Gale Warning 500, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
451 AM AKDT Wed Oct 16 2019

.ANALYSIS AND UPPER LEVELS...

An estimated 970 mb storm force low is centered just south of the
Pribilofs this morning while its associated front approaches the
southwest coast. This low has brought gusty westerly winds to the
Aleutians with the strongest winds nearing hurricane force on the
south side of the low. On the backside of the low, cold air is
filling in over the Bering. This instability has produced a few
thunderstorms over the far western Bering overnight.

Shifting eastward, a low over the Gulf continues to lift several
shortwaves over Southcentral. This has produced showers evident on
radar this morning along the northern Gulf coast and Kenai
Peninsula.

&&

.MODEL DISCUSSION...

Models have been in fairly good agreement regarding the short-
term synoptic pattern, and point to broad upper level cyclonic
flow over most of the southern Mainland. However, there is much
less agreement on the tracks and locations of both the Bering low
and the Gulf low for later this week. By Thursday morning, the
Bering low weakens and traverses the Alaska Peninsula, arriving
in the western Gulf. Meanwhile the low currently in the Gulf lifts
northward, and models have had a hard time resolving the position
of the low center.

&&

.AVIATION...

PANC...Initially, VFR conditions and light winds are expected
today. Conditions may drop to MVFR with some snow showers nearby.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...

Model consensus is relatively poor at the surface as a broad
upper level cyclonic flow sets up over the Gulf. Surface low
center positions vary considerably across the Gulf and make for a
challenging forecast. However, we can draw a few nuggets out of
the mire. It looks like easterly winds should increase across the
northern Gulf and westerly gales should increase over the southern
Gulf through Thursday. Precipitation overall will not be very
organized but will likely favor the northern Gulf and western
Gulf in general with limited chances inland. The exception would
be light overrunning snow/flurries spreading across the Anchorage
Bowl/Matanuska Valley this morning. Precipitation should remain
fairly light through this afternoon and will likely become mixed
with rain. Otherwise, precipitation should remain fairly spotty
inland.

&&

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

On satellite imagery the remnants of Hagibis are discernible and
extend from southwest Alaska to Siberia. Pockets of light
precipitation have been detected west of the Bethel radar (PABC)
and near the King Salmon radar (PAKC). All the while, a second
front continues to march towards the western Alaskan coast. The
leading edge of the next precipitation shield will move into
Goodnews Bay and Bristol Bay this afternoon and slowly push
eastward. Thursday the low will dive southeast of the AKPEN taking
the moisture advection with it.

&&

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

An unsettled pattern is on deck for this forecast period. On
satellite imagery there is an occluded front bisecting the Bering.
This new low has been convective with the weather observer at
Eareckson Air Station in Shemya reporting CB (cumulus nimbus)
yesterday and lightning strikes detected last night north of Attu
Island. The models indicate that the instability will continue as
this system moves eastward. Also impressive with this system are
the gradient force winds. Expect widespread sustained storm force
winds and the potential for hurricane force winds in the Pribilof
Islands today. Rough seas will accompany this low. There
continues to be multiple shortwaves embedded in the upper level
low which encompasses the entire Bering. Expect another shot of
energy from Kamchatka to move into the Western Bering as the
forecast period unfolds.

&&

.MARINE (Days 3 through 5)...

Westerly gales along the coastal waters near the eastern
Aleutians and Alaska Peninsula will diminish gradually Thursday
through Thursday night with winds across the Bering and Aleutians
expected for the most part to remain below gales through Friday
and Saturday. There are however, a couple of smaller troughs
moving through the broader troughing on Friday and Saturday that
do bear watching with the potential to produce brief periods of
localized stronger winds in the central and eastern Aleutians as
they spin up.

For the Gulf, westerly winds near gale force are possible at times
in the southern Gulf Thursday and Friday as small troughs rotate
through the broader westerly flow but otherwise winds are expected
to remain below gales through Saturday.

&&

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

By Friday, upper level troughing extending from a broad vertically
stacked low over the Bering will stretch east across much of
mainland Alaska, extending to a second vertically stacked low in
the central Gulf. A cut off upper level low over the Bristol Bay
area embedded in the broader troughing will lift to the northwest
over the Kuskowim Delta Friday night and Saturday while the low in
the Gulf moves slowly north.

A developing North Pacific frontal system located well to the
south of the Alaska Peninsula Friday night will track to the
northeast across the southern Gulf Saturday to reach the Southeast
Alaska Panhandle Sunday. In response, the upper low in the
central Bering will rotate southeastward over the eastern
Aleutians on Sunday before turning into a open trough and
continuing to the east just south of the Alaska Peninsula. Also
caught up in the same rotation, the upper low over the Kuskowim
Delta will swing to the northwest, moving offshore Sunday and then
turning south to swing by St Matthew Island and the Pribilofs
Sunday night and Monday before becoming quasi-stationary over the
eastern Bering offshore of the Kuskokwim Delta through midweek.

The next potentially rather strong low will track in from the
west, crossing the North Pacific well to the south of the western
Aleutians Sunday night and then beginning to turn to the
northeast Monday and Monday night while it is south of the
central and eastern Aleutians. While all the models are in good
agreement with the potential for this to be a powerful storm and
in fair agreement regarding the speed of its eastward progress,
there are very large differences regarding its north to south
position. The 12Z GFS has the furthest south track, keeping the
low well clear of the Aleutians as it rapidly deepens. Both the
ECMWF and the Canadian models curve the low to the northeast more
rapidly, bringing it just south of the western Alaska Peninsula
by Tuesday morning while the GFS solution's low remains roughly
350 miles further south. The ECMWF and Canadian models both then
bring low into Bristol Bay while the GFS tracks the low into the
Gulf for Wednesday and Thursday.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...High Wind Warning: 195.
MARINE...Storm Warning: 155, 165, 170-172, 179, 412, 414.
Gale Warning: 132, 150, 160, 173-178, 180, 352, 411, 413.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...KO
SOUTHCENTRAL ALASKA...RMC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...PJS
MARINE/LONG TERM...JR