Small Craft Advisory 845, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
425 PM AKST Sun Nov 10 2019

.ANALYSIS AND UPPER LEVELS...
A weak positively tilted trough is lifting northward across
Southwest Alaska today, producing showers, mostly scattered in
nature. The low level airmass remains quite warm across the
region, supporting rainfall. Surface temperatures in the
Kuskokwim Valley are below freezing, so could see some patchy
light freezing rain. The upper short-wave is just barely clipping
Southcentral, producing some rain to Kodiak Island and a few
showers farther north. For the most part, Southcentral is dry
and cloudy. Stratus has settled in across the Copper River Basin
and with nothing to mix it out, expect overcast conditions to
persist across the heart of the basin.

A negatively tilted trough over the southern Bering Sea (north
of the central to eastern Aleutians) is in the process of closing
off into a low. There is a weak surface low beneath this with a
cold front trailing to the south. This entire system is lifting
northward, with the cold front tracking north and east from the
low center. There is a narrow band of rain right along the front.
The strongest winds (gale force) are behind the front thanks to
cold air advection in instability.

A large occluded low over the northeast Pacific is lifting
northward toward the Gulf of Alaska, propelled by a southerly
jet streak on the east side of the low. The last system of
interest is a low tracking eastward across the North Pacific.
This is the remnants of Super Typhoon Halong, with warm and
moist tropical air embedded within. Just upstream of this a
short-wave trough is digging southeastward, with colder air
advecting across the far northwest Pacific. The interaction
of these two features will lead to development of an intense
low south of the Alaska Peninsula and Eastern Aleutians by
Tuesday.

&&

.MODEL DISCUSSION...
Models are in good agreement with large scale features over the
next few days and forecast confidence is above average.

&&

.AVIATION...
PANC...VFR conditions will likely persist. Some of the model and
MOS guidance is hinting at potential for stratus early Monday
morning. However, with increasing low level northeasterly flow
(as a ridge builds over Southcentral) this is not usually a good
situation for fog or stratus at the terminal. Thus, have not
included any indication of fog or stratus in the TAF.

&&

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

A shortwave trough moving north across Southwest Alaska is
influencing SOuthcentral with extensive mid and high level clouds
this afternoon. Over the Copper Basin, widespread stratus has
developed and will likely remain in place through much of
tomorrow before waning and clearing out. Monday is shaping up to
be a nice day as upper ridging builds overhead. A weakening low in
the Gulf of Alaska will bring rain to Kodiak Island and may clip
the North Gulf coast before falling apart as it interacts with the
cooler offshore flow, thus deforming and shearing the front
apart. Expect the dry weather to hold through Tuesday afternoon
before remnant moisture from the front begins to move into the
eastern Copper Basin Monday eve ahead of a larger frontal system.

As noted above, things change for Southcentral Wednesday as an
arctic trough tracking across the interior advects some arctic air
into the Copper Basin and northern Susitna Valley. As the front
moves inland Wednesday afternoon and evening, there should be
sufficient cold air for potential accumulating snow across the
aforementioned areas, along with coastal rain and increasing rain
chances west of the Chugach Mountains.

&&

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

A dying front currently over Southwest Alaska is expected to
gradually move westward towards the Bering through tonight. Shower
activity continues to move northward along the frontal boundary.
Almost all of Southwest Alaska is currently above freezing, except
the Hooper Bay area, which is very close to freezing, and some of
the more sheltered areas of the Lower Kuskokwim Valley. If any of
the shower activity makes it over the areas still below freezing,
then a brief period of freezing rain is possible. Everywhere else,
rain is expected.

On Monday, a reinforcing front will approach the coast, spreading
more rain to the Kuskokwim Delta and along the Western Capes. This
feature will clear the area on Monday evening, with breezy
offshore winds developing, leading to cooling temperatures as a
fresh, polar air mass makes its way southwestward out of the
interior. Most areas will turn drier from Monday night through at
least Tuesday night. The track of a front tracking over the
western Gulf may allow for some light snow for interior Bristol
Bay and the Lower Kuskokwim Valley, with chances for rain for
coastal Bristol Bay by Wednesday. There is a fair amount of
uncertainty with this feature, so stay tuned.

