Small Craft Advisory 18, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
449 PM AKST Sat Jan 8 2022

.ANALYSIS AND UPPER LEVELS...

The change in pattern is starting to get underway over Southern
Alaska as the cold 500 mb low moves from the Copper River Basin
this morning to the Kuskokwim Delta coast tomorrow. There is an
upper level wave associated with this low that is bringing some
snow to the North Gulf coast and as far north as Anchorage this
afternoon. This wave is prominent on satellite imagery and you
can tell it is not a big feature and skies should at least
partially clear out behind it. Southwest Alaska is also seeing
an increase in cloud cover in conjunction with this upper level
low approaching the area.

The next low which will become the main weather feature for the
next few days can be seen on satellite near 50N 150W this
afternoon and headed north on the satellite loop.

&&

.MODEL DISCUSSION...

Models remain in good synoptic agreement into the middle of next
week. A point of interest in the short term is with the upper
level disturbance that moved across the north Gulf coast this
morning and headed due west toward Southwest Alaska. Both NAM and
GFS show this wave best at 700 mb and are very close in track and
timing. The NAM does have it a little stronger by tomorrow morning
so that may determine whether there is enough juice left in it to
bring a little snow to Southwest AK or just some clouds.

For the second half of next week prefer the way the GFS and
GEM models respect the ridge over mainland Alaska and elongate
over the eastern Bering Sea in response to it instead of the
ECMWF solution of pushing a concentric, but weakening low, into
it over the Gulf. That is a ways off but is worth watching as it
gets closer.

&&

.AVIATION...
PANC...VFR conditions and north winds will persist.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 to 3/Tonight
through Tuesday)...

A broad longwave trough will begin to take hold of the north
Pacific Monday as a series of shortwaves move north into the Gulf.
The resultant increased cloud cover and a marginal airmass
replacement will help to warm temperatures across the region
after one last cold morning Monday. Expect highs to climb into
the mid to upper 20s from the Cook Inlet region north to the
Susitna Valley with single digits to teens in the Copper River
Basin. The Prince William Sound will increase into the low to
mid 30s by Monday with Kodiak possibly reaching into the 40s.

The front extending north from a slow moving, but moderately
strong north Pacific low will reach Kodiak Island early Sunday
morning and encompass the majority of the Gulf coast Sunday
afternoon. Precipitation type for Kodiak is expected to remain
snow, with northerly to northeasterly winds helping to reinforce
cold air. With moderately warm air at the surface, blowing snow
should not be an issue at sea level, though periods of heavy snow
may reduce visibility at times. There is still some uncertainty in
snow totals depending on the exact track of the low. Most of the
precipitation for this event will remain confined to coastal
areas and the Chugach mountains, though areas in the southern
Copper Basin may see some spill over near Chitina and the
Edgerton Highway cutoff. Downsloping appears likely from Kenai
north through Anchorage and into the Mat Valley though brief
periods of light snow are possible at times as weak shortwaves
ride over the mountains. Large discrepancies exist between global
models and high resolution models for QPF over the mountains. With
moderate east to southeast winds aloft, this forecast package
represents higher-end totals for QPF and snow over high terrain
and the Western Prince William Sound. As the event progresses,
warm air will slowly make its way into the Prince William Sound.
Expect the transition to rain or a rain snow mix to reach Cordova
and Whittier early Monday morning, spreading into the eastern
Turnagain Arm and Valdez area shortly after. With cold air
continuing to funnel out of the Copper Basin and into Valdez,
a snow and freezing rain mix is possible for Valdez on Monday.

By Tuesday another shortwave will make its way in from the north
Pacific, which will transition the flow aloft from southeasterly
to south to southwesterly. This will help but an end to the
downsloping, providing a better chance for snow for the Cook Inlet
region north into the Susitna Valley as the shortwave quickly
moves through. Accumulation will remain light, with a quick shot
of 0.5 to 1.0 inches for these areas. Colder air will accompany
this shortwave, which should transition areas with mixed
precipitation types or rain back to snow.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Day 1 through 3: Tonight
through Tuesday)...

