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Alaska Area Forecast Discussions


000
FXAK69 PAFG 261022
AFDAFG

Northern Alaska Forecast Discussion
National Weather Service Fairbanks AK
222 AM AKDT Tue Oct 26 2021

.SYNOPSIS...
The storm track remains well to the south of the Mainland, which
is keeping a weak pressure gradient in place. A front which
brought snow to the Interior and the North Slope has shifted
north of the Arctic Coast this morning. A closed arctic low
remains in place over the NW Arctic Borough, keeping snow showers
and blustery NW winds in place. Over the Interior, extensive
stratus and flurries have been left behind the departing front.

&&

.DISCUSSION...

Upper Levels and Analysis...
A series of lows tracks across the NE Pacific in conjunction with
the polar jet. Upper troughing dominates the Mainland, with the
main center over the NW Arctic Borough, with a 500 hpa height of
approximately 504 dam. A shortwave trough is seen lifting
northward across the Arctic Coast, with the associated front
moving offshore. Extensive stratus is occupying the Interior with
a very weak pressure gradient in place. The surface low over the
NW Arctic is the only surface feature of interest, which is
analyzed at approximately 987 mb near Point Hope. ASCAT winds show
this low to be at gale strength on the western periphery of the
low.

Model Discussion...
The numerical weather models are in very good agreement with the
large scale pattern, but are in much less agreement with the
details regarding several low amplitude waves of energy lifting
north across the AK Range from the Gulf of AK for the next couple
days. The overall consensus is for a surface low to form over the
Yukon Flats Tuesday night and Wednesday then shift north, bringing
areas of light snowfall. For now will continue to favor a blend of
models to average out the inconsistencies and to depict widespread
light snow chances through Wednesday. Out west, a blend of models
was favored to depict the low over the Chukchi Sea as the models
are not in good agreement with the exact placement of this low
after tonight given the cold core nature of this feature.

Central and Eastern Interior...
Extensive low clouds, fog, and perhaps some flurries will persist
today, with light snow developing tonight as a subtle disturbance
aloft shifts north across the Alaska Range and from the Yukon.
Snow accumulations by Wednesday night, after the low exits north
of the Brooks Range, will be around an inch or less most places,
with 1-2" for the AK Range and the southern Brooks Range. The low
exits for Thursday with partially clearing skies, which will
result in falling temps at night and during the day.

West Coast and Western Interior...
The surface low is now pretty much parked over the Chukchi Sea
with wraparound northwest winds impacting the coast. This low will
continue to spin in place bringing coastal snow showers and
blustery NW winds early today before diminishing briefly tonight.
A separate low over the N Bering Sea will shift east into the YK
Delta bringing snow showers chances and gusty northeasterly
offshore winds Wednesday. The low over the Chukchi Sea will
continue to bring snow showers and periodic NW winds into the 30
mph range before weakening through Thursday. For the Interior,
pretty quiet weather with low stratus and periodic fog, especially
near the Yukon River.

North Slope and Brooks Range...
A few lingering snow showers end this morning as the associated
weakening front moves offshore. More light snow chances move into
the Brooks Range and North Slope on Wednesday with very light snow
accumulations possible. Temps gradually cooling with weakening
gradients after today. Expect periods of dense fog to accompany
the lighter winds.

Extended Forecast Days 4-7...
The extended forecast still looks quite active for the weekend as
Friday starts out under the influence of the arctic high and
mostly quiet weather. The flow amplifies rapidly on Friday night
as a deep Pacific low, the former remnants of a tropical system,
move into the NE Pacific and shift inland, binging the threat for
heavy snowfall over the West-Central Interior and strong chinook
flow across the Alaska Range into the Eastern Interior. The
amplified southerly flow pattern looks to continue into next
week, although model uncertainty after Sunday is very high. Stay
tuned...

Coastal Hazard Potential Days 3 and 4...None.

&&

.AFG WATCHES/WARNINGS/ADVISORIES...
Heavy Freezing Spray Warning for PKZ235-PKZ240-PKZ245-PKZ500.

