Gale Warning 298, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
424 AM AKDT Mon Apr 8 2019

.ANALYSIS AND UPPER LEVELS...

A vertically stacked low continues to rotate south of the central
Aleutians, with the associated front bringing precipitation to
the central and eastern Aleutians this morning, while on the back
side of the low the western Aleutians, including Shemya are seeing
snow showers in cold air advection. Downstream, shortwave ridging
has set up over the AKPEN, while high pressure over northeast
Alaska, a low in the Gulf, and low pressure over the eastern
Bering support a deformation zone over Southwest. Associated
showers have developed over the Southwest mainland, mainly in the
Bristol Bay area though some radar returns can be seen along the
Kuskokwim Delta coast and in the lower Kuskokwim Valley. The low
in the Gulf continues to bring showers to the northern Gulf,
Prince William Sound, and eastern Kenai Peninsula, while farther
north in the Anchorage Bowl and Mat-Su Valleys the only impacts of
the low are areas of high clouds.

&&

.MODEL DISCUSSION...

Models are in generally good agreement through today, then diverge
somewhat Tuesday into Wednesday regarding the next low approaching
the western Aleutians. Of note, the 00z runs of the EC and GFS
have come into much better agreement, showing one low center while
several previous solutions divided the energy into multiple weaker
lows. So while confidence is growing that there will be areas of
gales, maybe even storm force winds over parts of the Aleutians
and Bering, there continues to be uncertainty in the exact
location/timing.

&&

.AVIATION...
PANC...VFR conditions and light winds will persist. Showers are
possible tonight as a front passes through, but there is
uncertainty with timing.

&&

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

The front draped along the northern Gulf and Prince William Sound
remains stationary through this afternoon and then pushes inland
late tonight. Gusty winds and rain are expected along the
boundary...except snow for elevations over 2,000 ft. Winds across
Turnagain Arm and the Anchorage Hillside should continue to stay
gusty through Tuesday afternoon as the pressure gradient tightens
between a ridge across the northeast Gulf and low pressure over
the Southwest mainland. The pressure gradient slackens Tuesday
evening as the ridge and low pressure pull toward the interior.

The next front moves to the southern Gulf Monday night, with quick
progression to the northern waters by noon on Tuesday. The
associated low center stays on an easterly track and fills as it
nears the Panhandle on Tuesday night.

The next system to monitor, for gusty winds and rain, crosses to
the Bering Wednesday morning as a 957 mb low. This storm pushes a
fast moving front across the Gulf on Wednesday with northward
progress through Thursday.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3)...
The deformation zone will linger over southwest Alaska today
bringing light precipitation to the area that will transition
more to rain heading into the afternoon. Precipitation will taper
down on Tuesday as the deformation zone diminishes. On Wednesday a
front will move in over the area from the southwest bringing rain
and strong, southeast winds to the region. The strongest winds
will be along the coast and through channeled terrain with gusts
to around 50 MPH. The rain and winds will spread farther inland
through the day on Wednesday.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3)...
The weak low south of the central Aleutians will continue to track
east as it weakens before diminishing tonight. As it passes it
will bring light precipitation to the central and eastern
Aleutians. On Tuesday a North Pacific low will approach the
central Aleutians bringing strong winds and rain to the Aleutians.
Models are in much better agreement with this system giving
higher confidence in gale force winds moving through the Aleutians
and into the Bering. These strong winds will continue for the
Bering and Aleutians through Wednesday as the low center moves
into the southern Bering.

&&

.MARINE (Days 3 through 5/Wednesday through Friday)...

...Aleutian Coastal Waters and the Bering Sea...
There is increasing confidence of deteriorating conditions by
Wednesday with building winds and waves as a 960 mb North Pacific
low approaches the central Aleutians. There is still some
uncertainty regarding the track and intensity of the system but
gales are likely to develop near the central Aleutians and the
southern Bering as well as parts of the eastern Bering. Seas could
build to over 30 ft on the Pacific side of the central Aleutians
with potential storm force winds developing in this areas by
Wednesday evening. This is a significant change from the previous
day's forecast where the highest winds and waves were over the
western Aleutians and Bering for the later half of the week.

...Gulf of Alaska...
 A front pushing east across the Gulf will increase winds and
waves during the day on Wednesday through Friday, though winds
should remain mostly sub-gale force. There could be some gale
force winds developing Wednesday night to Thursday through the
Barren Islands and along the North Gulf coast, but not expected to
be very widespread. Seas are expected to steadily build through
the end of the week over the open Gulf, with swells approaching
20 ft over the southern half of the Gulf due to a persistent
southwest fetch of 25-30 kt winds.

&&

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

A change to a more unsettled pattern is expected as a dominant
upper low develops over the Bering by mid-week. This will act to
reposition the major storm track north into the mainland. The
upper low will support a strong North Pacific surface low moving
into the Bering by Thursday with its associated front sweeping
east across Southcentral through the end of the work week. This
will increase cloud cover over the southern mainland and bring
periods of heavy precipitation to coastal areas as well as parts
of the southwest mainland, though it looks like inland/downsloped
locations across Southcentral should remain mostly dry.

Quite a bit of uncertainty creeps into the forecast by next
weekend with the GFS/EC differing on how the Bering low exits the
region. The GFS solution brings the low southeast into the
southern Gulf, potentially bringing a few decent days of weather
next weekend, while the EC keeps the low farther west near the
Y-K Delta, which would lead to more onshore flow and unsettled
weather over the southern mainland. Another strong North Pacific
low enters the Bering by Sunday and pushes east towards the
mainland, though models are nearly 24 hours apart in the timing of
the system at this point.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gales: 119
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...MM
SOUTHCENTRAL ALASKA...KH
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...DK
MARINE/LONG TERM...KVP