There is more certainty with the strength of the low causing the
precipitation on Wednesday. While the center will be well
southwest of the area, its strength will allow for increasingly
gusty northeast winds to overspread the area from Tuesday into
Wednesday, which will transport increasingly colder air with time
into the area. Thus, for the short-term, Monday will be the
warmest day of the next week, with a strong cooling trend expected
thereafter.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3:
Tonight through Wednesday)...

Two lows near the Bering will be the primary weather-makers across
the basin through Wednesday. The first is currently southwest of
the Pribilofs. It is a low that formed along a front, and now has
a well-defined circulation on satellite. The low is producing an
area of gale force winds to the south and west of the low
center, to the north of Atka. The low will track northeastward,
staying just west of the Pribilofs tonight. This will bring gusty
winds and rains to the islands. It will turn towards the northeast
Tuesday, spinning over the northern Bering until dissipation la
in the day.

The second low will be much stronger than the first. Fortunately,
it will only be delivering a glancing blow to the Alaska Peninsula
and Eastern Aleutians starting late Monday night. While the center
of the low will stay well south of the area, gales are likely all
across the Southern Bering on Tuesday. Storm force winds may
approach the Pacific side of the area Tuesday morning. Beyond
that, the low will be a strong, slow mover, so waves of rainfall
with gusty winds will move across these same areas through
Wednesday before it finally begins to drift towards the Gulf
allowing a much colder airmass to move in on Thursday.

&&

.MARINE (Days 3 through 5)...
The strong low south of the Alaska Peninsula will primarily bring
Gale to Small Craft Advisory level winds Tuesday night and
Wednesday to the waters along the Aleutians, Alaska Peninsula,
southeastern Bering, Bristol Bay and Gulf of Alaska with the
stronger storm force winds most likely remaining to the south of
the area. With the low filling and weakening as it lifts north
into the general winds in the Gulf will likely remain 30 knots or
less for Thursday and Friday with potential Gales isolated to
favored channeled terrain and possibly along the barrier jet
region of the northern Gulf Coastal waters. For the Bering,
increasing northeasterly flow will bring the potential for Gales
to the northern waters Wednesday through Friday with Small Craft
Advisory or less winds further to the south.

&&

.LONG TERM FORECAST (Days 3 through 7)...
By Wednesday, a large vertically stacked low containing tropical
remnants will be centered south of the Alaska Peninsula and
tracking slowly east around 50N. An associated frontal system with
a deep southerly moisture tap will stretch north across the
central and eastern Gulf to the northern Gulf coast. A weakening
portion of the front will extend to the west across the Bristol
Bay area and southeastern Bering with additional wraps of the
occlusion south of the eastern Aleutians and Alaska Peninsula
closer to and encircling the main low. Further to the north, an
arctic low over the northern Canada coast will extend a cold
trough over the northern half of mainland Alaska with an upper
level ridge extending south through the Bering Strait across the
northeastern Bering to the Yukon-Kuskokwim Delta coast.

With colder low level interior air entrenched in the Copper River
Basin, a rather moist easterly wave being propelled by an arctic
trough digging to the southwest across interior Alaska to the Y-K
Delta Wednesday and Thursday will bring the potential for heavy
snow to the Copper River Basin and far northern Susitna Valley
and rain to the remainder of Southcentral. For Southwest Alaska,
precipitation will spread in from the east across the Alaska Range
Thursday primarily in the form of rain over the southeastern
valleys and transitioning to snow to the west.

Thursday night into Friday, the cold upper level low will rotate
to the south into Bristol Bay while the steadily filling low south
of the western Gulf lifts north into the central Gulf. Surface
troughs in between these two systems will continue to track from
east to west across Southcentral and into Southwest Alaska. The
Gulf low will dissipate Friday night into Saturday leaving a front
stalled across the Kenai Peninsula and northern Gulf Coast while
the western upper level low tracks back onshore over the Kuskokwim
Delta with the accompanying cold air aloft spreading inland
across Southwest Alaska.

A more active westerly storm track will push into the Aleutians
for the weekend with a series of developing lows tracking up the
the chain and into the Bering. This evolution will push the upper
low over Southwest Alaska off to the northeast through Sunday and
then bring progressively strong storm systems in from the west
through early next week.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gale 132 170 173 174 175.
		 Storm 155 172.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...SEB
SOUTHCENTRAL ALASKA...JA
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...JW
MARINE/LONG TERM...JR