Gale Warning 765, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
436 PM AKST Fri Dec 22 2023

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

The powerful storm that is set to move into the Gulf of Alaska later
today is already starting to be realized as winds have increased to
storm and gale force across the central and southern Gulf. Snow
moved into Kodiak Island by mid-morning before transitioning over
to rain as temperatures warmed into the mid and upper 30s. The
effective warm front will continue to lift north into the southern
Gulf this afternoon with extensive cloud cover spreading across
the Gulf and into inland areas of Southcentral. In addition,
scattered rain/snow showers will become more widespread across the
northern Gulf, including the eastern Kenai and Prince William
Sound areas this afternoon. Some light snow has made it into the
western Kenai and Cook Inlet extending up towards the Anchorage
Bowl and southern Mat-Su Valley, but overall amounts this
afternoon will be light with a more defined downslope hole
developing tonight into Saturday morning as easterly winds
strengthen.

Overall, models seem to be in decent agreement with the upper low
tracking east into the central Gulf through tomorrow morning before
starting to lift north towards Prince William Sound by tomorrow
afternoon/evening. Meanwhile the surface low will track northwards
towards the eastern Kenai Peninsula then is progged to lift over the
Kenai Mountains towards the Mat-Su Valley. With the surface low
rapidly deepening before reaching the eastern Kenai, the pressure
gradient will steepen significantly over western Prince William
Sound. This will allow for winds of 35 to 45 mph to develop
tonight for Whittier and Portage Valley as 850 mb jet streak
points right into western Prince William Sound. Gusty winds will
also be felt on the Anchorage and Eagle River Hillsides late
tonight into Saturday morning as strong winds top the Chugach
Mountains. This will be the first round with a second round of
precipitation ramping up late Saturday through Sunday, but with
track shifting slightly to the east, main impacts will also shift
from the Kenai Peninsula to northern and eastern Prince William
Sound, including Thompson Pass.

The primary forecast challenge remains focused on precipitation
amounts and type. This storm will drag warm, moist air northwards
towards the eastern Kenai and Prince William Sound. Temperatures
will start out cold enough for snow in most locations down to sea-
level; however, as warmer air works north will likely see a change-
over to a rain-snow mix or to all rain for coastal areas near sea-
level. Higher elevations will remain all snow, but snow levels will
rise to about 1000 ft or so. The one caveat will be if this system
will be strong enough to dynamically cool resulting in snow reaching
the surface with temperatures above freezing. Right now, medium
confidence (40-60 percent) exists on precipitation type for areas
near sea-level, including Seward and Whittier. Turnagain Pass should
remain cold enough for all snow and should see accumulations of
between 10 to 18 inches.

- PP

&&

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

A North Pacific low south of the Alaska Peninsula will pivot into
the northern Gulf through Saturday. The pressure gradient on the
backside of the low has resulted in gusty winds across the Eastern
Aleutians and Alaska Peninsula. Winds earlier in the day across
Unalaska were gusting just under 60 mph with visibility down to
3/4 miles due to snow and blowing snow. Winds remain elevated this
evening across the Eastern Aleutians with gusts just under 50
mph. However, the heavier snow has tapered off and any
transportable snow has been moved. Therefore, visibility has
increased and the earlier Winter Weather Advisory was allowed to
expire at noon.

Currently, a Blizzard Warning remains active for both the Alaska
Peninsula and the Bristol Bay Coast. The Alaska Peninsula has
experienced the brunt of the stronger winds with gusts ranging
from 50 to 60 mph through the entire day across Cold bay.
Visibility was near zero at times and remains at 1/4 mile as of
the time of this writing. Winds will remain elevated into the
overnight hours and the Blizzard Warning will expire tomorrow at
noon barring any improvement in conditions later tonight/early
tomorrow morning.

Conditions across the Bristol Bay Coast have been slower to
develop. However, the latest observation out of Dillingham has
visibility down to 1/2 mile due to snow and blowing snow, with
winds gusting to 37 mph. There has been much uncertainty on which
locations would experience the highest snow amounts. Numerical
guidance has come into much better agreement with a deformation
band developing directly over Dillingham, northward toward
Sleetmute. Locations within this band will likely see upwards of 8
to 10 inches of snow, with locally higher amounts up to 12 inches
possible. This includes the cities of Manokotak as well as
Koliganek. Regardless of snow amounts, gusty winds and persistent
snow will promote very hazardous conditions for anyone traveling
or exposed to the elements. The Blizzard Warning for the Bristol
Bay Coast expires Saturday afternoon at 3pm AKST.

While the weather pattern across the Aleutians and Southwest has
been highly unsettled, there is hope beyond Saturday as weak high
pressure begins to move into the southern Bering. Calmer winds
are forecast on Sunday though scattered light snow showers will
continue to push across the Aleutians into early next week. The
other concern will be for cooler temperatures over the next few
nights as an arctic airmass spills out of the northern Bering
into Southwest through the weekend. Gusty winds will bring wind
chills down into the minus 30s for much of the Kuskokwim Delta
tonight. Wind chills for western portions of the Lower Kuskokwim
Valley down to Togiak should drop into the minus 20s. Sunday night
should see wind chills into the minus 20s for much of Southwest
Alaska, with only eastern portions of the Lower Kuskokwim Valley
and interior Bristol Bay in the minus single digits and minus
teens.

BL

&&

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

An elongated upper level low centered near Nunivak Island remains
through Wednesday before moving northeast. Multiple shortwaves
will rotate around the upper low through midweek. A low pressure
and associated fronts will produce areas of precipitation across
the central Aleutians and pushes into the southern AKPEN Tuesday
afternoon. The low and front continue across the gulf. Locally
heavy precipitation is expected, with rain near the coast, mixed
precipitation inland, and snow towards the interior, stretching
from the southern Kenai peninsula to the Canadian border. A second
front continues similar conditions across southcentral Tue night
into Thu. Gusty winds are expected throughout the forecast period
over marine locations. A westerly gale force barrier jet forms
along the north gulf coast late Tue and dissipates Wed.

Unsettled conditions are expected over the Aleutian Chain through
Wed. Transient surface lows will bring local areas of gale force
winds across the eastern Aleutians Mon, with the more active
weather pushing south into the northern Pacific by Wed. A weak
north Pacific ridge moves over the Aleutians before flattening out
Thu. Conditions will remain showery over the Bering through the
end of the period as a northwest flow continues.

&&

.AVIATION...

PANC...Light snow and pockets of low stratus / freezing will
prevail through the remainder of the afternoon into the evening
for Anchorage. An approaching system with strong low/mid-level
easterly flow will result in downsloping conditions for Anchorage
tonight into tomorrow morning. This should yield VFR CIGs, but
with some modest wind shear, particularly at or above 2kft.

As the flow aloft decreases, clouds should gradually lower
tomorrow. Next wave of snowfall should reach ANC Saturday evening,
resulting in degraded flight conditions.

&&