Gale Warning 117, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
534 AM AKST Sat Feb 4 2023

.ANALYSIS AND UPPER LEVELS...

With a longwave trough situated to the west over the Bering Sea
and a broad longwave ridge to the east over western Canada, the
southern mainland of Alaska lies in a continued southwesterly flow
regime this morning. Various sub-gale force lows are rotating
about a common center within the central Bering Sea, producing a
mostly showery pattern with several ill-defined fronts enhancing
precipitation found across the southern Bering and Aleutians. Over
the northern Bering, more widespread stratus is present.
Southwest Alaska remains mostly blanketed in low stratus, with
southwesterly flow allowing for some isolated snow showers in the
Kuskokwim Delta, which appear on Bethel radar.

To the east, a lifting shortwave is providing upper-level support
for a weak low in the northern Gulf. A baroclinic leaf structure
has developed overnight on satellite imagery with this feature
and light snow along the north Gulf coast has begun to spread
inland. Over the past several hours, reflectivities from the Kenai
radar have increased, with locations in Anchorage reporting
snowfall. Along the coast, snow levels are at sea level, with
locations like Whittier and Cordova below freezing and reporting
snow.

&&

.MODEL DISCUSSION...

Model guidance is in fairly good synoptic scale agreement for the
short term. Agreement has increased with the track of the low
entering the western Gulf Sunday morning. The track has shifted
slightly westward, with most models indicating the center tracking
over the Kenai Peninsula, with some portion of the low moving up
Cook Inlet. GFS remains the furthest west solution. On the smaller
scale, individual shortwaves within the broader low remain in poor
agreement.

&&

.AVIATION...
PANC...MVFR ceilings and visibility are expected with light snow
continuing into late morning. This afternoon, snow should taper
off, improving visibility. While not the prevailing forecast, IFR
ceilings may develop this evening, though this will depend on the
degree of clearing of higher clouds that occurs as the snow moves
out. Northerly winds will begin to increase at the terminal by
Sunday morning to around 10 kt and this should scour out any
lingering lower ceilings.

&&

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

Another shortwave trough will bring another round of light snow to
Anchorage and the Mat-Su valleys today, with 1 to 2 inches for
most areas. Up to 4 inches of snow is possible across northern
portions of Wasilla and Palmer due to upslope conditions. The
shortwave will move north this afternoon, bringing light snow to
the Copper River Basin, while snow will taper off across
Anchorage and the Matanuska Valley by the afternoon and evening
hours.

Our focus then turns to a strong low pressure moving towards the
southwestern Gulf and Kodiak Island Sunday morning. This will
bring a substantial increase in the winds with widespread gales
across the Gulf and areas of storm force winds near the Barren
Islands, the Kamishak Gap, and Shelikof Strait, eventually moving
into the northern Gulf producing storm force winds where the
barrier jet typically sets up near Middleton Island. This system
will also bring a brief period of snow to Kodiak City, with
perhaps an inch of snow by early Sunday morning quickly changing
to rain. Moderate to heavy precipitation will develop across the
eastern Kenai Peninsula and Prince William Sound, bringing up to
a foot of snow near Portage and Turnagain Pass. Winds will also
increase across this area Sunday morning, with blowing snow
likely through Sunday evening. A Winter Weather Advisory is in
effect on Sunday for blowing snow around Turnagain Pass and the
Portage Valley. Snow levels are expected to remain near sea level
as the warm air is shunted off to the east as the occluded front
weakens, allowing Cordova and Seward to see several inches of
snow as well.

As the low moves north Sunday night there is some model
disagreement on the track of the low. The NAM and GFS take it up
Cook Inlet while the GEM and EC take it near the eastern Kenai
Peninsula. However, the GEM and EC are tracking it farther west
on the latest runs. This track will influence the strength of the
winds across the Kenai Peninsula and the Anchorage area, with the
potential for gusty south to southeasterly winds up Cook Inlet
and around the Anchorage Bowl. Additionally, as this low moves up
Cook Inlet a band of snow is expected to spread across the western
Kenai Peninsula and move north into Anchorage and the Mat-Su
valleys on Monday, with a couple inches of snow possible.

&&

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

A mildly unsettled pattern continues today, becoming moderately
unsettled Sunday into Monday. Overall, nothing substantial is
expected. There will be drier conditions this morning, and with
the complex pattern shifting eastward there will be periods of
showery activity across Southwest this evening, with the bulk of
the precipitation chanced over western Bristol Bay (Dillingham and
surrounding areas) and along the Alaska Peninsula. New snow
accumulation is expected between 4 and 6 inches from Dillingham
north, and 3 to 4 inches along the Alaska Peninsula from Egegik
south. Winds will shift to northerly and become gusty during the
peak of the snowfall, so there is a chance for periods of blowing
snow. Cold air creeps back in behind the system, which will allow
temperatures to drop into the low teens and single digits Sunday
night and Monday night.

