National Weather Service United States Department of Commerce


000
FXAK68 PAFC 291422
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
522 AM AKST Sun Jan 29 2023

.ANALYSIS AND UPPER LEVELS...

Longwave troughing over East Asia and a sharp ridge rising out of
the Northeast Pacific into Southcentral Alaska continue to direct
a southerly jet of warm air and moisture toward Southwest Alaska
this morning. A shortwave trough situated over the
northern/eastern Bering Sea, along with a large, disorganized
area of enhanced vorticity to its east are aiding with lift and
instability over the region. Patchy returns on the Bethel and King
Salmon radars indicate that there are some areas of showers
ongoing across the Alaska Peninsula and up into Southwest Alaska.

To the east, patches of stratus can be seen around parts of
Southcentral in infrared satellite imagery underneath breaks in
overspreading cirrus. However, the area remains dry. Out west, an
occluding low in the far western Bering Sea is now tracking
northwest toward Kamchatka, away from the western Aleutians, where
storm force gusts continue to be reported at Shemya. An 0840Z
ASCAT-B pass suggests that hurricane-force winds remain present on
the south side of the low, though they remain some two hundred
miles or so from the islands. The low continues to push a well-
defined front eastward across the central Bering/Aleutians, where
it is bringing rain and snow, with winds below gale force. Nearly
all of the marine area is blanketed with stratus, with ceilings
lower than 1000 ft observed from Atka to Kodiak.

&&

.MODEL DISCUSSION...

Models remain in broad, synoptic-scale agreement through the short
term forecast period. With regard to smaller-scale features, there
remains uncertainty with disorganized, weak disturbances tracking
over the southern mainland through Monday, introducing uncertainty
with timing and placement of precipitation. There is, however,
increased agreement in less of a warm air intrusion over
Southcentral Alaska today and tonight. Lastly, there is increased
confidence with a front pushing across Southwest Alaska into the
western portions of Southcentral by Tuesday morning, introducing a
chance for light snow.

&&

.AVIATION...

PANC...VFR conditions and light winds are expected through this
afternoon. Then, precipitation chances increase and ceilings begin
to lower. Precipitation is expected to fall as light snow if the
column is able to saturate. Otherwise, the possibility of
freezing drizzle at times cannot be ruled out. MVFR ceilings with
intermittent precipitation are most likely this evening through
early Monday morning. Precipitation tapers off gradually Monday
morning while ceilings lift to VFR.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3/Today
through Tuesday night)...

A series of weak short-waves moving up the west wide of a high
amplitude ridge will track across Southcentral this afternoon
through early Monday, bringing widespread light precipitation to
the region. Warm air advection the last couple days was not quite
as strong as originally expected. However, the 12Z Anchorage
sounding does reflect a near freezing isothermal layer from the
surface all the way up to 7500 feet. The airmass is starting out
quite dry from 5000 feet on up. Lastly, the prime snow growth
region is way up at 12,000 ft elevation and higher. Thus, all
signs point toward freezing rain if precipitation were to fall
into the column, even with saturation and wet-bulbing. In
addition, easterly winds will strengthen across the Kenai and
Chugach Mountains today, which could provide some additional
warming in the first few thousand feet of the atmosphere. Aside
from precipitation-type issues, the QPF forecast is also quite
challenging. Forcing is quite weak and the very shallow cross-
barrier flow could keep it even lighter in the lee of the Kenai
and Chugach Mountains, minimizing any impacts from freezing rain.
For now, will hold off on issuing any Advisories. The best chance
for seeing freezing rain with some light ice accumulation is the
western Kenai Peninsula northward to Anchorage. Freezing rain is
also possible over the eastern interior Kenai Peninsula and as far
north as the Matanuska Valley.

Precipitation will diminish across the region Monday morning as
the short-waves exit to the east. Attention will then shift to a
stronger short-wave approaching from the Bering Sea. This trough
will slow its forward progress as it nears Southcentral late
Monday, pushing up against the west side of the upper level ridge
in place. An even stronger trough behind it may provide just
enough to push the first trough and existing ridge eastward.
Confidence in the interaction and exact placement of these
features is low. However, there does seem to be a trend toward at
least some eastward progression into Southcentral. Thus, have
trended toward high probabilities of precipitation Monday night
through Tuesday night. The most likely areas to see precipitation
are Kodiak Island, the Kenai Peninsula, Anchorage, and the Mat-Su.
The airmass will slowly cool Monday night into Tuesday, so would
expect precipitation type to be primarily snow, except for
continued rain for Kodiak. The upper trough will be in a weakening
state along the west side of the ridge, so snow accumulation
would be light.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3: Sunday
through Tuesday)...

