Small Craft Advisory 106, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
449 PM AKST Thu Feb 1 2018

.ANALYSIS AND UPPER LEVELS...
A strong blocking ridge centered over eastern Siberia continues
to dominate weather across the Alaska region, with cold and dry
conditions across Mainland Alaska. Active weather is currently
confined to the North Pacific, though systems are slowly lifting
northward, with progression severely limited by the strong ridging
to the north. The coldest air is located over the eastern
interior down into Southcentral. Although there is very little
ongoing advection of this air mass, tight thermal and pressure
gradients continue to produce strong gusty winds through the
Matanuska Valley and Valdez/Thompson Pass area. Gap winds also
continue along much of the Gulf coast. Lastly, an elongating upper
level trough extends from south of the eastern Aleutians
northeastward into the central Gulf. It is tracking slowly
northwestward, with bands of showers right out ahead of it. This
is bringing a steady supply of showers to Kodiak Island, mostly in
the form of snow. Surface temperatures are above freezing at sea
level which is limiting snow accumulation.

&&

.MODEL DISCUSSION...
Models remain in good agreement over Alaska, with differences
confined to systems over the North Pacific and the extent to
which they are able to eat into the dominant upper level ridge.
Do expect some intrusion of these systems into southern areas
(Aleutians/southern Alaska Peninsula) over the next couple days,
but the southern mainland will remain safely protected by the
ridge. Overall, forecast confidence is high.

&&

.AVIATION...
PANC...VFR conditions and light winds will persist.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
Most of Southcentral Alaska remains under high pressure to the
north keeping the area clear. The typical gap winds are
persisting in this patten with the Palmer-Wasilla are remaining in
the core of the Matanuska River wind channel. While some winds
have diminished a little in this area today it is looking like the
winds will remain gusty (but not as strong as early this week)
through Friday night. A front over the Kodiak area is bringing
strong northeast flow to the area and rain and snow showers. While
the precipitation type has fluctuated some today it looks like
the majority of the precipitation will be snow through tomorrow
morning. Winds will also significantly diminish tomorrow morning.
However winds will increase again Friday night into Saturday.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2...Fri and Sat)...
High pressure will remain in place over the mainland while a
series of fronts push up against the south side of the Alaska
Peninsula. The first front will move into the area on Fri and then
the next on Sat. The only real sensible weather impact from these
will be slight pulses to the strength of the winds. Precipitation
will be confined to the east side of the Alaska Range and the
Alaska Peninsula. Temperatures will slowly modify as the synoptic
flow switches from northeast to more of an east to southeast
direction as we head towards the weekend.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
The potent closed blocking high will remain firmly in place over
Eastern Siberia. Thus, expect little change to the pattern.
Easterly winds will continue to gusty across the Eastern Bering
out through the Western Aleutians. With this cold air advection,
we can't rule out a stray snow shower or flurry. A sprawling area
of low pressure will set-up just south of the Central Aleutians on
Fri. This will allow two warm occlusions to bring some more
moisture and slightly warmer air to the area. With the cold air in
place, the first front will bring widespread gale-force winds and see
precipitation start as snow from the Alaska Peninsula through
Shemya. However, warm air will continue to chip away and
eventually allow most of this precipitation to change over to rain
by late Fri. The sprawling low will drift slightly north on Sat.
This will bring warmer temperatures and a chance for widespread
precipitation to the Central Bering for the first time in over a
week.

&&

.LONG TERM FORECAST (Days 3 through 7)...

Beginning the long term forecast period Saturday night, the
strong omega blocking high will still be in place over Eastern
Siberia and northwest Alaska. There will be a weakening upper
trough (deforming and stretching) over Southern Alaska with a
strong arctic surface high over the interior. A relatively stationary
front will stretch from the western Bering Sea to Kodiak Island
and then to the Eastern Gulf of Alaska. Energetic shortwave
troughs will slowly but surely push the front farther north toward
the Gulf Coast, slowly eroding the arctic high in place Sunday.
However, with the stout blocking high in place, it now seems
quite likely that fronts moving up toward the coast will stretch
and deform, keeping most if not all of Southern Alaska dry (with
the exception of the immediate coastline and Kodiak Island).
Eventually, troughing will re-establish itself over the western
Bering Sea, keeping the low track to the west of the mainland.
Temperatures should moderate back to near normal next week as the
arctic high slowly weakens.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Gales 127 130 132 138 150 155 165 170 172-176 179 180.
         Heavy freezing spray 126-128 160 180 185 414.

&&

SYNOPSIS AND MODEL DISCUSSION...SEB
SOUTHCENTRAL ALASKA...EZ
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...MO
LONG TERM...JA