Small Craft Advisory for PKZ220.
&&

$$

AHSENMACHER OCT 21


000
FXAK68 PAFC 260100
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
500 PM AKDT Mon Oct 25 2021

.ANALYSIS AND UPPER LEVELS...
The 500 mb pattern has an upper level low in the Chukchi Sea with
another, weaker low, over the Northern Gulf coast this afternoon.
This is keeping southern mainland Alaska under light upper level
flow under the trough connecting these lows. A surface low is just
a little west of Middleton Island and pushing some rain and snow
onshore along the north Gulf coast. The larger and stronger
surface low is south of Kodiak Island and is the source of the
gusty north-to-northwest winds along the Alaska Peninsula and
eastern Aleutians. The 250 mb jet stream is running west-to-east
to the south of this low and can be seen well on satellite.

&&

.MODEL DISCUSSION...
Models are in overall good synoptic agreement through the week.
There is still a bit of uncertainty as to the way a low in the
northeastern Bering Sea on Tuesday night will progress
southeastward, but this is likely to be of little overall
significance. The main model item is the way the ridge over the
west coast of North America amplifies in conjunction with a low
moving just south of the Aleutians late this week. This overall
pattern is a rather high-confidence one in that the models are
likely resolving it correctly. However, there are important
details that differ between the models that will impact the
sensible weather we will be looking at as this system develops.
More on this in the long term section of the discussion.

&&

.AVIATION...
PANC...VFR conditions and light winds will persist.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3:
Tonight through Thursday)...

Generally quiet conditions will prevail across Southcentral for
the beginning of the short term period. Light showers occurring
in Prince William Sound, along the eastern Kenai Peninsula, and
eastern Kodiak Island will persist through tonight and then
gradually clear out in association with a broad area of low
pressure lingering in the Gulf. At inland locations, little
precipitation is expected with only weak shortwaves cycling
through the region. A stronger low pressure system south of Kodiak
Island this evening will track across the southern edge of the
Gulf through tomorrow, inducing a pressure gradient that will
drive gusty gap winds out of the typical areas along the coast. In
concert with the North Pacific low, a ridge over the eastern
Bering and Southwest Alaska will draw colder Arctic air across the
Aleutian and Alaska Ranges tomorrow and Wednesday. Cold air
advection will help to bolster gap winds and lead to a cooling
trend across Southcentral over the next several days, with highs
in the low-to-mid 30s in the inland lower elevations by Thursday
and lows in the 20s in the Anchorage Bowl and along coastal
locations Wednesday night. The next round of active weather will
arrive with a front pushing from the North Pacific over Kodiak
Island Wednesday night. While timing is still somewhat uncertain,
gusty winds and rain are expected to push toward the north Gulf
coast through Thursday.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3...Tonight
through Thu afternoon)...

Mostly dry conditions are expected across much of Southwest
through Tuesday afternoon. An upper level shortwave trough is
expected to move from the Kuskokwim Delta Coast this evening to
the western Alaska Range south to Kodiak Island by Tuesday night.
Only areas along the immediate Kuskokwim Delta Coast are expected
to see any precipitation as this shortwave trough passes through.
Expect flurries/light snow showers for Nunivak Island and areas
such as Hooper Bay, Chevak, Toksook Bay this evening through the
overnight hours with little to no accumulation. As this shortwave
trough moves over the Kuskokwim/Kilbuck Mountains Tuesday morning,
expect breezy conditions for much of the day Tuesday especially
for Iliamna and the Kamishak Gap area. This will be the result of
cold air advection combined with the upper level support Tuesday
causing the expected breezy conditions. Winds may gusts upwards of
30 mph around Iliamna. Also, expect gusts up to 50 kts out of the
bays and passes south of the Alaska Peninsula tonight and Tuesday.

