395
FXAK68 PAFC 051255
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
455 AM AKDT Wed Jun 5 2024

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

After the warmest and sunniest day of the summer for most of
Southcentral yesterday, cool and wet conditions are on tap for
today through Thursday. Looking at satellite imagery, a high
amplitude trough remains firmly entrenched over Alaska. A deep and
cold upper level low is dropping down the back side of the trough
across the eastern Bering Sea. This will serve as a new anchor
for the trough in the coming days. Meanwhile, a marginally weaker
vertically stacked low over the eastern Gulf is beginning to
rotate back westward, as it eventually is absorbed into the quite
large cyclonic flow around the Bering low. A series of short-waves
are rotating around the north side of this low, tracking from
British Columbia westward into Southcentral. Radar imagery shows
a rain shield spreading southwestward from the Copper River Basin
into much of Southcentral this morning. Areas of moderate rain
are embedded within the larger area of light rain. Thus far (as of
4am) the highest recorded rainfall amounts (where there are gauges)
are in Cordova with nearly half in inch. Temperatures are slowly
falling into the 40s as the air mass moistens.

The forecast for today remains largely on track, with just a few
tweaks. Steady rain will linger across Southcentral for much of
the day, which means temperatures will only warm back up into the
50s - roughly 15 degrees cooler than Tuesday`s high temperatures.
The one exception will be the Copper River Valley (including
Glennallen area), which will be mostly dry. While there are still
some minor model differences with individual short-waves, they are
much closer than previous days on locations of heaviest rain as
well as duration of steady rain. Based on the new guidance, have
trended higher with rainfall amounts through tonight, with a large
area of 0.40 to 1.00 inch extending from Prince William Sound to
Anchorage and the Mat-Su. Uncertainty is higher for amounts on the
western Kenai Peninsula, though generally expect lighter amounts
with the best forcing remaining to the north.

The Gulf low will weaken as it tracks to the north Gulf coast
tonight, with the upper center opening up into a trough. The GFS
remains stubbornly quite a bit stronger with the low, though
other models have trended just a bit that direction. Thus, have
introduced some small craft advisory level winds along the
northern Gulf coastal waters (south of Prince William Sound and
Cordova). As the upper low approaches Southcentral tonight the
short-waves bringing all of the rain today will begin to exit
off to the north and west. Precipitation over Southcentral will
diminish and become more showery in nature. Models vary on the
ultimate track of the remnants of the upper low across
Southcentral tonight into Thursday, which leads to some
uncertainty in the most likely spots to see showers. What is
certain is that strengthening onshore flow behind the remnants
of the low will lead to widespread precipitation along the north
Gulf coast and Prince William Sound regions through Thursday.

Gusty southeasterly gap winds are expected both today and Thursday
as the thermal trough retreats inland and a surface ridge builds
into Southcentral. Winds will likely be stronger and more
widespread on Thursday due to marginally warmer temperature inland
(and perhaps some breaks of sun) along with pressure rises behind
the remnants of the Gulf low.

The last of the short-waves will exit northward Thursday night
into Friday, with a weak short-wave ridge building overhead.
Thus, expect precipitation to taper off (lingering longest along
the eastern Kenai Peninsula). Friday looks like it could be a
nice day, with abundant sunshine and temperatures rebounding
back into the 60s for most areas.

Weather for Kodiak Island will be quiet the next couple days,
as they are situated away from the key features discussed above.
Guidance is in good agreement that a deep low will lift out of
the base of the long-wave trough and track up to the Gulf Friday
night/Saturday. This would bring a return of rain and wind to
Kodiak as early as Friday evening.

-SEB

&&


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

An arctic low is continuing to move southward across the Bering
Sea this morning. Cold air is advecting south with this upper low.
Temperatures have continued to decrease to around freezing in the
Pribilofs. Over Southwest Alaska, showers have lingered across
Bristol Bay with southerly flow.

Northerly flow is expected to follow behind the sinking low. Snow
showers have started in the Pribilofs this morning and will
continue through late tonight. Precipitation will spread south
towards the eastern Aleutians and the Alaska Peninsula where the
initial front has moved through and the next wave of precipitation
awaits. Precipitation for this area could be showery and should
start off as rain, but as the colder air advects southward, rain
could switch to a mix or even completed over to snow tonight.
Mixed precipitation could potentially extend as far west as the
central Aleutians and will depend on the location of the surface
low. Models continue to struggle with the wobbly and meandering
nature of the low.

Meanwhile over Southwest Alaska, a trough over Southcentral will
reach the western Alaska Range later this afternoon. Chances of
precipitation could spill over those mountains into the Kuskokwim
Valley. Showers will gradually decrease throughout Thursday for
most places across the Bering, Aleutians, and Southwest Alaska as
the low meanders west and weakens. A few isolated thunderstorms
are possible for the western Alaska Range late Thursday
afternoon/evening as a few easterly waves move through with
marginal instability. There is still some uncertainty with the
location of convective initiation as the embedded waves have the
potential to be too far north or slightly south of where it is
currently expected.

High temperatures for the Pribilofs and Aleutians will struggle
to make it out of the upper 30s to lower 40s over the next couple
of days. Temperatures for Southwest Alaska however will trend
warmer with highs climbing into the 50s and 60s by this weekend.

-ME/rux

&&


.LONG TERM FORECAST (Days 4 through 7) Saturday through Tuesday...

The upper level Alaska map continues under an elongated trough
stretching from Siberia across the Bering into the Gulf of Alaska
with low centers moving within the pattern. The first low center
in the Eastern North Pacific weakens and merges with a second low
coming over the Eastern Aleutians. This second low in the Eastern
Aleutians loses its energy from the North and begins an Eastward
track into the Gulf through the forecast period. A weak ridge over
the Western and Central Bering interrupts additional support from
the Russian Far East in the short term. A second weak ridge
continues its hold over the Central and Northern Mainland, which
support surface thermal troughs through Tuesday.

The reconstituted low center in the Gulf spreads easterly waves
across Southcentral Alaska, bringing onshore flow over the North
Gulf Coast. Expect locally heavy showers from the Canadian Border
to Kodiak Island through early next week. With the low center`s
closest approach to the coast, gusty winds spread across the
Copper River Delta and just outside of Prince William Sound for
Monday, diminishing Tuesday. Gusty winds will occur from Sitkinak
across the Shumagin Islands to the Eastern Aleutians on Sunday.
Showers will extend along the Aleutians through Tuesday.


-Kutz

&&

.AVIATION...

PANC...A strong low pressure trough moving in from the Gulf is
expected to bring light to moderate rain into the terminal
beginning later this morning. Ceilings will lower to MVFR range as
rain begins around 18z, and some temporary reduction to MVFR
visibility is also possible during periods of moderate rainfall.
In addition, expect turnagain arm winds to reach the terminal near
the time or shortly after rainfall starts, with gusts to around 25
kts possible at times through this evening. Some improvement in
prevailing conditions is likely by this afternoon as rain tapers
off to showers and as ceilings rise.

&&


$$