High Wind in Alaska, February 9, 2020

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
424 PM AKST Sun Feb 9 2020

.ANALYSIS AND UPPER LEVELS...

Weather conditions across the forecast area have calmed considerably
after yesterday's front passed through. In the upper levels, the
main upper level low is still located to the northwest, close to
Norton Sound. This extends into a long wave trough through the
Bering Sea. East of this upper level trough, a 135 knot jet stream
is supporting a developing surface low in the North Pacific,
evident on satellite by a large cirrus shield covering the Gulf
of Alaska. Further west, the next system approaches the western
Aleutians.

At the surface, the remnants of yesterday's low pressure system
still linger over the mainland. Skies have cleared west of the
Alaska range, but southwest flow continues to bring upslope flow
to the Alaska Range. A few snow showers persist through Broad
Pass and the northern Susitna Valley. Elsewhere across the
mainland, things remain relatively quiet.

In the far Western Aleutians, the next front is beginning to show
its hand. Winds and snow have increased ahead of the low, and a
High Wind Warning is in place for the evening hours.

&&

.MODEL DISCUSSION...

Model agreement has improved since yesterday, which is rather
surprising since it started out in pretty good agreement
yesterday. High pressure is currently building over the mainland,
and the timing of the front in the west is consistent between the
model runs. The next feature of concern is the low that develops
along the front late Tuesday night. Timing is variable between the
models, which will make a difference for storm force winds in the
Gulf of Alaska. A NAM/GFS blend was chosen for this time frame to
minimize any model differences.

&&

.AVIATION...

PANC...A developing low in the Gulf of Alaska is not expected to
bring any impacts to the mainland, with the exception of bringing
the possibility of outflow winds to the Southcentral area. Winds
should switch to be more northerly at PANC tomorrow morning, with
the possibility of some gusts as winds aloft mix down. Expect vis
and cigs to remain VFR as drier air pushes in.

&&

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

After a very warm weekend in Southcentral, relative to nearly the
entirety of January, a return to normal to slightly below normal
temperatures is imminent. Cold air is gradually squeezing through
the passes in the Alaska Range. The cold air will have more
success cooling things off overnight tonight as the southerly
winds over the area presently diminish at the same time as the
cloud cover over much of the area associated with a front retreat
off to the east. As this will take some time overnight to occur,
expect most of the temperature drops to happen well after midnight
tonight. The cold air will continue building across the rest of
Southcentral on Monday. While the February sun is getting stronger,
temperatures are unlikely to climb more than a few degrees above
tonight's lows for highs on Monday. The push of cold air through
the gaps will increase the westerly winds substantially through
the day on Monday as well, especially through Whittier and Passage
Canal, where gusts over 50 mph are expected in the afternoon.
Gusty northerly winds are also expected through Seward and
Resurrection Bay as well. Cold, westerly winds over 25 kt are
possible through Kachemak Bay and potentially into Homer during
the day.

Cold air returning to the Copper River Basin late in the day
Monday into Monday night will lead to increases in the winds
through Valdez and the adjacent waters as well. Northerly winds to
gale force will develop late Monday night through the Narrows and
the Copper River Delta. Gradual diminishing of the winds through
Seward and Whittier are expected Monday night. Elsewhere, the
clear skies and nearly calm winds will allow temperatures to
plummet across much of the area. Most communities will drop below
zero, with Kenai and Anchorage falling to right around zero.

On Tuesday, another day with plentiful sunshine is expected. While
there will be much better temperature recovery on Tuesday as
compared with Monday, highs will only get into the teens in most
non-coastal areas, with offshore winds continuing to allow cold
air to filter down the valleys. The cold air persisting over the
Copper Basin will keep Valdez and the Copper River Basin winds
elevated through the day. On Tuesday afternoon, all eyes will turn
towards the south, as a strong North Pacific low approaches the
southwestern Gulf. There is still some uncertainty with the low
track, but the models are in much better agreement that there will
be a strong low, tracking off Kodiak Island Tuesday night, that
will have plentiful moisture to work with. Thus, the winds and
the probability of snow have been drastically increased across
the entire Gulf.