Next, onto the bigger story, a low pressure system is expected to
move across the northern Bering Sea Tuesday reaching the Southwest
Coast by Tuesday night. This low`s associated front is then
expected to affect much of Southwest, especially coastal locations
through Wednesday and into Thursday. Right now it appears to be
a widespread light snowfall with any banding not expected to
remain in one place at this time. However, uncertainty is still
the name of the game with this system as some guidance hints at a
a band setting up shop somewhere between Dillingham to Koliganek
and New Stuyahok south and east to near Iliamna and near or north
of King Salmon. The other is also true that this band sets up
right over Dillingham or King Salmon. As of now, went with a
general 1 to as much as 4 inches in any one location for this
event, though, if a band remains in place somewhere for any
prolonged period of time in excess of 6 inches could be possible.
Therefore, stay tuned for the latest forecast updates as we
continue to hone in on this system. It also looks like it will be
cold enough to support all snow with any mixing issues either
right on the immediate coastline or even a little further off the
coast over the water.

&&

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

Northwesterly flow continues across the east-central and eastern
Bering through this evening and into the overnight hours. This
includes areas such as the Eastern Aleutians and the Pribilofs. An
upper level shortwave is also moving southward embedded in the
upper level flow that is bringing snow showers and a colder air
mass as well to the aforementioned areas this evening through the
overnight hours.

Next, a tightly compact system is expected to move across the
northern and eastern Bering Tuesday through Wednesday with high
end gale force winds and storm force gusts for these areas. The
corridor of strongest winds are expected on the southwest to west
side of the system Tuesday evening into Wednesday morning. There
may also be an area of storm force sustained winds but there was
not enough confidence to place into the forecast this package.
Stay tuned in case this is updated in subsequent updates. This
system is expected to bring a rain/snow mix to the Pribilofs
Tuesday into Wednesday with the best chance for snow Wednesday
when the colder air moves in on the back side.

Another low pressure system is expected to move across the Western
and Central Aleutians Wednesday afternoon through Thursday evening
with rain and high end gale force winds. The storm force winds are
currently expected to remain south of the coastal waters marine
area.

&&

.MARINE (Days 3 through 5: Thursday through Saturday)...
The main storm of concern for late this week will be one that
tracks jut south of the Aleutians and brings Gale and probably
Storms force winds to the Aleutians Thursday into Friday. This
low will then elongate along a north-to-south line from Kodiak
Island Southward which will likely bring storm force winds across
the Gulf of Alaska Friday night into Saturday with Gales and
possibly a few storms over Bristol Bay and the Alaska Peninsula at
that time. This overall pattern is one that is likely to develop
as described so the main uncertainty will be the details in where
and when the strongest winds and highest seas will be.

&&

.LONG TERM FORECAST (Days 4 through 7: Friday through Monday)...
Friday will be a day where the pattern starts to transition into
an active and stormy one for the forecast area. Southern Mainland
Alaska will start off under a cold upper level trough with a few
shortwaves overhead and then transition as a major storm which
will have just moves south of the Aleutians elongates over Kodiak
Island and southward. This will usher in much warmer and wetter
air to southcentral Alaska by Friday night (during the day Friday
for Kodiak). Strong winds will encompass the entire Gulf of
Alaska area and push inland some. The main impacts will be the
potential for heavy and prolonged rainfall from anywhere from
Kodiak eastward to Cordova (including the Seward area) in this
atmospheric river event. There remains a bit of uncertainty as to
where the heaviest rain will occur and for how long. This is one
of the main forecast questions that will need to be addressed
through the remainder of the week. High winds are possible for
Turnagain Arm depending on the exact track of the low.

Southwest Alaska, Alaska Peninsula, and the eastern Bering Sea
will be in the colder, drier northwest flow and see windy
conditions for Friday into Sunday. By Saturday night, the next
strong low will move to the western Aleutians and then encompass
most of the Bering Sea region for Sunday into Monday.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gale Warning 130-132 138 150 155 165 170 172-177 185
412 413.
FIRE WEATHER...NONE.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...EZ
SOUTHCENTRAL ALASKA...CQ
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...MV
MARINE/LONG TERM...EZ


000
FXAK67 PAJK 252252
AFDAJK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
252 PM AKDT Mon Oct 25 2021

.SHORT TERM.../Through Wednesday/ The short term starts off
relatively quiet with mid to high level clouds streaming into the
Panhandle due to weak mid level disturbances offshore. Increased
cloud cover today has kept temperatures on the chilly side this
afternoon with highs struggling to reach 40 across the northern
Panhandle. Very light and isolated showers have been reported
across the region already; therefore increased PoPs to include
isolated wording today and this evening. With dry air in place at
the surface, would not be surprised to see a few snowflakes or
mixed precip at the onset of any shower, especially along and
north of the Icy Strait corridor.