An upper-level shortwave will move across Southwest Alaska this
evening through tonight. With this, a chance for snow showers for
Bristol Bay is possible as the shortwave passes through. However,
any precipitation would have to overcome very dry air, so its a
virga scenario with no precipitation actually likely reaching the
ground. Models are showing snow showers possibly extending into
the Kuskokwim Delta and the Lower Kuskokwim Valley tonight into
Sunday, but again, the dry air in place will most likely dominate
resulting in some clouds at best, with a slight possibility of a
light snow shower. As the aforementioned upper-level shortwave
makes its way through the Southwest, pressure gradients will
tighten and result in gusty northeasterly winds tonight through
Sunday. Sustained northeasterly to northerly winds of 20 to 30 mph
with gusts as high as 40 mph are possible. Consequently, with the
combination of cold arctic air in place and high winds, wind
chills this evening through Sunday afternoon may reach as low as
35 below zero at times. Monday night into Tuesday, a stronger
shortwave with more moisture will approach from the southwest and
could produce more widespread snow shower activity over the area
due to more moisture availability.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Day 1 through 3:
Tonight through Tuesday)...

Northeasterly flow is expected to dominate across much of the
Bering Sea region throughout the weekend and into early next
week. This will act as a barrier and keep storms south over the
North Pacific or moving northward into the Gulf of Alaska.
Currently, a low is sitting in place just south of the Aleutian
Chain and is expected to remain there for the next couple days.
Its front will continue to impact the coastal marine waters and
the Aleutian islands as the low keeps the area unsettled, so an
occasional period of precipitation of snow/rain over the course
of the weekend is possible. Widespread gales paint much of the
central Bering and extend all the way to the Pacific side of the
central Aleutians as the aforementioned low sits in place. Heavy
Freezing Spray will impact much of the Bering Sea as the Arctic
air flows off the ice and over the relatively warm open water.
Heavy freezing spray will remain a concern through the weekend
and into early next week along with increased wave heights. A
potential for cloud streets to form with some snow showers
impacting Adak and Shemya is also possible in the coming days.

&&

.MARINE (Days 3 through 5 - Tuesday through Thursday)...

Gulf of Alaska: Gales and large seas of more than 20 ft will
build across the Gulf starting Wed night through Thu night as a
result of a strong frontal system from the North Pacific. This
phenomenon will also bring widespread gusty winds across the
western Gulf through Prince William Sound. With systems moving
up from the Pacific, air temperatures will be fairly warm and
freezing spray should not be much of a threat.

Bering Sea: A relatively quiet forecast period with benign seas
are expected through at least Wed afternoon. A strong North
Pacific front could potentially usher gales and large seas south
of the Alaska Peninsula and parts of the eastern Aleutians by Thu
morning through Thu night. A trough over the Bering could enhance
gales farther north and west of Pribilof Islands starting Tue
night through Wed morning. For now, will maintain small craft
conditions until gain better confidence in the large scale pattern.

&&

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

A predominant upper ridge over the Mainland could stick around
for several days as it latches to a strong upper high over British
Columbia, leading to clear to partly cloudy skies north of
Talkeetna and parts of Copper River Basin through the long term.
A series of short-wave troughs lifting north and across the Gulf
of Alaska and the southern mainland of Alaska could bring light
precipitation across the region with a rain/snow mixed near the
coastal areas including the northern Gulf. A split Arctic low
aloft skirts right through the southern Bering but north of the
western Aleutians by Fri morning. Meanwhile, a North Pacific low
and its associated front aims for the western Aleutians Fri night.
As these separate developing systems interact, the potential for
elevated weather and hazardous marine conditions could take place
between Fri and Sat, starting from the western Aleutians eastward.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Winter Storm Watch 131 Thompson Pass.
MARINE...Heavy Freezing Spray Warning 119 126 127 128 130 139 141
                                      165 179 185.
         Storm Warning 130.
         Gale Warning 119 120 127 128 131 132 136 137 138 139
                      150 170 172 173 174 175 176 177 179 185.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...EZ
SOUTHCENTRAL ALASKA...CJ
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...NS
MARINE/LONG TERM...CB