Area Forecast Discussion
Issued by NWS Anchorage, AK

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FXAK68 PAFC 191202

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
402 AM AKDT Tue Jun 19 2018


The upper level pattern remains largely the same as it has been
the past several days. An upper level low persists over the
eastern Bering. With the associated surface low now in a much
weakened state, precipitation directly associated with it over
Southwest Alaska has diminished in coverage and intensity to
spotty, nuisance showers. For Southcentral, little in the way of
organized precipitation remains except for an area of rain now
moving into Prince William Sound. That rain is associated with the
last of an atmospheric river of moisture moving northward out of
the Gulf into the coastal Chugach and Wrangell Mountains. The
south-to-north moving jet streak forcing the rainfall is oriented
along the Alaska/Yukon border. Thus, most of the precipitation
that isn`t purely upslope driven is focused near the jet along
eastern Prince William Sound and the Copper River Basin.
Temperatures across the area were very seasonable yesterday with
highs in the low to mid 60s across Southcentral and upper 50s to
lower 60s across Southwest Alaska.



Model agreement remains good as the pattern becomes increasingly
tranquil. The low over the Bering continues to weaken over the
next several days as it makes a loop over the eastern Bering.
Meanwhile the models agree that additional infusions of energy
into the low in the form of lows and atmospheric disturbances will
be of a weaker type for the short-term. Thus, model differences
through Thursday morning, while as usual becoming increasingly
apparent, are not cause to make major changes to the forecast. As
such, forecast confidence remains high. Generally the high
resolution NAM was used through Tuesday night followed by the GFS.


PANC...VFR conditions will continue through the TAF period. A
shower or two is possible in the area through the day. The gusty
SE Turnagain Arm winds will gradually diminish through the
morning, but will likely persist south and west of the airport
through Wednesday morning.


Moist southerly flow aloft will continue through Wednesday night
as the synoptic pattern of an upper level low over the eastern
Bering and ridging east of Southcentral Alaska remains in place.
Some gap winds will continue today as the surface gradient remains
fairly strong in the wake of Mondays low. Winds will then diminish
on Wednesday. A weak upper level system will move into the
Southcentral mainland later today into this evening increasing the
shower activity a bit. A wetter system will push into the area
Wednesday afternoon into Wednesday night, with increasing chances
of precipitation across the area, especially along the coast and
the Kenai Peninsula.


The mainland is getting into a steady state pattern, anchored by a
stacked low pressure system setting up in the eastern Bering Sea
through the end of the week. The front associated with the system
is currently lifting northward out of the Kuskokwim Delta and
Lower Kuskokwim Valley by early this morning. The next two days
will then be characterized by a weakly unstable cyclonic flow.
Expect scattered rain showers over most areas, with some lee-side
drying to the west of higher terrain. Mostly cloudy conditions and
below normal temperatures will persist with generally light
southeast winds through Thursday.


Generally light to moderate northwesterly flow will persist
through Thursday. A front associated with the low to the east will
slowly decay and linger over the eastern Bering and Pribilof
Islands through tonight, bringing rain to the area. High pressure
over the western Bering will promote fog and low stratus,
especially during the overnight hours through Thursday.


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

The long term forecast begins Thursday evening with the dominant
upper-level features being a broad, closed low over the eastern
Bering and a ridge downstream extending through the Yukon into
east-central Alaska. At the surface, this translates to a
weakening low remaining rather stationary over the eastern Bering
and a ridge over the Gulf of Alaska. A trough is situated just
south of the Brooks range, extending into the Yukon.

The broad low in the Bering and high downstream will result in a
predominant southwesterly through much of the vertical profile,
keeping clouds and showers over southern Alaska through Friday. By
late Friday though the weekend, a surface ridge builds over
southern Alaska as the low in the Bering fills in and retreats to
the west. This will result in a gradual warming trend across the
forecast area as an offshore flow develops. However, lingering
moisture, daytime heating, and added instability from a shortwave
trough traversing from the AKpen into central Alaska will still
support widespread shower activity (diminishing in areal coverage
each day) through the end of the weekend.

Models diverge with the timing, intensity, and track of a low
across the Aleutians for the weekend. Nonetheless, expect the
broad trough over the Aleutians to remain through the weekend
with clouds and rain moving across the Aleutians, reaching the
Alaska Peninsula for Monday.


PUBLIC...Flood Advisory: 125.



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