The next weather maker arrives late tonight as a weak low in the
Southern gulf moves into the SE gulf. Southerly mid and upper
flow ahead of the system will continue pump in moisture and clouds
across the entire region. Showers increase overnight tonight
across higher terrain and the Southern Panhandle then slowly
spread northward through Tuesday morning. Since the low is moving
in from the south, lower level offshore flow on the north side
will dry out the boundary layer and keep QPF pretty light across
the north. As the low slowly moves northward toward the NE gulf
coast Wednesday, shower activity and rainfall rates will increase
from south to north.

Winds remain relatively light tonight across the Inner Channels.
As the next low pushes closer to the Panhandle, expect winds to
increase to small craft conditions across the SE Gulf and
Southern Inner Channels by Tuesday afternoon. As the low pushes
northward on Wednesday, the northerly gradient already in place
across much of the region will flip to the south. Winds will
increase across the Inner Channels from south to north on
Wednesday as the gradient becomes southerly. May need to increase
winds in the Central and Northern Inner Channels Wednesday
afternoon as a quick gradient flip like this usually leads to
stronger winds than what guidance advertises.

Confidence remains average in the short term forecast. There is
some forecast uncertainty in the northward extent of the
precipitation tonight and tomorrow and whether it could start as a
rain/snow mix in Upper Lynn Canal.

.LONG TERM.../ Wednesday through Monday as of 10 pm Sunday / The
long term forecast starts with rain being the predominant area of
focus, as a decaying low in the gulf slowly pushes N. This low
will bring waves of precipitation across the area through Thursday
and Friday. Although no significant flooding concerns are
expected at this time there is the potential that some areas in
the N Panhandle and Icy Strait Corridor could see some snow mixed
in late Thursday night. However, this is a low confidence
forecast. While operational guidance does show that temperatures
could be cool enough for some of these areas to see snow flakes,
MOS Guidance is indicating warmer temperatures overnight. This is
likely symptomatic of the issues over the strength of anticipated
S flow during this time period. Given the marginal 850 mb
temperatures, it would not take much to turn the chance of some
snow flakes falling into nothing more than some additional
rainfall. For the time being, have indicated the possibility of
some areas seeing a mix, though do suspect that the Haines and
Klondike Highways will see significantly better chances for
snowfall.

Friday will most likely see another wave enter the area. While
there are indications that a final wave may try to enter SE AK
over the weekend, advancing ahead of a new system taking shape in
the W Gulf, do not think it will be able to overcome increasing
offshore flow.

This leads us into the question of whether or not Halloween will
be on the drier side. Ensembles and guidance alike have both begun
pushing the timing of a possible system back further and further.
Many of the individual ensemble runs have even gone so far as to
keep the system out of the area entirely, instead favoring another
system trying to reach the area towards the middle of next week.
While this will likely continue to pose a forecasting challenge -
the impact of offshore flow on systems can be notoriously
difficult to predict - it does signal increasing chances that
Halloween proper will likely be on the drier side for many areas.
The one possible exception to this could be Yakutat, should the
earlier mentioned system successfully advance far enough W.

Otherwise, the other area of note for the forecast will be the
temperatures. Cooler temperatures will likely prevail, especially
through the weekend. Lower sun angles and clearer skies across
much of the area will likely see nippy conditions for Halloween,
and through the end of the forecast period. Forecaster confidence
is average.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Small Craft Advisory for PKZ033-036-041>043-051-052.

&&

$$

CM/GFS

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