Gale Warning 175, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
450 PM AKST Thu Feb 23 2023

.ANALYSIS AND UPPER LEVELS...

The jet stream continues to stream moisture from well south of
the Aleutians into the southern mainland with a deep trough across
the western Aleutians and Bering and the ridge across eastern
Alaska. Radar is showing light snow from the Kenai Peninsula and
north towards the Mat-Su valleys. Temperatures are in the 20s
across the western Kenai Peninsula and northward with low to mid
30s across the Anchorage hillside and along the Turnagain Arm and
southward along the Seward Highway. Rain is occurring at Seward
and Homer with temperatures in the upper 30s. Out west
temperatures are mainly in the mid to upper 30s with scattered
rain and snow showers across the Bering, Aleutians, and the
Kuskokwim Delta.

&&

.MODEL DISCUSSION...

Models are in good agreement with all major features through
Saturday. The main forecast challenge for today is snow amounts
across Anchorage and the Matanuska valley as temperatures are
expected to top out in the low to mid 30s with the precipitation
type expected to remain snow, but there is still a slight chance
that rain may briefly mix in with the snow this afternoon.

&&

.AVIATION...
PANC...Light snow with MVFR and possibly periods of IFR ceilings
and visibility. The snow is expected to taper off later this
afternoon into the early evening hours with conditions improving
to VFR by this evening. Snowfall is expected to total around 2
inches and may briefly mix in with rain this afternoon, but the
chances of rain is low. There is another chance of snow tomorrow
morning with possible MVFR conditions.

&&

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

A wintry mix of precipitation across the region is on track to
end tonight as a front draped over Southcentral slowly moves
eastward. Meanwhile, southeasterly gap winds channeling through
Turnagain Arm and Knik River are ramping up in response to a
tightening pressure gradient between a mainland high and Gulf low.
Winds are expected to subside tonight as the Gulf low pushes
toward the southeastern Panhandle and the pressure gradient
relaxes.

In the wake of the aforementioned front, an upper level trough
moves over Southcentral on Friday, which will increase outflow
winds through the usual gaps and passes over the mainland. A few
weak shortwaves coupled with upslope flow may bring light snow
showers mainly in the higher elevations. Over the Gulf waters, the
strongest winds will likely happen between Friday night and
Saturday as the trough moves overhead and pulls enough colder
air with it. For the rest of the weekend, skies will clear out
and allow temperatures to drop back down below normal, with highs
on Sunday in the teens across the low-lying regions.

&&

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

Precipitation has ended across Southwest Alaska as last night's
front has pushed east of the area. A dry regime, punctuated by a
few periods of light snow showers, will take over the region as a
more seasonal air mass moves in on westerly flow. As a result,
temperatures are forecast to cool gradually through Friday. A
series of weak shortwaves move in from the Bering Sea beginning
early Friday morning. This will enhance snow chances through parts
of the Kuskokwim Delta and Lower Kuskokwim Valley through Friday
evening. The most likely areas to see measurable snow, up to
around an inch of accumulation, will be along and out ahead of
west-facing mountain slopes, where upslope flow will support more
widespread shower activity. A transient ridge works in behind
the shortwave troughing as it exits to the east Friday night. Dry,
northwesterly flow is likely to clear out much of the cloud cover
and allow for more efficient radiative cooling. Temperatures drop
into the 10s and single digits for lows Saturday morning.

Then, a Bering low pushes its cold front to clip the Southwest
coast midday Saturday. This front looks unlikely to cause
significant impact or snowfall. Instead, a trailing front dropping
south across Southwest Alaska will bring another chance for snow
on Saturday. This will once again favor the Kuskokwim Delta and
Lower Kuskokwim Valley (likely to see the most snow), but Bristol
Bay will not completely miss out. There is some uncertainty with
snow totals related to the placement and strength of this weak
front, but a rough range right now suggests the possibility of 1
to 3 inches of accumulation for the Kuskokwim Valley, with lower
totals in southern portions of Bristol Bay through Sunday morning.
Behind the front, much colder air drops temperatures 10 to 20
degrees for Sunday area wide.

