Gale Warning 334, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
521 PM AKDT Fri Apr 21 2023

.ANALYSIS AND UPPER LEVELS...

High pressure centered over the Arctic Ocean has a ridge
stretching over Alaska. This ridge is producing clear skies and
warmer temperatures with temperatures in the 50s to near 60 across
Southcentral. Across the Southwest and AKPen temperatures range
from the low 40s to low 50s with 40s across the Aleutian Island
chain. A shortwave currently over northern Alaska is moving south
with high clouds increasing ahead of it which will move over
Southcentral later this evening. Across the Bering an upper level
low is moving west with very little sensible weather other than a
few showers based on satellite trends.

&&

.MODEL DISCUSSION...

Models are in good agreement through Monday. However, there are
some minor differences of the evolution of weak surface lows that
form over the northern Gulf on Monday. This will affect how far
inland the precipitation develops. The main forecast challenge in
the short term will be temperatures Saturday through Monday as the
models have struggled especially with high temperatures.
Otherwise, nailing down precipitation type across the Copper
River Basin on Saturday will be challenging, but it does look
likely that a mix of rain and snow after midnight into the early
morning hours will change over to snow later in the morning.

&&

.AVIATION...

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

&&

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

After today's gorgeous weather, a pattern change will develop for
the weekend as the dominating ridge breaks down over Southcentral
in response to a deep arctic trough moving in from the north.
This trough will usher an unseasonably cold airmass with
precipitation spreading from north to south.

Models remain fairly consistent with the orientation and position
of the trough farther east, leaving the best dynamics and
precipitation in the Copper River Basin and surrounding mountains.
Precipitation may initially start out as snow/rain mix Saturday
morning with the warmer airmass in place, before shifting to all
snow as colder air filters in. Most of the snow accumulations will
be at higher elevation, but 1-3 inches is possible for the lower
elevation. By midday Saturday, precipitation for the lower
elevation changes back to rain as temperatures climbs up in the
mid 30s and low 40s.

Elsewhere, snowfall is expected mostly along the north and
eastern facing slopes of the Chugach and Eastern Kenai Mountains,
with light accumulations expected. Coastal areas also look
favorable for rain/snow showers through Monday as a surface low
develops over the Gulf. Meanwhile, a tightening pressure gradient
will increase winds through the gaps and passes through early next
week as the colder air is pulled into the Gulf by the low.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA AND BERING SEA/ALEUTIANS
(Days 1 through 3: Tonight through Monday)...

The high pressure ridge that has brought warm temperatures over
the past few days is in the process of retreating to the northwest
as two troughs converge over the Central Bering through the
weekend. The eastern trough currently over the northwest Interior
will drop south over Southcentral through the weekend. To the west
of the trough axis, a dry and unseasonably cold airmass will move
into Southwest and the Alaska Peninsula starting Saturday
afternoon, where it will persist into early next week. This will
result in temperatures cooling gradually through early next week,
with highs in the upper 20s to low 30s. To the far west, the other
trough will push it's front into the Western Aleutians overnight
tonight, bringing storm force winds and rain to the area. The
front will then weaken as it pushes east, reaching the Eastern
Aleutians and Pribilofs early Monday morning with 25 kt winds and
rain.

&&

.LONG TERM FORECAST (Days 4 through 7: Tuesday through
Friday)...

An active pattern across Southern Alaska looks to define the
long-term period as a series of low pressure systems look to sweep
through our region. Tuesday morning a vertically stacked low
pressure system located just south of the Alaska Peninsula aims to
push across Kodiak Island and into Southcentral throughout the
day Tuesday. This system appears to bring a rain/snow mix that
will persist until the following low moving in from the
southwestern Gulf pushes across Kodiak Wednesday night and
Southcentral by Thursday morning. The latter of the systems
appears to bring the potential for more gusty easterly winds,
primarily along the Southcentral coastline. This series of systems
is also expected to be accompanied by a warming trend, as winds
from the southern Gulf of Alaska is pulled into our area. This
will likely serve to change precipitation in Southcentral over to
all rain if the initial onset was snow or mixed. Out west, an
upper- level Arctic low will have dropped into the Central Bering
by Tuesday morning. This system will create an unsettled pattern
across the Aleutian Chain and Southwest Alaska featuring the
passage of several weak frontal boundaries and general showery
activity through next week. Additionally, the low pressure in the
eastern Bering will pull down an Arctic airmass through the Bering
Strait, reaching the Pribilofs Tuesday morning and the Chain by
Wednesday afternoon. This will likely drop the temperatures for
the week, and shift the rain showers in the area over to snow or
at least a rain/snow mix depending on surface level thermal
momentum.

&&

SYNOPSIS AND MODEL DISCUSSION...RC
SOUTHCENTRAL ALASKA...MF
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...CJ
LONG TERM...CL