Area Forecast Discussion
Issued by NWS Anchorage, AK

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000
FXAK68 PAFC 210353
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
753 PM AKDT Tue Jun 20 2017

.ANALYSIS AND UPPER LEVELS...
An upper-level low in the Gulf of Alaska is controlling the
sensible weather for much of Southcentral today. An extension of
this feature sits at the southern tip of the Alaska Peninsula. A
ridge extends from the North Pacific into the Eastern Bering Sea
and continues into the Alaskan Interior and Canadian Yukon.

At the surface, low pressure sits southeast of Kodiak Island
around 1006mb. The circulation is helping to move a slug of rain
through Southcentral. This has dampened the dust and raised levels
in the rain barrels, but it`s cooling Alaska summer-loving
spirits by locking daytime temps well away from mid June
standards... and closer to early March measures.

High pressure is building from the North Pacific toward Southwest
Alaska. Low stratus and occasional fog have returned. A trough
over the central Aleutian Chain cuts through the ridge.

Even farther West, a North Pacific gale near 40N is deepening and
tracking toward the western Chain.

&&

.MODEL DISCUSSION...
Models initialized well and remain in agreement with the main
synoptic features through the short term. Some divergence in
solutions begins to show up toward Wednesday night and Thursday
morning. As such, the forecast team used a well-blended model
approach today to make the weather sausage.

Extent of convection in the Copper River Basin and Matanuska
Valley will be the next forecast challenge in the coming days.

In Southwest Alaska and the Aleutians, challenges include the timing
of the next occluded low, the associated frontal passage, and
local wind effects will be tracked. Ongoing visibility
limitations will continue in the Bering Sea and coastal areas.

&&

.AVIATION...

PANC...Light westerly winds will take hold this evening and last
though most of Wednesday. Winds back to a southeasterly and gusty
flow Wednesday evening. VFR conditions are expected through the
period.

&&

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

The wave of moisture that brought wetting rains to much of
Southcentral is now moving southwestward down the Cook Inlet and
will overspread Kodiak tonight. A break in the action in terms of
precipitation is expected for most areas of Southcentral tonight
through Wednesday morning as the area is situated in light
northeast flow. The next wave is currently pegged by nearly all of
the models to bring wetting rains to the eastern Copper River
Basin tonight. Thus, the precip forecast has been increased for
that area tonight. Unlike this previous wave, the next one will
fall apart quickly as the upper low over the Gulf retreats
southeastward away from the area and thermal ridging quickly
builds in.

The ridging will set the stage for somewhat warmer temperatures
the next couple days over Southcentral, though mainly cloudy skies
with only peaks of sun will mitigate temperature rises for much of
the area. The exception will be over the northern and western
Susitna Valley, where much more sunshine will allow temperatures
to climb to near 70.

On Thursday, the center of the upper level high/ridging moves to
near the Alaska/Yukon border. The return of southwesterly flow
aloft will transport the cloud cover over much of Southcentral
back into the Susitna Valley, so the warmest temperatures will be
found across the Copper River Basin. Instability and lift from the
mountains will make for another round of isolated thunderstorms
Thursday afternoon in the Copper River Basin, though moisture
inflow along the Alaska Range may set off an isolated storm or two
in the Alaska Range of the far northern and western Susitna
Valley zone.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
Showers near the Alaska/Aleutian Ranges will slowly drift
diminish tonight then end Wednesday morning as the responsible
low in the Gulf moves east. High pressure will build over the
area, and this will keep things dry through Thursday morning. On
Thursday afternoon conditions will be unstable enough for showers
over the Kuskokwim valley and Bristol Bay areas, with just a few
thunderstorms possible near and over the Alaska Range.
Temperatures will be mild across the area, with afternoon highs a
few degrees above normal.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
The weather front associated with a low over the northwest Bering
will slowly drift northeast through Thursday morning then
dissipate Thursday afternoon just off the coast of the Kuskokwim
delta region. A strong low to the southwest of the western
Aleutians Wednesday morning will move to just south of Shemya
Thursday afternoon. An associated gale force front will push into
the western Aleutians Wednesday afternoon then push east into the
central Aleutians on Thursday.

&&

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

Over the Southcentral, a general warming trend is expected in the
short term as high pressure develops aloft, and the interior
thermal trough becomes re-established across especially the Copper
River Basin. However, with the approach of an upper level low from
the Gulf on Saturday, enough moisture and instability will be
present to support diurnal convection along elevated terrain Saturday
and Sunday. Currently models are trending to keep this low in the
Gulf, but cooler temperatures and more widespread cloud cover is
possible if this low pushes more towards the coast.

The upper level ridge from south of the Aleutians into southwest
Alaska across the interior is still progged to break down late
Friday into Saturday as the upper low over the Gulf of Alaska
pushes north while the upper level Arctic trough digs south into
the interior. This will only be for a short lived as the upper
level ridge is still on tap to build into the interior from the
north Pacific Sunday. Meanwhile out over the Bering sea a large
upper low will move across the central Bering Sea through the
weekend. Beginning Monday this upper low and the associated upper
trough push into the eastern Bering Sea producing moist cool
southerly flow over the western mainland by Tuesday. The upper
ridge is pushed east over the panhandle by Wednesday morning.

The Thermal trough across the interior should return Thursday
through Sunday. Monday the warmest low level air will shift to the
eastern interior. The southwest mainland will cool and moisten
beginning Monday.

Over the eastern Bering Sea and eastern Aleutians the weather
will transition from marine stratus and fog to a wetter and
windier regime one would expect with the surface low and
associated front moving across the Bering Sea and sweeping across
the Aleutians through the weekend.

Model agreement has remained consistent through the long term. The national
guidance remained heavily weighted toward the operational model
guidance through the weekend then follows the GFS into the mid
week time frame as the EC becomes more of an outlier.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gale Warning 177 178.
FIRE WEATHER...NONE.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...DS
SOUTHCENTRAL ALASKA...JW
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...BL
LONG TERM...SA



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