National Weather Service United States Department of Commerce


000
FXAK68 PAFC 201303
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
503 AM AKDT Wed Oct 20 2021

.ANALYSIS AND UPPER LEVELS...

An impressive 200 kt jet streak at 250 mb extends across the
central Bering but west-southwest of Pribilof Islands. East-
northeast of this feature lies an upper trough deeply anchored in
the North Pacific which wraps across the Southwest Coast through
a Siberian low. A strong upper high across Southcentral will
condense clouds and rain especially more inland for Southcentral
today. Shortwaves near the upper trough axis will bring light
mixed rain/snow further inland of the lower Kuskokwim Valley and
Kuskokwim Delta, and intermittent rain over Southwest Coast this
morning including areas over the western Gulf and around Prince
William Sound.

&&

.MODEL DISCUSSION...

Models are in accord for the next North Pacific low advancing
through the Gulf today, but not so much for the second low
entering the southeastern Gulf Friday morning. For the highly
anticipated Northwest Pacific low arriving this afternoon near the
western Aleutians, solutions are on track guiding the low toward
Pribilof Islands on Thursday until GFS splits from the rest of the
models Thursday afternoon. GFS will be a bit relaxed than the
other models, trailing behind the rest as it crosses the Alaska
Peninsula Friday afternoon. A second Northwest Pacific low could
potentially reach the central Aleutians as early as Sunday
morning, creating uncertainty for the Aleutians forecast and
whether this next system will draw excessive tropical moisture
across the Aleutian Chain and Southwest Coast. The placement of
the lows and frontal axis remains a challenge including the
arrival time of the aforementioned lows makes a huge difference
in the forecast for the next several days. For this reason, the
forecast confidence is low after Thursday afternoon.

&&

.AVIATION...

PANC...VFR conditions will continue through at least this
afternoon. Cloud ceilings are expected to lower starting 03Z
tonight through 18Z Thu. Also, intermittent rain and light and
variable winds could continue through the forecast period.

&&
.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...

Southcentral remains in an active pattern for the next few days
with the upper level longwave trough southwest of the area and
south to southeast flow aloft ahead of this trough. This set up is
allowing numerous upper level waves to travel through the area,
one of which is over the Kenai Peninsula, Anchorage and the
Susitna Valley early this morning. This wave will move
northwestward today with just a brief break before the next
system. This next system is a low moving along the east Gulf coast
which will move over Prince William Sound tonight and then
rapidly dissipate at the surface. Even so, the moisture and upper
level wave will move over northern Cook Inlet as well as the
Chugach and Talkeetna Mountains tonight. Exactly where the low and
remnants will move is still a little bit of a question. Anchorage
will be near the western edge, but looks likely to get
precipitation. The Precipitation type (P-type) was a big challenge
for this forecast package. Temperatures are borderline for rain
or snow over Anchorage with rain as the likely P-type on the
western Kenai Peninsula and snow in the Susitna Valley by the time
one reaches Talkeetna. The fact that is has been able to rain
throughout the night tonight with temperatures well into the 40s
today and warm advection with this incoming system bodes well for
rain to be the dominant P-type. However, that longwave trough
southwest of the region today will also be moving up Cook Inlet
and over Anchorage into the Susitna Valley overnight. There is
some cold air aloft associated with this trough which could also
influence P-type. Therefore went with a rain-snow mix in Anchorage
and Matanuska Valley with very little snow accumulation, if any,
at lower elevations.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...

Broad upper level trough resides within the longwave pattern
across Southwest today. Ridging over the Bering moves eastward,
breaking the longwave trough pattern over Southwest Alaska by
tonight. Weak onshore flow may promote the development of some
areas of patchy fog along the Bristol Bay coast, including King
Salmon and Dillingham, during the overnight hours tonight. A
second system out of the northwest Pacific enters the western
Bering tonight, whose front reaches the Southwest Coast tomorrow
afternoon. Winds transition to southeasterly across the Mainland
and become increasingly gusty through evening and overnight hours
Thursday night, especially along the coast. The bulk of the
associated precipitation mostly gets caught up along the upslope
regions of the mountain ranges and along the Alaska Peninsula.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...

