Area Forecast Discussion
Issued by NWS Anchorage, AK

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FXAK68 PAFC 160121

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
521 PM AKDT Thu Aug 15 2019

The upper level ridge over the Gulf of Alaska and Alaska Peninsula is
beginning to rebuild over the eastern Bering Sea today as the
upper level lows in the Arctic set up to begin the pattern shift
over the next few days. This current pattern continues to push the
moisture into the Interior of the state keeping the Southwest
mainland and Southcentral dry. There are some areas of marine
stratus along the southwest mainland coast under the stronger high
pressure and some higher clouds overrunning the ridge in the
Kuskokwim Valley and into Southwest Alaska.

The strong surface low near Attu is occluded and getting close to
becoming vertically stacked. However, the front associated with
it does advect moisture up all the way from around 30N.


Models have come into good agreement on the track of the upper
level movement of the short wave moving across Southcentral Alaska
Friday night and Saturday and remain in good agreement through
the weekend. The one item that stands out is that the NAM is
continuing to show the core of the upper level low dropping into
Southeast Alaska after tracking through the Yukon while the GFS
and ECMWF keep the main upper level low to the north. Since the
upper level trough moves though Southcentral at around the same
time with either solution, it should not be a big problem for the
forecasts in Southcentral and Southwest. That said, it is does
add a level of uncertainty overall as to if that indicates winds
could be a little higher than currently expected.


PANC...VFR conditions and light winds will persist through Friday
mid-afternoon. However, gusty northerly winds will begin to move
into the terminal area late Friday afternoon or early evening and
persist into Saturday.



A cold front is expected to move southward through the area
beginning Friday. Overall this is a dry front, although in the
Copper River Basin, showers are expected ahead of the front on
Friday. In the western portion of the area, winds will be the main
impact as this front progresses southward. Gusty winds should be
expected Friday night and Saturday for the Kenai Peninsula and
Susitna Valley, then on Sunday for the north Gulf Coast. The
marine areas should expect to see gusty outflow winds in the
northerly gap areas, creating choppy seas as well.

Temperatures will remain warm on Friday, but the air behind the
front is cooler, so expect more seasonable temperatures on
Saturday and Sunday.



Dry and windy conditions are expected for the weekend as the front
moves through Southcentral. On Friday, winds will begin to pick up
in the late afternoon in the Susitna Valley and Kenai Peninsula.
RH values should drop rather quickly with the onset of the winds
as they will mix drier air down from aloft. The one uncertainty
remains whether the warm temperatures will coincide with the
driest RH values. A Fire Weather Watch is out for these locations
indicating there is a possibility with the onset of the winds and
the drier air to match the warmest temperatures. By Saturday, the
cooler temperatures will have moved in so Red Flag conditions are
less likely. However, this remains one of Southcentral`s key fire
weather patterns so this weekend should be one to watch.



High pressure over Southwest Alaska becomes more amplified by
Friday afternoon. This will allow for a general clearing trend
with a shift to northerly, offshore flow by Saturday afternoon. A
pattern change is expected through the weekend as a cold front
moves in from the north for Sunday afternoon.



A gale force front associated with a low centered over the western
Bering continues to bring gusty southerly flow and precipitation
to the western and central Aleutians. Meanwhile, a strengthening
ridge of high pressure over the eastern Bering slowly drifts to
the west. Gale force southerly winds are expected to persist over
the western Aleutians through Saturday morning before the ridge
forces the front to retreat westward by Sunday afternoon.


.MARINE (Days 3 through 5)...

Confidence remains above average for the continuation of
northwesterly gales and waves in excess of 10 feet across the
Barren Islands through late Saturday. Small-craft northerly winds
and waves approaching 5 to 8 feet will also develop along the
north gulf coast, Prince William Sound, and parts of Cook Inlet
late Friday. Higher gusts are likely along channeled locations,
bays, and passes. Winds and waves relax on Sunday as the area of
low pressure responsible for the winds moves south along the
Alaska Peninsula. Light winds turn easterly for early next week as
another low moves across the southern Gulf.

For the Bering and Aleutians, a ridge over the eastern Bering
will produce an offshore flow across the channeled bays of the
southern AKPEN through the weekend. Low pressure south of Shemya
will produce southeasterly small-craft advisory winds through
early Sunday along a stalled front draped across the western and
central Aleutians. Easterly small-craft winds return to the
central and western Aleutians for Monday as the next low lifts
north toward the chain.


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

By the start of the weekend, an upper-level low will drop south
across the eastern half of Southcentral Alaska. As this system
drops south, the ridge that was in place over the northern Gulf
will be pushed to the west as a surface low quickly spins up
southeast of the Copper River Delta. This will induce a strong
northerly flow that will bring gusty northerly winds across
favored interior valley and gap locations, as well as coastal bays
and passes, through late Saturday. By Sunday, this feature will
track southeast along the Alaska Peninsula, allowing winds to
subside. The bulk of the precipitation will be confined to the
higher terrain of the Talkeetna Mountains and Copper River Basin
as much of the moisture associated with this system will be wrung
out as it crosses the Alaska Range. Fire weather concerns will
remain elevated through early Sunday as the combination of drier
air and gusty winds will push relative humidity values down around
25 to 35%, especially for the Kenai Peninsula, Susitna Valley and
Copper River Basin.

The northerly cyclonic flow over the state will continue through
early next week with a series of weak shortwaves dropping south,
helping to increase the potential for clouds and isolated to
scattered showers over the higher terrain. By midweek, a bigger
shift in the weather may be in store as a low moving east along
the Pacific side of the Aleutians early next week could sweep a
front into the western Gulf. This would increase the potential for
a shift to an onshore flow with increasing chances for rain and
cooler temperatures for Southcentral.

Farther west, a ridge over the eastern Bering will keep conditions
rather quiet over Southwest Alaska and the eastern Aleutians
through the weekend as a stalled frontal boundary allows southerly
winds and precipitation to persist across the central and western
Aleutians. The ridge will then lift northwest Sunday allowing a
shortwave to bring a slight chance of showers to portions of the
Southwest on Tuesday. In addition to this, a north Pacific low
will begin to move north toward the Aleutian Chain. As it does,
this system will sweep a front over the eastern Aleutians, with
precipitation and southeasterly winds reaching the AKPEN and
Kodiak Island midweek.


MARINE...Gales 130 131 175-177 411 413.
FIRE WEATHER...Red Flag Watch 121 125 145.



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