Small Craft Advisory 27, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion...UPDATED
National Weather Service Anchorage AK
915 AM AKST Tue Jan 8 2019

.ANALYSIS AND UPPER LEVELS...
A weak upper level ridge continues to sit over Southcentral and
the Gulf, bringing relatively quiet conditions across the region.
Even though the Wind Chill Advisory expired late yesterday
afternoon, Thompson Pass continued to observe wind chill values to
30 degrees below zero overnight as winds gust between 20 to 35
mph at times. Temperatures continue below normal across the southern
mainland, however observations are trending warmer than 24 hours
ago.

Across the Southwest, a front associated with an occluded front
is moving across the AKPEN, Bristol Bay and Kuskokwim Delta areas,
with snow showers and reduced visibilities along the boundary.
The eastern Aleutians have switched from rain over to snow behind
the front. The winter weather advisory for blowing snow over the
Kuskokwim Delta Coast was cancelled this morning as conditions
have improved due to the frontal boundary weakening as it runs
into the dominant ridge over the mainland. Weather over the
western half of the Aleutians and Bering remains active this
morning as a vertically stacked low near Kamchatka continues to
push a second and stronger front to the east...bringing rain
showers and gusty winds to Adak and Atka.

&&

.MODEL DISCUSSION...
Models generally remain in decent agreement over the next two
days with the synoptic pattern, so little changes were made to the
forecast.

&&

.AVIATION...
PANC...VFR conditions and light winds will persist. Fog remains in
the vicinity of the inlet so incorporated this as a VCFG for the
mornings hours today as it is not expected to push inland.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2: Today through
Wednesday night)...

Generally cold temperatures and locally windy conditions are
expected over the next couple of days. Temperatures will moderate
some across the Cook Inlet to MAT-SU corridor today with
increased cloud cover and low pop of snow/flurries associated
with a weakening frontal system. The Copper River Basin however
will stay fairly cold with many areas struggling to get above
-20f. Nighttime temps over many inland areas will drop below zero.
The Copper River Basin will be the coldest with temps hovering around -40f
in places. Another weak trough brings chances of snow to the Cook Inlet
to MAT-SU corridor Wed afternoon/evening. This will also help to moderate
daytime and evening temps in that region until the cloud over clears overnight.

Pressure and thermal gradients will strengthen and aided by
favorable upper level wind support should intensify outflow/gap
winds along the northern Gulf and eastern and southern Kenai
Peninsula tonight through Wednesday night.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3/Tuesday
through Thursday)...
The occluded front extending from the low over Kamchatka is
currently pushing through southwest Alaska. It is currently
sending bands of snow through the area. Some heavier bands of snow
and gusty winds have been present here and there dropping
visibility. A winter weather advisory was issued due to blowing
snow from these winds and snow showers along the coast. The
advisory was cancelled though as conditions have improved. As this
front moves through, a couple of inches of snow could fall in
areas around Dillingham. Up to 6 inches could fall in the
Kuskokwim Mountains, however there is not enough of a threat to
issue an advisory.

After the front moves through, some cloud cover will linger for
the next couple of days. Wednesday will see the entrance of cold
weather from the Interior and will start to substantially cool
temperatures, especially in inland areas. How much temperatures
cool will depend on if a low level stratus deck sets up. Looking
at the low level moisture profile, its appears any stratus that
does set up will move out Wednesday, but this can be tricky to
forecast so we will have to see how it pans out.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through
3/Tuesday through Thursday)...
The low that has been influencing the Bering and Aleutians
continues to sit over Kamchatka, with shortwave troughs rotating
around it. One such trough is creating a weak front at the surface
and is currently pushing through the western Aleutians. This front
does have a band of gale force winds associated with it. After
this wave exits, the Bering will be quiet for the next couple of
days, with just some showery activity due to cold air advection
wrapping around the low to the north over Kamchatka. Thursday will
see the arrival of the next big system in the form of a storm
coming out of the north Pacific. Currently, this system is forecasted
to bring storm force winds to the western Aleutians Thursday.

&&

.MARINE (Days 3 through 5)...

Beginning Thursday, forecast confidence remains high as a strong
945 mb North Pacific low approaches the Western Aleutians. This
system will spread gale force winds across most of the Western
Aleutians and north into the Western Bering Sea. Models have
actually been strengthening the low over the past couple of days,
so there is now increasing confidence that storm force winds will
impact locations between Adak and Shemya on Thursday. Areas of
storm force winds could also redevelop on Friday over zones 413
and 414 as the low pushes north then exits to the west of Shemya,
though models are still working out the details for this time
period. Regardless, there is rather high confidence that most of
the Western Bering (west of the Pribilofs) will see sustained
east to northeast gale force winds through the weekend with wave
heights increasing to 20-30 ft. Additionally, the potential for
heavy freezing spray will increase by Saturday over the Northern
Bering as frigid air spills south from mainland Alaska.

The Gulf of Alaska is expected to see rather benign conditions
with high pressure maintaining through Saturday.

&&

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

The long term forecast begins Friday as a large dome of cold
arctic air spills south across mainland Alaska under a descending
polar vortex. The coldest air will stay north of the Alaska Range
but cold air will still seep south across mainland Alaska. This
will likely lead to the coldest temperatures seen over the region
in the past couple of years, with lows in interior locations
across southern Alaska, especially southwest Alaska, dropping
below -30F Friday morning. Luckily, the cold outbreak will be
short-lived as a strong North Pacific Low south of the Aleutians
will help to re-establish a broad upper level low over the Bering
as we head into the weekend. As the low deepens, a downstream
ridge over the Pacific West Coast will amplify causing a portion
of the jet stream to push north up into the Gulf of Alaska. This
will lead to a return of strong southerly flow with much warmer
air spreading north by the end of the weekend. There is still
quite a bit of model uncertainty regarding the specific timing
and track of multiple lows and short waves pushing across the
Gulf, but there is increasing confidence of warmer, wetter, and
overall more unsettled weather over the southern mainland as we
head into next week.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gales 127 173 175 185.
         HEAVY FREEZING SPRAY 127 130 139 180 181.
.FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...ALH
AVIATION...KH
SOUTHCENTRAL ALASKA...BC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...BJB
MARINE/LONG TERM...KVP