244
FXAK68 PAFC 220108
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
508 PM AKDT Fri Jun 21 2024

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3:
Tonight through Monday)...

The low south of the Gulf of Alaska is drifting southward which
has allowed a ridge to build over the Kenai Peninsula, Anchorage
and eastward along the north Gulf coast. However, an unstable air
mass is descending into Southcentral with showers and
thunderstorms expected to develop along the Alaska Range and drift
southward through the evening. Saturday will see some clearing
for the morning, but temperatures will get quite warm over much
of the area with widespread 70s and the portions of the Susitna
Valley reaching into the lower 80s expected. With this unstable
airmass entrenched over Southcentral, the warm day will kick off
more widespread showers and thunderstorms across the area. These
storms should initiate over the mountains with some of them
drifting southwestward to lower elevations after they develop.
Sunday will see a similar pattern though temperature should be a
tick lower than Saturday.

Some of the warming Saturday will be driven by gusty northerly
winds. The strongest winds are expected to be across northern
portions of both the Susitna Valley and Copper River Basin. With
very warm temperatures and low Relative Humidity values, a Red
Flag Warning for fire weather conditions has been issued for these
areas for Saturday.

Monday will see continued warm temperatures with afternoon and
evening showers and thunderstorms. There is a little more intrigue
as well as models are trying to figure out whether there will be
a weak 500 mb wave that moves close to the area from the west or
if the upper level ridge will strengthen and re-establish itself
at that time. It still looks overall like diurnal convection, but
this could become more organized from this wave, or the ridge
could win-out and suppress the storms so there is more uncertainty
for Monday.

&&


.SHORT TERM FORECAST SOUTHWEST ALASKA, THE BERING SEA/ALEUTIANS
(Days 1 through 3: This afternoon through Monday afternoon)...

The big picture of the forecast remains largely unchanged, though
there continue to be updates to the precipitation and
thunderstorm forecast for Southwest Alaska. Expect thunderstorm
chances to persist through the weekend for Southwest Alaska, along
with a general warming trend. For the Bering Sea and Aleutian
Islands, most areas will see light winds less than 25 kt except
for coastal marine zones south of the Central Aleutians, which
will experience winds to small craft speed as a weak low ekes by
south of the Aleutians. Model disagreement increases by Monday as
models struggle with the track of yet another weak North Pacific
low.

Diving into the details... rain showers and isolated to scattered
thunderstorms are once again moving across Southwest Alaska this
afternoon and evening. Today`s convection looks to be a bit less
robust than yesterday`s, so expect a little less lightning and
rainfall. The major change from yesterday will be storm motion;
with the steering flow shifting northerly, expect storms to move
approximately north to south today.

Thunderstorm chances continue through the weekend, with forecast
confidence slowly improving for Saturday and Sunday afternoon.
There continues to be potential for thunderstorms to move out onto
the coastal waters of Bristol Bay, so mariners are advised to stay
weather aware this weekend. Otherwise, shower and thunderstorm
coverage gradually shift eastward and temperatures climb as we
head into the weekend.

Circling back to the model uncertainty, there have been major
shifts in the projected track of a weak, North Pacific low
approaching the Western and Central Aleutians on Monday. The
biggest change with this forecast package was to delay the onset
of stronger winds and the onset of rain. The forecast may continue
to shift as models attempt to better hone in on this low.
Regardless, this weak storm system is unlikely to have major
impacts on the Western and Central Aleutians.

-KC

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

A very dynamic weather pattern is continuing to develop across
the region. A low over the Sea of Okhotsk, with associated fronts,
will track slowly eastward and weaken as it approaches the
Western Aleutians producing showers and gusty winds along its
path. Its upper level low will merge with the long wave trough
that stretches back over the Bearing Sea and into the Kamchatka
Peninsula. A North Pacific low south of the Aleutian Islands will
slowly progress towards the east and slowly strengthen as it
approaches the Gulf of Alaska. This system has the potential of
producing locally heavy precip and gusty winds in Western Alaska,
Bristol Bay and the Eastern Aleutians. Models are in fairly good
agreement in the short term but diverge greatly as the GFS keeps
the system south of the Eastern Aleutians and ECWMF speeds things
up and has the system centered over Bristol Bay by the end of the
period.

A well developed low the Northeast Pacific and associated fronts
continues to track towards the east and front spreads locally
heavy rain and gusty surface winds less than gale force across the
region and into coastal Canada with the system dissipating early
Thursday.

-Kutz/Dellinger

&&

.AVIATION...

PANC...VFR conditions will persist through the TAF period. Winds
will become light and variable overnight before picking back up
out of the south on Saturday evening. Can`t rule out a few showers
or even a thunderstorm moving off the mountains into the area, but
the probability remains very low.

&&
$$