Gale Warning 230, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
530 AM AKST Mon Mar 4 2019

.ANALYSIS AND UPPER LEVELS...
The mature low that has been the main weather producer over the
past day continues to weaken this morning as it pushes into the
northern Bering. The associated occluded front has pushed eastward
and made its way over Southwest and the AKPEN. Southerly flow
with strong gusts continue as the front moves over land near the
Kuskokwim Delta coast. The latest ASCAT/Advanced Scatterometer
pass continues to detected gales over the Bering in association
with this low. A ridge setup over Southcentral and the Gulf has
amplified as it has shifted slightly eastward since yesterday. Fog
has settled in overnight along the Kenai Peninsula, reducing the
visibility. Mostly overcast skies remain under this ridge
stretching from Kodiak Island to Cordova, with temperatures
hovering around the freezing mark for many locations in Southwest.

&&

.MODEL DISCUSSION...
The NAM12 and the GFS both initialized well when comparing the
surface low position from the ASCAT which was NE of Kamchatka to
the progged surface low position at the commensurate model time.
The NAM, GFS and ECMWF are in good agreement with the major
synoptic features through 00z Thursday. An additional confidence
boost comes from the GFS ensemble members which are tightly
clustered with the current Bering low and the next cyclone coming
up from the NW Pacific. There do appear to be some timing issues
with the next precipitation shield moving up Cook Inlet on
Tuesday.

&&

.AVIATION...
PANC...The latest GOES Nighttime microphysics clearly has an area
of fog and low stratus over portions of Cook Inlet, Knik Arm and
Turnagain Arm. Cigs are going to be an issue this morning. As of
13Z or 4 AM AST the ceiling at PANC was SCT006 BKN040 OVC070, at
Kenai it was BKN024 and at Merrill Field it was OVC008. The light
winds will persist. At times, the cigs at PANC will drop below
VFR.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
A weak upper level ridge will be over Southcentral today. This
will keep conditions dry, but with some variable cloudiness. A
trough will approach the area from the west tonight. This system
is slowing down as it moves into the ridge. Precipitation chances
will move into Kodiak Island and the southern Kenai Peninsula by
late evening, then spread northward across the Kenai Peninsula and
into the Susitna valley on Tuesday. The flow aloft will be almost
directly from the south, so the Anchorage area and the Matanuska
Valley will likely remain dry. The front edge of the
precipitation will stall Tuesday night with precipitation chances
limited to areas from Prince William Sound westward, even as the
upper level trough continues to move eastward and weaken.

&&

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

A stalled front over southwest Alaska, Bristol Bay, and the
Alaska Peninsula continues to bring precipitation to the Kuskokwim
Delta this morning. It is mainly a rain/snow mix, with rain
further south and west along the coast, and snow further north.
Any snow is falling into temps at or a degree or so above
freezing, so no significant accumulations are expected. The front
is expected to remain stationary through the day, but as a low
tracks north between the Pribilofs and Nunivak Island this
afternoon and evening, a slow eastward motion will resume, along
with intensifying precipitation rates across many of the same
areas. The focus of the precipitation will move east during the
day on Tuesday with a continuous southerly flow along the front
largely keeping precipitation in the liquid form. Gusty winds are
expected through the Kamishak Gap and Lake Iliamna Monday night
into the day Tuesday. As a secondary cold front follows behind the
stationary one over southwest Alaska Tuesday night, that extra
push should help get the steadier precipitation mainly over the
Alaska Range by Wednesday morning. Much of southwest Alaska dries
out for the day on Wednesday, but the next front bringing more
precipitation follows right behind it Wednesday night. Currently
it appears that since it will be replacing a colder air mass than
the one over the area now, expect significantly more of Southwest to
be seeing snow with that next front late Wednesday night into
Thursday.

&&

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

The stalled front over the eastern Bering will slowly move east
later today as a low develops near or over the Pribilofs this
afternoon. Once the low moves west of Nunivak Island this evening,
the westerly winds behind the low will push the front into
Bristol Bay and southwest Alaska. The remainder of the Bering is
under a showery regime with broad westerly winds across the
southern Bering and Aleutians. This pattern will continue over the
central and eastern Bering through Tuesday.

The next strong low will barrel towards the western Aleutians
Tuesday afternoon. The low will produce another round of storm
force winds across the western and central Aleutians Tuesday
evening. The center of the low will slowly cross the western
Aleutians by Wednesday afternoon, as the leading front moves into
the eastern Aleutians and the Pribilofs. The leading front will
weaken to gale force winds, but to the south of the center of the
low Wednesday evening, storm force winds with hurricane force
gusts are expected over the western and central Aleutians.
Fortunately those worst conditions are expected to mainly stay
from Adak west as the low pressure center moves into the western
Bering. The leading front will move into the eastern Bering and
approach the southwest coast late Wednesday night.

&&

.MARINE (Days 3 through 5)...
A storm force front enters the western Bering on Wednesday with
the surface low deepening to 952 mb as it crosses into the
southern Bering Thursday morning. The low then fills rapidly and
is absorbed by the next powerful North Pacific storm which moves
across the Chain by Friday afternoon. This fast paced storm pushes
its front to the eastern Bering by late Friday. Monitor this
system as it is expected to bring significant winds and waves
during the second part of the week as the subtropical jet noses
toward the Alaska Peninsula.

&&

.LONG TERM FORECAST (Days 3 through 7)...

The long range forecast beginning Wednesday marks the beginning
of a synoptic pattern shift that breaks down the upper level split
flow pattern...where the ridge is currently dominant over Yukon
and Alcan border. This change is onset due to the combination of
strong storms moving along the Bering while the subtropical jet
streak noses to the Alaska Peninsula toward the end of the week.
The forthcoming changes in the storm pattern will bring higher
chances for precipitation across the southern mainland and
surrounding waters along with gusty winds as the storm generally
tracks to the Southwest coast at the end of the week and pushes
its front eastward next weekend.

Models are in good agreement with this overall synoptic shift;
therefore, a blend of the ECMWF and GFS ensembles were used to
make extended updates today.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gales 177 178.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...ALH/PJS
SOUTHCENTRAL ALASKA...BL
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...JPW
MARINE/LONG TERM...KH