Gale Warning 398, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
548 AM AKDT Thu Apr 18 2024

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

An Omega block is in place over Alaska and Canada, with a strong
high amplitude ridge centered over NW Canada, a deep trough and
closed low nearly stationary to the south of the Alaska Peninsula
and Kodiak Island, and a deep trough and low east of the ridge
over the heart of Canada. An atmospheric river extends from the
East Tropical Pacific north and west to the Kodiak Island and the
western Gulf of Alaska. A strong southeasterly jet can be found
at all levels of the atmosphere across the western Gulf, Kodiak
island, and the Kenai Peninsula. In addition, a stationary front
is draped across the southwestern Gulf. A series of upper level
waves rounding the upper low are tracking westward across the Gulf
to Kodiak Island. This is the focal point for the heaviest rain,
with 3.23 inches of rain recorded at Kodiak Airport yesterday.
While Kodiak can get this type of rain any time of year, it is
less common in the Spring. Yesterday's rainfall set a new daily
record, breaking the old record of 1.38" set in 1930. In addition
to the rainfall, widespread gale force winds are bing observed
across the western Gulf coastal waters.

As you head north to the Kenai Peninsula, there is not much in
the way of upper level forcing to act on all of the moisture in
the atmosphere. The primary mechanism for rainfall is upslope
flow, which is strong. The bulk of rain is falling along the Gulf
coast, with much lighter rain as you head over the Kenai Mountains
to Homer as well as north across the Peninsula to Turnagain Arm.
Model performance is notably very poor in the Whittier/Portage
Valley area, with all solutions depicting at least one quarter
inch of rain overnight - with some solutions in excess of 1 inch
of rain. In reality, rain has been very light with only one or
two hundredths through early this morning. It is pretty typical
to overdo upslope induced precipitation, but this is particularly
egregious. The latest forecast has been adjusted to reflect much
lighter precipitation totals for this area. Meanwhile, strong and
gusty winds across the Kenai Peninsula have led to warm temperatures,
hovering in the upper 30s to lower 40s all night and leading to
all rain at lower elevations. The rest of Southcentral is dry and
fairly balmy due to the influence of winds and cloud cover.

The upper level ridge will strengthen over Southcentral through
Friday, gradually pushing rain over the Kenai Peninsula off to
the south. Meanwhile, steady rain will continue for Kodiak Island,
with periods of moderate to heavy rain as upper level short-waves
continue to pass overhead. As we head into the weekend a spoke of
the upper ridge will build north and west across Mainland Alaska,
allowing the trough to begin to lift northward across the Gulf.
The tropical moisture tap will be lost and the surface front will
weaken. While portions of Kodiak Island can expect rain to
persist all the way through Saturday night, the intensity will
lighten significantly by late Friday. Southcentral will remain
warm and dry. While considerable cloud cover will persist for at
least the southern Kenai Peninsula, the rest of the region will
see quite a bit of sunshine.

-SEB

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA, THE BERING SEA AND THE
ALEUTIANS (Days 1 through 3)...

Satellite and observations show northwesterly winds just west of
King Cove and southerly winds east of King Cove with low pressure
south of Sand Point. This low will migrate southward through
tomorrow as weak high pressure moves south and east of Adak.
Northerly to northeasterly winds over the Eastern Aleutians
(Unalaska/Dutch Harbor) through this evening can be expected.
Gusts ranging from 35 to 45 mph will continue through most of the
day today. Precipitation will continue in the Kuskokwim Delta as
rain today while a rain/snow mix at sea level from Dutch Harbor to
King Cove as temperatures hover above freezing. Snow is likely at
higher elevations where temperatures will remain at or below
freezing in the Central Aleutians. A more defined area of
precipitation moves over the area overnight into the late morning
hours of Friday. This unsettled pattern continues into the
weekend. Northerly winds with Convective snow showers are likely
west of Dutch Harbor today. Elsewhere, southeasterly winds
continue through the Kamishak Gap westward into interior Bristol
Bay (including New Stuyahok and Koliganek) through tomorrow as a
trough moves back southward. Gusts ranging from 45 to 55 mph are
expected today. Temperatures across most of Southwest Alaska
remain in the upper 30s, keeping most of the precipitation in the
form of rain. Snow, low visibility and fog will continue in
Toksook Bay and Mekoryuk and the immediate coastal areas of the
Kuskokwim Delta.

Looking ahead at the weekend, southeasterly flow continues
through Southwest Alaska bringing precipitation to most of the
area. In the Central Aleutians, a series of short waves move
northwestward toward the Pribilof Islands bringing continued
unsettled conditions for the first half of the weekend.

-DJ

&&

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

An upper level ridge extending from a Northwest Canadian high
center continues its hold across Mainland Alaska through the
forecast period. Over the Gulf of Alaska, a closed low South of
the Alaska Peninsula and Kodiak Island is weakening and beginning
its movement away from the Gulf Monday. In the Far West, a well
developed low out of Siberia moves across the Northern Bering
before weakening and sliding back into the Arctic late Tuesday.
A Western North Pacific low picks up some cold air from across
the Russian Far East strengthening as it moves over the Central
Aleutians by Wednesday. This scenario appears to set up a longer
term duration over the Bering beyond the forecast period.

The remnants of a front extending into Western Alaska from the
Gulf low continue periods of heavier rainfall over Kodiak Island
and the AKPEN through early Monday. Some rain mixed with snow
should occur around Bristol Bay, with areas of new snow further
North along the West Coast. The approach of the Western Bering low
and its front will spread gusty winds and precipitation across
the Aleutians late Sunday, into the Pribilofs late Monday and
continue over the AKPEN through Wednesday. A second North Pacific
low moving East along the Southern Gulf brings another round of
heavier precipitation and gusty winds over Kodiak Island and the
AKPEN late Monday into Tuesday.

Kutz

.AVIATION...

PANC...VFR conditions will persist. The Turnagain Arm wind is
expected to continue bending southward down Cook Inlet while
generally northerly winds persist over the airport. Southeasterly
winds coming across the mountains are expected to remain largely
above the 2000 foot level. As a result, low level wind shear is
not expected.

&&