High Wind Warning 7, NWS Anchorage, AK

815 
WWAK72 PAFC 281758
NPWALU

URGENT - WEATHER MESSAGE
National Weather Service Anchorage AK
858 AM AKST Tue Feb 28 2023

AKZ195-281900-
/O.EXP.PAFC.HW.W.0007.000000T0000Z-230228T1800Z/
Pribilof Islands-
Including the city of Saint Paul
858 AM AKST Tue Feb 28 2023

...HIGH WIND WARNING WILL EXPIRE AT 9 AM AKST THIS MORNING...

Strong winds will continue through Wednesday.

$$

For more information from the National Weather Service visit
https://weather.gov/afc

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
656 PM AKST Mon Feb 27 2023

.ANALYSIS AND UPPER LEVELS...

In the upper levels the jet stream is pumping warm, moist air
across the Bering and Aleutians ahead of a low pressure system
that is currently moving across the Bering. This system is
producing gale force winds across the Bering and Pribilofs with
snow changing to rain. The trailing cold front across the
Aleutians is producing periods of rain. Across the southern
mainland a broad ridge is producing mostly clear skies with high
clouds increasing from the west.

&&

.MODEL DISCUSSION...

Models are in good agreement today, but then quickly diverage with
a triple point low forming across the western Gulf. At 500mb the
GFS, EC and GEM have a shortwave moving across the Gulf becoming
negatively titled Wednesday morning while the NAM is more
progressive with no negative tilt. At the surface all the models
have an elongated area of low pressure just east of Kodiak Island
and extending south of the AKPen Tuesday afternoon. Tuesday night
into Wednesday the models form on stronger consolidated low
moving east of the Kenai Peninsula and then towards the northern
Gulf hugging the coast line near Cordova. The NAM is the fastest
and farthest east with the GFS the slowest of the bunch, with the
EC and GEM somewhere in between. This low track will affect the
snowfall amounts and location of heaviest snowfall in the
deformation band. The GEFS and GEM ensembles show similar tracks
and timing, so we have opted to a blend of the GFS and GEM.
Another potential issue is both the GFS and GEM show the low
pressure stalling out across the northern Gulf near Prince William
Sound with lingering light snow Wednesday and Thursday which
could potentially bring several more inches of snow to Anchorage
and the MAT valley.

&&

.AVIATION...
PANC...VFR conditions and light winds will persist through
tonight. High clouds will increase tonight ahead of the next storm
system with ceiling and visibility decreasing to MVFR and possibly
IFR as snow develops tomorrow morning with up to 4 inches of
snowfall through the day on Tuesday.

&&

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

Gap winds along the north Gulf coast will diminish gradually this
evening as a large low pressure system approaches from the west,
shifting low-level winds out of the south. Clear, cold conditions
will continue, at least through the evening hours, before a shield
of cirrus begins to overspread Southcentral tonight out ahead of
the low's approaching front. The occluded front pushes across
Kodiak Island early Tuesday morning as easterly winds and snow
develop ahead of the front. The snow will change over to rain
across the island through Tuesday morning as the front lifts north
and warmer air filters in. A triple point low is then expected to
develop along the front northeast of Kodiak Island and move
toward Prince William Sound by Tuesday afternoon. Snow will
progress toward the mainland Tuesday morning, with an atmospheric
environment primed for snow production.

While upper-level dynamics are not particularly pronounced over
Southcentral on Tuesday, copious moisture streaming into the
region on southwesterly flow and a deep dendritic growth layer
through the atmospheric profile is expected to amount to a light,
fluffy snow going into midday Tuesday. By the afternoon, a
downslope hole starts to develop while the front weakens, causing
snow intensity to lighten or even stop for locations west of the
Chugach Front Range and the Kenai Mountains. Before this lull sets
in, the Anchorage Bowl should see 2 to 4 inches of snow, with
accumulations closer to 6 inches for the western Kenai Peninsula.
Light snow is likely to persist into the evening further from the
mountains, near Cook Inlet along the western Kenai Peninsula,
where localized accumulations may begin to approach a foot.
Additionally, strong southeasterly winds are expected to develop
through favored gap locations, with gusty winds likely for
Whittier, Portage Valley, and into Turnagain Arm. This is expected
to produce whiteout conditions through the Portage Valley and
eastern Turnagain Arm areas, for which a Blizzard Warning has been
issued.

