Gale Warning 177, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
534 AM AKST Fri Feb 24 2023

.ANALYSIS AND UPPER LEVELS...

An upper-level trough is beginning to swing over Southcentral this
morning. Outflow winds have already been reported and are expected
to continue to increase throughout the day. Lingering upslope
light snow is being observed on radar this morning as well. In
wake of a ridge tracking out of the area and moisture from the
previous system left behind, this combination is creating lower
ceilings and fog over portions of the Anchorage Bowl, western
Kenai Peninsula, Alaska Peninsula, and Bristol Bay this morning.
Warmer temperatures are also being noticed over Southcentral this
morning as the aforementioned ridge pushes eastward. Nighttime
Microphysics satellite Imagery is nicely displaying a low located
over the northern Bering near the Kuskokwim Delta and slowly
tracking northeastward.

&&

.MODEL DISCUSSION...

Models are in decent agreement with synoptic features through
Saturday. The main feature models seem to be struggling with is a
low that will track through the Bering and into Southcentral next
week. Models are having a hard time determining the track and
strength of the aforementioned low. In the short-term, models are
struggling with the finer details as shortwaves are anticipated to
track over Southcentral and Southwest.

&&

.AVIATION...
PANC...MVFR to IFR conditions will continue through early this
morning before becoming VFR by 20z. MVFR conditions may then
reappear by 8z as light snow could move over the terminal.

&&

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

The front that brought the snow and rain across Southcentral has
moved east of most of the area this morning. A cold, upper level
trough is now moving toward Southcentral today and will be the
catalyst for a change in the weather for the weekend. Before that
happens, the trough moving in will bring another shot of some snow
showers this afternoon through overnight, but it looks like most
of these will mainly occur over the mountains with lower
elevations seeing little to no snowfall. Look for gusty north to
northwest winds to develop Friday night along the Gulf coast from
Prince William Sound to Kodiak Island as the pressure gradient
increases and cold air pushes into the area. This will also clear
out skies for much of the region by Saturday and continue into
Sunday. Inland areas with light winds will see temperatures drop
significantly Saturday night with many places wither in single
digits or below zero. The windy coastal areas will not have
inversions set up due to the wind so temperatures in these areas
should be more in the mid teens to lower 20s for lows Saturday
night.

&&

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

A cooling trend is forecast through the weekend as a series of
troughs pave the way for colder air to make continued southward
progress into Southwest Alaska. In the short term, morning
satellite shows a shortwave trough just now overspreading Nunivak
Island. This trough will dive southeastward across the region
throughout the day with areas of light snow showers to linger into
the afternoon hours, especially across the higher terrain and on
the western mountain faces. Some clearing will develop later
tonight in the wake of the trough's passage, allowing overnight
low temperatures to drop into the teens and single digits. The
next shortwave trough will drop southward along the coast on
Saturday with another round of light snow for parts of the
Kuskokwim Delta and Bristol Bay. Most notably, however, will be
the much colder air mass behind it, which will arrive in earnest
through the morning hours on Sunday. Models are in good agreement
with 850 mb temperatures of around -20 degrees overspreading all
of Southwest Alaska. Bethel could see Sunday morning low
temperatures below zero while locations further south will again
dip down into the teens and single digits.

&&

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

An active pattern will prevail over the Bering Sea through the
weekend with multiple troughs and lows forecast to grace the
region. This will result in prevalent small craft winds across
much of the Bering on Friday. The next Bering low then lifts out
of the North Pacific and into the western Bering Saturday morning
with gales and storm force gusts forecast to clip the Western,
Central, and Eastern Aleutians through the morning hours. The
strongest winds are currently forecast to split the Pribilof
Islands and the Eastern Aleutians where gusts of 60+ knots will be
possible along with seas of 20 to 25 feet. The low and its
associated winds slip south of the Eastern Aleutians by Saturday
afternoon; however, yet another low and front enter the western
Bering on Sunday with yet another round of small craft and gale
force winds. Along with the arrival of the low on Saturday will be
a surge of warmer temperature, which will gradually lift across
the Aleutians from west to east through Sunday. This will see any
snow shower activity transition to rain Saturday afternoon
through Sunday evening.

&&

.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...NONE.
MARINE...Gale Warning: 120, 127, 130-132, 138, 150, 150, 165, 171-179
		 			   351-352, 411-412, 414.
		 Storm Warning: 170, 413.
		 Heavy Freezing Spray Warning: 185.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...NCS
SOUTHCENTRAL ALASKA...EZ
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...BL
LONG TERM...DAN

SPECIAL WEATHER STATEMENT
National Weather Service ANCHORAGE AK
1225 PM AKST Fri Feb 24 2023

AKZ101-250400-
Anchorage-
Including the cities of Anchorage, Eagle River, Indian,
and Eklutna
1225 PM AKST Fri Feb 24 2023

...LOCALLY DENSE FOG ALONG THE GLENN HIGHWAY...

Fog has been observed along the Glenn Highway from the S-curves to
Eklutna. Fog in combination with areas of icy roads are producing
hazardous driving conditions. Exercise caution when traveling on
area roadways, as areas of fog and ice may impact a driver's
awareness and perception.