Gale Warning 389, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
501 AM AKDT Fri May 20 2022

.ANALYSIS AND UPPER LEVELS...

Longwave high pressure ridge has shifted entirely over mainland
Alaska this morning with the ridge axis extending from Talkeetna
southward across Prince William Sound and into the Gulf. This
continues to promote warm and dry conditions across Southcentral
with a layer of marine stratus trapped over the northern Gulf.
High temperatures could reach 70 degree Fahrenheit for the first
time this year across Southcentral. Meanwhile, a North Pacific
upper low continues to lift northward toward the Aleutians with
high clouds already overspreading interior Southwest from King
Salmon to Bethel. Further south and west the front is promoting
scattered rain showers over the Eastern Aleutians, including Dutch
Harbor where perhaps up to a half an inch of rain may fall
through tonight. Regarding winds, east southeasterly gales will
become increasingly common throughout the day on the Pacific side
as well as the Bering side of the Eastern Aleutians and Alaska
Peninsula as the front continues to lift northward on Friday.
Seas, however, are forecast to stay below 20 feet.

&&

.MODEL DISCUSSION...

There remains good model agreement through the next 48 hours. A
broad trough of low pressure is overspreading the Aleutians this
morning with a front to eventually stretch into the Gulf by
Sunday. If any discrepancies can be found, it's toward the end of
the period with the development of a triple point low over the
western Gulf early Sunday morning. There are some minor
differences in its placement and strength though not enough to
reduce the forecast confidence at this time.

&&

.AVIATION...
PANC...VFR conditions will prevail through Saturday morning while
a ridge of high pressure remains over the region. The development
of Turnagain Arm winds is expected late this afternoon and
evening. The strongest winds will remain offshore of Anchorage;
however, some bending of the winds into PANC is expected with
southeast gusts up to 15 knots or greater.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3; Friday
through Sunday)...

Very little change in the overall thinking for the forecast. More
warm and dry weather for the interior of Southcentral today but a
front will move over Kodiak Island and bring rain and strong
winds. It still looks like some Turnagain Arm winds will move over
Anchorage this afternoon and evening with some Knik River winds
developing near Palmer. That will bring in a little more
afternoon wind than we have been seeing for Anchorage and
Matanuska Valley so that is a change from previous days. The other
nit of a change is a little unexpected and that is the large area
of fog and stratus that developed in the northern Gulf of Alaska
yesterday and persists into today. This stratus likely developed
in response to the surface ridge along the northern Gulf coast
enhancing ahead of the front. This increased the subsidence
allowing the stratus and for to develop. Currently it has moved
into Seward and Cordova and is starting to make inroads into
Prince William Sound. The stratus is also pushing westward to
Kennedy entrance of Cook Inlet though further progress is hard to
see as higher clouds are now moving in over that area and
obscuring the satellite imagery being used to track the stratus.
It is likely that the approaching front will start to mix enough
of the atmosphere to lessen the stratus, but it remains to be seen
if it can fully dissipate today or even tomorrow.

Expect increasing high clouds over Southcentral on Saturday with
the clouds lower by Sunday due to the front weakening the ridge.
This will also cool temperatures over Southcentral especially on
Sunday.

&&

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

A ridge of high pressure will slowly move east as a front
extending from a low in the southern Bering lifts northeastward.
Southeasterly winds have increased along the Alaska Peninsula in
response to a tightening pressure gradient between the mainland
high and Bering low. Winds will continue to increase throughout
today through Kamishak gap and the eastern corridor of Bristol
Bay, including Koliganek and New Stuyahok. Along with increasing
winds, a decent plume of moisture and warmer air will advect from
south to north ahead and along the aforementioned front. Chances
for light rain are expected to increase this afternoon/evening for
the Alaska Peninsula and Southwest regions. Due to the strong
southeasterly flow, rain associated with this system will be
mostly limited to upslope favored areas on the Kuskokwim and
Aleutian Mountains. Therefore, the bulk of the precipitation will
be concentrated along the coastline, while the interior valleys
stay relatively dry. Light rain will continue for most of the
coastal areas as we head into the beginning of the work week with
another low pressure system tracking near the western Gulf of
Alaska by Sunday. Models are still trying to resolve this feature
and how it will interact with the dominating high pressure over
the Mainland, so uncertainty increases by Monday.

&&

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

Areas of low stratus and patchy fog under a ridge of high
pressure blanket most of the Bering Sea and Aleutian Islands. As
the ridge axis shifts slowly east, an area of low pressure is
expected to lift northward near Dutch Harbor. The aforementioned
low's front will continue to bring gale force winds with higher
gusts for the central and eastern Aleutians while slowly
diminishing tonight as the low weakens and becomes quasi-stationary
south of Atka. A decent plume of moisture and warmer air aloft
will advect northward in correspondence with the front bringing
rain to the central and eastern Aleutians before pushing westward
between Kiska to Attu by Sunday afternoon. The aforementioned low
is expected to remain quasi-stationary through the beginning of
the week, therefore, keeping chances of light rain over much of
the region into Monday.

&&.MARINE (Days 3 through 5: Sunday through Tuesday)...

Gulf of Alaska: A front enters the Southern Gulf Sunday, and
moves across the Gulf through Monday. A surface low will move
over Kodiak Island by Monday. Gusty Easterly winds with the front
stretch across the Gulf, with areas of gales over Kamishak Bay,
Shelikof Strait, Sitkinak and along the Alaska Peninsula coast,
diminishing Saturday. An Easterly gale force barrier jet forms
along the North Gulf Coast. Seas to over 10 feet possible east of
of Kodiak Island. Cyclonic flow will persist over the Gulf for
the remainder of the forecast period.

Bering Sea: A mature low remains South of the Aleutians through
Tuesday. Widespread gusty winds expected for the North Pacific
low, with areas of gales from Bristol Bay into the Central Bering,
diminishing Sunday. Seas to 14 feet on the Pacific side of the
Alaska Peninsula, subsiding Saturday, and 10 feet or less over the
Bering, subsiding Monday and Tuesday.

&&

.LONG TERM FORECAST (Days 4 through 7: Monday through
Thursday)...

A Rex Block pattern is likely during the extended period as upper
level ridging extends across the central/northern Bering and into
northern Alaska. At 500 mb there are 2 closed lows south of the
chain and GFS keeps those lows south of the chain through Friday.
The ECMWF shows a similar evolution of the mass fields at 500 mb
this forecast period, but these two models are definitely not a
clone of each other. Expect an area of persistent ridging but also
expect a lingering closed low over the Gulf Of Alaska. Sensible
weather-wise the GFS keeps positive height anomalies over mainland
Alaska this forecast period which will translate to warm
temperatures at the surface and the continuation of snow melting.

With the closed low in the Gulf, expect easterly waves/shortwaves
to get ejected from this feature and move over portions of
Southcentral. But it is too soon to tell were these shortwaves
will track. All the global models have a closed low in the Gulf
with numerous shortwaves embedded in them.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Flood Advisory 141.
MARINE...Gale Warning: 130-132 138 150-172 180 351 352.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...BL
SOUTHCENTRAL ALASKA...EZ
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...NS
MARINE/LONG TERM...PS

SPECIAL WEATHER STATEMENT
National Weather Service ANCHORAGE AK
1055 AM AKDT Fri May 20 2022

AKZ141-202000-
Copper River Basin-
Including the cities of Glennallen, Eureka, McCarthy, Paxson,
and Slana
1055 AM AKDT Fri May 20 2022

A Flood Advisory has been issued for snowmelt in the northern
Copper River Basin. Please visit weather.gov/afc to access the
advisory and latest forecasts.