NWS Anchorage, AK wrote its last area forecast discussion before the first event at Feb 14, 5:59 PM AKST, 11 hours 21 minutes earlier.
Area forecast discussion, Feb 14, 5:59 PM AKST, 11 hours 21 minutes before
Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
559 PM AKST Mon Feb 14 2022
.ANALYSIS AND UPPER LEVELS...
A deep vertically stacked low is approaching the western Aleutian
islands between Adak and Shemya. The estimated central pressure is
around 965 mb. An occluded front is strung out from west to east
across the southern Bering Sea and over to Southwest Alaska. The
front is lifting slowly northward, with precipitation
overspreading all of Southwest Alaska. Precipitation is in the
form of snow north of the frontal boundary, with a transition to
rain along and south of the front. This transition from snow to
rain is positioned along the Bristol Bay coast. The strongest
winds with this storm are located over the central to western
Bering and Aleutians, where gale to storm force winds are being
observed.
Further east, a triple point is crossing the Alaska Peninsula into
the northwest Gulf of Alaska, with a warm front extending
eastward across the Gulf. Deep and moist southwest flow aloft is
leading to overrunning precipitation while weak short-waves
embedded within the flow are also providing some upward vertical
motion. This is leading to widespread snow across Southcentral
Alaska.
&&
.MODEL DISCUSSION...
Models continue to all show the same general pattern evolution and
same key features. However, run-to-run continuity is not great as
models struggle to track short-waves moving out of the central
Pacific up to southern Alaska, then eastward overtop of the
blocking ridge sitting over the east Pacific. As was the case
yesterday, the NAM is the notable outlier on the 12Z guidance.
In particular, NAM solution is different with track of surface
low in the eastern Bering Sea Tuesday night/Wednesday and with
track/timing of short-waves crossing southern Alaska Wed-Thu.
The other solutions are clustered together and will be preferred
for forecast updates. Will not get too cute with qpf/snow amounts
beyond the ongoing event over southern Alaska because expect
models will continue to show at least minor shifts in depiction
of short-wave troughs. Bottom line, it will be an active weather
week, with at least 3 distinct precipitation events over southern
Alaska.
&&
.AVIATION...
PANC...Snow will continue to limit ceiling/vis through about 12Z,
with prevailing IFR conditions. A weak surface low will head
inland across the Kuskokwim Valley tonight, which looks to be just
enough to switch around the pressure gradients and allow a
southeasterly Turnagain wind to bend into the airport right around
12Z. This should lead to an improvement and both ceiling/vis to at
least MVFR. This will cause surface temperatures to rise to
freezing or a degree or two above freezing. I could bring in just
enough warm air to produce some very light rain or drizzle before
precipitation completely ends. The wind will be short-lived as
pressure gradients quickly slacken between 15Z and 18Z. As has
been the case behind the last couple snow events, upper levels
will dry out, while lower levels will remain quite moist. As a
result, areas of low clouds and fog will likely develop sometime
Tuesday/Tuesday night, with a good chance of IFR or low end MVFR
conditions.
&&
.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through
3...Tonight through Thu afternoon)...
A VERY active weather pattern is expected to continue through the
week. First, the well-advertised storm system number one is
currently moving through Southcentral. A very strong upper level
ridge centered over the North Pacific and a strong upper level low
south of the Aleutian Islands is creating southwesterly flow in
between which is aimed right at Southcentral Alaska. A series of
upper level shortwaves will continue to move through Southcentral
through the evening and overnight hours. As a result, latest radar
data shows precipitation in the form of snow with some mesoscale
banding occurring within the main precipitation shield this
afternoon primarily over the Anchorage Bowl. This will result in
continued heavy snowfall rates up to 1 inch per hour at times
throughout the evening. A Winter Weather Advisory has been issued
for Anchorage and the Matanuska Valley for the evening commute as
a result. Snow is expected to continue through the overnight hours
and potentially even through around noon on Tuesday when the last
of the upper level shortwaves lifts on through Anchorage.
