Area Forecast Discussion
Issued by NWS Anchorage, AK

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000
FXAK68 PAFC 210208 CCA
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion...CORRECTED
National Weather Service Anchorage AK
608 PM AKDT Sun Oct 20 2019

.ANALYSIS AND UPPER LEVELS...
The overall pattern remains the same, with a large low circulation
centered over the Bering Sea, Aleutians, and Southwest Alaska with a
short-wave ridge downstream over Southcentral Alaska. Numerous
(mostly weak) short-waves are rotating around the low circulation
and are the focus of ongoing weather. One wave is lifting
northward across Southwest Alaska producing a narrow band of light
precipitation. It`s falling as mostly rain, but there are some
areas of snow and light freezing rain inland. A separate short-
wave just downstream over the western Gulf is lifting northward
across the Kenai Peninsula and northern Gulf coast, leading to
increasing rain showers. Another short-wave and associated surface
low are lifting northward across the Eastern Aleutians and
southern Alaska Peninsula into the eastern Bering Sea, bringing
small craft winds and areas of rain. Weather across the remainder
of the forecast area is quiet.

&&

.MODEL DISCUSSION...
Models are in fair agreement through about Tuesday, with some
minor differences in the many weak troughs traversing the area.
Focus will then shift to a rapidly deepening low over the north
Pacific. There has been a fairly large model spread in depth and
track of this low over the past few days, with the ECMWF on the
eastern edge of solutions across the western Gulf and Cook Inlet
and the GFS along the western edge of solutions across the
southern end of the Alaska Peninsula. The 12Z GFS, ECMWF, and
Canadian solutions are now clustered close together with a track
across the Alaska Peninsula around King Salmon. GFS and Canadian
are over 10 mb deeper than the ECMWF. The latest forecast will
trend toward this latest track and depth. The 12Z was an outlier
with a notably weaker and faster low track and this will be
ignored.

&&

.AVIATION...
PANC...An upper level short-wave will pass overhead late tonight
though Monday morning. With a weak surface low in Cook Inlet,
there will be some flow across the mountains, so it will be mighty
weak. Thus expect ceilings to drop to MVFR as light rain showers
move through. There is some uncertainty in when ceilings will
improve, with some potential MVFR conditions could persist into
the afternoon hours as weak southerly flow persists up Cook
Inlet.

&&

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

A weak front pushes inland from the Gulf tonight which will bring
light rain and snow through Monday afternoon. Only trace to minor
accumulations are expected with this frontal passage, however,
there will be challenges for the early morning commute as
temperatures drop to near freezing or just below across the
Matanuska Valley (see Special Weather Statement for details).
Rain will be the predominant precipitation type along the coasts
and just inland with snow in typically colder locations at the
base of the Chugach and across the the Copper River Basin.

The next front moves to the western Gulf late Monday night,
swinging to the northern waters by Tuesday afternoon. This system
quickly organizes as a strong short wave lifts from the North
Pacific. Gusty small craft winds and rain along the boundary may
have a few gale gusts with this fast moving front.

&&

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

A small band of light rain and snow continues to push across
interior Southwest Alaska ahead of a weakening front stretched
from the Kuskokwim Delta south to Bristol Bay. Scattered showers
will linger along the coast overnight, with areas of fog likely
developing from Bethel south to Dillingham due in part to light
winds, clearing conditions, and lingering low-level moisture from
the precipitation earlier today. Winds will be stronger offshore
and along the coast through Monday as a low lifts north from the
eastern Aleutians toward Nunivak Island. Periods of light rain and
snow will also persist through early Tuesday morning across the
Southwest as the front associated with the aforementioned low
moves inland. The next system then tracks to the AKPEN from the
north Pacific late Tuesday with widespread precipitation and gusty
northeasterly winds developing from south to north across the
region Tuesday night into Wednesday.

&&

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

The long-wave trough continues to sit over the Bering through
mid-week with a series of shortwave troughs and associated surface
lows rotating around the parent feature. The first of these is a
low north of False Pass tracking north into the eastern Bering
tonight. This system will produce areas of small-craft winds off
the Southwest Alaska coast through Monday. Farther west, a second
area of low pressure will produce a stretch of northerly small-
craft winds and showers across the western Bering to the central
Aleutians through Monday. The northerly winds and showers are then
reinforced by a second area of low pressure dropping south on the
heels of the first for Tuesday. As this second system slides
south, attention will then focus back over the eastern Aleutians
as a deepening low lifts north toward the AKPEN with widespread
precipitation and gale-force winds for mid-week.

&&

.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...SEB
SOUTHCENTRAL ALASKA...KH
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...TM
MARINE/LONG TERM...DK


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