Brisk Wind Advisory 52, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
540 AM AKST Wed Feb 23 2022

.ANALYSIS AND UPPER LEVELS...

An upper level ridge is becoming increasingly amplified in the over
much of Alaska this morning. The prevailing upper level winds
around its periphery are beginning to take on an omega block
formation, with streamlines extending from the Alaska Peninsula
well northwest into the western Arctic, then around the crest of
the ridge back down into the Yukon. Across Southcentral, areas of
fog and low stratus have developed overnight under this ridge
over low valleys, including parts of the Kenai Peninsula, MatSu
Valleys and Copper River Basin. Out west, a large upper low
centered south of Attu continues to spin in place with a
plethora of embedded waves rotating through the Bering and
Aleutians within the broad cyclonic flow. One of the stronger
waves moving out of the North Pacific is beginning to aid in the
formation of a new low near Nikolski as it lifts north along a
fragmented frontal axis stretching across the central Bering.
Gusty southeast winds up to gale force continue out ahead of this
frontal zone, with some of the stronger gusts beginning to pick up
through gaps along the Aleutian Range and over parts of Bristol
Bay.

&&

.MODEL DISCUSSION...

In spite of the smaller scale complexities involving the Bering
low, models are in very good agreement overall through the end of
this week. Models are overall handling even most of the series of
smaller waves expected to move north into the Bering around the
persistent blocking ridge in a fairly similar fashion. There
remains a good signal for a much deeper shortwave to move up from
the North Pacific into the Alaska Peninsula by early Friday
morning. Some subtle differences begin to pick up with this next
stronger system as it moves northwest into the Southwest on
Friday, with the GFS notably faster and slightly deeper with the
attendant surface low crossing into the eastern Bering by around
this point in time. Some differences remain for the amount of
cooling low level temperatures over Southwest near the low by
Friday as well, yielding questions as to whether any rain over the
interior Southwest could mix with or change to snow.

&&

.AVIATION...
PANC...Fog has managed to develop on the west side of town under
high pressure ridging and calming winds this morning. Periods of
LIFR visibility/ceilings are expected until around or just after
sunrise as the fog lifts into low stratus and then scatters out
later in the morning. Otherwise, expect light north winds and VFR
conditions for the remainder of the period.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Wednesday through
Friday night)...

The upper-level ridge that provided much of Southcentral with a
respite from the recent active weather is cresting over the region
this morning. Areas of stratus and fog continue to linger this
morning due to subsidence from the ridge combined with weak flow
near the surface and residual low-level moisture. The fog is most
prevalent in locations where melting occurred yesterday and clear
skies overnight allowed for radiational cooling.

With the ridge moving east today, the respite from the active
weather will end and the active weather pattern will return. The
first signs of this is already taking place in across Kodiak
Island as a front lifts north from the western Gulf this morning.
This front will weaken as a secondary front develops off a surface
low spinning up over the North Pacific and moves quickly on the
heels of the first. Multiple upper-level waves will move north
along the front as the surface front moves east into the Gulf.
Broad southeasterly flow ahead of these features will tap into a
deep fetch of moisture which will wring out along the Southcentral
coast from Kodiak Island to Prince William Sound through Thursday
night, especially in favored upslope regions along the coastal
mountains. The intensity of the precipitation will ebb and flow
with each passing shortwave. Downsloping is expected along the lee
of the mountains due to a strong and persistent southeasterly
(cross-barrier) flow. Thus, little, if any, precipitation is
expected from Kenai north to Palmer and Talkeetna. As the front
moves closer to the Kenai Peninsula, the pressure gradient will
tighten significantly, leading to strong Turnagain Arm winds
beginning Wednesday afternoon. A slight uptick in northeasterly
winds across the Matanuska Valley is also possible due to the
orientation of the pressure gradient.

With a broad southeasterly flow, temperatures are expected to warm
through the duration of this first event. Precipitation that may
start as snow or a mix of rain and snow along the coast should
quickly change to rain as snow levels climb to around 1,000 feet
around the southern Kenai Peninsula by Wednesday afternoon and
across the eastern Kenai Peninsula by Thursday morning.

By late Thursday, a surface low will spin up south of the AKPen
and quickly move north as it deepens. This feature will advance
yet another front into the Gulf, first impacting Kodiak with
strong easterly winds and rains by Thursday evening. The front
then lifts to the north Gulf Coast by Friday morning as the low
tracks north near Bristol Bay and continues to strengthen. The
combination of these actions will allow for another round of
heavy precipitation to develop across the Southcentral coast as
well as strong easterly winds. For the northern Gulf, the winds
will manifest in the form of a storm-force barrier jet for Friday.
Elsewhere, southeasterly Turnagain Arm winds will ramp back up,
with the potential for hurricane-force (to 75 mph) gusts Friday
morning as the front approaches the coast and the surface low
reaches its peak strength (lowest pressure) near Cape Newenham.
These gusts are also possible for the Upper Hillside of Anchorage
along with a period of strong northeasterly winds and gusts across
the Matanuska Valley, again due to the orientation of the
pressure gradient as the low tracks across the AKPen.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3 - Today
through Friday night)...

