000
FXAK68 PAFC 301301
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
501 AM AKDT Thu Mar 30 2023

.ANALYSIS AND UPPER LEVELS...

A negatively tilted trough extends from Siberia, through Southwest
Alaska, and into the southwestern Gulf of Alaska. At the base of
this trough is a strong shortwave around Kodiak Island which
drifts eastward this morning. The associated surface low, also
drifting eastward towards the central Gulf of Alaska, is helping
to pull moisture northward into the north Gulf coast and interior
Southcentral Alaska. The result is a continuation of off-and-on
showery and light precipitation over Southcentral, but especially
over Prince William Sound and the northern Gulf coast.

Out west, weak shortwaves continue moving on-shore into Southwest
Alaska from the Bering Sea as the trough axis moves overhead. The
result is a continuation of relatively low cloud ceilings for the
coast, especially the Kuskokwim Delta coast, while interior
locations such as Sleetmute, Sparrevohn, Aniak, and Iliamna
contend with light snow. Meanwhile, the southern Alaska Peninsula
and eastern Aleutians are under the influence of northwesterly
flow on the backside of the trough over Southwest. These areas
continue to have off-and-on convective and showery precipitation
within the cold air advection coming off the Bering Sea. The
western to central Bering as well as the western and central
Aleutian Chain remain under nearly west-to-east zonal flow this
morning.

&&

.MODEL DISCUSSION...

Guidance remains in fairly good agreement with regards to features
during the short-term period. Guidance, namely the 00z NAM, shifted
southward (the GFS solution) with the surface low in the Gulf for
this morning. As a result, the bulk of heavier precipitation will
remain off-shore with only light precipitation making it inland,
even for the coastal locations of Southcentral. Guidance continues
to be in agreement on this low drifting slowly eastward through
the central Gulf and eventually southeastward towards the Pan
Handle towards Saturday night as it weakens.

Out west, guidance continues to be in agreement on a northeast
Bering Sea low moving into the Yukon Delta Thursday afternoon
while weakening, then south and southeast into the Kuskokwim
Delta Thursday night. This will linger light snow in the
lower/middle Kuskokwim Valley, the Kuskokwim Delta, and especially
along the northwest facing slopes of Kilbuck and Kuskokwim
Mountains through Friday night. Guidance also continues to hone in
on a North Pacific low and its front lifting northward towards the
western Bering as well as the western and central Aleutian Chain.
Guidance has trended further north with this low towards the GFS.
Most guidance has the system a little southeast of Shemya by
Friday night, while the 00z Canadian guidance is the furthest
south in the North Pacific, but not far off of other guidance. The
forecast challenge will continue to be honing in on precipitation
amounts. There are hints that the central to eastern Aleutian
Chain could see the most enhanced precipitation due to being in
favorable southerly to southwesterly throughout most of the
atmosphere for an extended period of time at the end of the
short-term.

&&

.AVIATION...

PANC...VFR conditions with possible MVFR ceilings will persist
through the morning as light snow lingers through the morning
hours. There may even be some IFR ceilings as low-level moisture
lingers with light winds. Snow tapers off during the afternoon
hours. However, low-level moisture could linger longer to procure
a low stratus deck and thus, a potential to linger MVFR ceilings
from this afternoon into the evening hours. Expect light northerly
winds to continue through this morning and become light and
variable through this afternoon and evening.

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

Lingering precipitation across Southcentral will remain light as
the low over the Gulf begins to trek east. Overall precipitation
will consequently decrease gradually from west to east. Weak cold
air advection across the Alaska Peninsula and Kodiak Island will
allow for breezy conditions over Kodiak Island and gales over the
water through the end of this week. Northerly flow will also
prevail across Southcentral through the end of the week. Outflow
winds through terrain gaps will gradually increase Friday night
through Saturday as a dry shortwave off a polar low moves through
and a ridge builds behind. For the end of the weekend, warmer air
returns with quieter weather as a brief ridge moves into Southcentral
and winds taper off.

&&

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

Southwest Alaska will remain under an upper trough today and
tomorrow. Areas of light snow will continue from the Kuskokwim
Delta into the Lower Kuskokwim Valley. Minimal accumulations are
anticipated, with the lower elevations only seeing a dusting to an
inch through early Friday. Across the Kuskokwim Mountains, snow
amounts of 4 to 8 inches will be possible; while further east,
the great town of Sparrevohn could see around 4 inches.
Temperatures will remain mild while beneath the upper trough.
Clearing is expected by the start of the weekend as a shortwave
ridge moves across Southwest.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3)...

