Gale Warning 640, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
512 AM AKDT Tue Oct 25 2022

.ANALYSIS AND UPPER LEVELS...

The jet stream extends from eastern Russia to the south of the
Aleutian Chain and into the southeastern Gulf of Alaska. Along the
jet, a low-amplitude shortwave trough and deep surface low in the
eastern Bering Sea is tracking inland into Southwest Alaska,
bringing a wintry mix of precipitation. A 170+ jet streak coupled
with upper level forcing is aiding gusty southwesterly winds along
the coastline and Aleutian Chain. Meanwhile, a transient ridge of
high pressure is keeping the rest of Southcentral cold and dry.
The Nighttime Microphysics (RGB) this morning shows mostly clear
skies from the Mat-Su into Anchorage, and south toward the Kenai
Peninsula. Clear skies and strong radiational cooling is allowing
overnight temperatures to drop down below freezing across the
lower elevation regions. A combination of the interior high and
Bering low is helping to maintain localized gap winds along the
coast.

&&

.MODEL DISCUSSION...

The latest operational model runs are in decent agreement with
the placement and intensity of synoptic scale features at both the
surface and in the upper levels. Models are on track with the
aforementioned upper trough amplifying and progressing quickly
across the Alaska Peninsula and into southern Alaska today. A
triple point low will form near the southern Kenai Peninsula with
heavier band of snow expected over the Inlet and the Sterling
Highway corridor, extending up into the southern to western
Susitna Valley. As the low tracks eastward into the Gulf,
precipitation types and snow amounts will be the next forecast
challenge for Southcentral between today and Wednesday. There are
also small positional differences as the low tracks south of
Prince William Sound by Wednesday morning.

&&

.AVIATION...

PANC...VFR conditions with northerly winds at 5 to 10 kts will
persist. A triple point low will form this evening in the Gulf of
Alaska. There is a potential of LLWS due to southeasterly winds
aloft crossing the Kenai and Chugach Mountains. Areas of light
snow will move over the terminal this afternoon and evening with
ceiling/visibility lowering to MVFR.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3/Today
through Thursday night)...

The storm system headed for Southcentral today is on track and
only minor changes have been made to the forecast. The system is
moving a little faster than expected, so have moved up the start
time for precipitation. One new wrinkle in the forecast is
increased uncertainty with track of the triple point low across
the northern Gulf late this afternoon through tonight. The global
models have shifted the track southward while the hi-res models
continue to depict a track which hugs the Gulf coast. This will
affect strength of downslope winds across the Kenai/Chugach
Mountains, location of the barrier jet out ahead of the low, and
extent of warm air advection into the Prince William Sound/eastern
Kenai Peninsula area. Have decided to stick very close to the
inherited forecast which favors the further north track of the
hi-res models as they tend to verify better with low tracks near
the coastal mountains. Bottom line, forecast is on track to bring
widespread light snow to the Southcentral, with heavier snow
across the Kenai Peninsula and Prince William Sound regions. The
fast progression of the storm will tend to limit heavy
accumulation in any given location.

Snow will taper off across the region Wednesday as cold and dry
air advection ensures behind the exiting storm. This will lead
to widespread gusty winds Wednesday afternoon through Thursday
night, which will initially limit the drop in temperatures.
However, expect colder temperatures each day as we head through
the remainder of the week. The strongest winds will be along the
south side of the Alaska Peninsula and across the western Gulf
and Kodiak Island Wednesday night along the axis of strongest cold
air advection and on the poleward side of a strong upper level
jet streak, with strong synoptic scale subsidence. Have upped wind
gusts to hurricane force for Shelikof Strait up to Kamishak Bay
and the Barren Islands corridor and to storm force for the rest of
the Kodiak Island waters. Secondarily, cold air advection from
the Alaska Interior southward across Southcentral will lead to
strong gap winds through mountains passes and especially along
the typical coastal bays.

&&

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

Forecast is on track for a strengthening low pushing towards
Southwest Alaska. Rain has started overnight along the  A strong
jet streak extending across the Aleutians and southern Bering is
helping to drive the low eastward. As the jet amplifies, the low
will dig south- southeastward across Southwest towards Kodiak
Island. During this time, winds will increase to storm force along
the eastern Bering, as well as along the Alaska Peninsula and
surrounding waters.

