Gale Warning 305, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
501 AM AKDT Thu Apr 6 2023

.ANALYSIS AND UPPER LEVELS...

A large upper-level low is centered over Utqiagvik (Barrow) while
multiple shortwaves rotate around the southern periphery of low.
One of the shortwaves is currently located over Southwest Alaska
and is tracking southeastward to Southcentral. As a result, mostly
clearing skies are seen across Southwest while broken to overcast
skies blanket Southcentral, where light snow showers are scattered
across portions of the region. A surface low located over the
eastern Gulf extends its front northward, promoting rain and snow
for eastern Prince William Sound. Gusty southwesterly winds
persist along the northwest Gulf coast, especially near the Barren
Islands. Out west, another upper low is digging southeastward
near the western Bering and Aleutians and is promoting snowfall
for the Pribilof Islands. A surface low located in the North
Pacific extends it front north towards the central and eastern
Aleutians. Weak high pressure building between the two
aforementioned lows is promoting clearing skies across the
eastern Bering and Alaska Peninsula.

&&

.MODEL DISCUSSION...

Models are in decent overall synoptic agreement for the next few
days. The main disagreement arises with a shortwave that will
track across Southcentral today. Models have generally been
trending this feature farther to the north, and they are also
moving the wave more quickly to the northeast across the Copper
River Basin. Thus, a shorter duration precipitation event is
becoming more and more likely with this shortwave.

There is also some model disagreement in regards to precipitation
type across the eastern Copper River Basin for today. The GFS is
still the much warmer solution and suggests rain, while the other
models seem to favor more of a snow/rain mix.

&&

.AVIATION...
PANC...VFR conditions and light northerly winds are expected to
persist through the TAF period. There is a chance for scattered
snow showers this morning, which could drop visibilities and
ceilings at times.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3/Today
through Saturday night)...

A short-wave trough over the Gulf will lift northeastward today
with precipitation spreading from eastern Prince William Sound
northward across the Copper River Basin. Meanwhile, a stronger
Arctic short-wave will enter Southcentral from the west early
this morning along with low level cold air, leading to snow
showers from northern Cook Inlet to the Susitna Valley. Expect
little or no accumulation as the trough continues quickly eastward
toward the Copper River Basin. This will expand the area of
precipitation in the Copper River Basin. The short-wave will then
exit northward this evening. Warmer air which moved up from the
Gulf will lead to a rain/snow mix for Valdez/Cordova areas near
sea level. The southeast Copper River Basin could also see a mix
of rain and snow, though temperatures here are less certain.
In any case, precipitation will taper off tonight, with partial
clearing from west to east and falling temperatures. The cold air
advection will cause locally gusty winds through tonight from the
western Gulf coastal waters up to Resurrection Bay and Passage
Canal. For the rest of the region , lighter winds combined with
the Arctic air mass will lead to a frigid start to the day on
Friday, with temperatures generally ranging from single digits
to teens.

Another Arctic short-wave will dive southward across western
Alaska Friday then swing eastward toward Southcentral and the
Gulf late Friday night through Saturday. As the trough digs, it
will cause a low over the northeast Pacific to lift northward
across the Gulf and toward Southcentral. It is too soon to hone
in on the details of the forecast for the weekend, which will be
heavily dependent on the track and interaction of the upper trough
and surface low. However, it looks favorable for widespread
accumulating snow across much of the region, with potential for
moderate to heavy snow along the coastal mountains. This will
also reinforce the Arctic air across Southcentral, with below
normal temperatures likely through at least early next week.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3: Today
through Saturday night)...