Precipitation returns to Southwest Alaska from today through
Tuesday morning as a plume of moisture moves in from the North
Pacific, followed by a front sweeping inland from the Bering Sea.

For the most part, precipitation should fall as (or quickly
transition to) rain today given southerly flow and strong warm
air advection. However, there remains the potential for brief
periods of light freezing rain today, especially over the Lower
Kuskokwim Valley where surface temperatures look to remain just
below freezing. The current thinking is that, by the time
precipitation starts to fall, the warm air aloft will erode enough
that the column will be below freezing for these areas.
Therefore, freezing rain is possible but looks to be unlikely in
this scenario. By early Monday morning, cold air moving in behind
the front will gradually transition rain to snow before
precipitation comes to an end from Monday night into Tuesday
morning. There remains some uncertainty with the timing of
precipitation, which could have some impact on total precipitation
amounts for this event. For now, the general thinking is that
Kuskokwim Delta and the Lower Kuskokwim Valley will see about 0.25
to 0.5 inches of liquid, with about 0.5 to 1 inch for Bristol
Bay. Overall snow amounts will be around 2 inches or less.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3:
Sunday through Tuesday)...

A 954 mb vertically stacked low will continue to bring active
weather to the Bering Sea and Aleutian Islands through today. A
High Wind Warning remains in effect and looks on track to expire
at 6 AM this morning with the departure of this low. While winds
in the Western Aleutians and Bering should diminish below high
wind criteria (75 mph) later this morning, they will persist at
gale force through Monday given strong cold advection and a
compact low moving through the region. Further east, the low`s
occluded front is currently over Adak and set to bring snow and
rain as it makes its way across the Aleutian Chain through
tonight. Cold air and snow showers will overspread the Bering Sea
through Monday. Then, a surface low moves from the North Pacific
into the Bering Sea on Tuesday, bringing with it warmer
temperatures and winds to gale force. Some uncertainty persists
with the track of the low, but the primary hazard looks to be
moderate to heavy rain along the Aleutians.

&&

.LONG TERM FORECAST (Days 4 through 7: Wednesday through Saturday)...

The long term forecast begins on Wednesday with a broad upper-
level trough, and multiple embedded shortwaves, over the Bering
and Aleutians and a shortwave ridge near Mainland Alaska. As the
trough shifts to the east, the ridge flattens and various surface
lows are advertised to traverse the Bering/Aleutians before
approaching the Mainland on Thursday. The deterministic models
depict more variability with the lows in regards to track, timing
and evolution, however there is general consensus for these
surface features to dissipate earlier on Saturday as the next
system unfolds. Also, an upper trough and surface low near the
Panhandle looks to extend northward to Southcentral through at
least Thursday afternoon, however beyond this time, model
agreement diverges significantly with this system.

On Friday, there is good agreement for a large, deep upper-level
low to approach the western domain from the Northwest Pacific.
Its attendant surface low will extend its front across the
Western/Central Aleutians Friday morning before pushing
northeastward across the Bering and the rest of the Aleutians by
Saturday morning. The front is expected to reach Southwest Alaska
around Saturday afternoon, however model agreement weakens beyond
this time. Nonetheless, expect a generally active weather pattern
to continue for the long term period.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...High Wind Warning 191.
MARINE...Storm Warning 178
Gale Warning 175-177 411-413.
FIRE WEATHER...NONE.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...CQ
SOUTHCENTRAL ALASKA...SEB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...KC
LONG TERM...AF


000
FXAK69 PAFG 291611
AFDAFG

Northern Alaska Forecast Discussion
National Weather Service Fairbanks AK
711 AM AKST Sun Jan 29 2023

.SYNOPSIS...
A strong ridge of high pressure aloft stretching from the Eastern
Pacific north over Alaska to near the North Pole has brought very
warm temperatures along with periods of snow to Northern Alaska.
There will even by periods of light freezing rain today through
Mon from Isabell Pass to Noatak southwest through Mon AM, with
heavy freezing rain likely over Southwest Alaska.

