Flood in Alaska, June 2 to 5, 2023

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
452 AM AKDT Fri Jun 2 2023

.ANALYSIS AND UPPER LEVELS...

There are a multitude of low pressure systems scattered along the
waters surrounding the State. Farthest west, a weakening low near
Adak scoots along the Chain towards the North Pacific through
Saturday afternoon, its front tracking along the Alaska Peninsula
into the eastern Bering Sea. A North Pacific low hovering near
Southeast Alaska moves its trough east to west across the Gulf of
Alaska through Saturday afternoon. Lastly, a low up north near
the Beaufort Sea extends its trough down across the northern
Interior and northern portions of Southwest and Southcentral
Alaska.

&&

.MODEL DISCUSSION...

Models are in good overall synoptic agreement through the short
term. There is still not great agreement across the models with
the weakening low on Sunday. Guidance is all pointing to a good
pull of tropical moisture from the North Pacific that looks to
bring about much wetter conditions, especially along coastal
areas.

&&

.AVIATION...
PANC...The upper level shortwaves passing through today will keep
conditions relatively the same. Gusty Turnagain Arm winds will
continue through the day today and cloud ceilings are expected to
hover around or just below 5000'. Additionally, rain is likely to
continue into this afternoon.

&&

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

Rain showers will persist from the Kenai Peninsula north across
the Mat-Su Valleys this morning as an upper-level trough moves
across the northern half of Southcentral Alaska. Showers will
likely diminish for these locations through the afternoon hours.
Slow progression of the trough, however, coupled with a broad
southwesterly flow in the mid-levels of the atmosphere, will
likely allow showers to linger across upslope areas of the
northern Susitna Valley, Talkeetna and Chugach Mountains, and
across northern portions of the Copper River Basin through Friday
evening. With temperatures this morning hovering in the lower to
middle 30s from Broad Pass to Paxson and the Tok Cutoff,
precipitation may fall as a mix of rain and snow. Little to no
snow accumulation is expected, though.

A drying trend is then expected through the weekend for most
locations as a ridge builds over the northern and eastern Gulf. A
southerly flow in the mid and upper-levels, however, will likely
keep the threat of showers over the northern Susitna and across
the coastal Kenai Mountains through Sunday. Even with the general
decrease of precipitation for most areas, the southerly flow will
should also keep clouds over much of the western half of
Southcentral through the weekend with temperatures remaining
below normal for the beginning of June.

With the trough to the north, gusty southerly gap winds will
continue through the weekend, especially across Turnagain Arm and
along the Copper River Valley.

&&

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

An upper-level ridge is progressing eastward into Southwest
Alaska and continues to slowly taper off precipitation this
morning. Meanwhile, an upper-level low near the western Aleutians
north of Adak, continues to promote wet and windy conditions
across the Bering. An associated surface low currently has its
front near the central Bering/Aleutians, and it will continue to
lift east and gradually weaken as it reaches Southwest for
Saturday morning. The aforementioned parent low is anticipated to
strengthen over the Bering and then dive south of the Aleutians
while still tracking eastward, dissipating Sunday afternoon near
the Alaska Peninsula. As a result, another round of rain and windy
conditions will be brought to Southwest for Monday. Meanwhile, a
North Pacific low is expected to reach the western Aleutians on
Sunday morning, bringing gale force wind and rain to the
Bering/Aleutians as it tracks eastward throughout the week.

&&

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

Looking into the extended forecast, there is broad agreement
between deterministic and ensemble guidance that the weather will
remain active across southern Alaska through the long-term
period. The main mechanism responsible for the unsettled weather
will be a broad upper-level low located near the western and
central Aleutian Chain Monday. This upper low drifts slowly
through Tuesday afternoon before it retrogrades back westward into
the south-central Bering Sea through Thursday morning. Numerous
shortwaves look to pivot around the upper low and into mainland
southern Alaska causing showers over to break out especially over
coastal locations. While precipitation is likely for coastal
locations through Thursday, there is uncertainty in the
precipitation forecast for inland locations, especially interior
southcentral Alaska. Meanwhile, the surface low associated with
the upper feature looks to be relatively strong. Confidence at
this time is high for a gale-force low around the eastern
Aleutians and southern Alaska Peninsula (AKPEN) Monday and
Tuesday. Heavier rain possibilities will need to be monitored for
the southern AKPEN as well as for Kodiak Island as the front
pushes northeastward Monday afternoon through Tuesday. Enhanced
precipitation is also possible for the eastern Kenai Peninsula and
north Gulf Coast Tuesday through Thursday as the front looks to
linger in the Gulf. The low then retrogrades westward back into
the south-central Bering through Thursday where unsettled weather
will persist for the central/eastern Aleutians and AKPEN.

&&

SYNOPSIS AND MODEL DISCUSSION...KM
SOUTHCENTRAL ALASKA...TM
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...NS
LONG TERM...DAN