Winter Weather in Alaska, January 29 to 30, 2023

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

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