Brisk Wind Advisory 1, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion...CORRECTION
National Weather Service Anchorage AK
712 AM AKST Thu Jan 2 2020

.ANALYSIS AND UPPER LEVELS...

A 493 dm upper-level low continues to sit nearly stationary over
Bristol Bay this morning. A series of shortwaves are pinwheeling
around this feature. The first is positioned northeast of the low
and is lifting across the interior of Southcentral. This feature is
producing some low stratus across the northern part of Cook Inlet
over the Susitna Valley where isolated snow showers persist,
especially north and west of Talkeetna. The second shortwave is
draped along the northern Gulf coast and has helped spin up weak
surface lows situated near the Copper River Delta. The cyclonic
circulation associated with these surface lows is clearly visible on
both satellite and radar imagery. These lows are also pushing clouds
into the Copper River Basin (where overnight temps remain in the
single digits to mid teens) and is producing bands of snow showers
across eastern Prince William Sound. Elsewhere across Southcentral,
areas of low clouds persist over Cook Inlet and snow showers
continue for Homer and Seward, helped in part by the unstable
southerly flow.

A third and fourth shortwave are rotating around the backside of
the upper-level low and are moving south over the eastern Bering.
These are producing areas of snow and gusty northerly winds from
the Kuskokwim Delta coast to the Pribilofs and northern portions
of the eastern Aleutians and southern AKPEN.

Bands of heavy snow showers and areas of heavy freezing spray also
continue across the coastal and offshore waters as gusty winds
persist from the eastern half of the Bering to the western and
northern Gulf.

&&

.MODEL DISCUSSION...

Forecast guidance is keying in on a similar synoptic pattern
through the end of the week as the upper level low in Bristol Bay
shifts east. The biggest difference is with the development of a
complex surface low south of the AKPEN and how this feature
evolves as it moves closer to Kodiak Island by Friday. Models
differ on whether a secondary low (or a weaker inverted trough)
will develop from the main low and track toward the northern half
of the island. Snow and wind are the bigger challenges with this,
given whether or not this feature spins up (and how strong if it
does). With this in mind, any differences in the evolution of this
system will also have impacts on cloud cover and temperatures not
only across Kodiak Island, but also the Kenai Peninsula, and
possibly parts of Cook Inlet and western Prince William Sound.

In the nearer term, models are also struggling with the
development and evolution of two compact surface lows currently
spinning up just south of Cordova. While most guidance suggests
that these features will quickly dissipate as they enter Prince
William Sound, the NAM is most bullish in holding these features
together as they retrograde into western Prince William Sound. If
the NAM is correct, this would yield another round of snow for
Portage Valley, and perhaps some light snow all the way into the
Anchorage Bowl through this evening.

&&

.AVIATION...

PANC...Low pressure moving into Prince William Sound is expected
to keep low stratus along with occasional flurries / light snow
showers over the airport complex through the evening hours. MVFR
conditions are expected to persist through the evening with
ceilings at or below 3,000 ft. Visibility may also be reduced to
MVFR at times with any snowfall. There is also a chance that the
aforementioned low holds together all the way to western Prince
William Sound. If it does, there is the possibility for an
extended period of light snow. However, confidence in this
solution is very low and is currently not included in the TAF
package.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2...Thu and
Fri)...
We continue to transition into a relatively quiet pattern after
the snow event on New Years Eve. A very cold, nearly vertically
stacked upper level low is wobbling over Bristol Bay. The cold air
coming over top of the warmer Gulf of AK waters is creating
widespread snow showers and also a few small scale circulation
centers. One of these centers is approaching the N Gulf Coast
near Cordova and will bring some rather intense snow showers to
that area through the morning. The cyclonic (counter clockwise)
circulation is just enough to loft some of this moisture over the
mountains and into the Cook Inlet area. Thus, we expect some light
flurries around the Anchorage Bowl through the morning, with
little to no accumulation. As the circulation center drifts back
to the west across Prince William Sound, it could bring a few
inches of snow back to Whittier and possibly as far inland as
Portage. At this time, it looks like dry air will keep it from
making it much further west, so have held at flurries tonight for
the Anchorage Bowl. However, if this feature holds together a bit
better, we could not rule out some light accumulations for
Girdwood, Turnagain Pass, and the Anchorage Hillside.

