Area Forecast Discussion
Issued by NWS Anchorage, AK

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FXAK68 PAFC 191237

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
437 AM AKDT Sat May 19 2018

The flow pattern aloft features three main features, two high
pressure centers, and a broad/complex trough sandwiched in between.
One closed high pressure over eastern Russia is blocking the jet
from amplifying in that region. The other upper ridge is centered
over western Canada, and it is stopping the jet from making any
eastward progression, bending it northward toward the Gulf of
Alaska. Between these features is the broad long-wave trough,
which at this point, is made up of five different centers, none of
them particularly dominant as far as a parent circulation is
concerned. The jet feeds into the trough, and each embedded
disturbance will be the driver of active weather in the short term
across southern Alaska.

The latest in a series of shortwaves is propagating inland early
this morning. Rain is spreading from the north Gulf coast across
the Cook Inlet region, but mainly the southern Kenai Peninsula.
Cross-barrier flow and downslope is beginning to take hold from
the northern Kenai through the Matanuska Valley. The southwest
mainland is seeing spotty showers and rain associated with the
upper trough, but nothing major. Widespread cloudiness and
moisture continue to dominate.


The complexity of interactions of each short-wave trough continue
to give guidance troubles, especially in the day three and four
timeframe. However, the general consensus even in that timeframe
is continued Gulf of Alaska storminess.


PANC...VFR conditions will persist.


The broad upper level pattern undergoes little change with a
series of waves moving north and west across the Gulf through
Monday morning. This will generally result in cloudy, cool, and
wet conditions along the coasts. Inland areas, will be largely
downsloped, so they will experience only sporadic precipitation
and some cloud breaks.

A surface front moves north across Southcentral today. Pressure
gradients will continue fairly strong through the early evening
hours. So many areas will see generally windy conditions with
strongest winds in favored gaps (Turnagain Arm, Knik River
Valley, along the Copper River). Winds in most areas will diminish
later this evening and into the overnight hours. Yet another
surface front and low head north into the Gulf Sunday and will
bring gales to coastal waters and another round of winds to
Southcentral mainland. Rain will mostly be confined to the coasts
as strong cross barrier flow will mitigate precipitation
potential inland.



The radars at Bethel and King Salmon continue to detect
precipitation in portions of Southwest. With the longwave trough
dominating the region, expect a series of shortwaves to get
ejected keeping showers in the area. Southeast to east winds will
result in slowly warming temperatures.



In a nutshell, the pattern will be persistently wet and cloudy.
The longwave pattern features a trough over the Bering and the
Aleutians. At the surface, there is a decaying low south of the
AKPEN, a low southwest of Attu with a third low east of Japan. The
low near the Western Aleutians is occluded. The models are
pinging into gale force winds associated with this mature low but
the ASCAT pass has yet to detect and confirm it. The active
pattern for the North Pacific will continue. The Bering is also
being influenced by the remnants of a storm resulting in rain and
areas of fog.


.LONG TERM FORECAST (Days 3 through 7)...
The overall progressive pattern will continue through much of
next week, as one upper low sets up over the Gulf of Alaska
through mid-week and is quickly replaced by the next upper level
low/trough tracking in from the west mid-week into next weekend.
The initial system will allow several systems to rotate into the
southern mainland through mid-week, bringing precipitation and
some gusty winds to the coastal regions of southcentral Alaska
over the weekend and into next week. However, the strong
southeasterly flow associated with these systems will favor
slightly drier conditions over the downsloped areas along the
lee-side of the Chugach range.

The low and associated front will begin to impact the western
Aleutians Monday morning and steadily track eastward through
wednesday, covering much of the Bering and Aleutians with wet and
windy conditions. The low begins to stall over the central/eastern
Bering Wednesday night, and eventually begins to track southeast
into the north Pacific. The associated front will track through
the Gulf region Thursday through Friday, bringing a repeat
scenario of wet and winds along the Gulf Coast with downsloping
conditions along the lee-side of the Chugach. The models
continue to agree that at least through much of next week, the
persistent pattern of cooler, cloudy, and unsettled weather will
remain in place.





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