Tuesday afternoon, uncertainty increases, with two distinct
solutions possible. With the first, the triple point low
strengthens and continues to push eastward, leading to a
continuation of Tuesday afternoon's conditions into Wednesday
morning before the low exits to the east and snow ends rather
quickly from west to east across Southcentral. With the second
solution, a strong shortwave lifting out of the North Pacific
intensifies a weak surface trough into a closed low south of
Kodiak Island. This low tracks south of the Kenai Peninsula by
Wednesday morning, and contributes to another round of heavier
snow over the western Kenai Peninsula and potentially northward
into Anchorage on Wednesday. This forecast package sides closer
to the second solution based on the reasoning that the stronger
shortwave is more likely to assist the development of the western
low compared to the eastern one, which is much further away.
However, confidence in this solution winning out is still low.

Going along with this thinking, the heaviest snow tapers off
Wednesday afternoon across the Kenai Peninsula and Anchorage after
producing a widespread 6 to 12 inch amounts in the western Kenai
Peninsula, with locally higher amounts for the immediate west
coast along Cook Inlet. Tuesday through Wednesday, Anchorage may
see 4 to 8 inches of snow in total, with a bit less for the
Matanuska Valley, but these values may still vary with changes in
expected storm track. Cordova, Valdez, and the portions of the
Copper River Basin could also see storm total amounts ranging from
6 to 12 inches.

A return of colder air and gusty outflow winds is then expected
for the latter half of the week as the low exits the region.

&&

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

An active weather pattern is expected across Southwest Alaska as a
storm system moves across the area on Tuesday. Snow along with
strong winds will reduce visibility across the area. A Blizzard
Warning is in effect for the Kuskokwim Delta and Winter Weather
Advisories for Bristol Bay and the lower Kuskokwim Valley for
Tuesday. Conditions will then gradually ease Tuesday night into
Wednesday across the region from west to east.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 3)...

A large storm system will continue moving over the Bering Sea
through Wednesday evening. This storm system will produce
widespread gale and storm force winds. Conditions will then ease
Wednesday evening and night, however a second low will bring gale
force winds to the Aleutians on Thursday into Friday.

&&

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

Models have come into better agreement for the long-term in terms
of synoptic features, but are still struggling with the finer
details. By Friday afternoon the leading front of a northern
Bering low approaches Southwest Alaska. This front will bring
widespread light showers from the Kuskokwim Delta, to the Lower
Kuskokwim Valley and Greater Bristol Bay region through Saturday
afternoon. This wave is expected to break-up along the Alaska
Range, and not extend into Southcentral. High confidence is had
that a ridge of high pressure will build over the Mainland and
bring warmer temperatures to Southwest. These temperatures may be
moderated by shortwaves that traverse over the ride near the
Kuskokwim Delta/Valley, but the Bristol Bay region and AKPen are
expected to be "warmer". The aforementioned ridge will also aide
in keeping much of the activity out of Southcentral during this
period. Late Saturday evening a North Pacific low will surge
towards the Western/Central Aleutians, bringing widespread light
precipitation and southerly gales from Adak to Unalaska lasting
until Sunday morning. Precipitation associated with this system
will likely be blocked to the east, with only a few showers
possibly reaching the Southwest coastline late Sunday morning.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Blizzard Warning: 125
		 Winter Weather Advisory: 121
MARINE...Storm Warning: 119, 120, 125, 170, 175, 177-179, 181,
						411-414
		 Gale Warning: 125, 130, 131, 139, 150, 155, 160, 165,
					   171-174, 176, 180, 185, 351, 352
	     Heavy Freezing Spray: 126-128, 130, 139, 160, 180, 181,
							   185, 414
FIRE WEATHER...NONE.

&&

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