NWS Anchorage, AK wrote its last area forecast discussion before the first event at Feb 28, 5:46 PM AKST, 6 hours 14 minutes earlier.
Area forecast discussion, Feb 28, 5:46 PM AKST, 6 hours 14 minutes before
Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
546 PM AKST Tue Feb 28 2023
.ANALYSIS AND UPPER LEVELS...
The upper level pattern continues to amplify as a strong shortwave
is developing south of the AKPen deepening the longwave trough
across the Bering and Aleutians. The jet stream continues to
bring moisture into the southern part of Alaska. Currently a front
is moving across Southcentral with light snow observed across
most of the area, but has diminished across Anchorage and the
Matanuska valley. Across the Southwest light snow and blowing
snow is occurring across the Kuskokwim Delta and the lower
Kuskokwim valley. Across the Bering and Pribilof Islands high end
gales have been observed and will continue through tomorrow.
&&
.MODEL DISCUSSION...
Models still continue to show some differences on the development
and track of the low across the Gulf tonight, but overall this
will not impact snow totals much. The biggest challenge is where
the low deepens and where the strongest winds will occur. Currently
it looks like the eastern side of Kodiak Island may briefly see
high winds as pressure rises rapidly but will then decrease fairly
quickly as the low moves northeast. However, if the low tracks a
bit farther to the east than the high winds may miss Kodiak Island
Wednesday morning. Models are in fairly good agreement with high
winds across Kodiak Island and nearby areas by Wednesday evening
into Thursday morning as colder air advection enhances the winds.
&&
.AVIATION...
PANC...Low level windshear is expected until around midnight
tonight. Winds are expected to increase tomorrow near mid-day out
of the north with gusts near 25 knots possible.Light snow will
taper off this afternoon with conditions expected to improve to
VFR as downsloping begins. Another storm is expected to move into
the Gulf Wednesday morning, which may return IFR to MVFR
visibility and ceilings with light snow.
&&
.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3:
Tonight through Friday)...
A large low tracking into Western Alaska is pushing its occluded
front eastward across Southcentral this evening. The main focus
of activity is expected to be over Cook Inlet, though intermittent
periods of light snowfall will be possible across the western
Kenai Peninsula and Anchorage as moist southwesterly flow aloft
fights low-level southeasterly downsloping tonight. This will keep
snow accumulations scattered and spotty for inland locations.
Meanwhile, snow will persist along the north Gulf coast as a weak
triple point low drapes its front along the coast.
A vigorous upper-level shortwave trough will aid in the deepening
of a surface low passing south of the Alaska Peninsula this
evening. The low takes aim at Kodiak tonight, bringing another
round of precipitation which is likely to begin as rain, but could
transition back to snow. If this happens, there will be potential
for blowing snow to significantly reduce visibility as winds pick
up early Wednesday morning. The deep low passes just east of the
island and cold advection wrapping around the back side of the
low combined with pressure rises in its wake may lead to a brief
period of high winds during the morning hours. As the low tracks
into the northern Gulf, these winds subside somewhat for Kodiak,
while a storm- force barrier jet sets up along the north Gulf
coast.
As the low tracks south of the Kenai Peninsula on Wednesday
morning, a second round of steadier, heavier snow sets up across
the western Kenai Peninsula. This will combine with increased
winds, resulting in blowing snow, especially along Cook Inlet.
Blizzard-like conditions persist with gusty winds continuing to
blow through Whittier, Portage Valley, and eastern Turnagain arm,
leading to visibility as low as one quarter mile at times. These
conditions will also briefly be possible in Seward as the low
passes just to the east, drawing northerly winds through
Resurrection Bay gusting up to 50 mph during the morning hours.