The worst conditions with the low are likely to be seen across
Kodiak Island, including Kodiak City on Tuesday night into early
Wednesday morning. With enough cold air in place and plentiful
moisture, it's becoming increasingly likely that heavy snow will
be seen across the island, which may amount to over a foot by the
time all is said and done. Aforementioned differences in the
track between the models precluded any watch issuance, but it will
be watched closely over the upcoming forecast cycles. The general
trend in the models regarding the storm on Wednesday will keep the
center of the low well south of Middleton Island as it turns
eastward through the day. This will limit the impact to other
areas of Southcentral, though periods of snow are likely at the
coast late Tuesday night through Wednesday morning. Upper level
support to the north of the low center should allow some of that
snow, albeit light, to spread across the western Kenai and
Anchorage. For now it appears the Mat-Su will be spared from
anything more than flurries since most of the moisture stays
south. The low moves into the eastern Gulf Wednesday evening,
making for rapid clearing behind it for much of Southcentral.
Another round of strong gap winds through Whittier and Seward and
many of the other gaps will persist into Wednesday night. This
will keep cold, well-below-freezing temperatures across
Southcentral for the foreseeable future.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...

Arctic air continues to infiltrate the Southwest Mainland, and
tonight will be cold and dry. Surface conditions will trend even
colder Monday, as a trough tracks eastward through the Gulf/North
Pacific and cold air advection/north flow strengthens farther
north. An upper ridge over the Bering will track eastward late
Monday into Tuesday and the Arctic high will become centered over
the North Slope. Surface winds will transition to northeasterly
(cross-gradient) and Tuesday will be another cold day, especially
in the Kuskokwim Valley, though likely a touch warmer in the
Kuskokwim Delta. High clouds should start streaming into the
Mainland from the southwest as an anchor low near the western
Aleutians steers a front north/northeastward across the Bering
Sea. A trend to warmer conditions is indicated Wednesday.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...

A storm force low centered roughly 400 miles southwest of Attu is
bringing gales and storm force winds, with areas of hurricane
force gusts to the western Aleutians/Bering. A High Wind Warning
remains in effect for the western and central Aleutians tonight.
The leading front wrapped around the low is tracking
north/northeastward across the Bering and Aleutians, bringing
areas of southerly gales to much of the Bering Sea. With a
moisture fetch reaching almost into the tropics, expect a healthy
round of precipitation along the front. Any snow should change
over to steady rain along the front...then snow showers will be
possible in the cold air mass behind the front. The front will
track across the Pribilof Islands and AKPEN late Monday into
Tuesday. Blowing snow may impact visibility in the Pribilofs
Tuesday. With models depicting several compact lows rotating
around the main low, there will be potential for periods of
elevated winds over the central and western Aleutians behind the
front Monday into Tuesday. With poor model agreement on these
finer scale details, it's tough to have high confidence in these
details. Be sure to follow the forecast for updates.

&&

.MARINE (Days 3 through 5: Wednesday through Friday)...

A strong low pressure system is expected to move into the Bering
Sea early in the week, but by Wednesday the winds along the front
will be max gale force. Seas will be high with this system,
reaching 30 feet south of the Aleutian Chain on Thursday and
increasing to above 20 feet in the Western Bering Sea.

In the Gulf of Alaska, gale force winds will return on Wednesday
on the north side of a low that is moving across the Southern
Gulf. This will also bring some strong northerly gale force winds
through Shelikof Strait, and southern Cook Inlet. By late
Wednesday winds will increase to storm force along the north Gulf
Coast and south of Kodiak Island as the low progresses eastward.
They will rapidly decrease though, and by Friday, winds will
remain mostly lightly across the Gulf of Alaska.

&&

.LONG TERM FORECAST (Days 3 through 7: Wednesday through
Sunday)...

A strong ~960mb low will approach the western Aleutians from the
North Pacific on Wednesday. Gusty winds and moderate rain/snow are
likely as its associated front tracks across the Aleutians by
Thursday. It will become nearly stationary and weaken Friday into
Saturday as it becomes vertically stacked with an upper low near
Atka. While this will lead to gradually diminishing winds,
precipitation will continue through the weekend.

A series of lows will track west to east across the Gulf through
the weekend, bringing precipitation to coastal areas as well as
snow to the Copper River Basin. Exact timing and position of these
are still somewhat uncertain. High pressure will gradually weaken
over the interior, however as a result of the aforementioned
lows, the gradient will remain supportive of northerly winds and
thus temperatures are expected to remain slightly below average
for through end of the week.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...High Wind Warning 187 191.
MARINE...Storm Warning 177 178.
 Gale Warning 120 127 130 131 170 172 173 174 175 176 179 185.
 Heavy Freezing Spray Warning 121 127 128 129 130 139 160 179 185.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...LF
SOUTHCENTRAL ALASKA...JW
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...MM
MARINE/LONG TERM...LF/AP