NWS Anchorage, AK wrote its last area forecast discussion before the first event at Mar 18, 4:32 AM AKST, 13 minutes earlier.
Area forecast discussion, Mar 18, 4:32 AM AKST, 13 minutes before
Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
532 AM AKDT Sat Mar 18 2023
.ANALYSIS AND UPPER LEVELS...
Another low pressure system lifts northwestward to the west-
central Gulf by this afternoon in a similar fashion to yesterday's
system. The main differences being this next system is showing a
more elongated system initially before compressing as it reaches
the Barren Islands, and is indicated an somewhat stronger system
as a whole. The track of the front is also a glaring difference,
with an east/west orientation of the warm front versus the
northwest/southeast orientation associated with yesterdays's
storm. This will have an impact on where the heaviest
precipitation falls and how far north the warm air tracks. Cold
air will quickly wrap back around the low, producing a showery
pattern on the backside of the system. The system will move over
the Alaska Peninsula later tonight, but shows a slightly slower
decay as it moves over land. Further west, the ridge continues to
break down over the Central Aleutians as a low pressure system
moves over the Western Aleutians and into the Bering Sea Sunday
morning. The Bering low will quickly track northeastward towards
Saint Matthew Island before slowing down and drifting into the
Bering Strait.
&&
.MODEL DISCUSSION...
Model guidance continues to improve with the North Pacific system
approaching the Gulf of Alaska today. There has been a trend
towards a more elongated system but all models show the system
quickly consolidates as it reaches the Barren Islands. The overall
track of the low is consistent amongst all models, but the GFS is
placing the low center further south than the others and is
continuing to show a stronger system (~8 mb difference between
GFS and NAM/Canadian).
&&
.AVIATION...
PANC...VFR conditions and light winds will persist through most of
this morning. Late morning has a chance for another quick shot of
light snow, bringing visibilities down to MVFR conditions and
ceiling heights below 2000', with increased northerly winds.
Conditions are expected improve through the overnight hours,
however, increased winds will continue and transition to
southerly.
&&
.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3:
Saturday through Monday)...
Another day, another strong low tracking through the Gulf of
Alaska from southeast to northwest. This low will take a similar,
but slightly farther north, track than the one yesterday. That is
one of two significant differences from yesterday's strong system.
The second is the structure of this low compared to yesterday's.
Today's low is much more elongated than the one yesterday and
that will have a large impact on some areas, especially Kodiak
Island. The thermal gradient at 850 mb yesterday stretched across
northern Kodiak Island and brought in the strong winds and heavy
snow. The gradient today will be weaker and farther north which
will keep Kodiak City and Kodiak Island out of most of the
snowfall. Afognak Island, on the other hand, will see heavy
snowfall again this afternoon and evening.
The Kenai Peninsula will be in the cross-hairs of this system
again today. Strong winds and heavy snowfall are expected across
the eastern Kenai prompting a Winter Storm Warning. The western
Kenai is a little less certain as Kachemak Bay will likely see a
periods of snow and blowing snow, but temperatures there will warm
up above freezing bringing in the potential for rain to mix in or
have the precipitation turn to all rain there. The atmosphere
remains quite cold aloft which should keep the precipitation
mostly snow even toward Homer, but it will be close. Along Cook
Inlet from Nikiski southward, including the Sterling Highway
corridor, there will be strong northerly winds gusting to around
35 or 40 mph. The snowfall here is less certain due to
downsloping. Should the band of snowfall set up along the Inlet
instead of over the Inlet, it would bring in significantly reduced
visibilities in blowing snow for the Sterling Highway.
After this low moves through the region overnight tonight, the
should be less active weather through Monday. An upper-level
trough does move across Southcentral Sunday night and MOnday, but
it looks like it will have minimal impact at this time.
&&
.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3: Today
through Monday night)...
A low centered along the Alaska Peninsula will slowly track out
into the north Pacific today before a second system moves into
Southwest Alaska tonight. The vertically tilted first low extends
its influence northward across Bristol Bay this morning, with
light snow showers ongoing along the coast. These will diminish in
intensity through the morning as the low exits southward slowly,
leaving partly cloudy skies in its wake. Solar heating will bring
high temperatures into the 20s and 30s for much of the region.
Then, a deepening low in the Gulf of Alaska will take a similar
track to yesterday's system. This system, however, looks to bring
more snow and remain more consolidated as it tracks over Southwest
Alaska. Winds increase this evening ahead of the approaching low
as snow begins to push across the Aleutian Range into Bristol Bay.
