Small Craft Advisory 332, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
526 AM AKDT Mon Apr 18 2022

.ANALYSIS AND UPPER LEVELS...

A vertically stacked low over the Central Aleutians traverses
eastward, guided by a strong 160 kt jet south of the
Aleutian Chain. By Tuesday afternoon, the system then pivots
southwards, tracking towards the North Pacific. A swath of cold
air pulled in from Russia advects over the Bering Sea and
Central/Eastern Aleutians behind the low tomorrow afternoon
through early Tuesday afternoon. High pressure persists over the
North Slope, with an Arctic shortwave moving over Southcentral, which
caused the brief showers over the Anchorage area yesterday
evening. As this shortwave continues moving southwards through
the day today, areas of brief, light showers may pop up over
Coastal regions and portions of the Gulf of Alaska. The next
system moves towards the Central Aleutians Wednesday morning, not
quite crossing into the Bering, but opting to scoot eastward south
of the Chain.

&&

.MODEL DISCUSSION...

Models are in good overall synoptic agreement through the short-
term. Discrepancies begin to grow by Wednesday morning as the next
system approaches the Aleutian Chain. There is fair agreement on
storm track initially, with larger differences in strength. By
Thursday, there is better agreement on the strength of the low and
good consensus on the overall track of the system, but there are
heavier disagreements on speed and center location. The NAM/GFS
are showing a faster, more eastern solution than the Canadian/EC,
with the GFS being the furthest east.

&&

.AVIATION...

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

&&

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

The upper levels are transitioning from being controlled by a
ridge of high pressure to more of an easterly wave pattern.
However, the net effect on sensible weather will be minimal as
most locations will remain dry with a healthy dose of sunshine
from time to time. The first of the easterly waves moved through
Southcentral Sun evening. This helped to trigger some showers as
it moved across the northern Gulf early this morning. High
pressure will establish itself over the Arctic Coast while broad
low pressure will set up over the northern Gulf. This will help to
keep a weak offshore gradient to start the week leading to some
breezy winds in places like the Mat Valley and Thompson Pass.

Precipitation will be largely spotty and in the form of showers,
with the exception of Kodiak. The easterly steering flow will
leave most of the southern mainland vulnerable to weak waves
embedded within the flow. Any of these waves could trigger some
weak showers, especially along the mountains. The best chance for
these look to be Tue afternoon as a stronger wave makes its way
from the Copper River Basin towards Anchorage. In easterly flow,
anything that forms over the Chugach always has a chance of making
it down into the Anchorage Bowl. Meanwhile for Kodiak, the
persistent east-southeast winds should allow for more moisture to
advect into the island. This will likely create better chances for
steady light rain as we head into the early part of the week. We
have opted to increase PoPs (Probability of Precipitation)
through Tue to account for this.

&&

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

Much of the same is expected over Southwest for the next three
days. Cloud cover and southeasterly winds will persist along the
coast with brief showers possible over the northern Bristol Bay
and into the Kuskokwim Mountains. Expect highs in the 40s and lows
in the lower 30s to upper 20s. A bit of a pattern change will
occur Tuesday afternoon into Wednesday as an easterly wave over
Southcentral moves over the region. Some uncertainty remains on
the timing of this, but the forcing combined with daytime heating
may be enough to generate a few showers over higher terrain
Tuesday afternoon and into the evening. The mitigating factor will
be weak offshore flow and a drying pattern that will take place
through Thursday. Behind the easterly wave, expect clearing skies
and a more pronounced diurnal trend in temperatures.

&&

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

A strong vertically-stacked low exists north of Nikolski and will
move slowly to the east with the center moving just south of the
Alaska Peninsula Monday night. In the storm's warm sector, strong
southeasterly winds will persist over the Alaska Peninsula
through midday today before slowly weakening through Tuesday
morning. On the backside of the low, strong northwesterlies
currently exist over the Central Aleutians with the core of the
strong winds slowly moving east towards the Eastern Aleutians
today. Nikolski will likely see gusts in the 60 to 70 mph range
with Unalaska being more protected and therefore in the 40 to 60
mph range.

The weather will quiet down briefly Tuesday before another
moderately strong North Pacific low moves near the Central to
Western Aleutians. Models have come into good much better
agreement overnight with gale to storm force winds and rain
impacting the Central Aleutians on Wednesday. Wind will diminish
quickly Wednesday evening, but rain will sweep across the Chain
along the storm's front.

&&

.Marine (Days 3 through 5: Wednesday through Friday)...

Gulf of Alaska: Calm to light conditions will persist across most
of the Gulf Wednesday. Seas will generally remain below 5 ft. On
Thursday and Friday, a deepening low pressure will move a weather
front across the Gulf from West to East. 25 to 30 kt will peak on
Friday for areas near Prince William Sound. Low end Gales of 35 to
40 kt winds and seas increasing to 10 to 15 ft will peak Friday
Morning. A weak barrier jet is anticipated late Friday. Forecast
confidence for this outlook is high.

Bering Sea: A north Pacific low will move just south of the
Aleutian Chain through Friday. An accompanying weather front will
cross the central Aleutians Wednesday evening and will move east
through Friday. Widespread high end small craft, to low end Gales
will extend as far north as the Pribilof Islands and extend into
Bristol Bay by Friday. Northwesterly gales are anticipated on the
backside of this low, impacting the central Aleutians the most.
Seas of 15 to 25 ft are expected across the southern Bering. Seas
of up to 30 ft are possible on the Pacific side of the central and
eastern Aleutians.

&&

Long Term Discussion (Days 4 through 7: Thursday through Sunday)...

High pressure across the state will slowly be replaced with a weak
inverted trough as the work week comes to a close. A strong north
Pacific low will remain south of the central and eastern Aleutians
as it weakens and moves to the southern Gulf of Alaska through
Sunday. Accompanying this low is a weather front that will bring
rain and winds to the Aleutians and across the Pacific facing
coast of Alaska. Cloud cover should be a mainstay as this low
pressure system moves through the region, expanding from west to
east. By Friday afternoon and into Saturday, rain will span from
Kodiak Island and stretch through Seward and western Prince
William Sound. Anchorage and the MatSu should remain relatively
dry due to the drying aspects of cross barrier flow, though an
occasional light shower in the mountains is not out of the
question. Temperatures across the region will be around average,
but will warm as the weekend approaches. Despite the cloud cover,
the warm air mass will allow temperatures to reach anywhere from 3
to 10 degrees above normal for late April. Clearing skies on
Sunday could allow daytime highs in Anchorage and Kenai to be in
the lower 50s, while the Mat Valley may reach the middle to upper
50s.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...High Wind Warning 187
MARINE...Storm Warning 170 172 173 174 176
	  	 Gale Warning 150 155 160 165 171 175 177 180 181 185 412-414
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...KM
SOUTHCENTRAL ALASKA...MO
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...CJ
MARINE/LONG TERM...SS