&&

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

Cool and quiet weather continues across the Bering Sea/Aleutians
through Friday morning, with snow showers scattered to numerous across
much of the region. A weak shortwaves will bring localized gales
as it passes north of the Pribilof Islands tonight, but for most
of the area winds will be light. A North Pacific low approaches
the Western Aleutians Friday morning, bringing high end gales to
the islands. The low deepens as it tracks into the central Bering
Sea, cold advection wrapping around the south side of the low will
produce a swath of storm-force winds Friday night. The low
occludes Saturday morning and weakens slowly as it continues east
into Bristol Bay by Saturday afternoon. At the same time, it will
push a swath of high end gales to storm force winds across the
eastern Aleutians/southern Alaska Peninsula. The low weakens and
dips back into the North Pacific by Saturday night, with winds
diminishing across the Alaska Peninsula. The next dominant low
moves up from the North Pacific on Saturday night as well,
tracking across the western/central Aleutians and moving into the
western Bering Sea by Sunday.

&&

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

Deterministic and ensemble guidance continue to trend towards a
setup not unlike today's moist southwesterly flow regime for
Southcentral Alaska on Monday and Tuesday. Although, indications
are for a more amplified setup this go-around as opposed to today.
There are some differences in timing though in the eastern
progression of the northward-building broad ridge in the North
Pacific. The GFS and CAN deterministic and ensemble guidance, as
well as the ECMWF ensemble guidance, have a quicker eastward
progression of the ridge axis which puts Southcentral into moist
southwesterly flow earlier. However, the ECMWF deterministic is
slower with the eastward progression of the ridge axis. Thus,
there are timing issues of when precipitation makes into
Southcentral. There are also disagreements with the evolution of
the ridge itself. The GFS suite depicts a flatter ridge, while the
ECMWF/CAN suites has a little taller/more amplified look to the
ridge. The atmosphere also looks to be colder this time around as
well; therefore snow looks to be dominant, especially for inland
areas. The Gulf Coast will need to evaluated closely for potential
mixing issues. Southcentral looks to continue to be active even
as the majority of precipitation winds down Wednesday evening. The
big story towards the end of the long-term period will be
northwesterly cold-air advection coming in on the backside of the
southeasterly drifting gulf low that will aid in the cause of
active weather for Tuesday/Wednesday. The deterministic GFS/CAN
are more bullish on stronger cold-air advection for Thursday while
the ECMWF is not as robust with it. Regardless, the upcoming
pattern towards the end of the long-term period for Southcentral
appears favorable to support strong gusty gap winds through the
usual coastal bays and passes. Continue to monitor the forecast
for early next week as details become more clear on the upcoming
pattern.

Odds tilt towards Southwest Alaska, the Aleutians, and Bering Sea
look to remain relatively active during the beginning to middle of
the long-term period for Monday through Wednesday. A central
Bering low looks to push its front into Southwest Alaska Monday.
Precipitation would likely begin as snow, before transitioning to
a rain/snow mix or even changing over to rain for a time due to
warmer air pushing in from the southwest. While guidance generally
agrees on a warm air push to the coast, there are disagreements
with positioning and strength of the Bering low. The GFS and its
ensemble mean are weaker with the system and further east towards
the southwest coast while the CAN/ECMWF and their respective
ensembles have a stronger system that is further west in the
west-central Bering. The CAN/ECMWF deterministic and their
ensembles both hint at this same system continuing to maintain
strength while moving northward in the vicinity of St. Matthew and
St. Lawrence Islands by Tuesday. Meanwhile, the GFS and its
ensembles have a new North Pacific low spinning up and crossing
the central Aleutian Chain and moving into the Bering Tuesday as
it brings the previous Bering system inland and dissipates it. The
GFS suites are an outlier at this time with this particular
evolution of the long-term pattern and more credence is giving to
the CAN/ECMWF suites. Guidance hints at flow becoming more zonal
in nature, moving from west to east, for Wednesday into Thursday
with more benign weather relatively speaking compared to the
active pattern recently observed.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Winter Weather Advisory 111 145.
MARINE...Storm Warning 413.
		 Gale Warning 119 120 130-132 138 150 170 172-179 351 352
					  411 412 414.
FIRE WEATHER...NONE.

&&

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

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE ANCHORAGE AK
1140 PM AKST THU FEB 23 2023

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

0914 PM     SNOW             13 SE KNIK              61.31N 149.48W
02/23/2023  M0.6 INCH        ANCHORAGE          AK   PUBLIC

            MAJORITY OF THIS SNOW FELL IN THE EVENING OF
            02/22/2023.

&&

RUX