Area Forecast Discussion
Issued by NWS Anchorage, AK

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000
FXAK68 PAFC 070157
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
457 PM AKST Sat Mar 6 2021

.ANALYSIS AND UPPER LEVELS...

A relatively quiet weather pattern is present over Alaska today.
There is enough weather to provide for some discussion, but not
anything that will be producing big impacts to our forecast area.
Weak troughing over Southcentral AK is producing light snow from
the Susitna Valley south over Cook Inlet and into the Kenai
Peninsula. Light snow has intermittently worked its way into
Anchorage from this band. However, high pressure is keeping most
of mainland AK quiet and cool today. There is a weak front pushing
into Coastal Southwest AK, bringing some snow and blowing snow
there. This front is extending southeast from a low moving east
through the Northern Bering, with the low center currently just
south of St. Lawrence Island. The rest of the Bering Sea and
Aleutians are under moderately strong zonal flow, resultant from
high pressure to the South in the North Pacific creating a
gradient with the low in the Northern Bering. Gale force winds in
the Central Bering are the outcome there.

&&

.MODEL DISCUSSION...

On the synoptic scale, models are in good agreement and handling
all major features well. On the meso to micro scale, models are
doing a poor job in handling areas of snowfall in Southcentral AK,
specifically in the Anchorage Bowl. They also missed on low-level
cloud cover forming over Anchorage this morning. Models seem to
be handling fine scale features better in other locations.
Overall, confidence in models is still at least moderate, we will
just need to keep a closer eye on weather in the Anchorage Bowl.

&&

.AVIATION...
PANC...An MVFR level stratus deck had set up over the airfield
this morning, associated with a weak weather system in the area.
That has since moved out of the area and conditions should remain
VFR. Some low stratus around Knik Arm could slide over the
airfield during the overnight, but this looks unlikely that it
would develop into a ceiling or cause any visibility
restrictions. Light winds will persist, though cold air coming
down the Susitna Valley could make a light northerly wind at the
airfield tonight through tomorrow.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 to 3: Tonight
through Tuesday morning)...

The remnants of the band of snow that dropped as much as 6 inches
of snow over parts of the Kenai Peninsula over the past day are
winding down to flurries, and any snow lingering up against the
Kenai mountains will come to an end by tonight.  An upper level
shortwave will continue to push west towards the Copper River
Basin and northern Gulf tonight with cold air advecting in from
the northwest behind the trough passage. The northwest flow and
colder temperatures building into the interior will support
continued outflow winds through the typical locations along the
North Gulf Coast as well as small craft to gale force gap winds
through the Kamishak Gap into Barren Islands. Most of these winds
should begin to relax by Sunday as warmer air begins to spread in
from the west and as a strong upper ridge builds into
Southcentral. Areas of fog may develop overnight tonight in parts
of the Copper River Basin, Mat-Su Valleys and western Kenai
Peninsula with light northerly winds and clearing skies expected
behind the departing shortwave. Conditions will be even more
favorable for fog development across these same regions as the
ridge axis moves into place on Sunday night, potentially leading
to significant visibility restrictions where it forms over
interior valleys and lower elevations.

By Monday evening, an active pattern will begin to set up once
again with a front moving into the western Alaska Range, western
Gulf and Kodiak Island. A low is expected to form along this
boundary by Monday night near or to the north of Kodiak Island and
track northeast towards the Prince William Sound on Tuesday.
Expansive warm advection and strong southwest flow will commence
in the mid to upper levels as the front approaches and the ridge
advances westwards into the Yukon and Alaska Panhandle. The warmer
air moving in with the front and low may cause mixing or a
changeover to rain for low elevations along the North Gulf Coast
as the low approaches to the south, with mostly snow currently
expected over interior portions of the Kenai Peninsula and across
the Susitna Valley on Tuesday.

Southeasterly cross-barrier flow developing ahead of the front at
the lower levels should result in downslope warming/drying across
much of the Matanuska Valley and near Anchorage, likely limiting
precipitation onset until the low nears Prince William Sound on
Tuesday and quickly shuts off the southeast flow across the
Chugach and Kenai Mountains. This may allow for a period of light
to moderate snow with a snow band moving into these areas from the
west sometime around midday Tuesday. Stay tuned to the latest
forecast as details with this next system become more refined.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3: tonight
through Monday night)...

