Gale Warning 619, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
402 AM AKST Tue Nov 12 2019

.ANALYSIS AND UPPER LEVELS...

A broad 990 mb low continues to lift slowly northward into the
Gulf of Alaska this morning. The early morning ASCAT scatterometer
pass indicates a band of easterly gales ahead of the associated
occluded front as it, too, lifts north along the Southeast Alaska
coast. Inland, a 1023 mb high is anchored over the Yukon with an
axis stretching across the Copper River Basin. The tight pressure
gradient between it and the low in the southern Gulf has allowed
gusty northerly, outflow winds to persist along the Southcentral
Coast, especially out of the Copper River Delta and the Valdez Arm
and Narrows.

Temperatures across Southcentral this morning range from the
single digits below zero to the teens in the Copper River Basin,
to the 20s across the Susitna Valley and the lower to upper 30s
for coastal locations. Low stratus continues to linger across the
southern half of the Copper River Basin as well as along the
Southcentral coast where a few scattered showers are showing up on
radar. A weak, lee-side trough extends across the Alaska Range and
is producing areas of mid-level clouds across the interior this
morning.

Farther west, a vertically stacked low west of Saint Matthew
Island continues to weaken as it tracks to the northwest. An
occluded front associated with this low stretches across the
northern Bering to the Kuskokwim Valley. Scattered cloud cover and
a few isolated showers remain over the Y-K Delta but are
dissipating quickly as the front shears apart.

The main weather feature, and the focus for the upcoming forecast
across the Gulf and Southcentral Alaska, is a 953 mb storm-force
low currently 400 miles south of Dutch Harbor. This system
continues to deepen as it sits in the favorable left exit region
of a 130 kt cyclonic jet streak as is accompanied by a
strengthening upper-level shortwave and cold air advection digging
south across the Bering. The warm front associated with this
feature is lifting north toward the AKPEN and eastern Aleutians
this morning with widespread rain and gusty east to northeast
winds from Cold Bay to Nikolski.

&&

.MODEL DISCUSSION...

Models continue to struggle with the interplay between an arctic
trough over western Alaska dropping south over the Bering and a
low lifting north into the Gulf with associated upper-level
shortwaves. Specifically, there are subtle, yet important,
differences regarding the timing of the fronts as they approach
the northern Gulf coast, the orientation of winds aloft, and the
development and track of a secondary northern Gulf low late
Wednesday into Thursday.

For example, the latest NAM and GEM runs are a bit faster with
the progression of the initial front early Wednesday and keeps
the flow aloft oriented in a way to minimize the downslope
potential for the western Kenai Peninsula and Anchorage Bowl.
Conversely, the GFS is slower with the initial front and keeps
more of a southeasterly, cross-barrier flow aloft over the coast.
This could help limit precipitation amounts for the
aforementioned areas. Needless to say, all of this will affect the
onset of precipitation across Southcentral Alaska, as well as the
amount and type. Overall, the biggest challenge in the short term
will be precipitation type as conditions will be right on the
edge between freezing rain and snow. See the Southcentral forecast
discussion for more details.

&&

.AVIATION...

PANC...VFR conditions and light, northerly winds will persist.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
The main focus for the short term forecast surrounds the next
storm moving up from the Gulf on Wednesday, bringing increased
precipitation chances through Thursday. At the onset of this
event, temperatures will be in the lower to mid 30s just inland
with much colder temperatures in the 20s further north. Therefore,
precipitation will be a mix of rain, freezing rain and snow.
Another challenge with this system is snow amounts across the
Copper River Basin as this storm system brings a deep fetch of
southerly moisture Wednesday and Wednesday night. Thompson Pass is
expected to remain below freezing for this event and is expected
to have blowing snow as winds remain gusty out of the northeast.

For today, generally dry conditions are expected. The exception
to this will be Kodiak Island, where enough moisture remains over
the Gulf to produce precipitation. Tonight a front will move
north through the Gulf, bringing rain to Kodiak Island beginning
this evening. Rain will then spread north to the eastern Kenai
peninsula late tonight. Inland areas will remain dry.

&&

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

Weak ridging will sit over southwest Alaska today keeping
conditions dry through most of the day. Tonight a front will move
over the area from the south, bringing rain back to areas around
Bristol Bay with snow farther inland. There is also a slight
chance to see periods of light freezing rain into Wednesday
morning. The front will stall and weaken around Bristol Bay
bringing a mix of rain and snow to the area through Wednesday.
Meanwhile, northeast outflow winds will increase across southwest
Alaska through Wednesday dropping temps around the area with lows
in the Lower Kuskokwim Valley dropping to around 0F Wednesday
night.

&&

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

There are two lows impacting the area with one in the Bering and a
stronger one south of the eastern Aleutians. The Bering low is
weakening and will dissipate tonight. The North Pacific low will
slowly track east staying to the south of the eastern Aleutians
and Alaska Peninsula. However, it will bring rain and strong winds
to those areas as it moves through. The strongest winds will be
this morning and they will taper down through Wednesday.

&&

.MARINE (Days 3 through 5)...

From Wednesday night through Saturday, winds in the western and
central Gulf will generally remain 30 knots or less. Localized
Gales are possible at time from southern Cook Inlet, across the
Barren Islands through Shelikof straits as troughs and fronts
rotate through with brief periods of Gales also possible along the
barrier jet region of the northern Gulf Coast. Northeasterly
Gales are expected to persist over the northern Bering near Saint
Matthew Island Wednesday night through Friday and along portions
of the Kuskokwim Delta coast through Thursday. Winds across the
remainder of the Bering, Aleutians and near the Alaska Peninsula
are expected to generally remain 30 knots or less into Saturday.
A shift to a significantly stormier pattern is likely Sunday
through the middle of next week.

&&

.LONG TERM FORECAST (Days 3 through 7)...

By Thursday afternoon, the upper level pattern will have
progressed to a large double centered upper level low stretched
across much of the area. The colder upper level low center off of
the Kuskokwim Delta Coast will rotate to the south then east and
into Bristol Bay through Friday, while the warmer upper level low
to the southeast of Kodiak Island lifts northeast into the
central Gulf as it continues to weaken. By Friday afternoon the
Gulf low will dissipate into an open trough and frontal system
stretched across the northern Gulf coast with the low over
Bristol Bay becoming the dominant circulation.

The next North Pacific frontal system will track into the far
southern Gulf Friday afternoon and evening and then continue to
the northeast into the eastern Gulf Friday night through Saturday
to be followed by an additional frontal wave following a similar
track Saturday night and Sunday. Meanwhile, the low over Bristol
Bay will move slowly to the northeast sliding onshore over the
Kuskokwim Delta Saturday through Saturday night with several
associated frontal bands and troughs rotating through Southwest
Alaska late Thursday night through Sunday morning. The upper low
will open to a trough and lift northeast into interior Alaska
Sunday and Sunday night swinging a shortwave trough through
Southeast Alaska.

A strong westerly jet stream will push in south of the Aleutians
Sunday and Monday then strengthen through the middle of next week.
This pattern shift will open the door for a series of strong, fast
moving systems tracking in from the west along the Aleutian chain
and pushing progressively further east into southern Alaska and
the Gulf.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gale Warning 130 131 138 139 155 160 165 170 172 173 174
176 180 181 185.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...TM
SOUTHCENTRAL ALASKA...BL
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...DK
MARINE/LONG TERM...JR