Small Craft Advisory 17, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
537 PM AKST Sat Jan 5 2019

.ANALYSIS AND UPPER LEVELS...
The upper level pattern today consists of a deep vertically
stacked low in the western Bering, a sharp upper level ridge
extending from the eastern Alaska Peninsula north along the
western mainland Alaska coast up across the Bering strait and
an upper trough shifting across the Alaska Range and into
Southcentral Alaska. A swath of strong winds to the south of the
surface low in the western Bering, which has been bringing storm
force winds to the western Aleutians this morning, is lifting
north into the southwestern Bering with gales over much of the
rest of the Bering. The associated surface front is currently
swinging east, from the eastern Aleutians over the western Alaska
Peninsula. Low stratus which covered much of Southwest Alaska this
morning is now being eroded by gradually increasing offshore flow
ahead of the approaching front. Over Southcentral, stratus and fog
persist across portions of the western Kenai, Anchorage, and
Matanuska Valley despite the passage of an upper trough.

&&

.MODEL DISCUSSION...
Models are in good agreement with both the current synoptic
pattern and the next strong low tracking into the western Bering
Sunday. Model uncertainty increases Monday and Monday night with
regards to another smaller low around the 180 longitude line,
tracking north into the Bering and a surface low forming well
south of the eastern Aleutians and western Alaska Peninsula.

&&

.AVIATION...
PANC...Though the airport has cleared out this afternoon, areas of
fog and stratus persist very close by. Thus, expect LIFR
conditions to settle back in tonight. With no substantive changes
in the flow on Sunday, fog and stratus will continue to be a
threat.

&&

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

A weak shortwave trough moving across the region is spreading
clouds across the Chugach and Talkeetna Mountains east into the
Copper River Basin this evening. This trough is doing little to
alter the weak low-level flow across Southcentral, however, so
expect areas of freezing fog and low stratus to remain entrenched
over the Copper River Basin and across portions of northern Cook
Inlet and Turnagain Arm through early Monday as this trough is
replaced by another weak ridge. As the trough moves east, gusty
outflow winds will again pick up in the gaps and passes along the
coast Sunday through Monday morning. Fog and low stratus remain
the biggest challenges when it comes to the temperature forecast.
But given the continued weak low-level flow and lack of dynamic
upper-level features through the weekend, high and low
temperatures through the weekend will generally mirror those
today.

The next shortwave then slides across Southcentral on Monday in
association with a developing trough or closed surface low in the
northern gulf. From here, guidance diverges on the placement and
strength of this feature; however, it looks like there is now
higher confidence in the likelihood of a developing closed low
in the northern Gulf along with scattered snow showers for the
eastern Kenai Peninsula, Chugach Mountains, possibly extending
farther east along the coast late Monday into Tuesday. If this is
the case, the shift to a southerly flow would bring an end to the
outflow winds. The southerly flow will also help scour out the
fog, mainly in and around Anchorage, and bring a slight uptick to
the temperatures, especially along the coast.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3/Saturday
through Monday)...

Low level fog/stratus continued to have its hold on much of YK
delta today, and is finally showing signs of dissipating as the
overhead ridge slides east and offshore flow increases. The
primary front bringing snow to the coast and areas inland is
slowing and weakening, but will still bring some snow to the
areas, with maybe a few inches from the coast through Bethel and
Dillingham into Sunday. Winds with this snow will be the biggest
hazard to areas along the coast, as visibilities will likely be
reduced to 1 to 2 miles at times as the front moves inland. Monday
will repeat what the region saw last night into today with weak
onshore flow, ridging overhead and fog/stratus potential.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through
3/Saturday through Monday)...

There is little change to the forecast as two areas of low
pressure will be the dominant features through Monday. The first
low sits north of Shemya and is continuing to weaken, as an
attendant front stretches across the Bering and sits between the
Pribilof Islands and the AKPEN. This front is weakening as it
transits the eastern Aleutians. Stronger winds are confined to St.
Matthew Island and areas north.

The second low will lift out of the northern Pacific and across
Attu overnight, bringing another round of storm force winds to the
western Aleutians and Bering Sea. There is potential for a brief
period of hurricane force wind gusts early sunday morning from
Kiska to Adak, but decided against any high wind watch. As the
front races east, the low that it is attached to will continue to
weaken and slide west toward the Kamchatka Peninsula and becomes
completely detached from any upper level support. The front will
work across the eastern Aleutians through Monday bringing warm
air and rain.

&&

.MARINE (Days 3 through 5)...

Beginning Tuesday evening, conditions are expected to improve
across the Bering Sea as a storm system tracks north out of the
area while weakening. Winds and waves are likely to subside quite
a bit through Wednesday night before the next storm system
approaches from the south by Wednesday night. The storm is
expected to be quite strong with central pressures potentially
bottoming out below 950 mb, though the system is expected to
weaken as it approaches the Western/Central Aleutians and stay
south of the island chain. This would bring upper end gale force
winds to most of the Western Bering Thursday night into Friday.
Models have been fairly consistent with this storm so far,
thus confidence is above average in the track and strength.
Though, if the low takes a more northward track and maintains its
strength, winds will likely increase into the storm force
category.

Over the Gulf of Alaska, high pressure will continue to keep the
storm track to the south and west, thus expect generally good
conditions through the week. Localized higher winds may develop
out of bays and passes along the North Gulf Coast due to northerly
outflow winds.

&&

.LONG TERM FORECAST (Days 4 through 7)...
The long term forecast begins Wednesday with high pressure over
most of Southcentral and a cold Arctic upper level low over the
northern mainland. This will keep cold and dry conditions with
offshore flow over Southcentral and most of Southwest AK through
the end of the week. A few shortwaves rotating around a low south
of the AKPEN and the Arctic low will bring some snow showers to
parts of southwest AK on Wednesday but should diminish by the end
of the day. The Arctic low is expected to shift south some allowing
even colder air to filter in over the southern mainland on Thursday.
At the same time, a strong North Pacific low will move north
towards the Aleutians, but should stay south of the island chain
as a strong polar high over Siberia will prevent the system from
pushing further north. Regardless, the system will bring very wet
and windy conditions to the Aleutians and spread further east
towards the AKPEN by the end of the week. Models are now beginning
to show the low complex spreading east into the Gulf of Alaska by
Friday as high pressure shifts east at the same time. This would
bring a pattern change to the southern mainland with a return to
warm and wet southerly flow as we head into the weekend. There is
still a fair amount of disagreement between models as to how far
east the North Pacific low gets, so a lot could change between now
and then. Best to keep track of the forecast for updates through
the week as the details are worked out.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Storm Warning 175 176 177 178.
		 Gale Warning 170 172 173 174 179 185.
		 Heavy Freezing Spray Warning 185.
FIRE WEATHER...NONE.

&&

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