Small Craft Advisory 52, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
428 PM AKST Tue Jan 14 2020

.ANALYSIS AND UPPER LEVELS...
The upper level ridge over the central Bering Sea is amplifying
as expected. This is tightening the upper level gradient over
Southwest and Southcentral as well as turn it more to the north.
This upper level support will help to mix winds down to the
surface in some areas. It is also keeping any precipitation out of
mainland through the eastern Aleutians. A strong surface low is
situated near Kamchatka with the associated front moving through
the western Aleutians. This front will be the source of the Storm
force winds over the Bering Sea. A secondary low is developing
along this front to the south of Adak which will be a factor for
the central and eastern Aleutians tomorrow.

&&

.MODEL DISCUSSION...
Models remain in good synoptic agreement into the weekend. That
said, enough difference exists in the low that will move between
Adak and Dutch Harbor tomorrow that there is some uncertainty as
to how strong the winds will reach in the Unalaska area in
particular. The GFS has been the strongest and fastest solution
with the ECMWF and Canadian being weaker and 6 to 9 hours later in
crossing the Aleutians into the Bering Sea.

&&

.AVIATION...
PANC...Persistent fog and stratus around the airport may improve
this evening at as northerly winds increase just a little off the
surface. In theory this increased mixing with the flurries earlier
today should break up the stratus, but there does remain the
chance that the very low-level clouds will remain until the
stronger winds begin to mix to the surface late Wednesday
afternoon.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
Clouds are scattering out over Southcentral as a ridge builds
over the Bering Sea. Inland lows tonight will generally be 5 to 10
degrees colder than last night, absent the insulating stratus
deck. Highs tomorrow will be in the single digits to below zero
over most inland areas. Colder than normal weather will persist at
least through Thursday as Arctic high pressure at the surface
strengthens over the Alcan. Offshore winds will be enhanced by
northerly upper level flow and a strong vertically oriented jet
stream. Expect strongest winds in Valdez, Thompson Pass,
Resurrection Bay, the Copper River Delta and Whittier. Gap winds
will increase tonight, then peak during the day Wednesday. A Wind
Chill Advisory in Thompson Pass remains in effect through noon
Thursday. On a related note, moderate northeast winds in Broad
Pass and the Matanuska Valley will bring wind chills close to -30
at times Wednesday.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3)...
Strengthening high pressure over interior Alaska will increase
the offshore winds across Southwest Alaska through Friday. This
will lead to clearing skies and dropping temperatures, Gusty winds
are expected along the coast through Thursday morning, then the
winds will diminish. Most areas will be below zero by Friday
night, with the Lower Kuskokwim Valley returning to the 20s below
zero.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3)...
Unlike over the Southwest, the Bering will be very active through
Friday. A strong north-south-oriented front drifting across the
central Bering tonight is producing widespread storm force winds
and gusts over much of the open Bering west of the Pribilofs. This
front will become the focus along which a new area of low
pressure will develop tonight south of the central Aleutians.
There is good model agreement that a low will form, but the
disagreement is substantial on where and how strong this low will
be. There is a slight chance that if the low is strong, that it
could produce 75 mph or higher gusts in Dutch Harbor. For now,
forecast gusts have been increased to 60-70 mph for the day
Wednesday in Dutch Harbor. The most likely area of stronger winds
will be west of Unalaska Island.

As the low slowly tracks north Wednesday night, strong winds are
expected across the Pribilofs as well. The front will move through
the Pribilofs and Dutch Harbor late Wednesday night, which will
result in rapidly improving weather conditions. The front will
weaken substantially over the eastern Bering on Thursday as it
draws cold dry air into it from Southwest Alaska.

A separate North pacific low will move into the western and
central Aleutians on Thursday morning. While it too will feature
gusty winds, most of the worst weather will remain south of the
chain over the North Pacific. This is because the low will take a
dramatically different track, nearly stalling out south of the
central Aleutians on Friday and eventually drifting entirely south
of the chain by late Friday.

&&

.MARINE (Days 3 through 5/Friday through Sunday)...
After a low exits south of the Aleutians Friday, conditions look
fairly benign through the weekend. For the Gulf, it looks like a
deep low will approach the Gulf Friday and possibly move into the
Gulf Saturday through Sunday. At this time, forecast confidence
in the track of this system is low. There is potential for gale
force winds sometime this weekend, most likely over the southern
to eastern Gulf.

&&

.LONG TERM FORECAST (Days 4 through 7/Saturday through Tuesday)...
For the Bering Sea and Aleutians, conditions look relatively quiet
over the weekend, with some weak systems transiting the Bering in
fairly flat upper level flow. Deep lows will track south of the
Aleutians, along the jet stream. Some model solutions bring a
deep low up to the Aleutians Monday night through Tuesday, but
confidence in this is low.

Meanwhile, Southcentral will remain cold and dry for the beginning
of the weekend as a large deep closed upper level high crosses the
northern half of Alaska. As the ridge continues eastward into
northwest Canada, this will result in a bit of a pattern change
as upper level features start to track northward across the
state. Of most interest to Southcentral Alaska, energy from a high
amplitude trough over the northeast Pacific will be pulled
northward into the Gulf as early as Sunday. This will bring
increased potential for snow to Southcentral Sunday through
Tuesday. At a minimum would expect an increase in clouds and and
upward trend in temperatures.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Wind Chill Advisory 131.
MARINE...Storm Warning 170 172>174 179 185.
 Gale Warning 127 130>132 150 155 165 171 175 176 180 181.
 Heavy Freezing Spray 119 121 126 127 129 130 139 140 160 180 185.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...EZ
SOUTHCENTRAL ALASKA...MM
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...JW
MARINE/LONG TERM...SB