Small Craft Advisory 46, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
525 PM AKST Sun Jan 13 2019

.ANALYSIS AND UPPER LEVELS...
A deep vertically stacked low is nearly stationary over the southern
Bering Sea. An upper level short-wave rotating around the east
side of the low is driving a surface occluded front northwestward
across the southwest Alaska coast and eastern Bering Sea. This
brought snow and blowing snow to the Kuskokwim Delta coast as well
as Saint Paul Island. The occluded front wraps back southeastward
across Bristol Bay and into the western Gulf/Kodiak Island area.
Much warmer temperatures through this corridor are producing
rain. This portion of the front is lifting northeastward toward
Southcentral Alaska. Strong low level southeast flow out ahead of
it is leading to downslope drying across the western Kenai
Peninsula, Anchorage, and Matanuska Vally, and eastern Susitna
Valley. Meanwhile, upslope flow is bringing steady precipitation
to Western Prince William, the west side of Cook Inlet, and the
western Susitna Valley.

To the south of the primary storm system, a series of short-waves
embedded within the long-wave trough over the North Pacific are
tracking northward toward Southwest Alaska and the eastern Bering
Sea. The clouds are mostly convective in nature, with some
thunderstorms being observed over the North Pacific. Lastly, on
the back side of the Bering low cold air is advecting southward
across the western Aleutians leading to snow showers and gusty
northerly winds.

&&

.MODEL DISCUSSION...
Models have a good handle on ongoing weather, but quickly break
down after that. There is a large spread in solutions with the
many waves and surface lows moving up from the Pacific the next
few days. Run-to-run consistency is poor and doesn't really help
in identifying a preferred model. With low forecast confidence,
especially for Day 2 and 3, will generally use a broad-brush
approach to the forecast and try to show trends consistent with
the envelope of solutions.

&&

.AVIATION...
PANC...VFR conditions and light northerly winds will persist.
Strong easterly flow up above the surface will continue until the
occluded front finally passes through Anchorage sometime Monday
morning. Thus, low level wind shear will persist.

&&

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

Three separate systems are expected to impact the Southcentral
area through Tuesday night. None of them are expected to be
particularly strong or cause major impacts, but are worth noting.
All of the main effects will be felt along the coast, as inland
areas are expected to remain dry with well above average
temperatures. Here is the breakdown.

First is a front currently moving north and east across the
central Gulf. It is producing gale force winds through the Barren
Islands and northwestward through Augustine Island. The front will
rapidly weaken this evening, dissipating altogether by Monday
morning near Seward. Until then, gusty conditions and rain are
expected along the Kenai Peninsula coast.

The second system is a front that is expected to intensify late
tonight through Monday morning south of Kodiak and the Alaska
Peninsula. Most of the associated precipitation is expected to
remain west of Kodiak Island, though onshore flow may produce some
showers on the Gulf side of the island through the morning. The
larger impact will be gale force winds expected to develop along
and east of the front. The gales are largely expected to impact
the south side of Kodiak Island south of Dangerous Cape and around
the Sitkinak Island area during the day Monday. The strongest
winds are expected in the early afternoon. The winds will
diminish below gale force by the evening as the front begins to
drift west away from Kodiak Island.

The third system is a weak low that will track westward across the
central Gulf on Tuesday afternoon. Winds may pick up and the brief
reprieve from the rain along the coastal mountains Monday night
will end as the low approaches on Tuesday. There remains
significant disagreement in the models with how fast the low
tracks and the strength of the winds, but for now it appears even
the strongest winds will remain below gale force across the
northern Gulf Tuesday afternoon and evening.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3/Sunday
night through Wednesday)...
Steady warming is currently taking place through southwest AK.
This is due to the low center in the Bering Sea brining up
southerly flow out of the north Pacific. Areas of precipitation
continue to fall with this system, though the heavier
precipitation that caused the issuance of a winter weather
advisory has pushed north out of our forecast area. Thus, the
winter weather advisory has been cancelled. As temperatures warm
this evening, some areas of mixed precipitation and rain will be
present. It should be noted that freezing rain is not expected at
this time.

After the low drifts north the next couple of days, a chance of
rain and snow will exist along the coast. However, interior areas
will clear out. The departure of this latest system will signal a
quiet few days for southwest AK.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3/Sunday
night through Wednesday)...
A large low pressure system continues to spin in the southcentral
Bering. Its center is currently located just north of the
Central Aleutians. The worst of the weather associated with this
low has subsided, so the winter weather advisory for the Pribilofs
has been taken down. The main weather feature of concern are the
gale force winds that will continue to wrap around the low through
tomorrow.

Through Wednesday, the low center will drift north through the
Bering and gradually weaken as it goes. This will decrease the
strength of winds associated with the low, which is why gale force
winds are only expected through tomorrow. Snow showers and rain
showers will also continue to be associated with the low as well.

&&

.MARINE (Days 3 through 5)...

Beginning the marine extended period forecast on Wednesday, a low
over the northern Bering will continue to weaken as it drifts
north allowing winds to diminish to small craft or below. A
frontal system approaches from the west on Thursday which may
bring a short period of southerly gale force winds to the far
western Aleutians and Bering, but models show the system rapidly
shearing apart and weakening as it stalls out over the western
Bering. Other than the frontal system, winds are expected to
remain below gale force through the end of the week.

A low south of the Gulf of Alaska will lead to easterly small
craft winds over the southern Gulf on Wednesday, before subsiding
through the rest of the week as the low drifts south and west.

&&

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

Beginning Wednesday, a broad upper low will be located over the
eastern Bering while a high amplitude ridge will extend from the
Pacific West Coast north over Eastern Alaska and into the Arctic.
Models have been trending towards a more SE-NW tilt of the ridge,
nudging a bit further west over the eastern mainland. This will
result in more of a southeasterly flow over the Gulf and into the
southern mainland, leading to generally wet conditions over the
windward coastal mountains, with drier conditions further inland.
Models are still struggling with the specific features embedded
within the main flow, but are trying to key in on a short wave
trough pushing west across the northern Gulf and into the Prince
William Sound Tuesday night into Wednesday, with a good shot of
precipitation expected over the coastal mountains during this time.
Warm surface temps will likely keep precip as rain at sea level.
By the end of the week, the upper ridge will try to nose southwest
towards Southcentral bringing somewhat drier conditions, though
precip will likely still be seen along the coast with continued
onshore flow. Models show a broad surface low somewhere between
Bristol Bay to south of the AKPEN on Thursday with ridging
building in over the central Bering. A frontal system will
approach the western Bering on Thursday but looks to stall and
weaken as it runs into the upstream ridge. By the weekend, there
are signs that a stronger surface low will move up from the North
Pacific into the Northeastern Gulf. Right now, the system is
expected to impact the Panhandle and stay east of Cordova.
Overall, temperatures across the southern mainland are expected to
remain above normal through the end of the week, with a cooling
trend by the weekend.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gale 130 132 150-170 172-175 178-180 185.
		 Heavy Freezing Spray 185.
FIRE WEATHER...NONE.

&&

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