Expect 4-7 inches of snow through Tue AM over much of the
Interior and West Coast between 64N and the Arctic Circle.


Aloft...
A strong long wave ridge stretching from the Eastern Pacific
north over Alaska to near the North Pole and a deep long wave
trough over Eastern Russia and the Bering Sea will persist through
mid-week. A series of strong short wave troughs will move north
through this pattern bringing snow and freezing rain to much of
the West Coast and Western Interior, and to the Eastern Interior
south of the Arctic Circle.

Surface...
A weak low pressure trough along the Arctic Coast will move to
Barter Island to Point Lay by 3pm Sun and weaken, then strengthen
Mon and Mon night. Light snow along this trough will diminish
tonight.

Strong high pressure north of the Arctic Coast will persist.
These feature will cause east winds to develop along the Arctic
Coast today, then increase to 20-30 mph Mon and Mon night.

An Arctic front that lies from Eagle to Fairbanks to the Bering
Strait will remain quasi stationary through 3am Mon. then move to
Chicken to Fairbanks to Shishmaref by 3pm Mon, then to Northway o
minchumina to Nome by 3am Tue. This is a boundary that is setting
up potential for heavy snow as moisture from SW Alaska feeds NE
along this frontal boundary, with areas of freezing rain occuring
south of this front.

A warm front over the Yukon Delta will move north over the Seward
Peninsula this afternoon and dissipate over the southern Chukchi
Sea tonight. This will bring significant amounts of freezing rain
to Southwest Alaska today through Mon with between 0.10-0.20 inch
of ice accumulation. Other areas of the West Coast and Western
Interior south of Nome to Mcgrath will see up to 0.10 inch of ice
accumulation mixed with snow. The Eastern Interior south of the
White Mountains could see less than one tenth of an inch of ice.

A strong occluded front in the Western Bering Sea will move along
the West Coast of Alaska Mon and into the Western Interior on Mon
night. Another 4 inches of snow will fall just east of this front,
and freezing rain will end with this front.

.DISCUSSION...
Ar 12Z, models all verify 10-20 meters too low on 500 mb heights
over Alaska from McGrath south. This means that the 500 mb ridge
is stronger over the Gulf of AK and Southern AK than any models
indicated at 12Z. Expect that this will mean that the 500 mb ridge
will remain stronger than models indicate for the next day or two.
This will also be the case on other levels aloft, and will mean
that warm air and freezing precipitation will likely be a bit
further north than models might indicate. Models show fairly
similar solutions aloft through Tue, with similar solution on
synoptic feature through the middle of the week.

850 MB temperatures are near or above 0C from Isabell Pass to the
Bering Strait and remain there into 3am Mon before cooling back
below freezing Mon as cooler air moves in from the northeast.
This will lead to possible freezing rain in the area from Isabell
Pass to Noatak through Mon AM, with freezing rain likely southwest
of Nome to Denali.

With precipitation, models agree on light amounts today and
tonight over the North Slope, the Interior between 64N and 66N,
and over the West Coast south of the Bering Strait. Models differ
some on details near Fairbanks, but consensus is that most precip
stays north of Fairbanks until 12Z Mon. Models all bring heavier
precip into the West Coast on Mon, and into the Western Interior
Mon night and Tue, with disagreement about amounts over the
Eastern Interior Mon night and Tue. Will use a blend of the NAM
and GFS for precip location and amounts. Bottom line is expect
1-2 inches of snow between 64N and 66N through tonight, with 4 to
6 inches over the White Mountains. Expect another 2-4 inches of
snow SW of Eagle to Tanana to Kotzebue Mon through Tue. Expect
trace freezing rain SW of Isabell Pass to Noatak today and
tonight, with up to one tenth of an inch SW of Nome to Mcgrath.
Could see similar amounts those areas on Mon before freezing rain
ends from the north on Mon.

At the surface at 06Z, models initialize well on most features,
but all are 2-4 mb too weak on the low near St Paul Island, and
all except the Canadian are 2-3 mb too weak on the low over
MacKenzie Bay. Models show similar surface patterns through Tue.
Favor as blend of the NAM and Canadian models for surface patterns
an winds since the Canadian better resolves current conditions
along the Arctic Coast, and also the increasing winds there on Mon
and Mon night.