A longwave trough west of the Aleutians will remain nearly
stationary through the next 24 hours. East of the trough and
extending across the Bering into Southwest Alaska, south to
southeasterly flow will continue to bring an influx of moisture
and warmer temperatures into the region. Numerous showers are
noted on radar this morning as a front lifts across the Aleutians
into the Bering. Temperatures are expected to remain warm enough
to keep precipitation falling entirely as rain while the front
eventually lifts further north and out of the Bering. For interior
Southwest, the highest rainfall will be confined to upslope flow
over the Kuskokwim and Aleutian Mountains though light rainfall
will be possible over much of the region through early Thursday. A
new upper low is forecast to move over the Alaska Peninsula and
into the eastern Bering late Thursday into Friday with renewed
shower chances. Something to keep an eye on will be upper level
temperatures with the next low as some snow may be reintroduced
into the forecast, especially for the higher elevations of the
Alaska Peninsula and also along the Kuskokwim Coast and Nunivak
Island. Any snow accumulations would be light and quickly come to
an end by Friday afternoon.

&&

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

Near-gale to gale force southeasterly winds will be common across
the central and eastern Bering on Wednesday as a front lifts
northward toward the Chukchi Sea through this evening. Plentiful
moisture along and ahead of the front has resulted in numerous
rain showers as southerly flow persists over the Aleutians.
Through the gaps and passes along the Aleutian Chain small craft
to low end gale force winds are forecast to prevail through
through the afternoon hours. Milder conditions are expected to
develop later tonight into much of Thursday as the front departs
the region and weak ridging of high pressure briefly develops over
the Bering. However, a North Pacific low is forecast to pivot
northwestward across the Alaska Peninsula and into the eastern
Bering on Friday, which should see redeveloping showers for the
Pribilofs and eastern Bering, perhaps with a mix of snow as the
low advects some cooler mid-level temperatures over the region.

&&
.Marine (Days 3 through 5: Friday through Sunday)...

Gulf of Alaska:
A strong barrier jet with storm force winds along the Gulf coast
early Friday morning will taper to small craft by Friday night.
Relatively light winds are expected through the rest of the
weekend. Seas 15 to 25 feet Friday morning will subside on
Saturday and Sunday. By Sunday, seas up to 10 feet expected.

Bering Sea/Aleutians:
The passage of a surface low will continue north across Bering
sea will keep southerly flow along the Alaska mainland coast and
west to southwesterly winds through the Aleutians and over most of
the Bering through this weekend. Areas of gales on Friday morning
is expected near Bristol Bay and Cape Newenham, but should
diminish through Saturday morning. Seas to approximately 15 feet
on the Pacific side may subside slightly on Sunday. Bering side,
expect seas to remain near or below 10 feet.

&&

.Long Term Discussion (Days 4 through 7: Saturday through
Tuesday)...

The pattern should slowly become more active as we head into the
weekend. The biggest change in the upper levels will be with
regards to the 300 mb (30,000') jet. For much of the early portion
of the week, the jet has been oriented from the North Pacific into
the southern mainland. As we head towards the end of the week, the
jet will become zonal (west to east) pointing towards the west
coast of the lower 48. This will allow for a subtle, but fairly
significant, change in the pattern. The robust North American
Ridge (typically a stronger feature in the summer) will yield to
this jet. This will allow for a shift in the active storm track to
move further east. Thus, must of the moisture will miss
Southcentral AK and take aim instead on SE AK. A trough will
preside over the Aleutians, which will allow for some colder air
to return to that area. 850 mb temperatures should fall to around
-8C to -10C.

The net effect at the surface for most of the population centers
will be a return to quieter weather with more seasonable (colder)
temperatures. With a trough still established over the Aleutians,
there will remain chances for snow (and rain) showers, especially
across the chain on Sunday. Weaker waves will still be able to
track up the eastern side of the trough from Kodiak towards
Cordova, but none of these systems looks to be as large or dynamic
as we have seen in the early part of this week. A transient ridge
of high pressure will move quickly through the Bering Sea on
Tuesday reinforcing the mostly quiet weather for the southern
mainland. After that, stronger system will start to creep back
over the Western Aleutians as we continue towards mid-week.

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Dense Fog Advisory: 101.
MARINE...Gale Warning: 119,130,131,138,139,160,165,170,179-181.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...AS
SOUTHCENTRAL ALASKA...TM
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...BL
MARINE/LONG TERM...VR/MO