A bitterly cold and clear end to the week remains in store for
the entirety of Southwest, with the overall pattern in place
looking more characteristic of January than April. A deep upper
level low drifting over the northwestern Mainland will send
multiple Arctic troughs digging into Southwest over the next
several days, each reinforcing strong cold air advection from the
north and pushing temperatures marginally lower each day.
Temperatures have already plunged into the -10s this morning
across parts of the Middle Kuskokwim Valley and Kuskokwim Delta,
with similar temperatures likely to return to these areas tonight
after briefly spiking up into the 10s above during peak daytime
heating this afternoon. It will stay a bit warmer farther south
over the northern AKPen and Bristol Bay, with highs still expected
to poke up into the 20s both today and Friday.

A more potent Arctic trough will dig down into Southwest from
Friday night into Saturday, sending even colder air down to as low
as -25C at 850mb into the region and kicking up slightly stronger
northerly winds. Much stronger and gusty gap winds will also pick
back up along and south of the AKPen, increasing to/near gale
force along and south of the Pacific side coast starting Friday
afternoon and lasting well into Saturday. Nearly the entire region
will see temperatures dip below zero on Saturday night as an even
more unseasonably cold air mass advects south, with the coldest
temperatures again focused towards the north over the Kuskokwim
Delta and Lower Kuskokwim Valley. Suffice to say, it will not feel
like spring through at least the upcoming weekend.

&&

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

The main feature of interest for the next couple days will be a
low currently entering the western Bering that will elongated and
shift southeast towards the central Aleutians through Friday
evening. A broad swath of northwest gale force winds will spread
into the central and western parts of the Aleutian Chain today
along with widespread rain and snow showers transitioning to all
snow showers as low level temperatures cool. Some minor blowing
snow will be possible with the strong winds across spots including
Adak and Atka, but temperatures hovering at or above freezing
should result in a very wet snow for the most part near sea level
that won't easily be lofted by even the strong 30 to 40 kt winds
expected. The low will finally cross the Aleutians near Unalaska
into the North Pacific by Friday night, allowing winds to subside
and periods of snow to slowly clear out. A strong upper ridge will
build over the Bering on Saturday, leading to mostly quiet
conditions returning. A warm front will slowly push north into the
western Bering under the developing ridge, focusing a region of
light rain moving into the western Aleutians and spreading into
the central Aleutians by Saturday night.

&&

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

The main weather feature in the long-term continues to be an
upper-level trough anchored over the Mainland and an upper-level
ridge positioned over the western Bering. Models and ensembles
agree that temperatures will be below normal for the whole long-
term forecast period. Model spread increases in relation to how
features will interact and influence each other. A Kamchatka low
and it's associated front are expected to track into the western
Bering Monday and then will make their way into the eastern
Aleutian Chain by Tuesday. Gale force winds are still forecasted
to accompany the front as it tracks through the Bering Monday and
Tuesday. A triple point surface low is then expected to develop
near Kodiak Island by Wednesday as the aforementioned front
brings rounds of precipitation to Southwest. Models are struggling
to resolve the strength and track of the aforementioned surface
low, but precipitation looks to stay mainly confined to the
coastal locations with the possibility of precipitation spreading
inland remaining feasible depending on the strength and track of
the low. Meanwhile, out west, an upper-level ridge will build
back into the western Bering starting late mid-week through the
end of the week. No significant weather impacts are expected in
the long- term forecast at this time.

&&

SYNOPSIS AND MODEL DISCUSSION...AF
SOUTHCENTRAL ALASKA...SEB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...AS
LONG TERM...NS

PRELIMINARY LOCAL STORM REPORT...SUMMARY
NATIONAL WEATHER SERVICE ANCHORAGE AK
326 PM AKDT THU APR 6 2023

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

1215 PM     SNOW             NULL                    61.31N 149.48W
04/06/2023  M1.5 INCH        ANCHORAGE          AK   PUBLIC

            LIGHT SNOWFALL. 1.5 INCH STORM TOTAL
            MEASURED AT NOON.

0323 PM     SNOW             NULL                    61.06N 149.76W
04/06/2023  E1.0 INCH        ANCHORAGE          AK   TRAINED SPOTTER

            1 INCH OF SNOWFALL THE LAST 24 HOURS.

&&