Gale Warning 502, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
457 AM AKDT Mon Oct 21 2019

.ANALYSIS AND UPPER LEVELS...
A large upper level low continues to be centered over the Bering
with numerous shortwave troughs rotating around it. The most
organized of these troughs is vertically stacked with a surface
low located over the eastern Bering to the west of Bristol Bay
with an associated surface front rotating across the Alaska
Peninsula and on to the southwest Alaska coast. Additional
shortwaves are rotating south through the western Bering and east
across the central Aleutians with a stronger shortwave and
developing surface low well to the south over the north Pacific.
Another trough is lifting to the north-northeast across the Kenai
Peninsula while a stronger low south of the central Gulf tracks to
the northeast.

&&

.MODEL DISCUSSION...
Models continue to be in good agreement regarding the larger
scale synoptic features but struggle to resolve all of the weaker
small scale troughs rotating through the broader flow. Model
agreement continues to improve regarding the handling of the
strong low Tuesday night through Wednesday with the mean track
slightly further east as compared to the model runs last night.

&&

.AVIATION...
PANC...Showers moving through the area early this morning may
reduce ceilings to MVFR at times...otherwise conditions are
expected to remain VFR through today through tonight. There is a
chance of patchy fog forming Tuesday morning as skies clear,
however confidence in this is low.

&&

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

Light precipitation is moving over Anchorage and the Mat-Su this
morning as a weak shortwave trough moves over the region. Current
temperatures are above freezing in Anchorage, thus precipitation
is all rain. However, temperatures have dropped below freezing in
the Knik and Eagle River Valleys which could lead to potential
intermittent freezing rain and slippery roads in those areas early
this morning. Light snow is possible along the Parks Highway
generally north of Willow. Precipitation will taper off by this
afternoon and partly to mostly cloudy skies will persist though
Tuesday.

A strong low will move into the southwestern Gulf on Wednesday
bringing strong south to southeast flow and potentially heavy rain
for Kodiak and coastal areas along Prince William Sound. Waves
will also increase to near 40 feet across the southern Gulf
waters. Much of the Interior Kenai Peninsula and Anchorage Bowl
should remain dry in cross-barrier flow. Winds will also ramp up
along the Turnagain Arm, the Anchorage Hillside, and the Matanuska
Valley starting late Tue night and peaking during the day Wed.
For now, it looks like winds will peak near Warning level (75 mph)
over the Turnagain Arm, so we will be monitoring this closely for
a potential High Wind Watch.

&&

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

Clear conditions overnight along with light winds have caused
widespread fog to form across much of the Kuskokwim Delta and
Bristol Bay this morning. Areas near Bethel have experienced
visibilities less than a mile for much of the overnight hours,
which should improve throughout the late morning hours. Light rain
showers will continue across Southwest through Tuesday morning,
associated with a front moving inland from a low in the eastern
Bering.

Winds begin to increase on Tuesday afternoon across the Southwest
mainland as the next system moves into the area. This North
Pacific low will move to the AKPEN Tuesday afternoon, spreading
widespread rain as it lifts northward through Wednesday night.
Strong easterly winds across the Bristol Bay region will weaken to
a northerly flow by Thursday morning, with precipitation coverage
starting to diminish.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...

Low pressure over the central and eastern Bering will diminish by
Tuesday afternoon. Strong winds over Bristol Bay and the Southwest
coast will weaken through the afternoon. Small craft advisory
north-northwesterly winds over the western Bering and Aleutians
will continue through Tuesday, along with widespread showers.

A strong, gale-force North Pacific low remains the biggest
forecast concern beginning on Tuesday afternoon for the eastern
Aleutians and AKPEN. This system will bring widespread gale-force
winds and rain as it lifts northward. Storm force winds and high
seas are expected for waters south of the AKPEN starting late
Tuesday into Wednesday.

&&

.MARINE (Days 3 through 5)...
There is a fair amount of uncertainty Wednesday and into Thursday
with the winds associated with a low moving over southwest Alaska.
One of the areas of uncertainty is with how strong the winds will
get over the eastern Bering. The models vary from low end gales to
storm force winds in the area. However, there is higher confidence
with storm force winds on the Pacific side of the Alaska
Peninsula on Wednesday and tapering down through Thursday. This
same system has similar problems in the Gulf with uncertainty of
wind strength throughout the area with the most challenging areas
around Shelikof Strait and along the north Gulf coast. The primary
timeframe for these challenges is Tuesday night into Wednesday
with uncertainty between gales and storm force winds for both.

Thursday and Friday will see another low approaching the western
and central Aleutians from the North Pacific that most guidance is
showing to be gale force. Newer model runs are starting to hint
at this being a storm force low and with the strength of low they
are starting to key in on, there is growing confidence that the
winds may need to be upgraded to storm force.

&&

.LONG TERM FORECAST (Days 3 through 7)...
The long term forecast beginning Wednesday will see a strong low
over southwest Alaska that will track east across the Gulf as it
diminishes through the end of the week. There is still
disagreement with the exact track and strength of the low but the
primary impacts look to be winds over marine areas around
southwest Alaska and the Gulf. There also looks to be fairly good
agreement in a good shot of rain along the north Gulf coast
Wednesday into Thursday.

Another system is expected to move towards the western Aleutians
Thursday and then track east while ridging builds in over the
southern mainland. There is decent agreement amongst the models
with these two features through much of Friday, but then the
models diverge quite a bit with how the low pushes into the Bering
as it gets hung up by the ridging to the east. However, all the
models are looking at a long fetch of moisture caught between the
low and the ridge that will be headed toward the southern mainland
even though they disagree on where exactly it will setup.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...NONE.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...JER
SOUTHCENTRAL ALASKA...AP/MSO
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...AH
MARINE/LONG TERM...DK