The Bering Sea will remain in a northwesterly flow pattern while
a trough loiters over Southwest Alaska today and tomorrow. This
should promote gusty northwest winds offshore of the Southwest
coast with 30+ knot gusts stretching from Nunivak Island into
Bristol Bay. South of the AKPEN, gale-force gusts are expected to
continue through the morning hours on Friday. A North Pacific low
then lifts into and hangs up over the Western and Central
Aleutians on Friday with widespread shower activity expected. A
plume of Pacific moisture will accompany the low and its front,
with localized areas of heavy rain possible over Atka and Adak.
Models suggest the front will become more progressive by Saturday,
eventually scooting eastward and into the Alaska Peninsula over
the latter half of the weekend. While there are no flooding
concerns, currently, a close eye on the evolution of the front
over the next couple of days will be needed.

&&

.LONG TERM FORECAST (Days 4 through 7/Sunday through Wednesday)...

The pattern remains amplified during the extended period with
upper ridging extending across Southcentral Alaska on Sunday and
gradually transitioning to an upper trough pattern on Wednesday.
The odds tilt in favor of below normal temperatures and above
normal precipitation given the pattern in the extended period.

Closer to the surface, the most significant feature is a low
pressure system moving northeastward across the Gulf on Monday
and Tuesday. This low is likely to bring snow across the Kenai
Peninsula and Prince William Sound during that time. Forecast
confidence is low with respect to specifics at this time due to
discrepancies in the exact storm track. No other significant
weather is expected in addition to this aforementioned low.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...DAN
SOUTHCENTRAL ALASKA...RUX
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...LAW
LONG TERM...ED

000
FXAK67 PAJK 301406
AFDAJK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
606 AM AKDT Thu Mar 30 2023

.SHORT TERM...The forecast remains largely on track as a gale
force front advances across the gulf and approaches the panhandle.
Cloud cover has already begun to overrun much of SE AK and snow
is being reported at Yakutat. Anticipate gale force winds and
small craft winds across many of the maritime areas, and breezy
conditions across land. Wind directions across parts of the N
panhandle and locations like Lynn Canal could fluctuate at times,
as the pressure gradient force goes up against the surge of WAA
associated with the system, but am confident in elevated seas
regardless.

Precipitation wise, some areas in the northern third of the
panhandle may start out as snow or a wintry mix as the system
moves in through tomorrow morning and changeover to rain
relatively quickly as the day progresses along with the southerly
warm air advection out ahead of the front. Areas near the Canadian
border crossings should remain in wintry precipitation once it
starts, but amounts should remain light as the atmosphere will
remain drier there. Yakutat has started out as snow but will
likely transition to a rain/snow mix, and then change back over to
a wintry mix or snow for Thursday night. Snow accumulations
should remain below advisory levels, with snow totals between less
than an inch to up to 3 inches in total.

.LONG TERM.../Friday into next week/...The long term forecast was
focused on the aftermath of the next frontal passage. Previous
ideas of rain turning to showers, or on/off type rain, seems to be
still holding true.

Friday will start off with mostly rain found around the panhandle,
though some rain and snow is possible in parts of the north. But as
the diurnal heating warms the area up to the low to mid 40s, rain
should become the dominate precip type.

The low pressure center will track SE and out of the gulf Saturday.
This will give decreasing PoPS from north to south through the day
and night. Also, it will be the beginning some outflow winds.

Early evidence in the ensembles and deterministic models show a
quick moving, weak surface low tracking through the gulf on Sunday.
This will bump up the PoPS for showers to the chance-likely
category (briefly).

But once that low exits to the south, outflow winds will really
help to decrease PoPS and increase the sunshine for for Monday
afternoon. After that, the next front is set to move in from the
west on Tue/Wed.

Inner channel marine winds don`t look real strong through the long
term, with most areas seeing wind speeds around 15 to 20 knots at
the start, decreasing to 10 to 15 knots for Sunday, then increasing
to 15 to 20 knots for early next week.

Low temperatures will warm a touch, due to cloud cover and southerly
winds. But once the northerly winds kick back in, lows could dip
back into the 20s for early next week. High temperatures more-or-
less stay steady, in the low 40s through the weekend into next
week.

&&

.AVIATION...Clouds continue to increase across the panhandle this
morning. Ceilings have started to decrease during the overnight and
into the morning hours with some locations reporting MVFR
conditions. These conditions will become more widespread as the
front moves closer to SE AK. Precip will spread across the area
throughout the morning with most places seeing rain, but a mix of
rain and snow or straight snow can not be ruled out either. LLWS
looks to increase during the afternoon and evening as the front
nears the outer coast.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Small Craft Advisory from 4 PM this afternoon to 6 AM AKDT
Friday for AKZ322.
MARINE...Gale Warning for PKZ664-671.
Small Craft Advisory for PKZ022-031-033>036-053-641>644-651-652-
661>663-672.

&&

$$

SHORT TERM...GFS/JLC
LONG TERM....GJS
AVIATION...SF

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