Flooding in Alaska, May 19 to 22, 2023

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
421 AM AKDT Fri May 19 2023

.ANALYSIS AND UPPER LEVELS...

A large low pressure system over the northern Gulf has continued
to move north toward the eastern Aleutians. Bands of vorticity
maxima are pivoting within and around the low with the stronger
bands forcing surface boundaries/fronts, and occasionally light
rain/snow showers, mainly across the western Gulf and eastern
Aleutians. Outside of that, predominantly dry and mild conditions
ocurred across the forecast area.

&&

.MODEL DISCUSSION...

Models have been in very good agreement the last few days. Through
the weekend, only minor differences in evolution of the track of
the low noted as it crosses into the Bering. More significant
differences develop by Monday as the next N Pac low begins to
interact with the former low.

&&

.AVIATION...
PANC...VFR conditions will continue through the TAF period. Light
northerly winds early this morning will become southeasterly later
this morning, increasing to around 15 kts with higher gusts for
the afternoon. Winds are expected to diminish during the evening.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 2: Today
through Sunday)...

A broad North Pacific low south of Kodiak continues to retrograde
westward and will slowly cross the Alaska Peninsula through the
weekend. The dominant weather feature with this system is the
attendant front lifting northward, bringing moderate to heavy rain
into Kodiak. Rain chances are expected to increase for the rest
of today along western Prince William Sound and eastern Kenai
Peninsula. The slow progression of the low will also bring
easterly small craft to low end gales in the offshore marine areas
Friday afternoon through Saturday night. Further inland, drier
conditions will prevail for Anchorage Bowl and the Mat-Su Valleys
with the help of downsloping on the lee side of the Chugach
Mountains.

Meanwhile, the mainland will see fairly quiet weather under a
ridge of high pressure extending from western Canada across
southern Alaska. A series of easterly waves moves across
Southcentral, bringing increasing cloudiness and a chance of light
precipitation during the afternoon and evening. Daytime highs
will warm up nicely in the 50s to 60s, with overnight lows in the
40s. A combination of the Gulf low and mainland high will promote
a strong Turnagain Arm and Knik River wind developing today and
gradually easing tonight through Saturday morning.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA/BERING SEA/ALEUTIANS (Days
1 through 3: Today through Sunday night)...

A broad North Pacific low roughly 400 miles south of Kodiak Island
will slowly track northwestward today and is expected to center
over the Alaska Peninsula by Saturday night. Its front will
continue to push across the Alaska Peninsula this morning and
into the eastern Aleutians by this afternoon, bringing light rain
and increased winds. Some Bering Sea locations may see light snow
initially with the arrival of the front, but the warm air mass
accompanying it will allow for a quick changeover to rain. Further
north, the front will push across Southwest Alaska but is forecast
to be much weaker there, producing only a chance for scattered
showers, with increased likelihoods of measurable accumulations
closer to the coast. Ahead of the front, a warm air mass will set
high temperatures several degrees warmer than yesterday, reaching
near 60 for much of Southwest, with temperatures approaching 70 in
the Lower Kuskokwim Valley.

By tonight, cold air wrapping around the low south of the Alaska
Peninsula will overspread Southwest Alaska with the passage of the
front, leading to more moderated temperatures in the 50s at most
locations for the weekend. Saturday morning, there is a chance for
shower activity in the Lower Kuskokwim Valley, primarily expected
to affect Sleetmute and Stony River, as the colder air riding over
top warmer surface temperatures allows for some instability,
though thunderstorms are not expected.

As the low weakens over the Alaska Peninsula Saturday night, much
of the forecast area is expected to be dry, with the exception of
continued rain on the south side of the AKPEN east of the low
centered near Cold Bay. Some shower activity may spread to the
Southwest coast for Sunday, with more steady rain expected Sunday
night as a second low tracks up from the North Pacific and begins
to push a front into Southwest Alaska.

&&

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

The key feature in the long term is a broad upper level low in
place over the southern Bering/Aleutian Chain. This feature will
continue to produce southerly flow along the Alaska Peninsula,
introducing generally warmer and wetter conditions across the
eastern Aleutians, Alaska Peninsula, and Kodiak Island for Sunday
into Monday. By Tuesday, there is fairly good model agreement
suggesting a triple point low forming in the vicinity of Kodiak
Island. Depending on the low track, would expect unsettled weather
for Southcentral Tuesday and Wednesday with cloud cover, rain,
and gusty winds, especially along the northern Gulf coast.

Farther west, a strong jet streak forms over the western
Aleutians Tuesday. This will send a fast-moving Kamchatka low into
the western Bering for Wednesday keeping a generally cloudy, wet,
and windy pattern in place for the southern Bering and Aleutian
Chain midweek. As this feature continues moving eastward, the
same will be true for Southcentral by Thursday.

&&

SYNOPSIS AND MODEL DISCUSSION...NR
SOUTHCENTRAL ALASKA...MF
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...CQ
LONG TERM...KO