The low continues east, pushing heavier snow into eastern Prince
William Sound and the southern Copper River Basin on Wednesday as
well, where snow accumulations of near 6 inches in 12 hours will
be possible. Through Thompson Pass, strong winds contribute to
the threat of blowing snow. With the low shifting east, snow
begins to end from west to east over the Kenai Peninsula, and
winds shift out of the west through Passage Canal. Light snow will
linger along the western slopes of the Chugach Front Range and the
Kenai Mountains with a push of northwesterly cold air advection
wringing out moisture in the wake of the low, and upwards of 6
inches of snow accumulation will be possible along the Anchorage
Hillside midday Wednesday into Wednesday night, for which a new
Winter Weather Advisory has been issued. For Kodiak Island, this
push of cold air leads to a second potential round of high winds
Wednesday afternoon. Gusts to 80 mph will be possible, and there
is greater confidence in this round of winds exceeding the 75 mph
high wind threshold.
By Wednesday evening, the low moves into the eastern Gulf,
allowing snow to taper off across the Copper River Basin, and
leaving only upslope snow showers along select mountain ranges.
Drier, colder air works its way across Southcentral and the Gulf
of Alaska, bringing colder temperatures for Thursday and Friday.
As the low in the Gulf weakens on Thursday, its ability to draw
cold air across the Western Alaska/Aleutian Range eastward and gap
winds begin to wane. Upslope snow showers also gradually taper
off, with uncertain end timing. Friday, cooler, relatively benign
weather conditions take over for inland locations, with cold air
continuing to filter out through gaps in the coastal mountains.
&&
.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3)...
An unsettled weather pattern will continue across Southwest Alaska
as snow and blowing snow continue to reduce visibility this
evening. However, the general trend is conditions will gradually
improve over the course of this evening. Temperatures will rapidly
cool as the flow becomes northwesterly. Lingering snow showers are
likely, though no significant accumulations are expected.
&&
.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
Unsettled weather continues across the Bering/Aleutians as a
second low pressure system moves in the wake of this current
departing low. Widespread gale force winds with areas of storm
force winds are expected. This second low will then exit on
Friday. A third low will move into the western Bering on Friday
and produce gale force winds.
&&
.LONG TERM FORECAST (Days 4 through 7: Saturday through Tuesday)
The primary story in the extended forecast will be a high-
amplitude ridge moving over Mainland Alaska, bringing the
potential for above-freezing temperatures and rain. The ridge
begins to move into Mainland Alaska on Saturday. Increasing
pressure will lead to a spell of quiet weather for Southcentral as
gusty gap winds shut off and little, if any, precipitation is
expected through Tuesday. Maximum temperatures will steadily
increase from day to day under the ridge, though the development
of low stratus or fog under high pressure may help moderate
temperatures near the coast.
Southwest Alaska and the Bering/Aleutians can expect to see much
more unsettled conditions as various storm systems run up against
the ridge and are shunted into these regions. While there remain
model differences regarding the trajectory of individual storms,
there is decent consensus that warm and wet conditions will
prevail. The first storm will be a North Pacific low moving north
across the Central Aleutians and into Southwest Alaska, bringing
gales and moderate to heavy rain at times. Another low developing
near the Central Aleutians will likely bring an additional shot of
moisture. Overall, the primary hazards to keep an eye on will be
above-freezing temperatures and rain amounts/duration.
The ridge looks to persist through Tuesday, though it will be weakened
by the storms moving along its western edge. There is uncertainty
with the evolution of this ridge by Monday/Tuesday, with some
guidance suggesting the ridge will shift further eastward versus
other guidance suggesting that it will degrade in place.
&&
.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Blizzard Warning: 125
Winter Weather Advisory: 101, 121, 131, 141
High Wind Warning: 171
MARINE...Storm Warning: 119, 120, 130-132, 150, 155, 170, 171,
175, 178, 351, 352, 413
Gale Warning: 125, 129, 136-139, 141, 160, 165, 172-174, 176,
179-181, 185, 411, 412, 414
Heavy Freezing Spray: 130, 138, 139, 160, 180, 185, 414
FIRE WEATHER...NONE.
&&
SYNOPSIS AND MODEL DISCUSSION...RC
SOUTHCENTRAL ALASKA...CQ
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...ED
LONG TERM...KC