Gale Warning 54, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
516 PM AKST Fri Jan 11 2019

.ANALYSIS AND UPPER LEVELS...
A deep cold core upper low is over the southern mainland with an
upper level ridge extending from the North Pacific into the
eastern Bering Sea. At the surface weak low pressure is over the
Gulf of Alaska resulting in some clouds with isolated to scattered
areas of snow across south central Alaska. Southwest Alaska is in
the frigid air with temperatures ranging from the negative teens
to the negative 50s. Over the Aleutians we have large deep
vertically stacked low near Adak slowly moving east. The
associated front extends to the southeast to another surface low
low about 300 NM south of the Alaska Peninsula. Another low has
formed south of the low near Adak and is tracking to the
northeast.

&&

.MODEL DISCUSSION...
Models continue to be in good agreement synoptically through this
coming weekend agreeing on a significant pattern change and
warming for the southern mainland and a rather active weather
pattern as we head into next week. The main discrepancies arise
with where the low center will be come Sunday afternoon. In
general there is agreement it will be in the vicinity of the
eastern Aleutians to south of the Pribilofs. The main impact of
this is with respect to wind speeds and directions for that
region. Models are in agreement with strong northerly flow across
the central to western Aleutians and a strong warm southerly flow
into the southern mainland Sunday.

&&

.AVIATION...
PANC...Stratus will move in and out of the airport through the
night but should improve Saturday as the weather pattern changes.

&&

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

Lingering moisture and a weak onshore flow across eastern Prince
William Sound will produce a few scattered snow showers for the
region overnight, especially from Valdez to Cordova. The bigger
story, however is a developing surface low south of the eastern
Aleutians that will begin to spread clouds along an occluded front
northward toward Southcentral from the Gulf overnight. This will
signal the beginning of a significant change in the overall
weather pattern for across the forecast area as the front ushers
in southerly winds along cloudier and warmer weather with
increased chances of precipitation this weekend with more
unsettled weather arriving for early next week. This first front
lifts north over Kodiak overnight, where precipitation will start
as snow but change quickly over to rain as warmer air works across
the island.

The front then continues its northward track through Saturday,
bringing snow to the eastern Kenai Peninsula and portions of Cook
Inlet later Saturday, The snow then advances into Prince William
Sound Saturday night. Plenty of cold air at the surface will keep
precipitation mostly snow as the front moves inland. In addition
to very windy conditions over the marine areas, gusty gap winds
will likely develop in favored locals (Portage Valley, Turnagain
Arm) on Saturday. Gusty southeasterly winds ahead of the front
will produce blowing snow with reduced visibilities through
Portage Valley and Turnagain Pass Saturday evening early Sunday
morning. A Winter Weather Advisory is out for this area.

A second front then moves in for Sunday bringing warmer air along
with another period of gusty southeasterly gap winds. Areas along
the coast will see snow change to rain with this second system
with a heavy, wet snow for the mountains. In stark contrast from
what we have seen recently. temperatures along the coast, in the
lee of the mountains, and through the lower Mat-Su Valleys will
climb into the lower to mid 30s Sunday and into the mid to upper
30s Monday.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2...Sat and Sun)...
High clouds this afternoon signal the pattern change that is on
the doorstep. After several days of an Arctic airmass dominating
the SW mainland and multiple wind chill advisories, warmer air is
on the horizon. These high clouds are associated with a warm front
from a North Pacific low south of Sand Point. This low will be the
first in a series of lows destined to push through the area over
the next few days. Each one will bring a push of warm air along
with it and take a bite out of the cold dome that has been in
place. The process behind this will be twofold. First, the airmass
moving north is hovering between 0 and 5 degrees below zero at 850
mb (5,000'). This is compared to the current airmass that is
holding between 20 and 25 below zero. The second part will be some
southeast winds. These winds will come up and over the Alaska and
Aleutian Mountain Ranges and warm as they do so. This warm up
could be rather dramatic across parts of the Bristol Bay area
where maximum temperatures could warm by nearly 40 degrees from
Fri afternoon to Sat afternoon.

