Gale Warning 146, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
615 AM AKST Mon Feb 13 2023

.ANALYSIS AND UPPER LEVELS...

An upper-level trough continues to promote unsettled conditions
across Alaska with multiple shortwaves rotating around Southern
Alaska. One such wave has supported a surface low centered about
Prince William Sound. A tight pressure gradient at the surface has
also pushed gusty winds along the Cook Inlet into places such as
Homer and Kodiak Island. This system has remained relatively
stationary due to the lack of movement from the supporting upper-
levels, driving the prolonged snowfall around Southcentral and
Anchorage area. This system however will weaken this morning,
granting a brief pause in the snowfall Monday for Southcentral.

Currently in Southwest Alaska, a weak high pressure system has
built over the region, maintaining a relative benign pattern with
colder temperatures and occasional showers. In the Bering, a
North Pacific low is located just south of the Central/Western
Aleutians. This system has a tight pressure gradient and is
pushing storm-force winds with hurricane-force gusts through parts
of the Western/Central Aleutians. The leading front along the
northern side of the front will sweep eastward along the Chain,
reaching the Pribilofs by this afternoon and Southwest Alaska by
early Tuesday morning. As the front reaches the Pribilofs, winds
and snow are expected to create blizzard conditions until Tuesday
morning.

By Tuesday afternoon, the aforementioned front will have pushed
into the Western Gulf of Alaska. This system will bring the chance
for light precipitation across Southcentral into the mid-week.
Additionally Tuesday afternoon, the leading front of a new low
pressure system will be pushing into the Western Aleutians,
sporting the potential for more storm-force winds and hurricane-
force gusts.

&&

.MODEL DISCUSSION...

Deterministic models remain in fair agreement in the short-term
with modest agreement at the synoptic levels. Forecast confidence
begins mild but grows by Tuesday morning due to the shift toward a
weather pattern dominated by synoptic-scale features. As such, one
source of model discrepancies in the short-term is the expiration
of snowfall over the Anchorage area. While the general consensus
leans towards a morning expiration, it is difficult to determine
exactly when to expect the shut off, and how lingering localized
showers will affect snowfall into the morning hours. Model
agreement begins to come much more in-line as that weak system
departs and the strong low in the Central Aleutians dominates the
pattern. There are some disagreements regarding the progression of
the front sweeping eastward, with the 00Z Euro showing it
slightly faster, however the difference is minimal and impact of
the difference is negligible. The model solutions do struggle
with resolving the precipitation impact of this front once it
reaches Southcentral Alaska by Tuesday afternoon. As it stands for
Tuesday afternoon, the role of downsloping winds in the Anchorage
area is in question which muddles the confidence regarding
additional snowfall amounts at that time.

&&

.AVIATION...

PANC...Predominant IFR vis ranging from 1-3 SM due to light
snow, with intermittent periods of MVFR and LIFR visibilities to
continue through early this morning. Lingering MVFR cigs expected
to lift to VFR cigs by later this morning. Snowfall is expected to
diminish by late morning Monday. Steady northerly flow to persist
through the period.

&&

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

Snowfall is lingering across the Anchorage area this morning.
This is still expected to taper off throughout the morning. Breaks
in the clouds may even be possible later this afternoon. The peak
of the cold air advection is over. Extreme freezing spray will
remain possible through Kamishak Bay and the Barren Islands
through this morning but conditions should see gradual improve
with a brief lull in the weather. A return to south to
southeasterly winds will begin to ramp up after midnight into
Tuesday morning.

Around midnight into Tuesday morning, a front from an occluded
low out west will bring strong southeasterly winds and
precipitation to Kodiak Island. It should initially be cold enough
for snow at first. A brief period of heavier snowfall with
reduced visibility is possible. Going into later Tuesday morning,
relatively warmer air will start to nose into Kodiak. It will
generally remain near freezing enough for precipitation to be
mostly snow, but a mix of rain and snow will be possible. As
strong west to southwesterly winds move across the Island, some
downsloping may occur to cut off precipitation, and a brief period
of warmer temperatures could mix down.

While there will be warmer air advecting across at least the
coastal areas of Southcentral, much of the precipitation is
expected to remain as snow. Uncertainty in the forecast increases
as the low moves into Southcentral as well, particularly in the
accumulation of precipitation and how much downsloping will occur
on the lee of the Kenai and Chugach Mountains into Anchorage and
Kenai. The potential for snow to fall in Anchorage is possible
Tuesday morning however, but accumulations are expected to light.
Precipitation chances taper off again for Wednesday.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3: Today
through Thursday)...

A shortwave upper-level ridge builds into the Southwest Mainland from
the southwest through most of the day today, promoting clearing
skies and drier conditions. A front extending from a North
Pacific low lifts to the Alaska Peninsula later this morning and
early this afternoon, spreading precipitation and elevated winds
to the area. The front will track to the northeast, and winds and
precipitation with the front will weaken over the Bristol Bay
region starting Tuesday morning. An upper-level ridge will build
across the region from the Bering, tapering off any lingering
precipitation and promoting dry conditions for most of Wednesday
and Thursday.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 to 3: Today
through Thursday)...

A North Pacific low continues to approach the Aleutian Chain this
morning while pushing its front northward across the Central and
Eastern Aleutians. The core of strongest northeasterly winds are
currently located to the west of Adak. The front will lift
northward to the Pribilof Islands early this morning, promoting
snow and gusty northeasterly winds. Blizzard conditions are
expected to develop this morning and persist into Tuesday morning as
strong winds and snowfall wrap around the north side of the low.
For the rest of Tuesday, the low will weaken as it continues
tracking to the east, with the center remaining south of the
Aleutian Chain and the front tracking into Southwest Alaska. The
next feature of note is a strong Kamchatka low that pushes its
front northeastward across the Western Aleutians by Tuesday
afternoon. The front lifts across the Central Aleutians and
Western/Central Bering on Wednesday morning and then to the
Eastern Aleutians and Bering by Thursday morning. The low itself
is advertised to near the Western Aleutians on Wednesday but then
remain nearly stationary Thursday. With this system's front, the
strongest easterly winds are expected across the Western Aleutians
from Tuesday afternoon through Tuesday evening.

&&

.LONG TERM FORECAST (Days 4 through 7: Thursday through
Sunday)...

At the onset of this forecast period, expect a highly amplified
pattern with the trough axis near the western Aleutians. Expect a
series of strong lows forecast to track across the region. There
is model divergence that increases with time. But there are some
trends. The Gulf of Alaska continues to look active. Out west, a
low near Kamchatka, potentially as deep as 952 mb, pushes a front
into the central and eastern Aleutians on Thursday. The ECMWF and
the Canadian bring the remnants of this front into Southwest AK
on Friday. A new surface low forms south of Adak on Friday. The
GFS is the outlier. With a potentially strong low pressure at the
surface portions of Alaska will receive gusty winds and light to
moderate precipitation. This appears most likely for the Aleutians
but it is becoming more likely for the southern coast as well,
dependent on the eventual storm track. Additionally, expect a
series of shortwaves embedded in the long wave pattern that will
influence the sensible weather.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...High Wind Watch 191
		 Blizzard Warning 195.
MARINE...Heavy Freezing Spray Warning 121 129 130 131 132 137 139
									  140 141 150 160 179 180 185
									  412 414.
		 Storm Warning 130 175 177 178 413
		 Gale Warning 119 120 131 132 138 139 150 155 160 165 170
					  174 176 179 180 351 352 411 412 414
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...CL
SOUTHCENTRAL ALASKA...VR
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...AF
LONG TERM...PS