Gale Warning 520, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
518 PM AKDT Thu Sep 14 2023

.ANALYSIS AND UPPER LEVELS...

A small but potent low pressure system over the northern Gulf is
continuing to move swiftly north this afternoon. The center is now
approaching Cordova. Areas of light to moderate rain are occurring
all along Prince William Sound. The scattered rain showers that
lingered along Cook Inlet into the Mat-Su Valley diminished in
coverage. Farther west, a trough moving onshore brought areas of
showers to that region as well, although most activity was along
the coast. Along the western Aleutians, another system was
bringing rain and gusty winds.

&&

.MODEL DISCUSSION...

Models continue to struggle with the exact details for the series
of strong lows expected to track between the Aleutians/AKPen and
Gulf over the next several days. Models have displayed fairly poor
temporal and spatial agreement for two larger systems in
particular. The first low is still expected to form near the
AKPen later today or tonight, then move into the Gulf near Kodiak
on Friday morning. Models diverge with the track from there,
taking the center out to anywhere from the southern Kenai
Peninsula to out in the central Gulf by Friday night. Similar
track discrepancies remain for the track of a low expected to move
along or just south of the Aleutian Chain on Friday, then south
of the AKPen by Saturday. This second system will be moving in
right on the heels of the first, and the two centers could come in
close enough proximity to each other to alter each other's
trajectory by Saturday. There are still a lot of details up in the
air for the upcoming series of storm systems.

&&

.AVIATION...
PANC...Periods of rain and MVFR cigs expected to continue through
early Friday morning becoming VFR. Gusty south to southeast winds
will impact the terminal this evening through the overnight
hours. Winds will slacken after 12Z as winds turn to more north to
northeasterly after 18Z.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3)...
Steady rain and rain showers from the Susitna Valley through
Anchorage Bowl and the Matanuska Valley will continue early this
evening. Rain will diminish in area and intensity through the
evening from southwest to northeast as the upper level trough
moves inland. There will be a brief break in rain for most areas
except for Whittier/Cordova/Valdez. The next system develops in
the Gulf of Alaska through the day on Friday, continuing steadier
rain along the upslope coastal areas, however, the general
southeast flow aloft will keep the lee-side of the Chugach drier
from Homer through Anchorage to the Matanuska Valley. Late
Friday/early Saturday, a gale-force front associated with the
system will move along the coast toward Hinchinbrook Entrance.
The majority of the rain will stay away from the Anchorage area
but some sprinkles or very light rain can't be ruled out in this
pattern along with continued cloudiness.

The following system moves into the Gulf on Saturday, likely
bringing some storm-force winds to the far southern Gulf and
along the northern Gulf coast as well. That system looks to mainly
affect Kodiak Island and coastal areas with rainfall, though with
this system there is a better chance of some light rain sneaking
over the mountains as cross-barrier flow is less than the current
system. Overall expect a continuation of very fall-like
conditions, cool, cloudy and generally rainy.

&&

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

The unending progressive pattern continues. The first weather
system bringing rain to Southwest today will be winding down as
it slides to the southeast across the Gulf of Alaska. Despite
winding down, on and off showers will persist across Southwest
overnight with a lull towards the morning hours. Clouds and
onshore winds mean temperatures will be pretty stagnant through
the weekend. Highs will remain in the low 50s with lows right
around 40 degrees.

The next weather maker is lifting up through the western Bering
and will be bringing copious amounts of precipitation to the
western Aleutians tonight and into Friday. This low has an
incredibly deep fetch of warm and moist air from nearly 30
degrees north (which is nearly as far south as Hawaii). This low
will deepen to nearly 980mb Friday afternoon over Adak. Rainfall
totals with this storm could surpass 2+" over 24 hours and
driving, near gale force winds, will make travel difficult. By
Sunday afternoon, this low will deepen further as it moves towards
Kodiak. Winds behind this low will bring strong winds out of
bays, passes and gaps from Dutch through the AKPEN.

Sunday evening and into Monday is another repeat scenario, but
further east, of what will pan out this weekend. A new North
Pacific low is slated to charge north, hitting the central
Aleutians and sliding east early into the next week. Behind this
system is yet another low that will drop out of the Kamchatka
Peninsula bringing unsettled weather across all of the Bering.

&&

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

The latest long term forecast has a low moving through the Gulf
of Alaska and a second low moving into the Bering on Monday.
Surprise! Unsettled conditions with continued rain chances look to
continue for the foreseeable future. Yesterday there was mention
of Invest 93W, currently located in the West Pacific. Models have
struggled with whether this low will be picked up by an earlier
trough or get missed initially and lifted into the Aleutians over
the weekend. We will lean with the latter scenario and Monday's
Gulf low should possess a fair amount of moisture associated with
it. Thus, the Gulf will remain quite showery with potential for
heavy rain lifting into eastern portions of Prince William Sound
and Southeast Alaska. Additionally, a threat for high winds may
develop within barrier jet flow from Yakutat to Icy Bay as the low
finally moves into the eastern Bering. To the west, the low
moving through the Bering on Monday is expected to be much broader
in size, but also less intense, as it moves across the Aleutian
Chain through the middle of next week. Showery conditions will
plague both the Aleutians and the Bering through Wednesday. The
same low expands into Southcentral Wednesday into Thursday. Thus,
precipitation chances, initially low for Southwest, will increase
significantly by late Tuesday through Wednesday. Southcentral may
see a brief break from precipitation on Tuesday before
precipitation becomes more substantial and widespread across
Southcentral Tuesday night into Wednesday.

&&

SYNOPSIS AND MODEL DISCUSSION...NR
SOUTHCENTRAL ALASKA...ML
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...SS
LONG TERM...BL