Small Craft Advisory 62, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
619 PM AKST Fri Jan 21 2022

.ANALYSIS AND UPPER LEVELS...

Southern Alaska sits between a longwave trough stretching over
the Bering into the Northwest Pacific and a longwave ridge
extending northward from the Northeast Pacific into Southeast
Alaska. As a result, broad southerly flow continues to direct
several lows and shortwaves northward into the state along with
warm, moist air. The first shortwave stretches from Southwest
Alaska through the interior of Alaska this wave is producing light
snow across the northern Susitna Valley and northern Copper River
Basin. Additionally light snow is seen on radar across most of
Southwest Alaska with light rain from near King Salmon to Iliamna
as downsloping has warmed the atmosphere. The parent surface low
is spinning near the AKPen and is moving into the Bristol Bay
area. Rain and snow showers are seen on radar from Kodiak Island
north through Cook Inlet as well as rain showers near eastern
Prince William Sound due to the front moving inland. The MAT
valley winds have increased with gusts up near 40 mph and
temperatures into the 40s. Finally northerly flow with snow
showers spreads across most of the Bering with a few rain showers
across the Aleutians where temperatures are in the mid to upper
30s.

&&

.MODEL DISCUSSION...

Models remain in good synoptic agreement through the short term.
The timing and placement of upper-level shortwaves tracking
northward through the broad southerly flow is in good agreement
through Sunday, although some minor differences on timing of
shortwaves moving northward across the Gulf through the short term.
As we look towards late Sunday into Monday the next low and
shortwave show some uncertainty on strength and timing as it heads
towards Southern Alaska. The biggest challenge continues to be
the areal coverage of freezing precipitation for both Southwest
and Southcentral Alaska through Saturday. Another challenge is how
much precipitation and areal coverage of precipitation with each
weak shortwave moving across Southcentral Saturday and Sunday.
Currently shortwaves look very weak with weak forcing so
precipitation may be overdone a bit on some of the models
especially across interior valleys.

&&

.AVIATION...

PANC...Ceilings remain predominantly VFR through the forecast
timeframe. Wind shear will continue until the Turnagain winds
bend into the airfield. Timing is somewhat uncertain, however
winds at the surface are expected to turn southeasterly sometime
by late this afternoon through the evening hours. Gusty
southeasterly winds are likely to continue through at least
Saturday morning and then winds should decrease and become
northerly by sometime Saturday afternoon.

&&

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

An active pattern will continue for the next several days. Strong
southerly flow aloft is allowing for precipitation to persist
along the coast this evening, although it will be generally
light. Gusty winds along Turnagain Arm will occur through Saturday
morning with a tightening pressure gradient. Although these will
diminish thereafter, the same general pattern will continue and
thus winds will remain higher in this area. After a brief lull on
Saturday, another strong push of moisture will enter the Gulf
with slightly higher precipitation rates and stronger Turnagain
winds as today. Much of the precipitation will be confined to
coastal areas and stay all rain as temperatures in the low 40s are
expected.

&&

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

A warm and active pattern will continue to affect much of the
region with a variety of impacts ranging from rain and light
freezing rain to snow through much of the weekend into early next
week. To start off, a weakening front stemming from an upper level
low in the Bering will continue to work east through Saturday
morning as another weak low moves up along the Alaska Peninsula
into Bristol Bay. Warm air will continue to stream north out ahead
of the front, allowing for a wintry mix of rain, freezing rain and
snow across much of Bristol Bay and up into the Middle Kuskokwim
Valley. A transition zone will work east with time as colder air
briefly advects back in behind the front, with any mixed precip
becoming all snow by Saturday afternoon. It remains the
expectation for any ice accumulations to be very light, with only
a short window for freezing rain to occur before the cold air
ushering in changes everything over to all snow.

A brief pause in the active weather is expected for Sunday morning
as the low and associated snow band exit into the northern Alaska
Range and Susitna Valley, with dry and cooler low temperatures
ranging from the single digits over the Y-K Delta to the 20s over
the Alaska Peninsula and Bristol Bay. Unfortunately, the pause
will be quite brief, with another North Pacific low and attendant
front expected to lift north across the Alaska Peninsula and into
Bristol Bay by Sunday evening, sending another shield of snow
along with another push of warmer air back into place from south
to north. Once again, there may be enough warm air moving in to
change snow over to rain, with some returning threat for a mix
with freezing rain. Current thinking is that areas near and east
of Dillingham will have the best potential to see a period of snow
mixing with or changing to rain and freezing rain, possibly
expanding north into portions of the Middle Kuskokwim Valley
through Monday. A Special Weather Statement highlighting both the
more immediate concerns for wintry mix and snow and for the
second system moving in on Sunday and Monday remains in effect
this evening.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 2: Today
through Saturday)...

