Small Craft Advisory 73, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
600 AM AKST Sun Jan 22 2023

.ANALYSIS AND UPPER LEVELS...

The amplified upper-level pattern continues to rule the roost as
strong southerly flow in the middle and upper levels continues to
overspread the Gulf of Alaska while an upper-level ridge over
Southcentral Alaska continues to move northward into the interior
of the state. A front in the North Pacific also continues to track
northward towards the southern Gulf. Meanwhile, Anchorage, the
Susitna Valley, Matanuska Valley, and western Kenai Peninsula
remain under mostly clear skies, while low to mid-level clouds
are apparent for the Copper River Basin, eastern Kenai Peninsula,
and northern Gulf coast.

Out west, a deep trough stretches from Kamchatka southward across
the Aleutians, and into the North Pacific south of the Alaska
Peninsula (AKPEN). Upper-level ridging remains over southwest
Alaska and stretches northwestward over the northern Bering Sea
into Siberia while continuing to move slowly northward. Moist
southerly to southeasterly upper-level flow encompasses most
southwest, the Bering, and the Aleutian Chain. Conditions along
the southern AKPEN remain unsettled as Cold Bay currently reports
snow with winds around 40mph while Sand Point reports rain and
gusty winds near 25mph. Meanwhile, the Kuskokwim Delta deals with
strong northeasterly off-shore winds which is causing blowing
snow issues along with very low visibilities. Kipnuk reports winds
gusting over 50mph with one-quarter mile visibility while Bethel
has one-half mile visibility with northeasterly winds gusting to
over 45mph. As a result of these conditions, a Blizzard Warning is
in effect for the Kuskokwim Delta region until 9PM this evening.

Like the AKPEN and portions of coastal southwest Alaska,
conditions are unsettled along the Chain with Atka and Dutch
Harbor reporting rain and gusty northerly winds and easterly winds
respectively. The Pribilof Islands are also under a Winter Weather
Advisory for blowing snow which goes into effect 3PM this
afternoon as strong easterly to northeasterly winds will combine
with falling snow to create low visibilities.

&&

.MODEL DISCUSSION...

Synoptically speaking, guidance is in relatively good agreement
during the short-term period. All guidance shows a highly
amplified and active weather pattern for the entire domain through
the short-term with few breaks from activity. Upper flow across
Southcentral Alaska eventually switches from southwesterly to more
southerly during the day Tuesday. This will cause challenges in
the precipitation-type forecast for the Southern Mainland.
Therefore, while forecast confidence is above average for the
synoptic-scale features, confidence is low to moderate for the
mesoscale and timing of individual shortwaves. The track of
shortwaves will ultimately determine the timing of when the
warmest air will push into Southcentral and when precipitation-
type transitions from frozen to liquid will take place.

&&

.AVIATION...

PANC...VFR conditions and light northerly winds will persist
through most of the TAF period. Modest southeasterly flow in the
middle levels of the atmosphere should keep most precipitation out
of the terminal as a frontal system lifts northward from the Gulf
of Alaska through Sunday evening into Monday morning. However,
mid-level flow becomes more southerly at the end of the TAF
period into Monday morning allowing for lower ceilings (possibly
MVFR) and possibly some scattered snow showers to make their way
into Anchorage and the terminal.

&&

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

Clouds are already beginning to filter into Southcentral this
morning with the front lifting onshore. Most of the precipitation
for today will be for Kodiak Island, coastal locations, and the
Copper River Basin. The easterly winds with this front will keep
the western Kenai Peninsula and Anchorage downsloped. Multiple
waves are expected to progressively bring warmer air to the area.
Precipitation-type challenges continue with the timing of the
transitions early on. Once the flow becomes more southerly, a
fetch of moist, warm air will be enough to transition
precipitation to rain for locations up Cook Inlet and along the
Gulf Coast. Areas that hold on to near freezing temperatures at
the surface could see a wintry mix and perhaps a brief potential
for freezing rain cannot be ruled out. Since plenty of warmer air
is expected, the transition is not expected to be prolonged.

