Small Craft Advisory 122, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
512 AM AKST Wed Feb 5 2020

.ANALYSIS AND UPPER LEVELS...

There is a mature low near Middleton Island with an occluded
front impacting the Gulf Of Alaska. There is a decaying low in the
Eastern Bering west of Kipnuk. There is another decaying low west
of the Pribilof Islands. Last but not least, there is a surface
low southwest of Adak which also has an occluded front. On the
latest ASCAT (advanced scatterometer) data there are still gales
in the northern Bering and storm to gale force winds south of Attu
Island. The radars at Kenai (PAHG), Middleton Island (PAIH), King
Salmon (PAKC) and Bethel (PABC) have been active overnight. There
is a 150+ knot jet core moving into southeast Alaska. There is
another jet core with a magnitude of 120+ knots associated with
the system that is south of Shemya. Cordova, Dutch Harbor and
Port Heiden reached 41 degrees Fahrenheit in the past 24 hours.

&&

.MODEL DISCUSSION...
The GFS ensemble members are tightly clustered through 48 hrs.
The position of the surface lows amongst the GFS Ensemble Mean
and the operational runs of ECMWF and Canadian are very similar
through 48 hrs. Minor differences emerge with the precipitation
and the surface temperatures. Overall, the consensus is that most
of Southwest Alaska and Southcentral Alaska can anticipate a
warming trend or at least a respite from arctic air through the
weekend.

&&

.AVIATION...
PANC...There is a surface low over the northern Gulf Of Alaska
and there is low level moisture being wrapped around this
feature. Overnight at PANC, PAMR and at the NWS Weather Forecast
Office in Anchorage, light snow was observed. Looking at satellite
imagery, the METARS and the model data, the cigs will bounce
around this TAF package. The Kenai radar has been active overnight
along Turnagain Arm. There is the potential for MVFR conditions.
While the winds will be light this TAF package, the ceilings look
like they will be an issue for this TAF package. Amendments will
be made as needed.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3:
Wednesday through Friday evening)...

Low pressure near Middleton Island this morning will continue to
produce an area of widespread light snow from Prince WIlliam Sound
north and east across the Copper River Basin. Along the immediate
coast, a mix of rain and snow is expected as temperature remain
in the middle to upper 30s. Farther west, a weakening upper-level
trough and surface front are combining to help provide enough
lift for occasional, very light snow from Cook Inlet north into
the Susitna Valley. Snowfall amounts through the day are expected
to remain minimal, with a dusting to around an inch over most
locations. Tonight, as the front and upper-level trough lift north
of Cook Inlet, a southwesterly flow will develop. This will bring
about an influx of moisture and help induce some additional light
snow from Anchorage north and east to Talkeetna and Gulkana.
Again, snowfall amounts are expected to remain light, with an
additional inch or so expected. The flow behind the front will
also usher in a southerly wind across Anchorage. This will not be
the classic warm Chinook, but should provide enough mixing to keep
overnight temperatures at or above freezing as the snow comes to
an end.

Conditions improve on Thursday as a ridge temporarily transits
the region, with only scattered snow showers lingering mainly
across the mountains. By late Thursday, another front will begin
to move in from the western Gulf with another round of
precipitation likely. Precipitation type, especially along the
coast and Anchorage Bowl will be a bit trickier with this next
system. There is the potential for some clearing and cooling
temperatures due to the aforementioned ridge, but a southerly flow
and southeasterly surface winds around the Anchorage Bowl,
Matanuska Valley, and Copper River Basin could limit any potential
downward trend in temperature prior to the onset of
precipitation. Thus, with temperatures expected to be within a
few degrees on either side of the freezing mark, there remains
quite a bit of uncertainty as to the precipitation type across
theses areas. The good news is that any precipitation falls looks
to be light. At this time, it appears that the heaviest
precipitation and heaviest snowfall with this system will occur
over eastern Kenai Peninsula.

&&

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

A weakening low near Mekoryuk this morning will keep a showery
pattern over Southwest Alaska today. By this afternoon, snow
showers will move inland, with one band oriented north to south
over Bethel bringing a few inches of new snowfall. A second, more
defined band of snow will set up this afternoon stretching across
the eastern Kuskokwim Valley to Iliamna, which could see higher
snow totals through tonight, which should stay under advisory
level criteria. Thursday should start off in a drier pattern
before a low over the AKPEN develops in the afternoon, which will
bring the next round of light precipitation to the Greater
Bristol Bay area. Models are still uncertain in exact placement of
this low, which will drive how far north the snow will track over
southwest mainland.

Look for the cooling trend to continue over the next few days as
arctic air continues to move tonight, bringing areas in the
Kuskokwim Delta back into the negative temperatures. This cold air
will begin to push into the Kuskokwim Valley by Thursday night.
With colder temperatures moving in and strong northerly flow
across the Kuskokwim Delta, a possible wind chill advisory could
be issued later today with better model agreement of low
temperatures.
The Kilbuck Mountains will keep most of the colder air north, which
allows for less of a cool down over this region.

&&

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

As a low in the eastern Bering weakens and moves inland later this
morning, the focus quickly shifts to a low moving across the central
Aleutians near Adak by this afternoon. Storm force winds associated
with this system will stay south of our forecast area, while only
coastal waters will peak at gale force. Models are still uncertain
whether a second closed low will spin up north of Adak this
afternoon, which could bring a second small area of gale force winds
through this evening. By Thursday afternoon, another small low will
develop near Cold Bay, which models are struggling on placement and
strength. Expect widespread rain and snow showers to persists across
much of the Bering and Aleutians in this pattern.

By Thursday afternoon over the western Aleutians and Bering, the
next strong system approaches. There is still uncertainly in where
this system will move to and where the strongest core of winds will
be. However, high end gale force winds will begin to move into the
region late Thursday night into Friday.

&&

.MARINE (Days 3 through 5: Friday through Sunday)...

Gulf of Alaska:

Friday through Sunday remain modestly active. Friday will bring a
decaying front sweeping from Kodiak to Prince William Sound. Winds
are expected to be southeasterly small craft with the occasional
gale gust. On the heels of the first system, winds will switch out
of the southwest on Saturday to high end small craft again.
Confidence is gaining that winds will approach gale for much of the
Gulf, and confidence is high that winds will be strong gales through
Shelikof Strait, before abating come Sunday.

Bering Sea/Aleutians:

Benign weather will be coming to a close through the weekend.
Friday will open with increasing northeast winds, peaking well into
the gale range across the entire Bering. Into Saturday confidence is
gaining with a strong low lifting between St. Paul and Bristol Bay.
South and east of this low, southwest winds may reach high end gales
to low end storm gusts through Saturday. West of St. Paul, winds
will slowly turn more northerly and continue to diminish as a much
weaker low tracks along the same path through the end of the
weekend.

&&

.LONG TERM FORECAST (Days 3 through 7: Friday through Tuesday)...

Normal to above normal temperatures, unsettled conditions, plentiful
cloud cover, and a mix of rain and snow appears to be a satisfactory
summary of the long-term forecast at the end of this week and into
the next workweek. The mean longwave trough will continue to support
an active weather pattern for southwest Alaska and then
Southcentral. The first of three systems will slide up the Alaska
Peninsula on Friday bringing a surge of warmer weather. Well above
normal temperatures will be the continued trend through the weekend,
with Sunday being the warmest. With the warm weather will be the
potential for strong Turnagain winds this weekend. Guidance is still
uncertain through that time, and more details will be forthcoming.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gale 351 352 411 155 185. Heavy Freezing Spray 414 412
411 185 179 160.

&&

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