Another compact low will move up toward Kodiak Island through the
day today. This system looks to skirt along the E and NE side of
the island late today into tonight bringing the possibility of
another couple of inches of snow there as well. It will also bring
a return to strong (gale force) winds for many of the marine
areas such as Shelikof Strait and the Barren Islands. This system
will stall near the southern Kenai Peninsula and fall apart
through the day Fri. The overall pattern will then start to
reorient for the weekend with drier air settling in and a slight
uptick in offshore flow. This offshore flow will make for very dry
conditions inland and should allow skies to clear. At this time,
we expect some of the coldest temperatures of the winter thus far
for Sat morning.

&&

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

Cold conditions will prevail across the southwest mainland through
tomorrow. The mid-level low which has taken up residence over this
portion of the state is finally dropping south towards the Alaska
Peninsula (AKPEN). This continues to allow for decreasing cloud
cover and light winds to continue. Another artifact of the low
moving away will be warming temperatures at 850 mb (roughly 4000
feet above ground level), with the numerical guidance showing a 7
to 10 deg. C. warming at Bethel and King Salmon. It remains to be
seen though if this will translate to the surface, as an
initially isothermal (neutral temperature change as you increase
in height) layer between the surface and 850 mb develops an
inversion (increase in temperature with height...which helps
prevent any changes aloft from mixing to the surface). In either
case, it will remain cold through tomorrow...just to what degree
(pun intended).

&&

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

A mid-level low will continue dropping towards the AKPEN this
evening, crossing into the western Gulf on Friday. Cold advection
will increase on the northern through western flank of this
low...with the net effect being cooling temperatures for the
Pribilof Islands, eastern Aleutians, and towards Sand Point. This
decrease in temperature aloft will also increase the ocean-
induced instability, allowing for some heavier snow squalls, with
Blizzard conditions continuing at the Pribilof Islands through the
afternoon, before improving conditions commence there this
evening.

&&

.MARINE (Days 3 through 5: Saturday through Monday)...

A relatively quiet weather pattern sets up for this time of year
all across southern Alaska and the Bering. A low over the southern
Gulf of Alaska moves into the eastern Gulf Saturday, with a
chance of some northwesterly gales through the Barren Islands. A
new North Pacific low may move into the southern Gulf on Sunday,
but there is substantial model disagreement, and confidence in
that is low.

High pressure will keep all winds below gale force all across the
Bering Sea. Winds may approach gale force in the western
Bering/Aleutians Sunday night as a strong low approaches. There
is limited confidence as to the track of this low through Monday
night, however, confidence is high that gales will cross into the
eastern Bering/Aleutians by then.

&&

.LONG TERM FORECAST (Days 3 through 7: Saturday through
Wednesday)...

A quieter weather pattern is setting up for much of southern
Alaska in the long-term period as a cold air mass becomes firmly
planted across the area. This will divert the storm track to the
northern Pacific with any lows impacting the Panhandle. This is
generally agreed upon between models.

A weak low centered off the coast of Kodiak, over the
southwestern Gulf, will slowly move eastward across the southern
Gulf and into the eastern Gulf on Saturday. On Sunday, a new North
Pacific low may approach the Alaska Peninsula and Kodiak, but
there is substantial model disagreement on this. There is much
better agreement on the leading front of a strong North Pacific
low moving into the western Aleutians on Monday. The front should
slowly track across the southern Bering and into the eastern
Bering by Wednesday.

Elsewhere, cold and dry will be the prevailing conditions across
mainland Alaska, which means the main weather hazard will be
strong gap winds, particularly through Thompson Pass, but also
possibly through the Matanuska Valley. These winds coupled with
the cold air may lead to wind chill concerns, which unlike
previous days, will focus more on Southcentral, rather than
southwest Alaska. Polar air will continue to drift southward
across the Bering through the weekend, however, winds will begin
to diminish to light and variable compared to start the week.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Blizzard Warning 195.
 	     Flood Advisory 145.
MARINE...Gale Warning 120 130 138 139 170-172 178 179
		 181 185 412 414.
         Heavy Freezing Spray Warning 127 130 137-140 160 165
         179-181 185 414.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...TM
SOUTHCENTRAL ALASKA...MO
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...PD
MARINE/LONG TERM...CK/JW