Gale Warning 51, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
431 PM AKST Fri Jan 13 2023

.ANALYSIS AND UPPER LEVELS...

A large mature vertically stacked low continues to spin nearly
stationary over the Aleutians and southern Bering Sea. The
remnants of the occluded front and associated gale force winds
and steady precipitation continue to lift northward across the
Bering Sea, with a position today north and west of the Pribilof
Islands. That has left much of the region in a showery regime
with weaker winds. The atmosphere warmed just enough behind the
front that most of the showers are in the form of rain.

Meanwhile, a broad trough if lifting northward out of the northeast
Pacific into the Gulf of Alaska and toward southern Alaska. A
series of weak short-waves and surface lows are making their way
across the Gulf and Kodiak Island, leading to areas of rain along
with areas of small craft advisory level winds for the Kodiak
Island waters. As short-waves cross the Alaska Peninsula into
Bristol Bay, they meet up with opposing flow associated with the
Aleutian low. This is leading to frontogenesis from around Port
Heiden and Nelson Lagoon along the Alaska Peninsula northwestward
off the coast of Southwest Alaska. An area of steady
precipitation, mostly in the form of snow, is forming along this
front. Most of southern Alaska remains quiet for the moment, under
the influence of a west-east oriented short- wave ridge aloft.

&&

.MODEL DISCUSSION...

As would be expected, models are struggling with the host of weak
short-waves crossing southern Alaska the next 36 hours or so. This
creates a challenge for the timing and location of precipitation,
especially inland. An added challenge for the western Kenai Peninsula
and Anchorage areas is precipitation type, with marginally warmer
air streaming across the mountains and a chance for localized
areas of freezing rain on Saturday. This will be highly dependent
on track of short-waves and locations where precipitation is
reaching the ground. The next feature of interest is a low moving
out of the central Pacific on Sunday. The 12Z NAM has become a big
outlier in tracking this low eastward south of the Gulf. The
GFS/EC/Canadian and ensemble data all continue to support a track
to south of Kodiak Island Sunday, with a dissipating low backing
northwestward into Bristol Bay Sunday night/Monday.

&&

.AVIATION...
PANC...A series of weak short-waves will pass overhead on Saturday.
At a minimum this will cause ceilings to lower down to low end
VFR. The likelihood and timing of precipitation is highly
uncertain at this time. Any precipitation that does fall would be
light and mostly in the form of snow, with a slight chance for
freezing rain or freezing sprinkles. The steadier and heavier the
precipitation, the more likely it would fall as all snow. Worst
case scenario, would expect a few hours of MVFR conditions.

&&

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

Generally benign weather conditions continue across much of
Southcentral with weak flow, ample low level moisture, and areas
of fog in place under a weak upper-level ridge. Widespread fog has
primarily been confined to the valleys of the Copper River Basin
today. An elongated upper trough continues to lift into the Gulf
from the North Pacific. As a result, multiple embedded shortwaves
and surface lows traverse the Gulf and Kodiak Island and maintain
light rain for locations near sea level, snow for higher
elevations, and small craft winds for the Kodiak Island waters. As
the trough lifts northward, it will send a series of upper-level
shortwaves across Southcentral tonight through Sunday.
Precipitation will spread to Prince William Sound and the eastern
Kenai Peninsula earlier on Saturday morning and should begin as
snow before transitioning to rain later that morning/afternoon.
Homer and Seward may experience a brief period of freezing rain
before transitioning to rain. Areas of light precipitation (snow
and periods of freezing rain) are possible for the western Kenai
Peninsula and Anchorage area starting Saturday afternoon, however,
impacts are expected to be minimal. Going into Sunday,
precipitation lingers along the coast while the trough exits to
the north and the next system approaches Kodiak Island from the
North Pacific. Models have continued to struggle with the
evolution of this low and whether or not it will track
northwestward into Bristol Bay by Sunday night into Monday. There
is general consensus, however, for its front to reach Kodiak
Island on Sunday morning and then continue to the north Gulf
coast, maintaining precipitation there through Monday.