Strongly amplified pattern over the Bering includes a longwave
trough pattern over Southwest Alaska and a building ridge in the
western Bering. The gradient existing over the central Bering
keeps northwesterly gale force winds in tact through the morning
hours today, with winds briefly diminishing through the evening
before the next system enters the western Bering. This system
continues strengthening as it moves towards the central Bering
where it bottoms out. This supports widespread storm force wind,
with a high chance of hurricane force winds, along the back side
of the low where the arctic air has been pulled southward.
Additionally, gale force winds will occupy most of the rest of the
Bering tomorrow through Friday afternoon, diminishing to small
craft once the low crosses the Alaska Peninsula. Anticipate heavy
precipitation to fall along the frontal boundary, most
significantly along the Aleutian Chain and along the northern edge
of the low.

&&

.MARINE (Days 3 through 5/Friday through Sunday)...

Bering/Aleutians

Forecast confidence remains moderate during the 3-5 day period as
a strong low pressure system moves through the central and eastern
Bering Sea. Guidance shows minor differences in the placement of
this low. There is better agreement on the intensity of this low
which is likely to produce a very widespread area of gale force
winds with an area of storm force winds southwest of the low
center. This low will weaken on Saturday as it crosses into the
Gulf of Alaska, though strong northwesterly gap winds are still
expected along the eastern Aleutian Chain and western Alaska
Peninsula. Large long period northwesterly swell will accompany
these storm force winds along the north side of the eastern
Aleutians Saturday morning. This swell will then gradually abate
Saturday afternoon and evening.

Gulf of Alaska

Forecast confidence remains low to moderate on Friday as an area
of low pressure moves northwestward along the northern Gulf.
Guidance shows differences in solutions with the placement and
intensity of this low. However, it is likely there will be areas
of gale force winds accompanying this low along the northern Gulf
on Friday. Confidence still remains low on Saturday and Sunday as
guidance shows significant differences in a series of compact lows
moving northwestward in the Gulf.

&&

.LONG TERM FORECAST (Days 4 through 7/Saturday through Tuesday)...

A cool and wet pattern will gradually transition to cool and drier
across Southcentral during the extended period. Upper level
troughing will continue to extend southeastward from the northern
Bering Sea into the Gulf of Alaska. The trough-axis will remain
southwest of the Kenai Peninsula which will allow for
southeasterly onshore flow aloft across Southcentral, thus
increasing our chances of clouds and precipitation. With respect
to precipitation type, the chance for snow will increase with
elevation. The pattern across Southcentral then becomes drier
while still remaining cool as ensemble guidance shows the surface
low in the Gulf moving eastward on Monday into Tuesday. This will
result in a north-northeasterly offshore flow pattern near the
surface and will allow for a drier airmass to move into the
region.

Southwest will be colder than Southcentral as this region will be
closer to the center of the trough-axis. With respect to the
chance for precipitation, Southwest will follow the similar trend
as Southcentral with the airmass becoming drier later in the
extended period.

The Bering/Aleutians will mainly be cloudy, cool and have
widespread shower activity as broad upper-level troughing will
extend across the region for the majority of the extended period.
However, upper-level ridging will begin to move into the far
western Bering/Aleutians on Monday and Tuesday. This will allow
for an increase in temperature and a decrease in cloud cover
during that timeframe. Closer to the surface, strong low pressure
will move from Bristol Bay into the Gulf of Alaska Saturday
morning. This will result in strong northwesterly gap winds
south of the eastern Aleutian Chain. These gap winds will then
ease Saturday night into Sunday. A second surface low will move
along the Aleutian Chain Sunday through Tuesday and will bring
widespread gale force winds and rain.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Storm-force Warning: 170, 172-176, 412-414.
Gale Warning: 125, 150, 155, 160, 165, 171, 177-181,
185, 411.
FIRE WEATHER...NONE.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...CB
SOUTHCENTRAL ALASKA...EZ
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...KM
MARINE/LONG TERM...ED


000
FXAK69 PAFG 202150
AFDAFG

Northern Alaska Forecast Discussion
National Weather Service Fairbanks AK
150 PM AKDT Wed Oct 20 2021

.SYNOPSIS...
A weak low near St Lawrence Island and associated front that is
stalled over the West Coast and Western Interior will continue to
weaken and move north through the Bering Strait this evening and
dissipate on Thursday. The associated rain and snow showers in
these areas will diminish. Partly cloudy skies this afternoon over
much of the Central and Eastern Interior will become mostly
cloudy with flurries or light snow moving tonight. Winds and light
snow continue to diminish along the arctic Coast with low ceilings
and fog and light winds expected tonight and tomorrow.