The general weather pattern will remain about the same over the
next several days, with a train of North Pacific lows moving north
around a longwave ridge centered over the Gulf. This will keep
most of the active weather over the eastern portions of the
forecast area, with multiple rounds of rain and snow moving across
the eastern Bering and Aleutians through Monday with each
subsequent low passage. The strongest of these lows will move
north into Bristol Bay by Monday morning, with a band of light
snow and gusty northerly winds up to gale force moving across the
Eastern Aleutians from Sunday afternoon to Monday morning. Benign
conditions will persist for most of the western parts of the
Bering region, with Arctic air remaining in place and supporting
periods of convective snow showers across the Western Aleutians
and Pribilofs through Monday.

&&

.MARINE (Days 3 through 5 - Monday through Wednesday)...

Gulf of Alaska...A well developed Bristol Bay low moves to the
Northern Gulf of Alaska for Wednesday. Its front moves across the
Gulf by Wednesday. Forecast confidence is fair due to the low
track by Wednesday. Southerly gales ahead of the front become an
easterly gale force barrier jet along the North Gulf Coast for
Tuesday, and northwesterly gales along the Alaska Peninsula coast
for Tuesday and Wednesday. Seas to 22 feet from the Alaska
Peninsula across the western Gulf, subsiding Tuesday, and to 15
feet east of the Barren Islands, subsiding Wednesday.

Aleutians / Bering...A well-developed Bristol Bay low moves
inland late Monday. Northerly gales move across the Alaska
Peninsula by late Monday. Seas to 22 feet on the Pacific side of
the Alaska Peninsula, subsiding. Forecast confidence good through
the period. Areas of weak low pressure with gusty winds move
across the Bering through Wednesday. A well developed North
Pacific low intensifies as it approaches the Western Aleutians.
Widespread high end gales with areas of possible storm force winds
spread into the Central Aleutians and southern Bering through
Wednesday. Seas building to 18 feet on the Pacific side of the
Aleutians by Wednesday.

&&

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

The pattern will remain amplified during the extended period with
upper troughing extending across Southcentral and Southwest
Alaska on Tuesday while upper ridging builds across the eastern
Bering/Aleutians. The upper trough will then move eastward on
Wednesday and Thursday across Southwest and Southcentral as upper
ridging builds in the wake. Then, the upper level ridging will
extend across the eastern Bering/Aleutians, Southwest and
Southcentral Alaska by Friday. Upper level troughing will continue
to extend across the far western Bering/Aleutians during the
extended period. This means the extended period will start off
cold for Southwest Alaska and gradually become warmer as the
ridging builds across the area. Southcentral will remain cold for
a longer period of time as the ridge-axis is expected to remain
west of the area which will allow for northwesterly flow (cold air
advection) aloft. This pattern is also conducive to sunny skies
during the day and clear skies at night. This results in colder
overnight low temperatures across Southcentral due to radiational
cooling.

A weakening surface low is expected to move northeastward from
the Gulf into Yukon Territory on Tuesday and result in a chance of
light snow for Southcentral Alaska. The next chance for snow will
be on Thursday as a second low moves into the northern Gulf of
Alaska. Forecast confidence remains low at this time with snowfall
amounts due to significant differences in the placement of this
low.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gale: 130 132 139.
Heavy Freezing Spray: 179 185 412 414.

&&

SYNOPSIS AND MODEL DISCUSSION...RC
SOUTHCENTRAL ALASKA...AP
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...AS
MARINE/LONG TERM...KZ/ED

SPECIAL WEATHER STATEMENT
National Weather Service ANCHORAGE AK
344 AM AKST Sat Jan 22 2022

AKZ152-155-161-230145-
Lower Kuskokwim Valley-Kuskokwim Delta-Bristol Bay-
Including the cities of Aniak, Sleetmute, Bethel, Hooper Bay,
Nunivak Island, King Salmon, Dillingham, Naknek, and Pilot Point
344 AM AKST Sat Jan 22 2022

...SNOW AND POTENTIAL WINTRY MIX OF PRECIPITATION EXPECTED ACROSS
BRISTOL BAY, THE KUSKOKWIM DELTA, AND MIDDLE KUSKOKWIM VALLEY
TODAY THROUGH MONDAY...

Two active storm systems and their associated fronts will continue
to bring winter weather across Southwest Alaska. Additional snow
accumulations of 2 to 5 inches are expected for much of the
Southwest as the second front tracks north today, with higher
totals possible near the Kuskokwim Mountains. Snow may continue to
mix with freezing rain or transition to rain, leading to lower
snowfall totals. Some uncertainty remains regarding how and where
this transition will set up. Current thinking places the
transition zone from Dillingham to King Salmon and then Goodnews
Bay to Sleetmute, with rain further south. Any wintry mix is
expected to be brief with minimal ice accumulations.

As cold air returns behind the low later today, precipitation
will begin gradually transitioning back to snow from west to east.
Another low pressure system will move into the Southwest from
Sunday into Monday, sending warmer air north once again with the
potential for several more inches of snow and possible mixed
precipitation.