Storm Warning 149, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
511 PM AKDT Sat Nov 5 2022

.ANALYSIS AND UPPER LEVELS...

There are widespread sunny skies over Southern Alaska this
afternoon due to the strong northerly flow with high pressure in
the Interior of the state and low pressure in the southeastern Gulf
of Alaska. The exception to the sunshine is due to fog and stratus
packed along the western Kuskokwim Mountains. Strong winds are
occurring through channeled terrain and down Cook Inlet as the
cold dry air from the Interior pushes through the region.

Looking farther west into the Bering Sea, there is a strong front
moving through the Western Aleutians and Western Bering Sea this
afternoon. There is a long tap of warm air with this system with
the southern end of the front reaching around 35N. This is the
system that will usher in much warmer air and a change in pattern
for next week and likely into the week after that as well. More
details about this are in some of the following sections of this
discussion.

&&

.MODEL DISCUSSION...

The last few models runs were showing some difference in the
speed of the movement of the front as it moves through Southwest
Alaska Sunday night into Monday. The latest 12Z and 18Z runs
appear to be in a little better agreement in trending to the
slower solutions. Therefore the timing of precipitation and winds
has been adjusted for Southwest Alaska. The next meaningful model
discrepancy shows up for the Kenai Peninsula and north Gulf coast
Monday night into Wednesday. The GFS is showing a secondary low
developing along the front south of the Kenai Peninsula on Monday
night and keeping it there through Wednesday. This would keep more
cold air over Southcentral and limit how far north the threat of
mixed precipitation will go. The GEM and ECMWF both show this
secondary low development later which would allow more warm air up
Cook Inlet toward more inland areas of Southcentral but they do
develop the low on Tuesday night in the northern Gulf. The
progression of this feature will be a key point of emphasis with
the Southcentral Alaska for Monday night through Wednesday.

&&

.AVIATION...
PANC...VFR conditions will persist. Strong northerly winds will
steadily diminish overnight as a high amplitude ridge builds in
from the west, shifting the northerly jet and pressure gradients
off to the east.

&&

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

Mostly clear skies and arctic air are currently in place across
southern Alaska. Strong, gusty winds from the north will continue
to funnel through terrain gaps for the rest of this evening before
decreasing through Sunday morning. Strong gusts may last a bit
longer in the Valdez area, with the potential for brief secondary
peak Sunday morning as the finally waves of energy from a trough
are replaced by an upper level ridge from the west.

A shift in the weather pattern is expected as clouds filter into
Southcentral Monday morning ahead of the next system. Winds will
shift southeasterly and move moisture and relatively warmer
temperatures back into the area. Precipitation may begin early
Monday morning for Kodiak Island and spread north and east
towards Kenai by late Monday morning. Any lingering cold air near
the surface could begin a snow briefly and transition to rain for
coastal locations. As the front continues towards Southcentral, a
surface low develops in the western Gulf of Alaska. There is still
enough model disagreement with regards to the surface low
development and the timing of the front that presents challenges
to the precipitation type forecast, the onset, and timing of these
transitions for Monday afternoon through Tuesday. At this time,
one of the challenging locations appears to be for the land area
west of the Kenai mountains on the Peninsula. Another challenge
during this time is the extent of downsloping possible for the
Mat Valley, Anchorage, and northwestern Kenai.

&&

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

With the exception of a few passing high clouds, today was a gorgeous
day across the forecast area under a ridge of high pressure. Not
many changes are expected on Sunday as the ridge remains in place
over western Alaska. Daytime temperatures will range in the 20s
to 30s with overnight lows in the teens to single digits.
Meanwhile, a pattern change will get underway as the ridge axis
shifts east in response to a North Pacific low lifting northward
in the Bering Sea. Ahead of the low, a front tracks eastward
toward western Alaska between late Sunday and early Monday morning.
Gusty southeasterly winds will accompany the front as it moves
inland. The main impacts will be heavy wet snowfall combined with
strong winds reducing visibilities in Bristol Bay around the same
time. A Winter Weather Advisory was issued to highlight these
impacts, with total snow accumulations between 4 to 8 inches for
this region. For the Kuskokwim Delta and Kuskokwim Valley, light
snow amounts are expected on Monday with southeasterly winds
downsloping most of the precipitation. Additionally, there may be
a brief period of freezing rain developing along the Bristol Bay
coast, but warmer air will help transition precipitation type
quickly to all rain for rest of day on Monday. The front exits the
area overnight Monday with a brief break of drier early Tuesday
before unsettled conditions returns with another system approaching.

&&

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

An elongated front extending ahead of a low pressure system in
eastern Russia continues to lift northward, with winds slowly
subsiding and rain tapering off sometime tonight. Meanwhile, a
ridge of high pressure is providing benign conditions for the rest
of the Bering/Aleutians. The next weather feature is associated
with a North Pacific low lifting north of Atka early Sunday
morning. In addition to moderate to heavy rain, south-southeasterly
storm force winds through the central/eastern Aleutians will
initially accompany this system. Seas above 20 feet are also
expected south of the Chain between Sunday and Monday. The winds
will then decrease to gales as the low tracks west of the Pribilof
Islands on Sunday night. Unsettled conditions will likely persist
through early next week under a general troughing pattern.

&&

.LONG TERM FORECAST (Days 4 through 7: Wednesday through
Saturday)...

The overall pattern progression for the long term starts off
fairly clear with reasonably close model agreement, but this
quickly deteriorates later in the period. On Wednesday, an upper
trough will be positioned over the eastern Gulf and Alaska
Peninsula (AKPen), with an associated surface low slowly moving
across the eastern Gulf. This system will be shouldered by upper
ridging both upstream over the Bering/Aleutians and downstream
over the Yukon and Southeast AK. There is already some notable
model spread for the location of the main system in play over the
Gulf by this point. The ECMWF brings the surface low as far north
as the Prince William Sound (PWS) on Wednesday morning, while the
Canadian shows a slower progression, with the low beginning to
stall out over Kodiak Island. The GFS projects a separate low
wrapping in from the southeast that phases with the main upper
level trough, resulting in a much stronger low persisting over the
Gulf compared to the consensus all the way into Thursday morning.
These differences open up a lot of forecast uncertainly already
from Wednesday to Thursday, particularly in terms of winds over
the Gulf and inland extent of precipitation over the southern
mainland. One factor that is more clear is that the frigid air
mass will be long gone by this point, with some coastal and lower
elevation spots around Southwest and Southcentral likely warming
back to or even above freezing by the middle of next week.

Looking further out in time, the forecast details and even the
larger scale pattern resolution begins to fall apart, especially
by next weekend. Large differences begin to appear for a North
Pacific low expected to move approximately along the Aleutians
from Thursday to Friday, with some solutions lifting the low north
into the eastern Bering, while the GFS tries to plow the center
straight east and south of both the Aleutians/AKPen and Gulf by
Friday. Similarly significant differences are apparent for another
low tracking towards the western Bering out of the Kamchatka area
going into Friday and Saturday. It appears the models are struggling
quite a bit with an increasingly 'blocked' large scale pattern
developing late next week, where significant meridional and even
retrograding (easterly) upper level flow results in slow,
meandering progression of storm systems across Alaska. Needless
to say, there is much left to be determined for the forecast from
Friday onwards at this time.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...High Wind Warning 111 131.
         Winter Weather Advisory 161.
MARINE...Storm Warning 127 160 165 170 172 174 180.
         Gale Warning 119 120 121 125 126 128 129 130 131 132
                      139 150 155 171 173 175 176 179 181 185.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...EZ
SOUTHCENTRAL ALASKA...VR
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...MF
LONG TERM...AS