Gale Warning 148, NWS Anchorage, AK

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

.ANALYSIS AND UPPER LEVELS...

The previous trough that brought snow to Southcentral is shearing
out with the energy sliding to both the Panhandle and Bering
Strait region. Arctic air flowing through the gaps of the Alaska
Range is bringing gustier winds from Seward through Whitter.
Otherwise, one major feature remains over our area of responsibility,
a large mature storm system south of the Aleutians between Atka
and Unalaska. The front associated with the system is currently
bringing blizzard conditions to the Pribilof Islands, as well as a
period of heavy wet snow for the Unalaska area earlier today. The
front has a good fetch of sub-tropical moisture with around one
inch of precipitable water detected by satellite, which is 200% of
normal for this time of year. Given the extent of the arctic air
mass over the area, the warm sector of the system is sliding to
the east keeping snow in the area as opposed to rain.

&&

.MODEL DISCUSSION...

There is good agreement among models today as the upper level and
lower level features have peaked in intensity and are weakening.
The front over the Aleutians slides onto the southwestern Mainland
and the Gulf through Tuesday. Attention then turns to an extremely
strong storm system in the northwestern Pacific Ocean, where
guidance is in good agreement with a sub-940 mb low. The
associated front will affect the western Aleutians on Tuesday,
sliding eastward through the week. Later in the week model
agreement gets a little messier but the general consensus is that
a new disturbance riding the front will spin up a new circulation
in the eastern Bering Sea on Thursday.

&&

.AVIATION...

PANC...VFR conditions and light winds will persist. There is a
chance for fog and lower ceilings for a short period late this
evening into Saturday morning. Fog and stratus formation is lower
confidence, but winds are going to be light and skies clear which
make it more likely. However, winds are going to be shifting to
the north in response to the incoming front/low which should limit
how long fog does stick around.

&&

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

An unsettled but benign pattern is expected across Southcentral
over the next few days. A front will move across the region
Tuesday afternoon and bring another round of snow. As of now,
less than one inch of snow is expected in Anchorage. The highest
snowfall accumulations are expected across the Chugach Mountains
near Prince William Sound. Snow will then taper off Tuesday night
into Wednesday morning across Southcentral.

The other story is the winds in Passage Canal will continue to
ease this evening and tonight. Otherwise, no additional significant
weather expected.

&&

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

A switch from the bitter cold to a bit more seasonable temperatures
will begin to take place between tonight and tomorrow, but not
without a return to more snow and gusty wind for many. A front
stemming from a now weakening but still storm force low over the
Aleutians will make its approach into the northern Alaska
Peninsula and towards Bristol Bay tonight, sending another round
of snowfall inland as east to northeast winds begin to pick up and
become gustier near the coast. Areas of blowing snow and reduced
visibility will be likely as the front moves in with the strongest
winds, but this should improve as the front weakens throughout
the day on Tuesday and winds begin to relax. By Tuesday evening,
the low will shift towards the northern Gulf as a shortwave ridge
moves in from the west, allowing for snow to end from west to east
and even partially clearing skies. Between Wednesday afternoon
and Thursday, yet another front from the Bering will push onshore
with additional accumulating snowfall across much of the outlook
area. Fortunately, this front will be weakening rapidly on
arrival, resulting in low potential for blowing snow and keeping
accumulations light.

&&

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

The parade of powerful lows/fronts across the Bering is set to
continue full steam ahead through Thursday. In the near term,
blizzard conditions will continue unabated across the Pribilof
Island tonight. Improvement is not expected until the weakening
but still storm force low and occluded front shifts towards the
Alaska Peninsula, allowing falling snow to retreat to the
southeast and winds to finally drop off. Further south across the
central/eastern Aleutians, the heavy snow observed earlier today
has since changed over to rain showers, with winds now much
weaker near the stacked low's center. Gusty north winds at gale
force range will progress east across the Aleutian Chain through
Tuesday evening as the low shifts into the Gulf, with cooling
temperatures shifting any falling precipitation back over to snow.

Attention then quickly shifts back to the western Aleutians, with
a potent front expected to push into the region in association
with a rapidly deepening low bottoming out in the 930-940 mb range
south of Kamchatka. Sustained storm force winds will move in
coincident with heavy snow, resulting in a period of blowing snow
and significantly reduced visibility before temperatures warm and
allow snow to mix with rain Tuesday evening. A Winter Storm
Warning (replacing the High Wind Watch) has been issued for the
western Aleutians beginning late Tuesday morning for the
combination of snow, blowing snow and high winds.

On Wednesday, the front will continue across the Aleutian Chain
and reach the Pribilofs, with the preceding cold again resulting
in a transition from snow to rain as the front moves across. It's
looking more likely the warm air will not reach far enough north
to change precipitation type over across the Pribilofs, resulting
in a return threat for significant snow and blowing snow along the
front. Unsettled conditions will continue behind the front on
Thursday, with yet another frontal system and warmer air set to
cross into the Bering with more rain, snow and wind.

&&

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

At the beginning of the forecast period, the jet stream looks like
it will move from the northern Pacific and cross near the eastern
Aleutians and northeast towards the southern mainland and northern
Gulf of Alaska. This will drive a low pressure system into the
northern Bering on Friday which could potentially bring strong
winds along the Kuskokwim Delta as well as blowing snow with
possible blizzard conditions. The occluded front with this low
will impact much of the southern mainland with snow on Friday
and Saturday. There is some model differences with this system,
especially with surface winds, however, it looks like there is
a good chance of snow across Southwest and Southcentral Alaska.
As we head into Sunday and Monday there is a bit more model
disagreement, but the trend is for continued southwesterly flow
across the southern mainland with short-waves bringing chances
of snow. Otherwise, there is no indication of any strong systems
with a more amplified pattern developing by Monday with a ridge
building over the Bering Sea and Aleutians and deepening lows/
troughs over the northwest Pacific and Gulf of Alaska.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Winter Storm Warning 191.
         Blizzard Warning 195.
MARINE...Heavy Freezing Spray Warning 121 129 130 139 140 150 160 165
                                      179 185.
         Storm Warning 175 177 178.
         Gale Warning 119 130 131 138 139 150 155 160 165 170 172 173
                      174 176 179 180.
FIRE WEATHER...NONE.

&&

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