Therefore, the morning commute on Tuesday may also be affected.
This last upper level shortwave is expected to only slowly move
northward towards the Alaska Range through Tuesday night.
Therefore, areas of the Susitna Valley (mainly from Talkeetna on
north) and across the Copper River Basin may see snowfall
continuing through Tuesday evening. This will especially be the
case on the west side facing Talkeetna and Wrangell Mountains as
well as the south side of the Alaska Range. Also, this pattern
continues to favor Hatcher Pass where upwards of a foot to 16
inches of snow is expected between now and Tuesday afternoon.
Heights will slowly build from southwest to northeast behind the
aforementioned upper level shortwave during the day on Tuesday.
However, the next upper level shortwave will be quickly
approaching Southcentral lending to only a very brief break in
the weather perhaps Tuesday afternoon and evening for Anchorage
and the Matanuska Valley. With the overall westerly flow aloft,
any clearing that does occur will likely not make it into the Cook
Inlet region on Tuesday. Therefore, thinking the low level clouds
will remain in place. While the upper levels are expected to dry
out some, this will leave an atmospheric profile resembling that
of potentially freezing drizzle. For now though, current thinking
is that enough moisture will be in place to result in on and off
flurries sort of like what occurred over Anchorage Sunday evening.
Next, another storm system which will be the stronger and warmer
of the two makes its way into Southcentral Tuesday evening and
affects the area through Wednesday. This system will do the same
as the first and ride up and over the periphery of the upper level
ridge over the North Pacific as the energy from the upper level
low centered south of the Aleutians moves northeastward. This
upper level shortwave will be much stronger than this recent one
today and will bring a return of deep moist southwesterly flow
into Southcentral. This will result in precipitation breaking out
yet again from southwest to northeast. However, this time the
previous system will have virtually eroded all the cold air for
places such as Kodiak and the southern Kenai Peninsula (including
Homer) resulting in all rain this time around. Further north,
thinking enough warm air moves northward to result in potentially
a rain/snow mix for the Kenai/Soldotna area as well as for the
Sterling Highway between Soldotna and Cooper Landing. Right now it
appears Anchorage, Mat-Su Valleys, and Copper River Basin will
remain all snow with this event with heavy snow accumulations
likely. This snow will likely be of the wet snow variety due to
warmer temperatures aloft and at the surface. Cordova may also see
enough warm air come in to result in a rain/snow mix with the
Valdez and Thompson Pass area remaining cold enough for all snow.
Hatcher Pass will yet again be the favored area for this system
with deep moist southwesterly flow aloft bringing potentially
another foot or more of heavy wet snow. There is the potential for
this one to also bring a heavy amount of snow to the southern
Copper River Basin including the Richardson Highway and Edgerton
Highway areas.
Behind this system, a similar setup looks to occur for Wednesday
evening into Thursday with the upper levels drying out but low
level moisture remaining trapped resulting in potentially freezing
drizzle or on and off light snow showers during this time frame.
Then just will quickly touch on this here, there is yet a third
system that may bring another round of snow to much of
Southcentral Thu afternoon onward.
&&
.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3 - Today
through Thursday)...
Busy weather persists for Southwest through the period. As the
upper-level shortwave behind today's weather moves out of the
area, precipitation will gradually taper off from south to north
through Tuesday morning. For now, a Winter Weather Advisory for
blowing snow remains in effect over the Kuskokwim Delta coast
through this evening. A rain/snow transition has set up across
southern Bristol Bay, where the AKPEN is seeing rain while the
Dillingham area is seeing mixed precipitation. As temperatures in
northern Bristol Bay are expected to warm above freezing only when
precipitation is ending, the transition zone is not expected to
move much further north than its current location.
An upper-level shortwave moves north on Tuesday, spinning up a
surface low and front that move into Southwest Alaska.
