High Wind in Alaska, October 8, 2022

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
528 AM AKDT Sat Oct 8 2022

.ANALYSIS AND UPPER LEVELS...

A broad upper-level longwave trough is situated out west this
morning, with an expansive cold air mass beneath it extending
across much of the Bering Sea and into Western Alaska. To the
east, a warmer, moister air mass is being drawn up from the North
Pacific and across the Gulf of Alaska into Southcentral and parts
of Southwest Alaska along the western periphery of a longwave
ridge extending up the west coast of North America. A digging
trough over the eastern Bering Sea is tapping into this
temperature gradient, supporting a strengthening surface low
centered over the southern Alaska Peninsula. Moderate-to-heavy
rain is occurring along its cold front across the peninsula, while
out ahead of the low, lighter stratiform rain has begun to
overspread the Bristol Bay region along its warm front. A weak
front also continues to linger in the western Gulf, just east of
Kodiak Island, extending north across the Kenai Peninsula into the
Cook Inlet region as the front pivots slowly westward. As a
result, rain showers have diminished in strength overnight for
Prince William Sound as rain fills in on radar around Cook Inlet.
East of the front, gusty south to southeasterly winds are being
observed in eastern Prince William Sound and through the Copper
River Basin.

&&

.MODEL DISCUSSION...

There continues to be increased consistency in the track of two
lows set to affect southern mainland Alaska through the short
term. There is increased confidence in a more southerly track
taking the low over the Alaska Peninsula this morning into the
northern Gulf for Sunday, which increases the likelihood of cold
air filtering in over the Cook Inlet region on Sunday night,
setting up snow chances for higher elevations on Monday. More
uncertainties remain with the second low tracking into Southwest
Alaska on Monday, though there is increased confidence in a
southerly track for this system as well. This decreases the
likelihood for coastal flooding concerns in the Kuskokwim Delta,
though some potential remains for the Bristol Bay coastline.

&&

.AVIATION...
PANC...VFR conditions will prevail through the day on Saturday,
with light and variable winds expected this morning. Rain showers
will also be likely this morning, which may drop ceilings below
5000 ft periodically. However, as a weak front shifts westward
this morning, high pressure in Prince William Sound will cause
gusty Turnagain Arm winds to return around 08/18Z. This should
clear out any lower ceilings, keeping conditions solidly VFR for
Saturday, though intermittent light showers will remain possible.
As the front shifts back eastward late Saturday night, winds are
expected to turn out of the northwest, and the potential for lower
ceilings return, possibly as low as MVFR for Sunday morning.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3:
Saturday through Monday)...

Rain continues across much of Southcentral today with the low near
the Alaska Peninsula early this morning, and its front,
approaching the area from the west. There will also be the return
of the gusty south to Southeast gap winds in the typical areas
such as Turnagain Arm and the Copper River. In the Copper River
Basin, there will likely be enough downsloping off the Chugach
Mountains to keep most of the rain away through tonight. Anchorage
and the Matanuska Valley will also see a bit of downsloping by
late morning and through the afternoon as cross-barrier flow
increases. Rain will increase again for those areas this evening.
Over the past few days there has been some question as to whether
there will be any snow tonight with this system and the short
answer is: No. With 850 mb temperatures remaining above 0C, it
looks unlikely to see snow even in the passes overnight tonight.
With the low track heading across Kodiak Island and into the
northern Gulf, the coldest air will pack up along the Alaska and
Aleutian Ranges and then begin to gust strongly though the gaps in
these mountains by late tonight and then through the day Sunday.
This low track will also wrap the warmer air over Southcentral,
delaying the onset of air cold enough for snow until after the
rain ends on Sunday.

There may be some snow at higher elevations of the Chugach and
other mountain ranges late Sunday, but then there will be some
clearing behind it on Sunday night. That clearing on Sunday night
will likely bring freezing temperatures for the first freeze of
the season to a lot of the area Sunday night.

The next low will track into Bristol Bay from the west on Monday
and it is taking a more southerly track than from previous
forecasts. That will bring in a better chance for snow at
elevations from 2000 ft and higher on Monday. We will keep an eye
on this system to see how that may change and if there will be
accumulating snowfall through the highway passes. At this time,
the most likely area to see impactful snowfall along the highway
system will be the Parks highway north of Talkeetna and especially
toward Broad Pass.

&&

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

Southwesterly flow aloft ahead of a deep upper trough over the
eastern Bering Sea and associated surface low over the Alaska
Peninsula are leading to rain across the Bristol Bay area this
morning. This will gradually track north and eastward through the
day. Northerly flow behind the aforementioned trough will usher in
much colder air, with 850 mb temperatures approaching -10C by
Sunday morning. However, by the time this cold air is in place,
much of the precipitation will have shifted off to the east.
Despite lows below freezing, only areas generally east of
Sleetmute in the Middle Kuskokwim Valley will see light snowfall
accumulations of around a couple inches. Benign conditions are
expected for much of the remainder of Sunday under a trailing
ridge.

A low will move into the eastern Bering late Sunday into Monday,
brining rain and gusty winds across the region through the day.
As the low will slightly weaken as its center approaches Cape
Newenham, forecasted water levels have slightly dropped and any
coastal flooding/high surf issues would likely occur in Bristol
Bay south and east of Cape Constantine. A Coastal Flood Watch
remains in effect for this area. Conditions will improve Monday
evening and partial clearing is possible by Tuesday in a more
zonal flow pattern.

&&

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

A deep upper trough and associated surface low centered over the
Alaska Peninsula is bringing unsettled conditions this morning to
areas east of and including Unalaska and the Pribilofs. Cold
advection behind the trough combined with a good amount of upper
forcing will increase gap winds on the south side of the AKPEN
through early Sunday morning. A trailing ridge will bring a brief
reprieve before another low enters the western Bering and tracks
eastward Sunday afternoon through Monday. Rain will track west to
east across the Aleutians. The strongest core of winds looks to
be located between the Pribilof Islands and Unimak Pass early
Monday morning. A dry slot will build in as the low begins to
occlude over Bristol Bay, however stronger westerly winds will
persist north of the AKPEN through much of the day. Quieter
conditions are expected over much of the Bering Tuesday ahead of
surface high pressure in the North Pacific.

&&

.LONG TERM FORECAST (Days 4 through 7: Tuesday through
Friday)...

Expect a parade of lows this forecast period. The latest run of
the GFS/ECMWF/Canadian are reasonably clustered on Tuesday and
consistent with the ensembles. Tuesday cold temperatures will
persist across Southcentral and the snow level is decreasing.
Recent runs of the global models suggest a more southerly track
for the first low to impact Western Alaska veering it towards
Bristol Bay. The models continue to have a highly amplified
pattern. By Wednesday, divergence in solutions has emerged over
the Bering but the Gulf Of Alaska is still in good agreement with
the low there and bringing a tropical fetch towards Southcentral.
By midweek next week there is a high probability of additional
pattern amplification as an upper low dropping southeast out of
NE Russia and moves across the Aleutians. Late this forecast
period another low will move from China into the Northwest Pacific
and towards Attu.

&&
.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Coastal Flood Watch 161.
MARINE...Storm Warning 130 131.
         Gale Warning 119 120 132 138 139 150 155 160 165
                      170-178 180 351 352 411 413 414.
FIRE WEATHER...NONE.

&&

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