&&

.DISCUSSION...

Aloft...A deep and sharp longwave trough extends from the Pole
southward along the dateline to the Bering Strait and then
southeastward to near the Washington coast. A large blocking ridge
is centered to the east of Alaska from near Great Slave Lake
southward into the Prairie Providence`s of Canada. Several strong
shortwaves will push south and east through the trough over the
next several days as the upper level ridge remains in place. A
weak shortwave will push north along the back of the ridge over
southern Alaska and over the Alaska Range tomorrow and will be the
focus for strong winds through the Alaska Range and light snow
and flurries over the Western Interior. A 498 dm upper level low
with favorable upper level dynamics over the Southern Bering Sea
on Friday will provide an ideal environment for rapid deepening of
a surface low pressure over the Southern Bering Sea late Thursday
and on Friday. Strong winds aloft moving over the Alaska Range
will produce a mountain wave and will produce strong and gusty
winds along and near the northern foothills of the Alaska Range on
Thursday.

Surface...A 983 mb low near St Lawrence Island will continue to
weaken and move north through the Bering Strait this evening and
dissipate on Thursday. A stalled front associated with the low
over the Western Interior and West Coast will continue to weaken
tonight and Thursday and the associated rain and snow showers
over these areas will diminish. A weak trough over the Arctic
Coast will continue to weaken and push to the west and will be
absorbed by the low moving north through the Bering Strait on
Thursday. Light snow and gusty easterly winds along the coast will
diminish this evening. A 980 mb low in the northern Gulf of
Alaska will move northwest and weaken rapidly over the Western
Interior on thursday and will produce mostly cloudy skies and a
chance of light snow over much of the Western Interior. A 980 mb
low currently over the Western Aleutians will deepen rapidly
tonight to around 960 mb over the Southern Bering Sea and deepen
even further to around 945 mb as it approaches the Pribilof
Island on Friday. The low will push southeast into the
northwestern Gulf of Alaska Friday night and Saturday as a 960 mb
low. Gusty northerly winds will develop through the Bering Strait
and northern Bering Sea behind the low and will likely produce
elevate water levels in the 1 to 2 feet range above normal high
tide line along the north shore of St Lawrence Island on Friday
night and Saturday.

Arctic Coast and Brooks Range...Gusty east winds and light snow
that diminished this morning to the east of Utqiagvik has been
replaced by light winds, low ceilings, flurries and fog this
afternoon. Expect a similar transition this evening to the west
of Utqiagvik with winds decreasing, low ceilings, fog and flurries
to continue into tomorrow. Winds in the Brooks Range mainly south
at 5 to 15 mph. Cloudy conditions will also prevail with a chance
of snow or some flurries, mainly in the plains and on the coast,
but not significant accumulations are expected. Highs generally in
the 20s with lows in the teens.

West Coast and Western Interior...Decaying low remains in the area
with the decaying from over the Seward Peninsula and southwest
mainland. The lingering showers this evening will diminish as the
low moves north across the Bering Strait and into the Chukchi Sea.
Weak high pressure will build in over the area Thursday. A strong
low will move to the Pribilofs Thursday evning and Friday and
will spread showers to the Lower Yukon Delta by Thursday evening.
Gusty northerly winds will develop over the Western Capes and
over the Bering Sea south of the Bering Strait Thursday afternoon
and continue into Saturday on the back side of the deep low moving
into the Pribilof Islands Friday and into the northwestern Gulf
of Alaska on Saturday. variable to around 10 mph today and
tonight. High temperatures in the 30s and lower 40s, while lows
will be in the teens and 20s.

Central and Eastern Interior...Increasing clouds tonight with
flurries or light snow developing especially to the north and west
of Fairbanks. Strong winds will develop along and near the
northern foothills of the Alaska Range as a mountain wave develops
in response to strong winds aloft crossing the Alaska Range from
the south. A Wind Advisory has been issued for the Eastern Alaska
Range where wind gusts to 55 mph are expected. Winds are expected
to remain light in the Central and Eastern Interior except around
Delta Junction where southeast winds to 20 mph are expected. Lows
in the teens and 20s above with highs in the mid 20s to mid 30s.