This front will also bring a return to precipitation across the
area. The first shot will be some snow early Sat across the
Western Capes of Bristol Bay. With abundant dry air to overcome,
we are not looking for more than a few inches of accumulation.
However, as this snow butts up against the cold air, we do expect
some pockets of blowing snow along the capes and through the
coastline of the YK-Delta. Saturday's front will "prime the
atmosphere" to see slightly better snow from the second front on
Sun. This front will be a bit stronger, meaning a better chance
for precipitation. However, it will also bring a better chance for
warm air to intrude into SW. Weather models continue to struggle
to lock onto all the exact details with the low track and the
precipitation type for Sun, so we have elected to keep changes
minimal. For now, it still looks like a decent shot for a couple
inches of snow across the interior locations with snow turning to
rain near the southern coastal areas.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2...Sat and
Sun)...
As one system starts to wind down, another triple point low will
deepen to take its place. Storm-force winds will continue to wrap
around the low near the Western Aleutians into Sat morning. These
gusty northeast winds will also create some blowing snow
conditions for the Pribilof Islands (St George in particular). A
decaying frontal boundary continues to stretch out along the chain
with cold air to the north and warm air to the south. This is
creating a breeding ground for triple point lows. Several systems
will try to churn up Sat. However, models are starting to converge
on the dominant system just west of Dutch Harbor late Sat into
early Sun. In this somewhat uncertain pattern, there was enough
agreement to introduce southerly gale- force winds east of Sand
Point. There is also high confidence in widespread cold air
advection snow showers across the northern portion of the Bering
through the weekend.

&&

.MARINE (Days 3 through 5)...

Beginning the marine extended period forecast on Monday, a ~965 mb
low will be slowly moving north over the central Aleutians and
into the Bering, centered near the Pribilofs by Tuesday. The
Bering will be under broad cyclonic flow during this time with
areas of gale force winds expected on the periphery of the low, to
the east and west of the Pribilofs. Winds will diminish through
the day as the low weakens and slowly moves north, with mostly
just small crafts expected by Tuesday afternoon. Wave heights will
also be subsiding through Wednesday, decreasing from near 20 ft
west of the Pribilofs on Monday to only 10-15 ft by Wednesday.

The Gulf of Alaska will see a more active pattern as a series of
storm systems move through, kicking up winds and wave heights
through the first part of the week. Right now, it looks like winds
should remain predominately below gale force, though areas east
and north of Kodiak Island and though the Barren Islands will
likely see periods of gales Monday night into Tuesday morning.
Another system is expected to push through the northern Gulf
Tuesday into Wednesday, but there is still a fair amount of
uncertainty regarding the strength and timing this far out.

&&

.LONG TERM FORECAST (Days 4 through 7)...

Beginning Monday, the southern mainland will be under broad
southerly flow as the area will be caught in between an upper
level low over the Bering and an upper ridge axis over the Pacific
west coast. Warm and moist air will be pumped north into the Gulf
Coast, with a barrage of fronts and lows streaming into the area.
Models still show a chaotic mess in terms of specific features,
with timing and placement differences, but overall it appears the
windward (east) side of the AKPEN, Kodiak, and the Kenai Peninsula
will get the brunt of the action with typical leeward locations
expected to remain mostly dry due to downsloping. These systems
don't look to be as strong the ones that moved through the area
over the New Years holiday due to weaker upper level jet support.
Temperatures are expected to remain well above average through the
middle part of the week. For snow lovers, snow levels look to
rise above sea level in the mountains, meaning rain may fall at
the lower elevations along the coastal mountains from the Kenai
Peninsula to the Chugach along the Gulf Coast.

By the end of the week, models begin hinting at another pattern
change with the upper low over the Bering retreating north
allowing ridging to potentially build back in over the southern
mainland, allowing for a drying/cooling trend over the area.
Still a fair amount of disagreement in the models this far out so
specific details will need some time to get worked out.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gale 120 131-139 150 160 175 177 179 185.
		 Storm 130 178.
		 Heavy Freezing Spray 130 140 160 180 185.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...SA
SOUTHCENTRAL ALASKA...TM
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...MSO
MARINE/LONG TERM...KVP