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fxak68 pafc 161243 
afdafc

Southcentral and southwest Alaska forecast discussion
National Weather Service Anchorage Alaska
443 am akdt Mon Jul 16 2018

Analysis and upper levels...
the low pressure aloft and responsible for the rain and showers
yesterday is moving into the Canadian Yukon. The northern stream
jet is coming over the Mainland from the northwest, aiding in
changing the flow pattern. A strong disturbance is riding the nose
of this jet aloft, spreading rain across the southwestern
Mainland early this morning. The whole of the Mainland is under
the influence of an upper trough that extends toward the pole,
while nearly everywhere else from Siberia to the northern Pacific
is under a fairly warm and ridgy air mass with 850 mb
temperatures into the positive double digits. A strong shortwave
is moving overtop of this airmass near the western Aleutians,
bringing quite a bit of lightning activity to the area, above the
marine layer stratus.

&&

Model discussion...
there's pretty good agreement with the evolution of the pattern.
Though the models themselves continue to shift around concerning
how the disturbance out west affects the overall pattern as it
shifts to the east and builds a ridge over the Mainland.

&&

Aviation...
panc...VFR conditions and light winds will persist until this
afternoon when southeast winds are expected to increase out of Turnagain
Arm and rain showers develop primarily along the mountains. With
west-southwesterly movement to these showers most of the shower
development should remain to the east of the terminal.

&&

Short term forecast southcentral Alaska (today through wednesday)...
the dominant feature that will take most of the focus of the short
term forecast is the elongated shortwave trough that is beginning
to enter the Alaska Range. Ahead of this shortwave, showers
continue to develop in the Susitna Valley under the cyclonic flow
aloft, which will become reinvigorated this afternoon as the
shortwave trough moves overhead. This shortwave is also expected
to cause showers to develop further south into the Chugach
Mountains, but with west-southwesterly steering flow most of these
showers should remain out of the Anchorage bowl and western
portions of the Matanuska Valley. As is usually case with
shortwaves passing through during peak heating, there is also a
chance of thunderstorm development from the talkeetnas eastward
into the Copper River basin, however with areas of clouds from the
cyclonic flow aloft these are not expected to be significant or
widespread.

This shortwave will then slowly move through the Copper River
basin on Tuesday, allowing for high pressure from the Bering Sea
to begin spreading into the south Mainland. This will allow for
warmer, drier, and sunnier conditions to develop over most areas
for the middle of the week, with the biggest forecast concern
being a potential for early morning patchy fog in low lying areas
and around Cook Inlet.

&&

Short term forecast southwest Alaska (today through wednesday)...
wet conditions are expected today as a weak front moves eastward
across the region. Showers taper off by Tuesday with a ridge
settling across from the Bering. Warmer and drier conditions
return through mid week. Westerly flow today becomes light and
variable for Tuesday and Wednesday.

&&

Short term forecast Bering Sea/Aleutians (today through wednesday)...
a front across the western Bering and Aleutians swings northeast
through late this afternoon...with a few thunderstorms possible
along the boundary this morning. A ridge ahead of the front stays
on an eastward moving track through mid week. Low pressure
associated with the front moves across the southern Bering
tonight through Wednesday, then it crosses back to the Pacific
Thursday night. The next front moves to the western Aleutians on
Wednesday bringing another round of rain and isolated chances for
thunderstorms.

&&

Long term forecast (days 3 through 7)...
there have been some subtle changes with the global models. The
pattern is still highly amplified for this forecast period.
However, the ridge has slowed down its progression. At the onset
of the period, Wednesday evening, the longwave ridge is hovering
over Kodiak and the Cook Inlet with a closed low over the central
Aleutians. With the ridging slowing its progression expect the
warming trend over south central to be extended possibly into
Friday as well. With widespread subsidence in place, the Anchorage
Metro area and the mat-su valleys will easily reach Max
temperatures in the 70s. Meanwhile upstream, a mature low will
bring a vast precipitation shield into the Aleutians, akpen and
portions of southwest. With the latest run of the GFS and ECMWF,
the remnants of this storm will reach the Kenai Peninsula on
Saturday.

&&



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

&&

$$

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