A couple of weak shortwaves pass over Southwest this afternoon and
this evening, allowing for some brief, light snow showers along
the AKPEN and upslope (western) side of the Kilbuck Mountains.
Upper level ridging keeps most of Southwest relatively dry as it
moves across the Mainland tonight. A push of warm air gets
advected into the region behind the ridge and ahead of an
approaching front. This will increase temperatures to above
freezing tomorrow and Monday. Please see the Special Weather
Statement for more details. The front extending off an Arctic low
reaches the Southwest Coast tomorrow afternoon. Widespread
snowfall, or a snow/rain mix at times for some areas, will track
west to east with the front, with the heaviest amount along the
Kuskokwim Delta coast and along the Kilbuck Mountains. Winds
become gusty across the Mainland as the front pushes onshore.
Thus, blowing snow is likely to be an issue along the Y-K Delta
Coast and Nunivak Island overnight Sunday. Temperatures will begin
to drop again overnight Monday behind the front with an inflow of
colder air.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3:
tonight through Monday night)...

A front off an Arctic low track across the Bering through tomorrow
night, weakening as it reaches the Southwest Coast. A push of warm
air out ahead of the front will increase temperatures across the
Aleutian Chain enough for precipitation to be rain or a rain/snow
mix. Moderate to heavy precipitation is expected along the Eastern
Aleutians and Southern AKPEN as the front passes. Weak low
pressure remains behind the front as well as persistent westerly
flow. Winds should also diminish behind the front, becoming mostly
small craft along the Aleutian Coasts.

&&

.MARINE (Days 3 through 5: Tuesday through Thursday)...

Bering: An Eastern Bering front moves into Western Alaska Tue
night. Forecast tracks vary somewhat, but confidence is good.
Areas of small craft winds and waves dissipates Wed. Seas to 12
feet, subsiding. Several troughs cross the Bering through Thu,
with winds less than small craft level. A new low and front moves
into the Western Bering for Wed night and Thu. Widespread
increasing gale force winds move across the Western Bering. Seas
building to 16 feet Thu.

Gulf of Alaska: A low and front move across the Gulf for Thu.
Forecast tracks vary somewhat, but confidence is good. Widespread
southerly small craft winds and waves move across the Gulf for
late Tue, becoming widespread westerly small craft winds with an
area of gale force winds from the Barren Islands into the Northern
Gulf for Wed. Winds diminish Thu over the Northern Gulf. Seas to
12 feet, subsiding Wed.

&&

.LONG TERM FORECAST (Days 4 through 7: Wednesday through Saturday)...

An analysis of long term guidance leads us to have moderate
confidence that we can expect changing weather conditions for the
Bering and Gulf of Alaska, while mainland AK stays quiet with
cold overnight temperatures through the week.

Wednesday, on the synoptic scale, longwave troughing will
generally encompass our forecast area. A high amplitude ridge is
exiting to the east and over the Yukon, while a low amplitude
ridge is moving into the far Western Bering. On the surface,
models are indicating a compact low skirting along the north side
of the Aleutians in the Bristol Bay area. Low pressure is also
lingering in the Prince William Sound area. The rest of the
forecast area looks to be quiet and under high pressure. This
means cooler overnight lows continue for mainland AK.

Going forward through late next week, in the upper levels models
are showing the low amplitude ridge in the Western Bering moving
east and building over Western AK. Troughing re-emerges over the
Western Bering and over mainland AK south into the Gulf of Alaska.
On the surface high pressure holds on in Mainland AK and Eastern
Bering, though models are teasing a surface low moving into the
West Coast. Low pressure continues in the Gulf and Western Bering.
Models are having discrepancies in handling specific features, at
most hinting at what might happen. So for now, we are sticking to
identifying the general pattern, which the long range guidance
does have at least moderate agreement on.



&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Storm Warning 411.
 Gale Warning 121 130 131 155 165 170 172-185 412-414.
 Heavy Freezing Spray Warning 185 411.
FIRE WEATHER...NONE.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...BB
SOUTHCENTRAL ALASKA...AS
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...KM
MARINE/LONG TERM...MK/BB


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