Coastal Hazard Potential Days 3 and 4...Elevated surf on the
north side of St Lawrence Island Friday and Saturday as a strong
north winds develop in the area. Wave runup of up to 2 feet above
the normal high tide line is expected.

&&

.AFG WATCHES/WARNINGS/ADVISORIES...
Wind Advisory for AKZ226.

Heavy Freezing Spray Warning for PKZ230-PKZ235-PKZ500.

Small Craft Advisory for PKZ220-PKZ235.
&&

$$

CCC OCT 21


000
FXAK67 PAJK 202219
AFDAJK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
219 PM AKDT Wed Oct 20 2021

SHORT TERM.../Wednesday evening through Friday as of 3PM/...A
weakening low pressure migrates NW from the central Gulf Wednesday
evening, resulting in a few shower bands moving quickly across the
panhandle. A second low-pressure system is located to our south
and will move N/NW along the panhandle through the short term and
is discussed in the long term as well. This system is stronger and
will bring gusty winds and more precipitation.

Dimishing showers through Wednesday night as the next system moves
up from the south. Precipitation from this second system will
reach the central panhandle by Thursday evening, leaving a slight
chance of partly cloudy skies to start the day on Thursday.

A High Wind Watch is in effect from Thursday night to Friday
morning for Metlakatla, Ketchikan, Hydaburg, Craig, and
surrounding areas. Timing and track of the low is still somewhat
uncertain, especially with how close to the coast the low center
actually comes. However there is some confidence that at least a
brief period of gusts to around 60 mph are possible as the low
passes early Friday morning. Elsewhere, breezy conditions are
expected across the panhandle as the low moves NW. Storm force
winds of up to 52 kt are possible near Dixon Entrance late
Thursday.

Minor adjustments were made to temperatures, which remains
slightly above normal for the short term forecast. PoP/Sky/QPF was
slightly nudged to the NAM, but below average confidence on timing
of each band of precipitation from the multiple lows passing
through our region.

LONG TERM.../Friday through Wednesday/...The primary concern in
the earlier part of the long term forecast continues to be a
system which is progged to move N through the eastern gulf early
Friday. A Special Weather Statement remains in effect, although at
this time no other products have been issued.

The intensity of the anticipated shortwave continues to remain
less than certain. While operational GFS is persistent at
indicating 50 kt plus wind in Dixon Entrance, the southeast gulf,
and portions of the southern Panhandle; ensembles, while agreeing
geographically, are much less inclined to indicate such a deep
feature. Yet even so, some special credence needs to given to
operational runs, not least because of the much larger data sets
involved in their initial conditions. Consequently, chose to
further strengthen the winds associated with the system. While
keeping winds below storm force, widespread gales are anticipated
in the outer coastal waters and in the southern inner channels.
Winds were further increased as well in the southern panhandle,
with strong wind conditions expected across parts of the S
panhandle and outer gulf coast. Confidence in strength at this
stage prevents us from posting any kind of watch, so the special
weather statement suffices for now.

Towards Juneau, with a critical level in place, we could see some
stronger gusts set up in Downtown Juneau and Douglas Thursday
night/Friday ahead of any precip bands. As such a strong system
passes northwest along the coast, a safe bet is to swing winds
through the Inner Channels at least briefly from north to south
through Friday night.

Yet another storm appears behind the first, though considerable
differences in timing and strength continue, but it appears likely
that it will follow a similar path to the previous wave. Behind
this system, a break may be possible Sunday into Monday before the
active weather looks likely to resume.

Little changes were made across most other fields. The emerging
pattern favors wetter conditions across the south with somewhat
drier regions across the north as low level offshore winds add a
drying element to the atmosphere. Clearly any heavy rain trapped
in the North Pacific jet should remain to our south. With mean
southerly flow within the mid-range period, we expect temperatures
to be seasonal to above normal.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...High Wind Watch from late Thursday night through Friday
afternoon for AKZ027-028.

MARINE...Gale Warning for PKZ022-041>043-051-052-310. Small Craft
Advisory for PKZ021-033-053.

&&

$$

KRT/GFS

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