Small Craft Advisory 382, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion...CORRECTED
National Weather Service Anchorage AK
559 AM AKDT Sat May 7 2022

.ANALYSIS AND UPPER LEVELS...

The majority of the coverage area remains under the influence of
weak, northerly flow between a very positively-tilted longwave
ridge moving over the Bering Sea and a broad, stacked low drifting
over the eastern Gulf. Across the mainland, a weak midlevel
shortwave driving southeast near the Middle Kuskokwim Valley
separates two smaller areas of ridging aloft, one over
Southcentral and the other stretching between the Y-K Delta and
Norton Sound. The main upper jet mostly remains mostly confined
outside of our region across the North Pacific, except where it
loops up into Kamchatka and down into the Bering around the
aforementioned longwave ridge, where a weak (about 70 kt at 300mb)
northerly jet extends down towards the western Aleutian Chain.
Weak north to northwest prevailing winds are also in place at the
surface, with some enhancement through gaps and passes up to
around 30 mph along the Alaska Peninsula. Earlier shower activity
across the Kenai Peninsula, Talkeetna/Chugach Mountains and Copper
River Basin (plus a few thunderstorms over Bristol Bay) has
mostly died down with diurnal cooling, leaving behind scattered
mid to upper cloud cover over most of the southern mainland. A
blanket of marine stratus covers the Bering under the ridging
aloft, some of which is encroaching onto the Kuskokwim Delta.

&&

.MODEL DISCUSSION...

Models are staying in very good synoptic agreement through early
next week, with high confidence for an Arctic trough to initiate
a pattern shift as it digs first across Southwest on Sunday and
then into Southcentral by Monday morning. There are some
differences in terms of low level temperatures with the polar air
mass entering Southwest behind the trough and effective cold
front passage, with the NAM notably colder than other solutions
across Southwest by Monday afternoon. The main forecast challenge
will be determining the degree of cooling as northwest flow behind
the trough passage sets in between Sunday and Monday, and whether
this cooling will be sufficient for rain showers moving past with
the trough to mix with or change over to snow.

&&

.AVIATION...
PANC...VFR conditions will persist. Turnagain arm winds are once
again not anticipated this afternoon, with a light westerly sea
breeze again possible this afternoon and evening.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3...Sat
through Mon)...Conditions will overall remain quiet through most
of the weekend before a pattern change sets up for early next
week. First, the showers that formed along the Wrangell and
Chugach Mountains Fri afternoon continue to track from NE to SW
into the Gulf of Alaska this morning. In their wake, some
localized low clouds are expected, and even a little patchy fog is
possible in some of the lowest valleys. Beyond that, many places
will see a good amount of sunshine today allowing for temperatures
to climb back into the mid 50s. As things warm up in the
afternoon, we expect another round of showers to develop over the
mountains. Once again, the primary focus area looks to be from the
Talkeetna Mountains over through the Copper River Basin. One
notable difference from yesterday is that the steering flow will
now be from NW to SE (vs NE to SW like Fri).

Ridging moves overhead on Sunday, which should make for a healthy
amount of sunshine and seasonable temperatures for those
celebrating Mother's Day. However, as the ridge moves in, we start
to see some pressure rises bring breezy conditions into many of
the favored gaps. Places like the Barren Islands, Kachemak Bay,
and Whittier should be on the lookout for gusty conditions by Sun
afternoon.

This will be a sign of things to come for late Sun into
Mon as a fairly robust system plows from SW AK into the AK Range.
This pattern looks much more like October than May. An impressive
cold front will slide through the area causing 850mb (5,000')
temperatures to drop to near -8C. Given that the system is coming
through the Alaska Range, we do not expect many population centers
to receive much in the way of precipitation on Mon. However, it
could be a rather different story in the mountains where a couple
inches of accumulating snow are likely (especially Hatcher Pass).
The cold front will also bring strong westerly winds to many of
the favored areas with the Barrens reaching gale-force on Monday
and Resurrection Bay on track to see small crafts.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2: Today and
Sunday)...

A shift in the weather pattern will get underway as a series of
fronts moves across the forecast area this weekend. The first
front will move to the Kuskokwim Delta coast by this evening
spreading a mix of precipitation to all areas. The next front
quickly follows on Sunday morning, bringing another round of mix
precipitation with a transition to snow possible over the
Kuskokwim Delta and Lower Kuskokwim Valley by Sunday night. Total
snow accumulations will generally be light for the low-lying areas
with higher amounts (2 inches) possible along the mountains. A
tightening pressure gradient will strengthen the winds out of
southwest beginning this evening and lasting through Sunday. An
Arctic airmass accompanying the aforementioned front will bring
below normal temperatures for this time of the year as well. By
Monday, light precipitation with cooler than normal temperatures
will persist through early next week.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2: Today
and Sunday)...

The next weather feature for the weekend will be a well- develop
surface low moving into the Sea of Okhotsk. A swath of small craft
winds with higher gusts ahead of the low will mostly be
concentrated in the central Bering Sea. The Pribilof Islands can
expect increasing southwest winds along with some rain between
tonight through Sunday. With a northerly track of this system,
most of the precipitation will stay to the north of the forecast
area. An area of low pressure will lift northward near the Central
Aleutians with winds and precipitation staying to the south of
the area.

&&

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

Conditions in the Bering should remain fairly quiet for the
beginning of next week. A frontal boundary over the eastern Bering
will move onshore Monday afternoon. Westerly to northwesterly
small craft winds across the eastern Bering can be expected. A
ridge is expected to build over the Bering through Wednesday.

Meanwhile for the Gulf, Gale force westerly winds can be expected
Monday as a low develops and moves to the central Gulf for
Tuesday. A weak trough remains over the Gulf for Wednesday.

&&

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

Models generally agree that a polar low located over Southcentral
on Tuesday will track southeastward over the Gulf into Wednesday,
and then it will continue southeastward and exit the eastern Gulf
for Friday. Out west, a ridge of high pressure is expected to
remain in place over the Bering Sea and Aleutians into Friday
while gradually inching eastward to Southwest. Multiple
shortwaves appear to ride along the ridge from northwest to
southeast across the mainland through the week, although model
agreement still diverges regarding the placement of the
shortwaves and how upper-level energy maxima will interact with
the ridge.

Nonetheless, the bottom line is that the Bering Sea
and Aleutians can still expect to see mostly calm weather
conditions in the long term while under the ridge, and
Southcentral and Southwest will experience a more active weather
pattern into the end of the week as the polar low and multiple
shortwaves rotate through the region.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Flood Watch: 152.
MARINE...NONE.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...AS
SOUTHCENTRAL ALASKA...MO
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...MF
MARINE/LONG TERM...KO/AF