&&

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

The complex pattern with multiple weak embedded surface lows
shifts eastward over the next couple of days and widespread,
light, showery conditions will continue across much the the Bering
Sea and Aleutian Chain. There remains some model inconsistencies
with pinpointing low centers and timing, which is common in these
complex systems, but the impacts, however, will be limited.
Colder air will filter in around the backside of the system and
increased northerly winds will spread across the western Bering
and Western/Central Aleutians by Sunday.

&&

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

Overall confidence remains rather high with the long-term weather
pattern remaining relatively active over Bering Sea/Aleutians, and
average for Southern Alaska. For Southcentral and Southwest
Alaska, there is reasonable agreement Tuesday through Wednesday
morning with guidance depicting a negatively tilted trough,
stemming from a Siberian upper-level low, lifting northeastward
from the eastern Bering Sea/North Pacific and through Southern
Alaska. The result is greater precipitation chances for Bristol
Bay communities, Prince William Sound communities, as well as for
the northern Gulf Coast. Interior Southcentral Alaska, including
Anchorage, could also see precipitation from this upper trough
system, but the degree to which potential downsloping occurs makes
the degree of uncertainty greater. The surface feature and
frontal feature associated with the upper trough is also somewhat
contested. While the GFS/CAN ensemble means have the surface low
near Prince William Sound, the ECMWF ensemble mean is slower with
low progression, and has it more south in the southern Gulf of
Alaska. After Wednesday, deterministic guidance agreement breaks
down tremendously. All have varying solutions from zonal west to
east flow over Southern Alaska, to potential ridging and a period
of quieter weather, to continued activity. However, the various
ensemble means hint at a possible upper ridge moving from west to
east from the Bering Sea and to the Southern Mainland Thursday and
Friday. However, confidence this far out is low.

Out west, the pattern remains quite chaotic throughout the long-
term period with the continuation of the Siberian trough and
multiple troughs digging southward from Kamchatka, through the
Bering Sea, and into the North Pacific while progressing eastward.
Each set of guidance has varying solutions for position/timing
and strength on the surface features with these upper-level
systems. Also, between systems, there will be little shortwave
west to east transient ridges. However, odds tilt toward little in
the way of sustained ridging across the Bering and Aleutians. One
such system that does have reasonable model agreement at both the
deterministic and ensemble levels, is a deep upper-level low
progged to impact the western Bering and western Aleutian Chain
towards the end of the long-term on Thursday into Friday. At this
time, the GFS and ECMWF deterministic and ensemble means both
show a more northerly track from the North Pacific into the
western Bering and a stronger system. Meanwhile, the Canadian
deterministic and ensemble guidance both show a more southerly
track and weaker system. There are strong signals that this low
could bring storm-force winds to the western and central Aleutian
Chain Thursday and Friday in addition to heavy precipitation.
Stay tuned to the forecast as details on this potentially strong
storm system come into better focus with time.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Winter Weather Advisory 125.
MARINE...Storm Warning 119 130-132 138 139
         Gale Warning 120 125 136 137 140 150 155 175
         Heavy Freezing Spray Warning 180 185.
FIRE WEATHER...NONE.

&&

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

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE ANCHORAGE AK
1005 AM AKST SAT FEB 4 2023

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

0830 AM     SNOW             6 SSE ANCHORAGE         61.14N 149.82W
02/04/2023  M3.5 INCH        ANCHORAGE          AK   PUBLIC

&&

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE ANCHORAGE AK
1038 AM AKST SAT FEB 4 2023

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

0830 AM     SNOW             SOUTH ANCHORAGE         61.11N 149.85W
02/04/2023  M3.5 INCH        ANCHORAGE          AK   NWS EMPLOYEE

            SPOTTER MEASURED 3.5 INCHES OF NEW SNOW AT
            THE INTERSECTION OF THE SEWARD HIGHWAY AND
            HUFFMAN ROAD.

&&

ED

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE ANCHORAGE AK
1124 AM AKST SAT FEB 4 2023

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

1047 AM     SNOW             EAGLE RIVER, AK         61.31N 149.48W
02/04/2023  M3.0 INCH        ANCHORAGE          AK   PUBLIC

            SPOTTER MEASURED 3 INCHES OF SNOW.

&&

ED