556
FXAK68 PAFC 081320
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
520 AM AKDT Wed May 8 2024

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

Multiple shortwave troughs are moving north around a large upper
low sitting out over the Bering Sea this morning, one now crossing
the Alaska range, and the other nearing the Gulf Coast this
morning. A surface low southeast of Middleton Island is expected
to lift north with the new shortwave lifting towards Southcentral,
eventually moving into Prince William Sound this afternoon as it
weakens and shears apart over high terrain.

Looking at the pattern into the remainder of the week, things will
unfortunately look much more reminiscent of fall than late
spring. As the shortwave trough and low arriving near the Gulf
Coast begin to move inland this afternoon, rain and higher
elevation snow will spread from the coastline into interior
Southcentral, first into the Kenai Peninsula, then up into
Anchorage and the Mat-Su Valleys. Lighter rainfall is expected to
briefly lift past lower elevations of the Copper River Basin, with
amounts of generally a tenth of an inch or less through tonight
not expected to noticeably exacerbate ongoing flooding concerns
across the Glennallen area. Farther east, heavier rainfall
amounts as high as half an inch will be possible with the main
wave of precipitation moving through Anchorage and the Mat-Su
through tonight.

Late tonight into Thursday morning, steady rain will end from
south to north as the shortwave trough exits towards the northern
Alaska Range. Rapid pressure rises at the surface behind the
trough passage will also lead to a short lived burst of stronger
gap winds late tonight into early Thursday, most notably out of
the Copper River up into Gulkana/Glennallen. Gusty gap winds will
also be aided by a push of cold air advection from the south until
the pressure gradient weakens along the coast later on Thursday
morning. Cooler than average temperatures will prevail as cooler
air streams in from the Gulf, with widely scattered rain showers
and mountain snow showers expected to persist in general.

The main low in the Bering will swing east into Kodiak Island and
the western Gulf by Thursday afternoon, pushing another wave of
showers past Kodiak before becoming yet another open wave trough
on approach to Southcentral. There is some lingering uncertainty
regarding the exact trajectory with the main energy with this
trough, but overall expect more cold rain to spread back into the
Prince William Sound and out to the Mat-Su/Anchorage areas as the
wave lifts north late Thursday night into Friday morning. Low
level temperatures will start out notably cooler than what we`ll
have in place for this evening`s rainfall event. While
accumulating snow is not likely down to sea level, we very well
could see falling snow reach all the way down to the lowest
elevations for a short time late Thursday night into Friday
across the Mat-Su and Anchorage before the trough axis lifts to
the north on Friday. Cooler than normal but drier conditions
(except near Kodiak) will persist into Friday.

-AS

&&


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

A broad upper low resides over the central Bering Wednesday
morning with weak high pressure over Southwest Alaska and the
Western Aleutians. Low pressure over the Gulf of Alaska has aided
in the movement of easterly wave activity along the boundary into
interior Bristol Bay, and forecast models suggest this
precipitation may continue into the afternoon.

A polar low near the Pribilof Islands drops southward across the
Alaska Peninsula. The low will bring cooler temperatures, gusty
winds, and snow. The combination of winds and snow will result in
periods of reduced visibility down to one half mile. Gusty
conditions are expected to linger into Wednesday evening from
Nikolski to Unalaska. Westerly gusts up to 45 mph will be
possible.

After the polar low departs the Aleutians and moves into the
North Pacific, a Kamchatka Low is forecast to spread a broad front
into the Aleutians through Thursday night. Widespread
precipitation will accompany the front and span the Aleutian Chain
as it tracks from west to east, beginning Wednesday night.
Previously cooler temperatures over the Aleutians should lift
northward and become replaced by warmer North Pacific
temperatures. Thus, any initial snow will be brief and quickly
transition to rain.


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

A broad upper level trough extends across the Bering and most of
Mainland Alaska through the forecast period. A weak upper ridge
moves out of the Russian Far East Sunday, but flattens out over
the Aleutians by Tuesday. Model guidance is good through late
Sunday, but becomes uncertain across the Aleutians as the ridge
collapses and a new overall flow sets up. A couple new features
out of Siberia begin to influence the pattern Tuesday. A well
developed upper low moves across the Alaska Peninsula into the
Gulf of Alaska by Sunday, then weakens and opens to a broad trough
for Tuesday. Its surface reflection moves from the Eastern
Aleutians into the Gulf, spreading a very active weather pattern
along its track Eastward.

Widespread precipitation spread across the Aleutians, AKPEN and
Southwest Alaska into Kodiak Island Saturday, and continues along
the Eastern Kenai Peninsula into Prince William Sound and the rest
of Southcentral Alaska through Sunday before tapering off in the
Western portions. Locally heavy rainfall is expected for coastal
locations from the Eastern Aleutians and AKPEN, over Kodiak
Island, and across to the Gulf into Monday, with decreasing
amounts moving inland. Gusty surface winds to just below gale
force levels precede the low across the Gulf through Sunday before
diminishing. Breezy conditions over the Eastern Bering and
Bristol linger into Monday.

- Kutz

&&

.AVIATION...

PANC... VFR ceilings this morning likely to begin transitioning
to MVFR by this afternoon. Variable winds this morning will shift
southerly similarly by the afternoon, introducing gusts up to 20
mph through this evening. Showers are expected to develop over the
terminal by this afternoon as well with reductions in visibility
possible down to MVFR levels. Showers to become increasingly
sparse by late this evening.

&&


$$