Snow will spread westward through Saturday night, bringing total
accumulations of 2 to 4 inches through Sunday, with lower amounts
extending northward into the Lower Kuskokwim Valley. Blowing snow
will be a brief threat with a band of heavier snow, focused near
the villages of New Stuyahok and Koliganek Sunday morning, which
should reduce visibility to one half mile at times. There is also
some potential that Dillingham could see visibilities this low as
well, but the western edge of the heaviest snow looks to set up
near the city, which will limit the likelihood of any prolonged
visibility reduction. By late Sunday morning, the low center
moves over Southwest Alaska, reducing winds and the threat of
blowing snow.
Snow then retreats back to the east and begins to taper off as
the low weakens and is pushed back to the east by a transient
ridge out ahead of a larger system approaching from the Bering
Sea. This large low will send a front eastward into the mainland
Monday morning. Temperatures aloft and a rapid occlusion suggest
that snow will be the primary precipitation type, but strong
southerlies and the March solar intensity may allow for some rain
to mix in as the front moves east across the region through
Monday night.
&&
.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3: Today
through Monday night)...
Cooler, northerly winds continue over the Eastern Aleutians and
Alaska Peninsula through Sunday morning as low pressure persists
along the Alaska Peninsula and over Southwest Alaska. Out west,a
weak front pushes into the western/central Bering today and
tonight. Then, a deep low in the North Pacific approaches the
Western Aleutians Sunday morning, bringing increasing winds, snow,
and rain to the islands. As the low tracks into the Bering, it
will bring hurricane force winds to the region. The main question
is the exact track of the low, which will determine whether Shemya
sees 75 mph gusts or greater on Sunday. The threat is currently
high enough that a High Wind Watch remains out for that area. The
low pushes to the central Bering Sunday night as it occludes,
bringing storm force winds and high seas along with it. Rain is
likely in the Pribilof Islands with a strong push of southerly
flow out ahead of the low. By Monday, the low weakens and tracks
into the northern Bering as it pushes its front into Southwest
Alaska, allowing rain and snow showers to overspread much of the
Bering Sea going into Monday night.
&&
.LONG TERM FORECAST (Days 4 through 7: Tuesday through Friday)
The long-term period opens with a Bering Sea front working into
coastal and interior Southwest Alaska providing good chances at
snow. An additional shortwave trough digs southward from the
parent trough in Siberia through the Bering Sea, across the
Aleutian Chain, and into the North Pacific Tuesday afternoon. This
will generate a low pressure system in the central Bering Tuesday
morning that moves quickly eastward to Southwest Tuesday afternoon
bringing widespread precipitation to coastal Southwest as well as
the Alaska Peninsula before working its way to interior Southwest
during the evening. Meanwhile, gusty northerly flow and cold air
advection on the backside of this system ensues for the central
and eastern Aleutian Chain giving the chance at snow showers
through most of the rest of the long-term/Friday morning. A triple
point low then looks to spawn either in the western Gulf or North
Pacific Tuesday evening as the upper trough becomes increasingly
negatively tilted. There is disagreement on how the trough
evolves Tuesday evening. The 12z GFS and 12z ECMWF have a more
negatively tilted trough with storm formation in the vicinity of
Kodiak Island, while the 12z Canadian guidance is not as
negatively tilted and forms the storm further to south in the
North Pacific. Regardless, this system looks to give coastal
Southcentral Alaska another good chance at amplified precipitation
Wednesday and Thursday, while interior Southcentral will still
have precipitation chances, just not quite the chance at heavier
precipitation. Questions also arise for Southcentral at the end of
the long-term period Thursday evening as guidance hints at
another low forming in the Gulf then. However, confidence remains
low on timing, strength, as well positioning of this feature.
&&
.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Winter Storm Warning: 125
Winter Weather Advisory: 121 161
High Wind Watch: 191
MARINE...Hurricane Warning: Western Aleutians
Storm Warning: Northern Gulf of Alaska, Eastern/Central Bering,
Central Aleutians
Gale Warning: Prince William Sound, Passage Canal, Barren Islands,
Kodiak Islands Waters, Cook Inlet, Kachemak Bay, Western Gulf of Alaska,
Heavy Freezing Spray Warning: Western Bering, Alaska Peninsula - Bering
Side, Pribilof Islands
FIRE WEATHER...NONE.
&&
SYNOPSIS AND MODEL DISCUSSION...KM
SOUTHCENTRAL ALASKA...EZ
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...CQ
LONG TERM...DAN