Small Craft Advisory 109, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
507 PM AKST Sat Feb 1 2020

.ANALYSIS AND UPPER LEVELS...

The overall synoptic pattern across the area is changing as an
upper-level ridge is moving east over mainland Alaska from the
Bering. This upper-ridge currently extends northwest from the
Alaska Peninsula to the Seward Peninsula. The upper-trough is now
centered over the Yukon Territory with a closed low center over
the eastern Gulf of Alaska. The trough-axis associated with this
upper-trough extends southwest from the eastern Gulf into the
north Pacific. A second low 240 NM south of Shemya has an
occluded front moving northeast across the Bering Sea and Aleutians.

At the surface, radar imagery shows snow showers moving
northeast across the Kuskokwim Delta. Radar also shows second
area of snow showers moving southeast from Middleton Island to
over the northern Gulf. Observations show strong gap winds across
the Aleutians due to the southeasterly winds ahead of the
aforementioned frontal boundary funneling through the straits.

&&

.MODEL DISCUSSION...

Models remain in good agreement over the next three days with
respect to the overall synoptic pattern. The higher resolution
data from the NAMNest was favored for the strong gap winds in the
Aleutians as this model has resolved the situation the best when
comparing to real-time observations. There is some indication
(ASCAT passes, ship obs, etc) the front is slightly stronger than
models indicated. Overall confidence in the short term forecast
remains high due to a high degree of consistency between guidance.

&&

.AVIATION...
PANC...VFR conditions and light northeasterly flow will persist.
There is a possibility we may see some patchy fog overnight and in
the morning as skies clear and winds calm. Winds aloft will
increase Sunday afternoon as a low- level jet develops over the
area due to an occluded front moving into the region.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3)...

Strengthening high pressure over the interior is currently
bringing gusty winds to Resurrection Bay, Passage Canal and
Thompson Pass. These will diminish overnight as the high departs
to the east and an upper ridge builds over Southcentral. Skies
will clear overnight and patchy fog is possible with the lighter
winds.

A front will quickly move over Kodiak Island by Sunday morning
with snow and blowing snow likely before changing to light rain
thereafter. Approximately 6 inches of accumulation are expected in
Kodiak City before the changeover. A Winter Weather Advisory has
been issued to address this concern. The front will track over
the remainder of Southcentral by Sunday afternoon. The heaviest
snowfall is expected over the southern/eastern Kenai Peninsula.
Periods of significantly reduced visibility associated with
blowing snow are likely in the Portage Valley by evening,
persisting into Monday morning. It is still difficult to determine
if Anchorage will see any snow or remain downsloped for the
duration of the frontal passage. In any case, any snow would be
light with little/no accumulation, although the front will bring
gusty southeasterly winds up to 55 mph along Turnagain Arm. The
front will then stall along the northern Gulf coast Monday into
Tuesday, bringing additional snow to that area.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3: Tonight
through Tuesday)...

A major pattern change is on its way to Southwest Alaska. A
strong front associated with a strong low is moving across the
Bering currently and will begin impacting Southwest Alaska tonight
as it moves into the coast. The front will bring much warmer air
into Southwest Alaska. Before that happens though, some areas are
expected to pick up some healthy amounts of new snow, along with
gusty winds. This combination will cause significant visibility
reductions to one half mile or less in blowing snow in most areas
north and west of King Salmon and along the coast of the Kuskokwim
Delta. Snowfall amounts will generally be in the 4 to 6 inch
range from Bethel west and 6 to 10 inches north and west of King
Salmon. The heaviest snowfall rates are expected Sunday morning.
Winter Weather Advisories have been issued for the Kuskokwim Delta
along the coast and for Bristol Bay north and west of King
Salmon.

As the front moves inland and dissipates Sunday night, gap winds
through the Kamishak Gap will remain elevated through Iliamna and
Igiugig. The primary change most people will notice are the
rapidly rising temperatures. The temperatures will climb into the
30s for downslope areas as soon as Sunday, with more widespread
30s expected on Monday. The weather will remain unsettled Monday
and Tuesday for most areas, as shower activity from off the Bering
is expected to continue due to the parent low stalling. This will
keep chances of snow in the forecast, with perhaps some rain
mixing in at times along the coast and the warmer areas, along
with above normal temperatures.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3: Tonight
through Tuesday)...

A very strong 946 mb low currently located south of Shemya and its
associated fronts and disturbances will be the only weather
feature impacting the Bering through Tuesday. That said, its
strength will mean there will be plenty of impacts to all areas
through then. The low itself is near peak intensity currently, and
slow weakening is expected through Tuesday. The low is not
expected to move much from its present location through Sunday
afternoon, after which the center will track eastward along and
just south of the Chain through Monday afternoon, before turning
north with its center near the Pribilofs on Tuesday afternoon. A
strong front moving out ahead of it is the leading edge of a much
warmer air mass. Thus, precipitation has already changed over to
rain in Dutch Harbor and points west, while a very wet snow is
falling with temperatures in the mid 30s from Cold Bay and Sand
Point up through the Pribilofs. This warm air will continue
spreading north and east, reaching the coast of Southwest Alaska
tonight. As the low slowly spins along the aforementioned track,
rain or a rain/snow mix along the coast will remain in the
forecast through Tuesday, as the weather remains unsettled.

&&

.MARINE (Days 3 through 5)...

Bering Sea/Aleutians: A weakening low will lift north from the
central Aleutians into the Bering Sea Tuesday into Wednesday,
leading broad cyclonic flow over the Bering with widespread areas
of small craft advisory level winds and possible embedded gales
through Wednesday. A strong low will approach from the western
Pacific Thursday, likely bringing gales and perhaps storm force
winds to the western Aleutians.

Gulf of Alaska: Swell-driven small craft advisory level seas will
continue, with no significant systems expected.

&&

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

Unsettled weather and a cooling trend will be on tap Wednesday
into Thursday over the Southern Mainland as an upper low in the
Bering steers a cold front from west to east across the area.
Model uncertainty increases substantially Friday, given
disagreement over whether an Arctic trough dives down into
mainland Alaska, or dips farther west into Siberia, keeping all of
mainland Alaska in a south flow regime. This feature, and the
coincident strength of a North Pacific low Friday will determine
whether a warm, wet pattern comes into play Friday vs a very cold,
less wet pattern. In any case, most solutions converge and show
the cold air eroding Saturday 8 FEB. Meanwhile, wet unsettled weather
will continue over the Aleutians and Pribilofs in this progressive
pattern.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Winter Weather Advisories 155 161 125 171.
MARINE...Heavy Freezing Spray Warning 119 121 126 127 129 130 131
		 132 136 138 139 160 185.
		 Storm Warning 130 178 411 412.
	     Gale Warning 120 121 125 129 131 132 136 138 139 351 352
					   150 155 160 165-174 179 180 185 413 414.
FIRE WEATHER...NONE.

&&

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