A swath of cold air pulled from the Interior filters into
Southwest on Wednesday. Additionally, wrap around precipitation
will make its way into Southwest on Wednesday. Anticipate a drop
in temperatures and precipitation type to be all snow for most
areas by Wednesday. Winds will remain relatively gusty through at
least Wednesday night. Thus, there may be periods of blowing snow
that could reduce visibilities at times, but it is likely the
heaviest snowfall will be along the Kuskokwim and Kilbuck mountain
ranges. The Alaska Peninsula north to Koliganek/Iliamna will
continue to see precipitation into Wednesday morning. Along the
AKPen to King Salmon will be mostly rain, and areas north will be
a rain/snow mix. As the cold air advection moves in Wednesday
evening, rain will transition to snow.

A high surf advisory was issued yesterday for areas along the
Kuskokwim Bay and down to Togiak. A high wind warning has also
been issued for the Alaska Peninsula including Cold Bay early
Wednesday morning through Wednesday afternoon. Gusty winds through
the bays and passes south of the AKPen will remain gusty through
Wednesday night.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...

Gale force winds encompass much of the Bering Sea as a low moves
towards Southwest Alaska. A strong jet extends along the Aleutians
and southern Bering before amplifying on Wednesday. As a result,
the low shifts, tracking southward across Southwest. Winds will
become northwesterly, and coupled with cold air advection pulled
from the Interior, will become increasingly gusty. Winds reach
storm force early Wednesday morning, with gusts reaching as high
as 80 mph along the eastern Bering and along the Alaska Peninsula
and surrounding waters. Winds through bays and passes south of the
AKPen will continue to be gusty through Wednesday night.

&&

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

Colder than normal temperatures across southern mainland Alaska
continue to be the main headline through the extended period.
Low temperatures in the 10s are expected for inland locations
through Monday, with single digit temperatures in the Copper River
Basin and Lower Kuskokwim Valley. Most precipitation will fall as
snow, with the exception of coastal areas as a persistent
longwave trough situated over the state draws cold air across the
forecast area for the duration of the long term forecast. A
surface low in the Gulf of Alaska aiding this cold advection will
weaken on Friday, allowing north/northwesterly gap winds out of
bays and passes along the Gulf coast to relax going into the
weekend.

Beyond the large-scale pattern, there continues to be significant
spread in model guidance for the long term forecast, lending low
confidence to any particular evolution of features. Model guidance
hints at the development of two streams of activity, a northern
one across the Bering and a southern one across the North Pacific,
with the balance between which of these is expected to be stronger
remaining highly uncertain at this time. Two lows, one from each
stream, or some permutation of them, looks to traverse from the
central/western Bering Sea on Friday into the vicinity of the
Gulf of Alaska by Sunday or Monday. All the while, northerly flow
across the eastern Bering appears highly favored, reinforcing the
cold air mass in place. While the southern mainland is expected to
be mostly dry on Friday, uncertainty increases for the weekend
depending on the strength of the northern feature. A stronger
northern low pressure system would likely mean another round of
snow for Southwest Alaska, with even more uncertainty further
east. Overall however, a drier period of weather is the favored
solution across the domain through early next week, with the
exception of the Aleutian Islands and Alaska Peninsula, which can
expect rain.

By Sunday, another potential pair of features enters the picture
in the western Bering and North Pacific, with the potential to
reverse the flow across the western Bering and bring warmer air to
the region on southerly flow for Monday. Further east, low
pressure in the Gulf once again enhances gap winds on Sunday and
Monday out of bays and passes along the Gulf coast.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Winter Weather Advisory: 121
		 High Wind Warning: 181
 		 High Surf Advisory: 155 161
MARINE...Storm Warning 119 125 130-132 138 150 155 160 165 180
		 Gale Warning 170-177 179 181 185 351-352 411-413 414.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...MF
SOUTHCENTRAL ALASKA...SEB
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...KM
LONG TERM...CQ