National Weather Service Raw Text Product

239 
FXAK68 PAFC 261324
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
524 AM AKDT Sun May 26 2024

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3: Today
through Tuesday Night)...

We did it! Anchorage finally cracked 60 degrees yesterday, 
marking the first 60 degree since September 5th. This is 
approximately two weeks later than the average first 60 degree day
and the latest occurrence of the first 60 degree day since 2000. 
Similar weather with highs around 60 are on deck for Southcentral
Alaska for the next several days. 

GOES water vapor imagery shows a couple distinct features that'll
play a role in our weather to start the week. The first and 
foremost feature impacting weather across southcentral is a very 
broad upper-level low positioned across the Gulf of Alaska / far 
Northeast Pacific. Satellite also shows an upper-level low moving 
from the North Slope towards west-central Alaska, as well as a 
series of low-amplitude shortwaves from eastern AK back through 
Canada. This places much of southcentral Alaska in a col, or 
essentially a saddle between troughs and ridges. Precipitation for
the next 2-3 days will largely be driven by 1) westward- 
propagating shortwave troughs (easterly waves) on the northern 
periphery of the Gulf of Alaska low into the Copper River Basin 
and 2) diurnally-driven instability. 

As of 4am, satellite imagery shows one of these subtle easterly 
waves moving across the Copper River Basin. Radar imagery and 
ground observations note rainfall primarily from Glennallen south 
into the central and eastern Chugach and Prince William Sound. 
This area of rainfall (and high-elevation snow) will continue 
shifting east through the morning but essentially taper off as the
wave shears apart. High-resolution ensemble forecast (HREF), 
particularly the HRRR, suggests convection across the Matanuska 
Valley and into Anchorage later this evening. The probability 
remains low and will be dependent on instability and what's left 
of the aforementioned wave- but did increase PoPs from the 
previous forecast. Otherwise, today will be a rather pleasant day,
particularly for areas west and south of the Talkeetnas, where 
breaks in the cloud cover are likely observed. 

Monday and Tuesday will be similar to Sunday in that the highest
PoPs will be focused across the Copper River Basin southwards 
towards the eastern and central Chugach. In fact, confidence is 
increasing that much of the Copper River Basin will receive 
rainfall throughout Monday. The Mat-Su Valley, Anchorage, and 
Kenai Peninsula may see isolated showers with daytime heating- 
driven instability, but synoptic-scale features are lacking for 
more organized precipitation.

-Brown

&&


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

Nighttime microphysics satellite imagery shows clearing 
conditions spreading southward into Southwest Alaska this morning.
Weak northerly flow and "drier" conditions will filter their way 
down into Bristol Bay. As a result, afternoon highs are expected 
to warm into the upper 50s with low 60s possible for parts of the 
Lower Kuskokwim Valley and Greater Bristol Bay areas. Saturday 
saw some showers and thunderstorms develop along the Kuskokwim 
Mountains in the afternoon and evening hours. On Sunday 
instability will be more limited, but roughly 200 J/kg of MUCAPE 
may be realized over eastern parts of Bristol Bay, nudged up 
against the Western Alaska Range, where renewed showers and wet 
thunderstorms will be possible.

Over the Bering and much of the Aleutians, widespread low stratus
and areas of fog have developed beneath subsidence created by the
transient ridge of high pressure. A Kamchatka low is bringing a 
front into the Central Aleutians with increasing southeasterly 
winds gusting to gale force. However, this front will weaken 
throughout the day on Sunday on the thermal gradient along the 
front becomes more diffuse. An elongated area of low pressure is 
expected to form along the front on Monday as the ridge begins to 
break down over the Bering. Unsettled conditions are forecast over
the Eastern Aleutians and Lower Alaska Peninsula on Monday, with 
low pressure becoming more amplified over the Bering on Tuesday. 

-BL

&&


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

Ridging over mainland Alaska on Wednesday will help clear skies up
over Southcentral during the day. The calmer weather will be short
lived however as energy from an upper-level trough in the eastern
Bering surges eastward and pushes the ridge to the north. This 
pattern change will re-introduce widespread cloud cover and 
chances for precipitation across the region as the system 
progresses. The trough will dive further south and east into the 
North Pacific by Thursday afternoon before the upper-low migrates 
northward into the Gulf and towards Prince William Sound by 
Saturday afternoon. 

Another upper-low will start to form near the western Aleutians 
late Thursday and move eastward through Saturday, providing a 
chance for precipitation across the Aleutians and Bering. The 
positioning of this low and the one in the central Gulf by 
Saturday is still undetermined. Some model guidance is suggesting 
that they will interact and even start to merge near the Alaska 
Peninsula, while other models keep both systems separate from each
other. This would result in the Gulf low remaining closer to 
Prince William Sound and the western low positioning itself near 
the central Aleutians. In either scenario, broader troughing will 
persist over most of the forecast area, producing cooler and 
unsettled weather through at least the start of next weekend. 

-BS

&&

.AVIATION...

PANC...VFR conditions and light winds will generally persist. A
week upper disturbance moving in from the east could help set off
a few rain showers near the terminal later this afternoon. 
Increasing cloud cover ahead of this approaching upper wave is 
likely through this afternoon as well, and ceilings with this deck
could hover near the 5000 ft threshold at times.

&&


$$