipitation will shift eastward on Friday as southerly
flow sets up over the Alaska Peninsula.

Areas of marine fog and stratus are expected to be pushed
northward through Friday night as the frontal system moves into
the central Bering Sea.

&&

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

For the start of the weekend a ridge transits the Gulf and south
central suppressing rain except for along the mountain ranges
of the Susitna and and Copper River valleys where afternoon
showers develop along a trough that moves across the interior. To
the west...a low pressure system over the western Aleutian chain
pulls a front north from the Pacific. This front is expected to
move to the Alaska Peninsula and southern Gulf early Saturday
morning. The northward progression still remains uncertain as
model solutions still lack agreement. The Alaska Peninsula...Kodiak
Island and the eastern Kenai will see the highest precipitation
amounts from this front during the weekend. Models do agree on
bringing a swath of rain across Bristol Bay Saturday night and
into the Kuskokwim on Sunday. Increased cloud cover can be
expected across the rest of the southern Mainland this weekend
with scattered showers mainly along the mountains.

Overall forecast confidence decreases in time as models have
struggled with handling the upper trough deepening across the
interior through the weekend. The GFS and European model (ecmwf) were used to
update the weekend forecast with no significant changes made
beyond Monday. The beginning of next week models are suggesting
that a ridge amplifies across eastern Alaska keeping southcentral
dry on Monday. Low pressure in the Bering brings another
reinforcing front late Sunday spreading rain to the southwest
Mainland and Bering into Monday. This low pressure system will be
the pattern to watch next week as it may become the dominating
system that brings a regular pattern of clouds and rain.

&&



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

&&

$$

Synopsis and model discussion...dek
southcentral Alaska...rmc
southwest Alaska/Bering Sea/Aleutians...rf
long term...kh

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