NWS Anchorage, AK wrote its last area forecast discussion before the first event at Feb 3, 5:11 PM AKST, 10 hours 18 minutes earlier.
Area forecast discussion, Feb 3, 5:11 PM AKST, 10 hours 18 minutes before
Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
511 PM AKST Fri Feb 3 2023
.ANALYSIS AND UPPER LEVELS...
The pattern remains amplified as upper level troughing currently
extends across the Bering Sea while upper level ridging extends
along the west coast of Canada and across Southeast Alaska. An
upper level low currently in the western North Pacific is
currently moving eastward towards the western Aleutians. A weak
low is currently nearly stationary over the north central Bering
Sea. A negatively tilted upper trough currently extends from the
aforementioned central Bering low southeastward into the Gulf of
Alaska.
Closer to the surface, radar imagery shows areas of snow moving
northeastward across the Kuskokwim Delta. Radar shows a second
area of light snow moving northeastward across Southcentral
Alaska.
&&
.MODEL DISCUSSION...
Guidance remains in fair agreement with respect to the placement
and intensity of synoptic scale features. The biggest challenge
continues to be refining small localized features. The EC/GEM
blend continues to be the most plausible solution by taking the
low into Prince William Sound. Forecast confidence remains around
average.
&&
.AVIATION...
PANC...IFR to LIFR conditions continue through 04th/20z due to low
ceilings and restricted visibility. Conditions improve to MVFR
after 04th/20z when ceilings rise and visibility improves.
&&
.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Friday evening through
Monday)...
We could see a break in the persistent snowfall of previous days.
The stronger shortwave trough that was responsible the quick
uptick in snow intensity today is pushing out of Southcentral,
leaving the area on the subsiding side of the trough. The question
for the overnight period in most places is does the low and mid-
level clouds stick around the Cook Inlet region, or erode enough
to allow temperatures to drop and fog to form. As of forecast
issuance (Friday afternoon), we are leaning toward the clouds
sticking around as has been the case between weak waves the last
few days. As is the case with the last few days, shallow moisture
with the drying aloft will make freezing drizzle a possibility
tonight. Yet another shortwave trough comes through on Saturday
morning which will bring another round of light snow which should
pass by the afternoon/evening hours.
Sunday will bring a stronger front and low to the area. While
details on exact track of the system are yet to be determined, the
impacts should be much the same. As the system intensifies and
peaks near Kodiak Island, Kodiak City should turn from snow to
rain, then back to snow as the system passes. The front along the
north Gulf coast looks to be locked into storm-force. The system
occluding will keep much of the warm air away from the Mainland,
so most locations will see snowfall, except for the coastal
locations at sea level which could see a mix of rain and snow.
There will be a period of snow moving up Cook Inlet, associated
with the upper trough passage which could bring 1-3 inches to
most locations on Monday.
&&
.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 to 3: Tonight
through Monday night)...
A relatively mild and unsettled pattern will continue through
Saturday as multiple shortwaves originating from a complex low
over the Bering push onshore with multiple waves of snow showers.
Predominantly onshore, southerly winds and ample cloud cover
should help keep temperatures average to above average for early
February, with most locations still on track to warm into the 20s
on Saturday. By Sunday morning, a maturing North Pacific low will
approach Kodiak Island, then up towards the Kenai Peninsula as it
weakens by Sunday night. A band of light to moderate snowfall is
expected to form northwest of the low, mainly over Bristol Bay.
The best potential for higher snowfall accumulations will be
focused near and north of Dillingham, where between 4 and 6 inches
of new snowfall will be possible between Sunday morning and late
Sunday night. By Monday, the stacked low over the Bering will
meander east right across Southwest, resulting in continued
potential for areas of light snow rotating around the center. A
colder air mass will also arrive with this system, with
temperatures dipping back into the 0s to 10s by late Monday night.
&&
.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 to 3: Tonight
through Monday night)...
A complex, stacked low harboring a myriad of smaller centers will
continue to lumber east across the Bering Sea towards Southwest
through Monday. The track, timing and strength of individual
centers spinning up and dying off has not been well-resolved by
today's suite of model solutions, casting uncertainty for timing
of higher winds and waves of rain/snow showers moving along the
Aleutian Chain through Sunday morning. Prevailing winds will
generally be in the 20 to 30 kt range through Saturday along the
central and eastern parts of the Aleutian Chain, however winds
could locally be higher as small lows move past from west to east.
By Sunday, the main low center will begin to approach the
Southwest coast as it begins to wrap a colder air mass into the
western Bering behind it. Gusty north to northwest winds will
develop across western portions of the Bering and Aleutians with
the push of cold air along with intermittent snow showers across
the western Aleutians on Sunday, then spreading into the rest of
the Aleutian Chain and Pribilofs heading into Monday as the low
continues to drift east into the southern Mainland.
&&
.LONG TERM FORECAST (Days 4 through 7: Tuesday through Friday)...
Overall confidence remains rather high with the long-term weather
pattern remaining relatively active over Bering Sea/Aleutians, and
average for Southern Alaska. For Southcentral and Southwest
Alaska, there is reasonable agreement Tuesday through Wednesday
morning with guidance depicting a negatively tilted trough,
stemming from a Siberian upper-level low, lifting northeastward
from the eastern Bering Sea/North Pacific and through Southern
Alaska. The result is greater precipitation chances for Bristol
Bay communities, Prince William Sound communities, as well as for
the northern Gulf Coast. Interior Southcentral Alaska, including
Anchorage, could also see precipitation from this upper trough
system, but the degree to which potential downsloping occurs makes
the degree of uncertainty greater. The surface feature and
frontal feature associated with the upper trough is also somewhat
contested. While the GFS/CAN ensemble means have the surface low
near Prince William Sound, the ECMWF ensemble mean is slower with
low progression, and has it more south in the southern Gulf of
Alaska. After Wednesday, deterministic guidance agreement breaks
down tremendously. All have varying solutions from zonal west to
east flow over Southern Alaska, to potential ridging and a period
of quieter weather, to continued activity. However, the various
ensemble means hint at a possible upper ridge moving from west to
east from the Bering Sea and to the Southern Mainland Thursday and
Friday. However, confidence this far out is low.
Out west, the pattern remains quite chaotic throughout the long-
term period with the continuation of the Siberian trough and
multiple troughs digging southward from Kamchatka, through the
Bering Sea, and into the North Pacific while progressing eastward.
Each set of guidance has varying solutions for position/timing
and strength on the surface features with these upper-level
systems. Also, between systems, there will be little shortwave
west to east transient ridges. However, odds tilt toward little in
the way of sustained ridging across the Bering and Aleutians. One
such system that does have reasonable model agreement at both the
deterministic and ensemble levels, is a deep upper-level low
progged to impact the western Bering and western Aleutian Chain
towards the end of the long-term on Thursday into Friday. At this
time, the GFS and ECMWF deterministic and ensemble means both
show a more northerly track from the North Pacific into the
western Bering and a stronger system. Meanwhile, the Canadian
deterministic and ensemble guidance both show a more southerly
track and weaker system. There are strong signals that this low
could bring storm-force winds to the western and central Aleutian
Chain Thursday and Friday in addition to heavy precipitation.
Stay tuned to the forecast as details on this potentially strong
storm system come into better focus with time.
&&
.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gale Warning: 138, 176
Heavy Freezing Spray Warning: 185
FIRE WEATHER...NONE.
&&
SYNOPSIS AND MODEL DISCUSSION...ED
SOUTHCENTRAL ALASKA...ML
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...AS
LONG TERM...DN