Area Forecast Discussion
Issued by NWS Anchorage, AK

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FXAK68 PAFC 211331

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
531 AM AKDT THU JUL 21 2016


The main feature is the front that continues to weaken as it
moves northeast across western and Southcentral Alaska this
morning. The front has become tattered as it moves further away
from the parent surface low that is stacked underneath the upper
level feature over the far western Bering Sea. Some showers remain
across the Kenai Peninsula, Copper River Basin and Susitna Valley.
Winds shifted overnight to the southeast along Turnagain Arm which
has funneled the smoke from the nearby McHugh Creek fire into the
Anchorage Bowl area. High pressure that was over the eastern
Bering Sea continues to slowly shift south and east over the
southwestern gulf and north Pacific.

A second upper level wave is moving from the North Pacific over
the central and western Aleutians as evident from IR satellite
and this is bringing another round of showers. A weak surface
ridge just ahead of this feature is helping to tighten the
gradient and allow for gusty winds.


All models are in fair agreement and continue to handle the
placement and movement of the front as it moves through
Southcentral this morning. Blend of models were used in
precipitation placement and amounts for this morning as the front
continues to take on a shredded appearance. Going into Friday,
models are handling well the development of a secondary low over
Cook Inlet that will eventually move into Prince William Sound and
bring a better chance of rain for Southcentral.

Across the west, models are in agreement with the next wave
moving in from the North Pacific and the central and western
Aleutians. A blend of models was used here as well as this feature
traverses eastward to the western Mainland shores by late
Thursday. Yet another weak low moves across the Bering on the
heels of this first wave early Friday and models for the most part
are in agreement with the general movement, though the exact timing
remains in question.


Radar this morning is indicating showers across much of
southcentral due to the decaying front. However, due to low level
dry air, and relatively weak upper level forcing, little of this
precipitation is making it to the ground. While relatively weak,
this front is strong enough to support pressure gradients across gaps
and gusty winds in particular through turnagain arm. However,
winds will briefly weaken by this afternoon as the front
progresses eastward and the pressure gradient temporarily
relaxes before increasing again late this evening as the next
system approaches.

By late Thursday into early Friday morning, a much more potent
upper level system approaches the Gulf of Alaska. As a result,
much more widespread and steady rain is anticipated across much of
Southcentral. As the associated low pressure system will remain
cetnered mainly over the Kenai Peninsula and slowly drift to the
west, relatively light winds are anticipated for Turnagain Arm. In
contrast, coastal ridging will be sufficient for gaps winds
through the Copper River basin Friday.&&


Gusty winds along Turnagain Arm will present a challenge today as
a fire continues to burn near McHugh Creek. Recent webcam imagery
shows the gusty southeasterly winds beginning to fan the flames
not too far from the highway and this should continue throughout
the day today. Luckily relative humidity values will be higher
today across Southcentral Alaska and high temperatures will be a
good bit cooler thanks to increasing moisture and cloud cover. It
was originally thought that decent rainfall would fall across much
of the area today but it looks like the best chances for wetting
rains have been postponed until Friday. However, the Copper River
Basin has the best shot of seeing wetting rains today associated
with a front pushing through the area. Confidence is growing that
widespread wetting rains will be possible Friday with parts of
Anchorage potentially seeing upwards to a half of an inch of
rainfall. In the meantime, smoke has moved into the Anchorage Bowl
as the increasing southeasterly winds usher in smoke from the fire
along Turnagain Arm.

Across Southwest Alaska, widespread wetting rains were seen with a
front that pushed through the area on Wednesday. This helps a bit
with the ongoing fire concerns but gusty winds following the front
today will have the potential to create some fire growth. These
gusty winds are expected to continue through the remainder of the
week but another shot of rain is expected on Friday which is
expected to bring yet another round of wetting rains to the region

The frontal system which pushed through Southwest Alaska last
night is now crossing the Alaska Range and will continue to the
east today. Light rain behind the front will continue off and on
through the day as westerly flow continues to stream moisture
onshore. The next frontal wave will reach the Alaska Peninsula and
Southwest Alaska coast this evening then spread more rain onshore
tonight. The supporting upper level trough will swing inland on
Friday changing rain over to showers which will stay abundant
through the day then taper off from northwest to southeast Friday
night. The next frontal system will dive out of the northwest on
Saturday and Saturday night bringing additional rain to Southwest


The low out in the western Bering will gradually fill as it tracks
east today and tonight before swinging inland as a trough on
Friday. A surface low associated with a developing frontal wave
will cross the central Aleutians this morning then track east
towards Bristol Bay this afternoon through tonight. Once both
these systems swing onshore on Friday, flat ridging will build
over the Bering putting the area into west-northwesterly flow
which will persist into the weekend.


.LONG TERM FORECAST (Days 3 through 7)...

Beginning Friday evening, a rather dynamic low moving from the
Eastern Bering across the Alaska Peninsula will quickly move to
the Northern Gulf coast during the overnight. Rain will have
already overspread much of Southcentral with showers over
southwest Alaska. This low will deepen Saturday morning then move
eastward, bringing rain to an end from west to east across
Southcentral, although showers will likely form in the afternoon
across the mountains. Another shortwave trough will dig into
southwest Alaska during the afternoon and evening, quickly
spreading more rain into southern Alaska Sunday and Monday.
Thereafter, all the global models are in good agreement that a
large trough sets up over the Eastern Bering Sea and southwest
Alaska by Tuesday, keeping cooler and wetter weather in place
through the end of next week.





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