Gale Warning 335, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
508 PM AKDT Fri Apr 15 2022

.ANALYSIS AND UPPER LEVELS...

The upper level ridge that has been over mainland Alaska this week
remains in place in spite of the low in the Bering Sea running
into it. This low is vertically stacked in the northern Bering
Sea and has become nearly stationary. The jet stream is just
south of the Aleutians and reaching around 180 kt at its core
at the 250 mb level. This set-up is bringing more clouds into
Southcentral today. The front is over the the northern part of the
Bristol Bay zone and the Kuskokwim Valley and there are still
some areas of rain and snow in those areas, but most of it has
ended as the front dissipates.

&&

.MODEL DISCUSSION...

Models remain in good synoptic agreement into Tuesday before some
noticeable differences emerge in the Bering Sea and Aleutians
with a low moving across the Aleutians from the west. Until then,
just the smaller meso-effects that drive Turnagain Arm winds and
other such effects will be the main difference in models.

&&

.AVIATION...
PANC...VFR conditions will persist. Winds are a challenge for this
afternoon and evening, as the airport is right in the transition
area between northerly winds and southeasterly winds. A lack of
strong forcing for one wind to dominate another means winds may
switch back and forth multiple times. However, this will be
short-lived and lighter winds should settle back in by 06Z this
evening.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3...Tonight
through Monday afternoon)...

A ridge of high pressure over the mainland is retreating northward,
while a front extending from a low in the Bering Sea is slowly
moving eastward toward the central Gulf of Alaska. Ahead of the
front, a decent plume of moisture and warmer air aloft is advecting
from south to north. Precipitation type for Kodiak will continue
as rain as the atmospheric column of air warms above the surface.
With a slow progression of the front, another 0.5-1.00" of rainfall
is expected for the region through Saturday afternoon. A chance
mix of rain/snow will works its way toward the north gulf coast,
including Whittier, Cordova, and Valdez, while inland valleys
remain relatively dry under mostly cloudy skies. Gusty,
southeasterly winds will continue over the Gulf waters and
channel along Turnagain Arm and higher elevations. Winds will
diminish Saturday afternoon as the aforementioned front weakens.

From Saturday evening through Sunday morning, an Arctic shortwave
trough pushes southward from the AK-Yukon Territory. With weak
instability, cooler air aloft, and mid-level forcing ascent,
isolated to scattered mountain snow showers are possible for the
Copper River Basin and Hatcher Pass. As we head into Monday, a
ridge of pressure will reestablish over the mainland, with mostly
clear skies and seasonable temperatures.

&&

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

Unsettled weather continues across Southwest Alaska over the next
couple of days as a mix of rain and snow showers continue. Shower
activity will decrease during the later half of the weekend as
upper level ridging nudges into the area.

&&

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

An active pattern is expected for the Bering/Aleutians as a series
of low pressure systems move through the area. The first low is
currently over the central Bering and is in the process of
weakening. This low will continue to weaken and then the energy
from this low will be absorbed into the next low that is the
extra-tropical remnants of Typhoon Malakas. The resulting low will
produce widespread gale force winds with storm force gusts across
the Aleutians Saturday night through Monday.

&&

.Marine (Days 3 through 5: Monday through Wednesday)...

Gulf of Alaska: Generally calm conditions will prevail across
most of the Gulf with light winds and seas less than 10 ft
throughout the outlook period.

Bering Sea: The post-tropical remnant of former Typhoon Malakas
will essentially be an ordinary and weakening Bering low by early
next week, with the center expected to cross the eastern Aleutians
into the North Pacific on Monday. Expect widespread gale force
winds with this system Sunday through Monday, with good potential
for a small corridor of storm force gusts in both the southeasterlies
ahead of the low and northwesterlies behind the low. As with the
most recent storm, southeasterly winds will be particularly strong
through bays and passes along the southern Alaska Peninsula. The
extended duration of steady gales will maintain 15 to 20 ft seas
across the far southern Bering through early Tuesday, with up to
25 ft seas on the Pacific side of the eastern Aleutians.

Winds and waves will diminish in the wake of this storm Tuesday,
but there is potential for a large North Pacific low to enter
the southern Bering Sea and possibly undergo rapid deepening.
However, forecast uncertainty increases markedly for this next
system, and confidence for timing/location of higher seas and
winds is low at this point.

&&

.Long Term Discussion (Days 4 through 7: Tuesday through Friday)...

The outlook for next week deteriorates from reasonably clear to
very unclear remarkably quickly, with model agreement and run to
run consistency sorely lacking by the end of next week. What's
more clear is that a turn from mostly quiet to very active
conditions is becoming increasingly likely, especially out west.
Looking at the start of the period on Tuesday, what's left of
post-tropical Malakas should finally be exiting the picture as
the remnant low is steered southeast from south of the Alaska
Peninsula out to sea by strong northwest flow downstream from a
transient ridge developing across the Aleutians. Areas of rain or
rain/snow mix along the eastern Aleutians and southern Alaska
Peninsula should mostly shut off by Tuesday evening as the low
departs. Steady, light rain and snow along a stalled out frontal
axis stretching from near Dutch Harbor to St Matthew will hang
around a bit longer into early Wednesday as the front degrades.
Meanwhile, a stubborn blocking high centered up near the North
Slope will remain in place through at least Wednesday, while a
weak upper low drifts across the southern mainland within weak
easterly flow on the south side of the blocking high. Cool
mid/upper temperatures and weak lift around this easterly wave/low
will support isolated to scattered shower activity as it moves
across Southcentral on Tuesday and Wednesday, especially over
inland valleys lacking snow cover where afternoon heating will
be most effective.

Pattern details begin to fall apart for the latter half of next
week, with operational runs diverging significantly for the
progression and eventual interaction of two separate shortwave
troughs moving east/northeast towards the Bering from the
northwest Pacific. However, there are ever increasing signs
these two features will phase together as they reach the
Bering/Aleutians late on Wednesday or Thursday, supporting
potential for strong cyclogenesis and resulting development of
a large, powerful surface low near or over the southern Bering.
This low appears most likely to move east roughly along the
Aleutians between Wednesday and Thursday, then approach the Alaska
Peninsula or western Gulf by Friday. While it's difficult to get
into details due to major differences in model handling of this
system, it's likely we will see far-reaching impacts for much of
the forecast area from this system, assuming support continues to
grow for the scenario above late next week. This could range from
potential moderate to heavy precipitation, very strong winds, and
high seas for portions of the forecast area, depending on
how/where the system develops and tracks east. Check back for
forecast updates for the Wednesday to Friday timeframe as details
for this possible stronger system become more apparent.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gale Warning 173 175 177 178.
FIRE WEATHER...NONE.

&&

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