Gale Warning 104, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
513 PM AKST Mon Feb 20 2023

.ANALYSIS AND UPPER LEVELS...

In the upper levels the jet stream extends south of the Aleutians
and east towards Southeast Alaska. An upper level ridge is
dominating the southern mainland with areas of fog and stratus
across Cook Inlet, the Knik and Turnagain Arms and across the
Copper River valley. Most of the fog has lifted but stratus
remains in place. A couple of shortwaves across the AKPen and
Southwest Alaska are moving northeast and weakening with brief
periods of enhanced winds and scattered showers. A stronger low
pressure system is lifting out of the northern Pacific towards
the western and central Aleutians with increasing south to
southeast winds at Shemya and Adak. Otherwise areas of stratus are
located over Southwest Alaska.

&&

.MODEL DISCUSSION...

Models are in fairly good agreement with the synoptic scale
features, but show some differences in the details of the smaller
scale features. The main challenge out west initially will be
determining if high winds will occur across the Pribilofs tonight
and tomorrow morning. While across Southcentral fog and stratus
will pose problems Tuesday morning as well as a shortwave moving
across the area Tuesday evening through Wednesday morning with
chances of light snow. Most models are showing brief periods of
light snow but differ on the timing and coverage, so this lends to
lower forecast confidence. Otherwise, two strong low pressure
systems will move across the Bering Tuesday and Wednesday which
will pose Ptype challenges for Southwest Alaska.

&&

.AVIATION...
PANC...VFR conditions with light winds are expected through this
evening with a chance of fog and stratus moving off of the water,
which could bring periods of IFR conditions after midnight into
the morning hours on Tuesday.

&&

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

A quiet weather pattern will persist across Southcentral for
Tuesday and the first half of Wednesday. Clouds will increase
Wednesday afternoon as the upper level ridge shifts eastward and
the subsidence associated with this upper level ridge ceases.
Forecast confidence decreases Wednesday evening and remains low on
Thursday with respect to forecast specifics. The general trend is
snow will move across the region Wednesday afternoon and taper off
Thursday morning and afternoon. Confidence remains low with
respect to exact forecast snowfall amounts, though there is
confidence that the highest accumulations are expected across the
Hatcher Pass area.

&&

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

A ridge of high pressure over the Southwest mainland will slowly
shift eastward midweek. Meanwhile, low stratus and fog trapped
underneath the ridge will likely stay overnight. For the rest of
the workweek, an active weather pattern is getting underway as a
series of storm systems impacts western Alaska. The first system
is associated with a North Pacific low approaching from the Bering
into the Chukchi Sea early Tuesday. Daytime temperatures will
increase into the mid to high 30s as gusty southerly winds move
into the region. Precipitation with this system will spread over
the Kuskokwim Delta and Bristol Bay between Tuesday and Wednesday.
The region will initially start out as snow before warmer air
results in snow mixing with or changing to rain. However, there is
still some uncertainty about the initial colder air in place,
leaving a small chance of freezing rain early in the morning on
Wednesday.

After this system pushes northward, the next warmer system
arrives shortly afterwards on Wednesday. Daytime temperatures will
be in the mid 30s to low 40s along with gusty, southwest winds.
Precipitation type is likely to be be rain as the atmospheric
column of air warms above the surface for the entire forecast
area. Rain will be more widespread for the low-lying regions
through Thursday evening. As the system exits the region, cold,
dry conditions returns as a weak ridge moves overhead later this
week.

&&

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

The main weather feature is associated with a strong North
Pacific low approaching the western Aleutians. The leading frontal
boundary will overspread the region, bringing elevated seas,
heavy precipitation, and widespread gale force winds, with
localized areas of storm force winds. The strongest core of winds
are expected Monday night through early Tuesday morning for the
central Aleutians as the wind direction shifts to the west-
southwest. A High Wind Warning remains in effect from midnight
tonight to 9am Tuesday. Precipitation type will predominately be
rain as the atmospheric column of air warms above the surface.

As the low lifts northward on Tuesday, the Pribilofs can see
increasing southerly gales to storm force winds and precipitation
as well. There is moderate confidence that the region could
reach hurricane force gusts as a cold, unstable air wraps around
the low. A High Wind Warning remains in effect from 3am to 6pm
AKST Tuesday.

Conditions are expected to improve briefly Tuesday followed by a
second system arriving in the evening. This system will bring
another round of rain and southerly gale force winds between
Tuesday night and Thursday. Conditions will slowly improve for the
rest of the week as a weak ridge of high pressure moves overhead.

&&

.LONG TERM FORECAST (Days 4 through 7: Friday through Monday)...

Model disagreement is becoming more noticeable by the end of the
week towards Friday, but the overall trend towards much colder,
drier conditions developing across most of the southern Mainland
going into the weekend still looks probable. The GFS in particular
appears to be struggling with the interaction between a shortwave
trough diving southeast across the Alaska Peninsula and a separate
low set to be entering the Gulf on Friday and Saturday. The 12z
GFS is depicting partial trough phasing between these upper
features, resulting in a much deeper low compared to other
solutions developing over the Gulf through Saturday. Aside from
the apparent outlier scenario in the GFS across eastern parts of
the outlook area, models are in good agreement for a much colder,
drier period to take shape across most of Southcentral and
Southwest this coming weekend, as an Arctic air mass filters in
from the northwest under deep synoptic troughing developing
aloft. Out in the west, another potent gale to storm force low
will traverse the Bering from west to east as it rides around a
flat longwave ridge. Most solutions show the low weaken rapidly as
it moves downstream from the strengthening ridge and as it
crosses the southern Alaska Peninsula late on Saturday, keeping
broader impacts from this system limited more to the Aleutian
Chain and Pribilofs.

Looking out towards the start of next week, solutions are
continuing to key in on another much stronger system entering the
western Bering by late Sunday into Monday. This pattern is
beginning to look almost like a 'reset' back to what we will see
unfold over the next few days, with a strong ridge over the Bering
again shifting towards Southwest while another deep low pressure
moves into the Bering in its place. While the exact details for
this next system well out in time are unsurprisingly not well-
defined, it's becoming more likely for another very deep low to
cross the northern and western Bering between Sunday and Monday. A
strong trailing front could approach Southwest with increasing
potential for strong winds and heavy precipitation by Monday.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...High Wind Warning: 187, 195.
MARINE...Storm Warning: 170, 173-177, 179, 412-414.
		 Gale Warning: 165, 172, 178, 180, 181, 185, 351-352, 411.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...RC
SOUTHCENTRAL ALASKA...ED
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...MF
LONG TERM...AS