Moisture will push up Cook Inlet into the Susitna Valley, where
temperatures will remain cold enough to remain as snow. Some of
the highest snowfall amounts, possibly around a foot over a 24 to
36 hour period (Monday afternoon through Tuesday evening) will be
along the highway near Broad Pass where precipitation will be
upslope enhanced.

&&

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

A deep low in the North Pacific pressing up against strengthening
high pressure over the Bering Strait will contribute to a strong
pressure gradient and continued offshore flow today across
Southwest Alaska. 30 to 40 mph winds are lofting snow and
reducing visibility to one half mile or lower this morning across
the Kuskokwim Delta. The worst conditions and stronger winds
have led to the development of a ground blizzard along the coast.
Winds are expected to only slowly diminish, suggesting that these
conditions will persist throughout the day before they begin to
let up somewhat this evening. Still, northeasterly winds will
continue at 25 to 35 mph through Monday evening and this will
contribute to persistent low visibility. These strong winds also
combine with cold temperatures to keep wind chills hovering from
30 to 40 below zero through the same time period.

A front associated with the deep North Pacific low pushes slowly
northward today, bringing some warmer air and light precipitation
along the Alaska Peninsula and into Bristol Bay. Easterly cross-
barrier flow will keep precipitation light and scattered for the
Bristol Bay region, with the best chances with the initial arrival
of the front this afternoon and early evening. A better chance
for snow comes starting Monday as the low center weakens and
tracks up along the Alaska Peninsula, with around one to two
inches of snowfall accumulation forecast through Tuesday morning
for the Bristol Bay region. Light snow then pushes its way north
gradually into the Kuskokwim Valley on Tuesday. Another
disturbance arriving Tuesday night will have the potential to
bring another round of warmer air with some mixed precipitation or
rain working into parts of Southwest Alaska.

&&

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

Widespread gales across the Bering Sea will persist as a front
stalls in the Bering Sea over the next several days. Light
snowfall is expected along the front in combination with gales,
which should result in a prolonged period of significant
reductions to visibility for the Pribilof Islands once it arrives
this afternoon. Arctic air will continue to flow across the
Bering Sea from the north, resulting in extreme freezing spray
near the sea ice edge where icing rates of greater than 4
cm/hour can be expected. Winds begin to diminish on Tuesday as low
pressure along the Aleutians starts to shift eastward, relaxing
the pressure gradient somewhat. By midweek, winds increase to gale
force for the western Aleutians as another front from a low near
Kamchatka begins to encroach on the forecast area.

&&

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

Agreement between the deterministic models in the extended period
remains loose, continuing the low-to-mid forecast confidence for
this timeframe. Wednesday morning, a low looks to enter Southern
Alaska. However, further placement of this low remains difficult
to determine. The GFS places this low at the Southwestern edge of
the Alaska Peninsula Wednesday morning with a front extending
northeastward moving over Southcentral. In contrast, the Canadian
and Euro models place the low center over Kodiak Island Wednesday
morning. Furthermore, the 12Z GFS moves a Northeastern Pacific low
rapidly through the Gulf into coastal Southcentral by Thursday
morning, a feature not represented by the equivalent Euro/Canadian
runs. These disagreements have made the wind field, and resultant
weather inland difficult to determine at this time. Following
this agreement is good that moderate ridging will begin to develop
over Eastern Alaska, diminishing activity for the area through
the weekend.

Out west, agreement is fair that a North Pacific low will move in
west of Attu with a long front that will sweep the Chain eastward
beginning Wednesday morning reaching Southwest Alaska by Saturday
morning with diminished intensity. Strong precipitation currently
expected along the boundary of the front, with lingering showers
behind throughout this period. Gale-force southerly winds will
advance eastward with the frontal boundary, with Storm-force winds
currently possible Wednesday morning as the front clips the
western-most Aleutians.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Blizzard Warning: 155.
         Winter Weather Advisory: 195.

