Gale Warning 249, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
535 AM AKDT Fri Mar 17 2023

.ANALYSIS AND UPPER LEVELS...

A North Pacific low pushes into the Gulf of Alaska this morning,
tracking towards northern Kodiak Island/Barren Islands before
weakening and moving over the Alaska Peninsula this evening. There
is much better agreement with this system resulting in higher
confidence for impacts along the Southcentral Coast and Kodiak
Island. The pull of moisture from the Pacific and wrap around cold
air will transition snow to a more showery pattern with varying
intensities. An additional North Pacific low is set to move into
the Gulf of Alaska on Saturday. As with the current system, there
is still quite a bit of model divergence and uncertainty regarding
impacts remains high. Ridging is still in place over the western
Bering Sea today, but will be replaced by a weak Kamchatka front
come Saturday. The ridge will eventually flatten out with the
arrival of a system looking to approach the Western Aleutians by
Sunday.

&&

.MODEL DISCUSSION...

Models are in good overall agreement through the first 40 (ish)
hours and have come into much better agreement with the low
entering the Gulf of Alaska this afternoon regarding both track
and intensity. Model spread begins to grow with the approach of a
second North Pacific low looking to push into the Gulf on
Saturday. Much like the first, there are consistency issues with
center placement and strength. The GFS is much more gung-ho,
showing stronger system, while also being slower and keeping further
south.

&&

.AVIATION...
PANC...VFR conditions and light winds will persist. Winds will
remain northerly for most of the day, switching to southerly
briefly this evening. There will be periods of light snow during
the morning hours, with cloud ceilings hovering around 4000'.

&&

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

The change in pattern is underway with the strong low in the Gulf
of Alaska. This low moved in from the southeast and is tracking
from the central Gulf early this morning and will weaken as it
crosses through the Barren Islands and into the Alaska Peninsula
this evening. Due to this track, the warm sector of the low is
along the north Gulf coast with Kodiak Island remaining in the
cold sector of the low. Therefore Kodiak is likely to remain all
snow even with temperatures that may creep up into the mid 30s at
the lower elevations today. The winter weather advisory remains
in effect for Kodiak with periods of heavy snowfall likely as well
as gusty northwesterly winds reducing visibilities in some
blowing snow. The north Gulf coast region, which is in the warmer
air, is the region that is hardest forecast today. There will
likely be some rain mixed in at coastal locations, but it is
unclear how far inland that rain will make it. The front moving
into the area with this low will bring some gusty winds so places
like the interior of the Kenai Peninsula may see some reduced
visibilities in snow and blowing snow today, though there is also
a chance for rain to mix fairly far inland there as well. The
western Kenai Peninsula as well as Anchorage and the Mat-Su are
more likely to see a brief, light snowfall as this front moves
across this morning, and then downslope out the rest of the day as
the cross- barrier flow over the mountains increases.

The low pressure festivities do not end after this low moves
westward and weakens tonight as another low will track into the
Gulf from the southeast again on Saturday. This low will take a
similar track to the one today, though it may bring stronger
winds to the northern Gulf marine areas, including Cook Inlet,
that the one today. It also will have a little bit different
structure in regards to the front wrapped around it as it should be
a little more elongated. This will keep the tight thermal
gradient,which will be over Kodiak Island today and a
significant contributer to today's heavy snowfall, farther to the
north so Kodiak should not see as much snow as today. However, a
small change in track or structure could change that so it is
worth keeping an eye on. The Kenai Peninsula will again get strong
winds, but the Saturday low should be warmer than today's so it is
more likely to bring rain farther inland.

Sunday should be a quieter day overall for Southcentral with some
residual snow showers along the Gulf coast being the main
precipitation threat.

&&

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

No significant weather expected for today, Saturday and Sunday. A
front will move on shore on Monday and bring precipitation to the
area. Forecast confidence is low with respect to the precipitation
type.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 3: Tonight
through Sunday)...

A storm system will move across the western Bering/Aleutians on
Sunday evening into Monday. This storm system will produce
widespread storms and high seas. Conditions will then abate from
southwest to northeast on Monday afternoon. No other significant
weather is expected.

&&

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

Looking into the extended forecast, both deterministic guidance
and their respective ensembles concur on the continuation of an
active weather pattern through Thursday for both domains. A pair
of negatively tilted shortwave troughs lift northward from the
Gulf of Alaska and into Southcentral Alaska through Wednesday
morning. The best chance of precipitation associated with these
shortwaves will be for coastal Southcentral due to having the best
upslope enhancement. A more significant trough digs southward from
Siberia, through the Bering Sea, across the Alaska Peninsula, and
into the Gulf Wednesday as it becomes negatively tilted in nature.
However, both deterministic guidance and ensemble guidance are not
in agreement with the ultimate evolution and behavior of this
trough. The 12z Canadian deterministic guidance is the furthest
north with the closed upper-level low in the northern Gulf, while
the GFS is way further south with the upper low in the North
Pacific and south of Kodiak Island. The 12z ECMWF is in between
the GFS and Canadian. Where this upper trough decides to
negatively tilt and where the upper low closes off will ultimately
determine the track and strength of the associated surface low
for Wednesday into Thursday and its effects for Southcentral.

Out west, Southwest Alaska will initially be unsettled as a deep
Bering Sea low sends its front into the coast and inland Monday
afternoon bringing a chance of moderate to perhaps heavy
precipitation, especially for coastal sections of Southwest. An
additional front on Wednesday and Thursday may impact Southwest,
but as alluded to previously, there is a lot of uncertainty with
this system at both the lower levels and upper levels. The Bering
Sea and Aleutian Chain both look to remain active as well with
continued lower heights and overall trough conditions persisting
through Wednesday. The front that affects Southwest on Monday
afternoon, first sweeps the eastern Aleutian Chain Monday morning
with moderate precipitation and gusty winds. After that,
conditions remain unsettled with additional shortwaves digging
southeastward from Kamchatka, through the Bering, and across the
Chain through Wednesday. Zonal flow, from west to east, tries to
establish itself through the Bering on Thursday, but there is a lot
of uncertainty there as guidance hints at a North Pacific low
trying to lift northward around the western Aleutian Chain around
that time as well.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Winter Weather Advisory: 131 171
MARINE...Storm Warning: Northern Gulf of Alaska
		 Gale Warning: Prince William Sound, Barren Islands,
		 Kodiak Island Waters, Shelikof Strait, Cook Inlet,
		 Western Gulf of Alaska
		 Heavy Freezing Spray Warning: Alaska Peninsula, Pribilof Islands,
		 Bristol Bay, Eastern Bering Sea
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...KM
SOUTHCENTRAL ALASKA...EZ
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...ED
LONG TERM...DN

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE ANCHORAGE AK
1245 PM AKDT FRI MAR 17 2023

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

1240 PM     SNOW             NULL                    61.32N 149.54W
03/17/2023  E1.0 INCH        ANCHORAGE          AK   NWS EMPLOYEE

            MODERATE SNOW COMING DOWN AS OF 12:40PM.
            ESTIMATED AN INCH (MAYBE A LITTLE BIT MORE).
            SOUTH WIND AT 3,000 FEET ON HIKE.

&&

DAN

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE ANCHORAGE AK
1251 PM AKDT FRI MAR 17 2023

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

1248 PM     SNOW             NULL                    57.80N 152.38W
03/17/2023  E10.0 INCH       KODIAK ISLAND      AK   TRAINED SPOTTER

            REPORTED 6 ADDITIONAL INCHES OF SNOW SINCE
            9:30AM THIS MORNING; UP TO 10 INCHES TOTAL.

&&

DAN