Area Forecast Discussion
Issued by NWS Anchorage, AK

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142
FXAK68 PAFC 151222
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
422 AM AKDT Wed Aug 15 2018

.ANALYSIS AND UPPER LEVELS...
The longwave pattern features a deep trough covering most of
mainland Alaska and a minor ridge over the Western Aleutians. Once
the different layers of the atmosphere get dissected, its very
apparent that there are multiple weak shortwaves across
Southcentral, the interior of Alaska and over Southwest Alaska.
The most organized disturbance is west of Bethel and Kipnuk with a
trough axis extending to Sand Point. This feature has resulted in
diffluent southwest flow over the Cook Inlet and the Anchorage
Bowl.

.MODEL DISCUSSION...
Models have come into better agreement with the next storm out of
the Bering as it transitions into the Gulf of Alaska and with the
synoptic pattern over the North Pacific. As frequently the case in
Alaska, there are some minor timing issues with the distribution
of the QPF. The model consensus is more wet weather for
Southcentral Alaska, Kodiak and the AKPEN for the next 48 hrs.
Friday will be the driest day of the week for the Anchorage Metro
Area and then another organized wave of precipitation for the
weekend.

&&

.AVIATION...
PANC...VFR conditions expected. The pattern is going to remain
unsettled, expect clouds and pockets of precipitation for PANC for
the forecast period. OCNL gusty winds possible. The Kenai
Radar/PAHG has been in precipitation mode and has detected showers
near Willow and a band of precipitation over the northern Cook
Inlet at 12:20z which justified adding VCSH and a TEMPO group to
the PANC TAF.


&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3)...
Weak short-waves moving through a very flat upper level ridge
over Southcentral will work with a moist environment to produce
another cloudy day with areas of rain or showers. An upper trough
south of the Alaska Peninsula will then swing northeastward across
the Gulf tonight, pushing some of the more stable air from Prince
William Sound inland. This will likely lead to fairly low ceilings
tonight and some areas of light rain or drizzle, especially across
the Kenai Peninsula.

The best chance of seeing some sunshine looks to be Friday, as
the trough exits and a more substantial short-wave ridge builds
overhead. This will be a transitory ridge, with a major storm
system moving up from the Pacific as we head into the weekend.

.HYDROLOGY...From a climate perspective, historically August is
the wettest month of the year for Palmer and Anchorage. This
persistent wet pattern has brought some streams and rivers out of
their banks. Yetna River at Lake Creek has exceeded flood stage as
a result of recent and ongoing rainfall and minor flooding is now
occurring along the river. Stay tuned to Flood Warning information
for more.
&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3)...

A compact area of low pressure south Nunivak Island will continue
to drift southward toward Bristol Bay today. Bands of scattered
shower activity will occur mainly along the coast with this low
from the Kuskokwim Delta south through Bristol Bay, especially
during peak heating this afternoon. Interior sections of the
Southwest should remain mostly dry, though an isolated shower
can`t be ruled out. By Thursday morning, the weakening low will
drift closer to the eastern Aleutians, though instability
associated with an upper level wave may be the focus for
additional showers, particularly along the western flank of the
Alaska and Aleutians Ranges. An isolated shower or two will remain
possible Friday as the region goes under a surface col, resulting
in calm winds. A warm front moving over the Alaska Peninsula will
result in another round of locally heavy rain and gusty
southeasterly winds beginning Friday evening. This is in advance
of a strong low tapping tropical moisture moving north out of the
north Pacific. The rain and wind will move across the southwest
mainland Saturday as the front advances north.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3)...

Northerly winds on the west side of the compact low will keep
conditions breezy through the Pribilofs down to the Alaska
Peninsula through the evening hours. The low will drift south
towards the eastern Aleutians on Thursday then dissipate by
Friday morning. High pressure centered over the western Bering
will shift east remain firmly anchored over the central Bering
through Friday. Over the far western Bering, a broad front will
move across Attu and Shemya today. its parent low, located farther
west, will be shunted south and east into the North Pacific as
the high pressure over the central Bering persists. As the low
consolidates and shifts east Thursday night, rain over the
western Aleutians will dissipate. This will allow the central
Bering high to build westward through Friday. A strong low will
develop over the north Pacific on Friday. Widespread heavy rain
and east-southeasterly gales will develop over the eastern
Aleutians and Alaska Peninsula late Friday morning and continue
through Saturday.

&&

.LONG TERM FORECAST (Days 3 through 7)...
The long term beginning Friday night starts with a North Pacific
low sandwiched between two ridges. The first ridge will be over
the eastern Gulf while the other is over the central Bering. There
is some discrepancy between the models on the exact position of
the low and subsequently its front, but the general consensus is
that the front will bring rain to the Alaska Peninsula and Kodiak
Island Friday night. Through the weekend the system will slowly
track north spreading rain to the southern mainland with the
heaviest amounts along the north Gulf coast and Alaska Peninsula.

Meanwhile out west, another system will push into the Bering over
the weekend as the central Bering ridge breaks down. Early next
week the upper level low centers of the two main lows look to
merge into a broad area of low pressure over the Bering with
ridging off to the east. This setup would keep a rainy pattern
for the region into mid next week.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Flood Warning 145.
MARINE...None.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...PJS
SOUTHCENTRAL ALASKA...SEB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...TM
LONG TERM...DK



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