Small Craft Advisory 236, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
433 PM AKDT Tue Mar 10 2020

.ANALYSIS AND UPPER LEVELS...
There is an upper level trough axis just west of the Alaska/Canada
border moving slowly eastward. There are some lingering showers
along and east of this axis. Clear skies are over most of the
southern Alaska Mainland to the west of this trough as high
pressure builds in. There is an upper level trough and associated
surface low over the Bering Sea to the north of the western and
central Aleutians. This low is producing some precipitation over
that area, and is moving to the southeast and weakening. High
pressure is building in to the west of this feature.

&&

.MODEL DISCUSSION...
The numerical models are in very good agreement. The high
resolution models are preferred due to the better handling of gap
winds. Forecast confidence is above normal.

&&

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

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...

An upper trough continues its track east over mainland Alaska. A
steep pressure gradient between the accompanying surface ridge
over northern/interior Alaska and lower pressure/warmer air over
the Gulf will continue to drive gusty offshore winds through the
usual gaps and passes, including Resurrection Bay, Passage Canal,
the Valdez waterways, through Thompson Pass and out of the Copper
River Delta. Otherwise, clear skies prevail as expected with
general offshore flow. Winds should diminish from west to east
tonight and tomorrow. Arctic air will continue to spread
southward, and temperatures should drop substantially tonight...
likely a good 20 degrees colder than Monday night in most of
Southcentral. A ridge building over the Bering will push eastward
Wednesday. Cold air will recede towards the Alcan and conditions
will trend warmer by Thursday. Of note, a shortwave is expected to
track across the top of the ridge Wednesday night, bringing
another period of gusty offshore winds to Whittier, Valdez waters,
Thompson Pass and the Copper River Delta late Wednesday night
into Thursday. The ridge axis will become centered over mainland
Alaska by Friday and clear, dry weather will persist.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3)...
Dry and cold conditions are expected to continue across Southwest
Alaska tonight through Wednesday. There remains the chance for
snow showers across the Hooper Bay area overnight Wednesday into
Thursday as an upper level wave moves through. Behind this upper
level wave, a strong upper level ridge will build into the region
bringing a significant moderation in temperatures for the
second half of the week.

&&

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

Cold northerly flow will continue through the gaps of the Alaska
Peninsula through Wednesday keeping heavy freezing spray in the
forecast along with the gusty winds. While winds will diminish
tonight as the pressure gradient weakens, a front associated with
a low over the Pacific will slowly move north allowing the gap
winds between Dutch Harbor and Cold Bay to increase to small craft
advisory criteria winds once again tomorrow morning into tomorrow
night.

Currently, a mix of rain and snow is falling in Adak as a storm
system moves through. This storm system will continue to weaken as
it tracks southward due to a strong upper level ridge building
into the western Bering and western Aleutians. This upper level
ridge will aid in the weakening of the upper level wave associated
with the storm system moving through Adak shearing and stretching
the energy apart.

The focus then shifts to a storm force low moving northward in the
North Pacific towards Russia. The front is expected to begin
impacting the western side of the Aleutian Chain and western
Bering Wednesday night into Thursday with widespread
precipitation. This precipitation will mainly be in the form of
rain as a strong southerly push of warm air at 850 mb helps to
warm the air at the surface well above freezing. Strong southerly
winds are also expected due to the tight pressure gradient between
the low pressure over the North Pacific and the high to the east.
As a result, gale to storm force winds are expected across a wide
swath of the western Bering and western Aleutians. Due to the
strength of the upper level ridge to the east, this front will
stall across the central Bering with a weakening precipitation
shield as the front becomes elongated.

The aforementioned front lifting toward the Alaska Peninsula on
Wednesday will continue northward into the Bering Sea Thursday
night through Friday. This will bring widespread precipitation
and small craft advisory winds to the eastern Aleutians, southern
Alaska Peninsula and on northward into the eastern Bering.

&&

.MARINE (Days 3 through 5)...

Thursday and Friday, the offshore and enhanced gap winds will
continue across the Barren Islands and the Copper River Delta.
These winds will slack off late Friday.

A storm force system over the northern Bering will keep an area
of storm force to high end gale force winds west of St Matthew
Island and north of 56N on Thursday. By Friday, this system will
have lost its gusto but enhanced winds and rough seas still
anticipated into Saturday. Shifting to the North Pacific, a low
will approach the central and eastern Aleutians Thursday night,
bringing the next round of precipitation to the eastern Aleutians,
including Dutch Harbor, through Friday night. A ridge will set up
over the Gulf Of Alaska and mainland. Once this ridge gets
established, the active corridor for low tracks will be the NW
Pacific to the Western Bering. This ridge is expected through
Tuesday March 18th.

&&

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

Both the GFS and ECMWF ping into an "Omega Block" setting up over
the Gulf of Alaska. This will keep clear skies and dry weather
over most of Southcentral Alaska. Temperatures will continue to
run slightly below normal. However, the weather will be active
over the Western Aleutians and Western Bering. But at this time,
none of these systems look particularly ominous. The ridge remains
steadfast the entire forecast period.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gales 127 128 130-132 138 150 155 172 178.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...BL
SOUTHCENTRAL ALASKA...MM
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...SEB/MV
MARINE/LONG TERM...PS