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


&&

.AFG WATCHES/WARNINGS/ADVISORIES...
AK...Winter Weather Advisory for AKZ211.
Winter Weather Advisory for AKZ212-213.
Winter Storm Warning for AKZ214.
Winter Storm Warning for AKZ215.
Winter Weather Advisory for AKZ216.
Winter Weather Advisory for AKZ219-220.
Winter Weather Advisory for AKZ221-222.
Winter Weather Advisory for AKZ227.
PK...Brisk Wind Advisory for PKZ200.
Brisk Wind Advisory for PKZ201.
Brisk Wind Advisory for PKZ210.
Brisk Wind Advisory for PKZ220.
Brisk Wind Advisory for PKZ225.
&&

$$


000
FXAK67 PAJK 291457
AFDAJK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
557 AM AKST Sun Jan 29 2023

.SHORT TERM...Clear skies and sunny conditions across much of the
panhandle are anticipated through the first half of Sunday, as
the influence of upper level ridging lingers across the area.
Winds have significantly diminished, and anticipate that most
areas will see winds of around 10 to 15 kt through Sunday across
the inner channels and most land-based areas, barring the
potential for somewhat windier conditions in Skagway. Conditions
in the outer coastal waters will remain on the moderate side - at
least by winter expectations.

Cloud cover, currently moving into Yakutat, will spread back
across the panhandle through the latter half of Sunday, with the
break in the active pattern brought to an end Sunday night
as a wave manages to successfully advance over the ridging and
enter the panhandle. By Monday, anticipate much of the area will
be experiencing accumulating snow, rain, and windier conditions
once more. Although 850 mb temperatures will remain on the more
marginal side for a snow event during this time of the year,
overall atmospheric thickness in the lower levels of the
atmosphere will remain more favorable with 1000-850 mb remaining
around 1288m or lower for much of the area. This, along with
cooler temperatures near the surface through Sunday, will provide
the support needed for said snowfall to occur. That being said, at
this time, do not expect any truly substantial snow accumulations
from this wave given the lack of a significant low associated
with it, but some areas will likely see at least some impactful
snow. For more information on this system, see the long term
forecast discussion.

.LONG TERM.../Monday through Saturday/...As the high pressure
ridge shifts east and flattens the first in a series of short
waves will move over the AK Panhandle. First wave should be fairly
weak, bringing a mix of snow and rain to the northern areas first
then tracking southward. As of now only expecting a couple of
inches of snow from this system. With an upper level trough
remaining over the gulf through most of the week we`ll continue to
have surface lows and fronts with increased winds and
precipitation. The best way to describe model prediction of these
systems is chaotic. Ensemble model surface pressure basically puts
a broad low over the gulf and leaves it there for the week.
Meanwhile operational model runs have shifts position, timing, and
strength of a more detailed depictions. Later in the week may see
a break in precip for the northern areas as a stronger low tracks
into the SE Gulf resulting in higher QPF amounts there, falling
as mostly rain. Or the low tracks north hitting most of the
panhandle with initially a few inches of snow accumulation then
transition to all rain. If you haven`t guessed by now, it`s and
uncertain forecast, which is typical dealing with upstream waves
after a blocking ridge breaks down. Started to see some better
agreement between the GFS and ECMWF operational models Tuesday
into Wednesday, but with the constant shifts and run to run
differences can`t put too much confidence is these latest
solutions. 850 mb temps and 1000-500 mb thickness values are both
just at the cusp of precip will be all snow, or it will be a mix,
or it will be just nudged to all rain. So going with a mix for now
and keeping snow accumulation with a lower snow ratio. Expect the
forecast to change as model consensus will hopefully improve and
better details are hashed out.

&&

.AVIATION...VFR conditions and low winds rule the skies for
Sunday. These good conditions will start to deteriorate late Sun
night into Mon as clouds and precipitation moves in from the West.
Expect visibility and ceilings to drop to MVFR or possibly lower
as precip moves in, especially in areas where the main precip
type is snow rather then rain. Little in the way of wind with this
system so turbulence or LLWS are not expected.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...None.

&&

$$

SHORT TERM...GFS
LONG TERM....PRB
AVIATION...EAL

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