Scientific Forecaster Discussion
fxak68 pafc 230033
Southcentral and southwest Alaska forecast discussion
National Weather Service Anchorage Alaska
433 PM akdt Thu Aug 22 2019
Analysis and upper levels...
An occluding surface low over the southern Gulf is moving slowly
eastward, as it is north of the upper jet. Its associated front
however, is being carried rapidly eastward under a strong westerly
jet. This has caused the showers/rain along the northern portion
of the front to stall over the north Gulf as the flow aloft
becomes more east/northeasterly. Rain over Kodiak Island
becomes more sporadic this afternoon as the whole complex heads
eastward. Smoke continues to be fairly widespread across the
eastern Kenai Peninsula with the Swan Lake fire and also over the
mid Susitna Valley with fires in the area. Lower clouds over the
northern Susitna Valley are burning off from the south. An upper
trough and associated surface front are heading south across the
Delta and Kuskokwim valley. Mostly clouds have been observed
along this band with little in the way of precipitation. The best
area will likely be along the upslope portions of the Alaska
Range. Broad north to northeast flow continues over the Bering
Sea. A weakening low south of the western Aleutians continued
clouds and a little light rain along the western and central
The models are in decent agreement through Saturday in regards to
the synoptic features. Significant differences occur Saturday
night and Sunday with the timing of a upper low moving over the
Gulf. This translates into fairly significant positioning and
timing issues with the associated surface reflection over the
panc...southeast winds across the Airport complex will diminish
late tonight. Smoke from the Forest fires will likely bring MVFR
conditions to the Airport Friday morning. There will likely be
some improvement during the afternoon hours as winds become
Short term forecast southcentral Alaska (days 1 through 3)...
The low southeast of Kodiak will continue to push east across the Gulf
of Alaska tonight. A triple point low has developed with this
system and this storm will dive southeastward. The lion's share of
the rain will remain over the Gulf of Alaska with the possibility
of wraparound moisture from Cordova to portions of the Prince
William Sound. The radar at Middleton Island (paih) has been very
active today and expect more activity tonight and tomorrow over
the water. Anchorage will be shadowed by the mountains for this
event. A stray shower may make it over the Kenai Mountains to the
western Kenai, but most areas will remain dry. An upper level
trough continues to drop down from the Arctic and will move south
of both the Brooks and the Alaska ranges. Cold air over warm air
is inherently unstable and showers are expected to develop. The
antecedent airmass has been pretty dry, so some areas may just get
virga but other areas may actually receive measurable
precipitation at the surface. Upper level flow will become
northerly this forecast period.
Fire weather (southcentral)...
Susitna Valley...light southerly winds are generally expected
through this afternoon and evening shifting light northerly
Friday morning. Northerly flow will increase and become gusty
from Talkeetna north and over the western Susitna Valley late
Friday and into Saturday with the passage of an upper trough.
Winds in these areas will slacken again Saturday afternoon. Upper
wind support and temp advection are lacking, so would not
expected to see a repeat of last weekends wind event.
Precipitation will be lacking, but upper trough on Friday and
Saturday will bring a few showers with low probabilities of
wetting rains. There is an outside chance of a thunderstorm or two
along the Talkeetna Mountains Friday afternoon, but stability
indices and lack of moisture would keep probabilities low. 700 mb
steering flow is fairly light, so if something does develop along
the mountains they would not move much.
easterly bl winds this evening will shift to the west after
midnight and becoming northwesterly Friday. Although winds will
remain light over the Swan Lake fire area, gusty outflow winds are
expected over the southern and eastern Kenai Peninsula. Upper
troughs dropping down from the north Friday and Saturday will
likely favor showers over the Kenai Mountains east of the fire
area with little chance of wetting rains to the fire area.
Short term forecast southwest Alaska (days 1 and 2)...
Showers along the mountains over the Alaska Peninsula, associated
with a weak shortwave, will diminish through this evening. The
remainder of interior southwest Alaska will will remain dry
through tomorrow afternoon when a trough drops down over the
region. This will lead to a slight chance of thunderstorms for
Friday afternoon in the Kuskokwim valley and the Bristol Bay
region. The instability has moved to the south a little faster
compared to yesterday's forecast. Heading into the weekend, the
southwest Mainland can expect to cool down a few degrees and see
Short term forecast Bering Sea/Aleutians (days 1 and 2)...
As the stacked low continues to move into the Gulf, winds along
the akpen will start to weaken overnight. Northerly flow will be
the dominant feature across the Bering Sea starting Friday
through the weekend, with increased winds through the channeled
terrain along the eastern Aleutians and Bering. Small Craft
Advisory winds are forecasted out of bays and passes extending
from Dutch Harbor to Sand Point starting Friday night through
Marine (days 3 through 5: Sunday through tuesday)...
Westerly flow will persist across the Gulf through the long term
period. There is increasing confidence that a low will develop
south of the Alaska Peninsula Sunday and track eastward into the
Gulf of Alaska Monday with small craft winds likely. A second,
potentially stronger low forms in the North Pacific and tracks
northward into the Gulf late Tuesday. Currently, there is low
confidence in the track and strength of this second low. Meanwhile
in the Bering, a ridge of high pressure remains in place through
Tuesday ahead of an incoming low entering the western Bering by
Long term forecast (days 4 through 7: Monday through
The general long-term pattern consists of an upper level longwave
trough draped over the state with an upper level ridge building
over the Bering. An unsettled weather pattern is expected for
the southern Mainland with cloudy skies and showery conditions
in store for early next week. A new feature of note is a North
Pacific low that approaches the Gulf of Alaska as early as
Tuesday, though model solutions disagree on the position and track
of this low through the end of the week. One main steering factor
for the low's track will be a ridge building over the alcan
public...dense smoke advisory: 121.
Flood advisory: 121 125.
Marine...gale warning: 351 352.