MARINE...Heavy Freezing Spray Warning: 139, 140, 160, 179, 180,
                                       185, 412, 414.
         Gale Warning: 119, 120, 130-132, 137-139, 150, 155, 160,
                       165, 170, 177-181, 185, 351, 352,
                       411-414.
FIRE WEATHER...NONE.

&&

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

SPECIAL WEATHER STATEMENT
National Weather Service ANCHORAGE AK
1108 AM AKST Sun Jan 22 2023

AKZ101-111-121-230815-
Anchorage-Matanuska Valley-Western Kenai Peninsula-
Including the cities of Anchorage, Eagle River, Indian, Eklutna,
Palmer, Wasilla, Sutton, Chickaloon, Kenai, Soldotna, Homer,
and Cooper Landing
1108 AM AKST Sun Jan 22 2023

...WARMER TEMPERATURES WITH SNOW TO RAIN EXPECTED ACROSS THE
MATANUSKA VALLEY, ANCHORAGE BOWL, AND WESTERN KENAI PENINSULA
THROUGH MIDWEEK...

A shift in the weather pattern is expected to bring warmer
temperatures along with a transition from snow to rain across
the region through the first half of the this week.

Light snow is expected to develop sometime Monday morning or
early Monday afternoon as a series of weather fronts move from
the northern Gulf over Southcentral Alaska. The precipitation is
expected to transition briefly to a wintry mix of snow and
freezing rain Monday afternoon as warmer air moves in aloft ahead
of the front. The front will then move farther inland by late
Monday afternoon. Warmer air will move in behind the front along
with an increase in southerly winds. This combination of warmer
air and southerly winds will allow temperatures to climb above
freezing across the region with any wintry mix changing to rain.
Temperatures above freezing along with areas of light rain are
expected to linger into Tuesday morning.

Rain, or mixed rain/snow, is also possible for Wednesday as
another front moves over the region. While temperatures are
expected to remain in the mid 30s for this event, any deviation
in the track of this system could introduce slightly cooler air
and result in a rain/snow mix or wet snow.

Any freezing rain or rain falling on cold or snow covered roadway
surfaces will likely lead to icy conditions and hazardous travel
conditions. Rain may also lead to water ponding on area roadways.

There is still some uncertainty as to the timing of and extent
of the precipitation for Monday. Please monitor the forecast
closely for updates at www.weather.gov/afc.

AKZ141-230815-
Copper River Basin-
Including the cities of Glennallen, Eureka, McCarthy, Paxson,
and Slana
1108 AM AKST Sun Jan 22 2023

...WARMER TEMPERATURES WITH SNOW TO RAIN EXPECTED ACROSS THE
COPPER RIVER BASIN THROUGH MIDWEEK...

A shift in the weather pattern is expected to bring warmer
temperatures along with a transition from snow to rain across
the region through the first half of the this week.

Light snow is expected to develop by late Sunday afternoon as a
series of weather fronts move from the northern Gulf over
Southcentral Alaska. The precipitation may transition briefly to a
wintry mix late Sunday night through early Monday morning along
the Edgerton Highway and the Richardson Highway south of the
Edgerton Highway junction as warmer air moves in aloft ahead of
the front. The front will then move farther inland by Monday
afternoon. Warmer air will move in behind the front along with an
increase in southerly winds. This combination of warmer air and
southerly winds will allow temperatures to climb above freezing
across the southern half of the Copper River Basin, transitioning
any lingering wintry mix to rain. Temperatures above freezing
along with areas of light rain along the Edgerton Highway are
expected to linger into Tuesday morning. A wintry mix of
precipitation is also likely for Wednesday as another front moves
over the region.

Any freezing rain or rain falling on cold or snow covered roadway
surfaces will likely lead to icy conditions and hazardous travel
conditions. Rain may also lead to water ponding on area roadways.

There is still some uncertainty as to the extent of the
precipitation across the Copper River Basin through Tuesday.
Please monitor the forecast closely for updates at
www.weather.gov/afc.