&&

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

Relatively quiet weather will persist over the region for the
next few days. A narrow upper-level ridge is located roughly along
an east-west axis over southern Alaska, running from roughly
Yakutat and Cordova, across Southwest, and over the northern
Bering Sea. Simultaneously, a nearly stationary and large
vertically stacked low continues to meander slowly across the
western Aleutians/Bering. A shortwave associated with the
aforementioned low will track northward across the region and will
bring light snow showers to the Alaska Peninsula tonight, work
its way north into Bristol Bay for Saturday, before finally
reaching the Kuskokwim Delta and Kuskokwim Valley Saturday night
into Sunday. Accumulations from the aforementioned system will be
light. Offshore flow will continue through the forecast period and
increase in response to a North Pacific low tracking across the
Alaska Peninsula. Models are having a hard time resolving the
aforementioned low, which will impact the sensible weather as a
result. Confidence is high that the impacts from this system will
overall be benign, but be sure to check back in with the forecast
for updates as the finer details become resolved.

&&

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

An unsettled weather pattern will continue across the
Bering/Aleutians as a nearly stationary and large vertically
stacked low continues to meander slowly across the western
Aleutians/Bering, with the center located near Amchitka this
evening. The aforementioned low's occluded front continues to
slowly track northward between the eastern Aleutians and much of
the central/western Bering. A narrow upper-level ridge is located
roughly along an east-west axis over southern Alaska and extends
into the eastern and northern Bering Sea. Areas of gale force
winds associated with the large low located in the northern
Bering will continue to shift north through tonight and be
replaced by areas of small craft winds. This trend of small craft
winds will continue as the aforementioned low slowly tracks across
the Bering. A North Pacific low will track across the Alaska
Peninsula and into the Bristol Bay region early next week. Models
are having a hard time resolving the track and strength of the
aforementioned low, so be sure to check back in with the forecast
as we continue to monitor the potential impacts of this system.

&&

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

The general pattern remains on track, with unsettled weather
expected over Southern Alaska and the Bering Sea. The area to
watch continues to be the North Gulf coast as several lows make a
beeline for this region. Models diverge by Tuesday, so it will be
difficult to dial into forecast specifics for these lows.
However, areas of consensus and overall model trends can give us
an idea of what to expect for next week. For Tuesday, guidance
continues to suggest the development of a surface low near Kodiak
Island. However, forecast confidence has diminished as the GFS
deterministic model and ensemble mean are suggesting that the
surface low remains in the North Pacific, with few appreciable
impacts to Southern Alaska. This is a major departure from the
current Canadian and ECMWF models, and from the model solutions we
saw yesterday. With the low remaining fairly weak, the main
impact for the Canadian/ECMWF solution will likely be light to
moderate snow (with a mix or rain at lower elevations and near
the coasts) for Eastern Kenai Peninsula and Prince William Sound.
As this system looks to be weaker, there is also the potential
for some precipitation to creep inland.

The next storm to move into the Southern Mainland should arrive
around Thursday and linger through Friday. Timing discrepancies
have diminished since yesterday's model runs, and there is
increasing confidence that this could be an impactful storm. The
main hazards look to be elevated winds along the North Gulf coast
and potentially in Matanuska Valley as a barrier jet develops
along the coast. Heavy precipitation may also be a concern for the
Eastern Kenai Peninsula and Prince William Sound. For Southwest
Alaska, the current forecast track of the low means that elevated
northerly winds, especially through Alaska Peninsula gaps, may be
the primary hazard. These hazards may shift as models better hone
in on the low track in subsequent runs.

Quieter overall weather is expected for the Bering Sea and
Aleutian Islands. The main story will be a low near the Kamchatka
Peninsula, which will slowly slide southeastward towards the
Western Aleutians and Bering. The track of the low center itself
is subject to uncertainty, but this system looks to be fairly
benign, with small craft winds and snow showers expected.
Northerly flow with the departure of this low will likely lead to
dipping temperatures.

Looking at Friday and beyond, there is increasing confidence for
a change in the storm track. With the jet stream amplifying into
next weekend, we are likely to see a return to stronger, more
impactful systems moving up into Southern Alaska.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gale 185. Heavy Freezing Spray 180 185.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...SEB
SOUTHCENTRAL ALASKA...ADI
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...NS
LONG TERM...KC