Precipitation will slowly spread north from Tuesday afternoon
through Wednesday morning. Much of Bristol Bay will likely see
rain as the low brings an influx of warm air, though the Kuskokwim
Delta and Lower Kuskokwim Valley should see mostly snow except
for areas of compressional warming downwind of the Kuskokwim
Mountains. As the surface low moves towards the Kuskokwim Delta
early Wednesday morning, increased winds and potentially heavy
snowfall rates could create another period of blowing snow and
reduced visibilities. Some uncertainty remains with where the
heaviest precipitation will occur, so the severity of blowing
snow and potential reduced visibilities remain unclear. Snow will
continue through Wednesday evening, diminishing as the surface
low moves east out of the area.
There is little break in precipitation as an occluding low in the
Bering pushes its front into Southwest early Thursday morning.
For now, precipitation looks to be mostly snow except for rain
along the AKPEN. There remains model disagreement with the track
of the Bering low and where a triple point low, if it forms, will
track. As such, precipitation amounts and finer details remain
uncertain at this time.
&&
.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3 -
Today through Thursday)...
A strong low lingers near the Western Aleutians, stretching its
front across the Bering and into Southwest Alaska. As the low
occludes, winds will slowly diminish below gale force along the
Western Bering through Tuesday morning. Elsewhere in the Bering
and Aleutians, the weather remains quiet through Monday evening.
The weather becomes more active Tuesday. Over the Eastern
Aleutians and Bering, a quick-moving surface low and its front
bring rain and small craft winds as it crosses from the Pacific
into the Bering. Further west, a strong North Pacific low pushes
its front towards the Western and Central Aleutians Tuesday
evening. Rain and gale-force winds spread across the Bering as the
low and its front push northwards. The front brings light
precipitation as it progresses across the Bering and Aleutians,
reaching Southwest Alaska by Thursday morning. As the surface low
occludes through Thursday, winds around it will diminish below
gale force, and precipitation will transition to a showery regime.
&&
.Marine (Days 3 through 5: Thursday through Saturday)...
Gulf of Alaska:
Gales and seas up to 12 to 15 feet will brush through Kodiak
Island, Shelikof Strait, the southern Cook Inlet and south of
Kenai Peninsula Thu and Thu night as a result of a rapid-moving
frontal system. The next episode of potentially widespread gales
and large seas could reach the southwestern Gulf by Sat evening if
not sooner. The forecast confidence is moderate.
Bering Sea/Aleutians:
An active weather pattern continues for the Bering Sea/Aleutians
into the end of the week, with the first low bringing gales and
seas of 18 to 20 ft across the central/eastern Aleutians and south
of Pribilof Islands starting Thu morning through Fri evening.
Trailing behind this system would be another broad frontal
boundary that may reach the western Aleutians by Fri morning,
bringing potentially storm force winds Fri afternoon and much
elevated seas of more than 20 ft across the western/central
Aleutians and the Bering Sea into Sat night. The latter system
will usher widespread gales across the Bering with much higher gap
winds across the Aleutian Chain. The forecast confidence is high.
&&
.Long Term Discussion (Days 4 through 7: Friday through
Monday)...
The potential for more snow and rain/snow mixed is highly
favorable for southern AK as a result of a combination of upper
level troughs and frontal systems. Warm southerly winds combined
with tropical moisture could invite rainfall for parts of the
Aleutians especially over the western Aleutians and potentially
near Kodiak Island. Meanwhile, an upper ridging over the state
will aid to brief periods of calm and quiet weather in spite of
uncertainties with the placement and motions of the synoptic lows
and upper level dynamics. The forecast confidence is low after
Friday.
&&
.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Winter Weather Advisory 101 111 155.
MARINE...Gale Warning 175-178 185 411 412.
Heavy Freezing Spray Warning 185 411 412.
FIRE WEATHER...NONE.
&&
SYNOPSIS AND MODEL DISCUSSION...SEB
SOUTHCENTRAL ALASKA...MV
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...KC
MARINE/LONG TERM...CB