Area Forecast Discussion
Issued by NWS Anchorage, AK

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000
FXAK68 PAFC 301305
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
505 AM AKDT Fri Jul 30 2021

.ANALYSIS AND UPPER LEVELS...

Stagnant pattern continues with the longwave trough extending
across the Bering, supported by a decent jet and some tropical
influence. Meanwhile, a front pushes across Southwest, producing a
good amount of rainfall across the Kuskokwim Delta. Another,
separate wave moves out of eastern Russia and over Southwest
Alaska on Saturday. Upper level ridging from the North Pacific
through the AKPen and into Southcentral Alaska promotes weak
southwest flow, keeping much of the region socked into the low
cloud cover. By the late weekend and into early next week, a
digging trough dips into the Bering while a low in the North
Pacific slowly meanders into the Southern Gulf. This allows for
ridging to set up over Southcentral which will possibly create a
break in the cloud cover.

&&

.MODEL DISCUSSION...

Models are in good overall synoptic agreement through the short
term. There are some minor discrepancies with a low skimming the
northern Bering through tonight, including strength and center
location. Models are struggling with a low entering the western
Bering by late Saturday night. Almost none of the models are in
agreement on center location, with the Canadian being the furthest
south, and path varies slightly across the models.

&&

.AVIATION...
PANC... Light winds will persist. MVFR conditions are likely
throughout the day and may drop IFR at times through the morning
hours. Conditions should improve by this evening.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3...Fri
through Sun)...

A battle will ensue between the low stratus (and patchy fog) and
potential clearing/some sunshine as we head into the weekend.
Let`s break it down starting with synoptics. The pattern that has
been in place most of the week will persist. Weak upper level
ridging continues to hold on and provide some subsidence across
the area. This is leading to mostly dry surface conditions for
nearly all locations in Southcentral. However, courtesy of a broad
trough over Western AK, the lower levels (850mb or 5,000`) are
featuring southwest flow. This flow continues to grab moisture
from the Gulf and Cook Inlet and ferry it up into the mainland.
This is especially true along the south and west facing terrain,
where the clouds pile up and even some drizzle can fall out of it.
Thus, we have kept a mention of slight chance to chance PoPs
across much of the area. Anything that does fall will be extremely
light and will not amount to much.

Into the weekend, various pieces of energy will ride through the
trough over Western Alaska. For most of the area, there will see
little if any perceptible change in the pattern. The best chance
for any true rain will be over the Susitna Valley as these waves
clip nearby. The strongest of the waves and best chance for
precipitation should be Sunday morning. After that feature lifts
north, it will open the door for some drier air to replace the low
level moisture/stratus. It may take a while for this drier air to
spread in from the east, but we should start to see some more
breaks in the cloud cover stretching from east to west by late
Sunday. As soon as the sun does pop out, expect temperatures to
climb quickly as the airmass remains quite warm.


&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 to 2: Today through
Sunday)...

Very little deviation from the existing wet and overcast pattern
is expected for the rest of the weekend. Little remains of the
front that has been stalled in place over the Y-K Delta, with
the steady rain now breaking up into widely scattered, light
showers to start off this morning. Unfortunately, the break from
the blustery and wet weather will be short lived, with a potent
upper level shortwave and attendant surface low tracking across
the northern Bering and into the Seward Peninsula by this evening.
The trailing front will bring another round of moderate rainfall
inland across a majority of the southwest starting by tonight and
continuing into much of Saturday and Sunday. This second frontal
system will once again stall out near a very similar axis to the
one previously in place, focusing the heavier rainfall mainly
along and near the Kuskokwim Valley. Most of the heavier rainfall
totals will be confined to this vicinity, as well as across the
high terrain of the Kilbuck Mountains, where storm total rainfall
of around 1 to 2 inches continues to be anticipated through
Sunday afternoon. Much of Bristol Bay will stay out of the more
intense rainfall following the front, with more showery rainfall
through Sunday 0.25 inches or less expected.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 to 2:
Today through Sunday)...

A deep longwave trough centered over northeast Russia will
continued send a series of shortwaves and associated low
pressure systems across the Bering during the course of the next
few days. The first of these lows will track across the northern
Bering this afternoon through late tonight and bring an area of
moderate rainfall with it as it moves towards the Norton Sound and
Seward Peninsula by Saturday morning. The wind field with this
low will be compact but formidable, with a small and brief period
of low end gales possible west of St Matthew Island this afternoon
and evening before quickly weakening to lower as the center lifts
towards St Lawrence Island on Saturday morning. To the south,
sensible conditions will remain nearly steady state, with south to
southwest winds continuing across the southeastern Bering and
Eastern Aleutians through the end of the weekend.

By early Sunday, another low will enter the far western Bering
and lift northeast with a small craft strength wind field. There
is some uncertainty for how fast the low will lift north as it
matures and occludes, so expect further adjustments to the timing
and track of this next system as forecast confidence increases.

&&

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

A Western Aleutian low intensifies as it tracks northward across
the Bering Sea Sunday through Monday. An associated surface front
will march eastward toward the western Alaska coast. It`s looking
more and more likely that there will be some gale force winds near
the low center. However, confidence in the track of this storm is
low, making it hard to pin down where the gales will be at. Most
likely, the strongest winds would be over the Bering offshore
area. Secondarily, strong southerly winds ahead of the front could
bring some gale force gusts to bays and passes along the southern
Alaska Peninsula Monday.

&&

.LONG TERM DISCUSSION (Days 4 through 7: Monday through Thursday)...

A broad upper level low will continue to drive generally active
weather across the Bering/Aleutians. A surface low will track from
south to north over the western Bering on Tuesday. As it occludes,
another low will split along its associated front and track west
to east across the Aleutians through Tuesday evening bringing rain
and southerly winds. Model agreement degrades thereafter, with the
GFS showing the aforementioned low significantly deepening to
around 975 mb and stalling west of the Pribilofs whereas the ECMWF
takes the original low much farther west, thus having minimal
impact on the Bering/Aleutians. An upper ridge in combination with
a large surface high in the central Pacific will lead to mostly
quiet conditions and warmer temperatures across much of mainland
Alaska next week. If the GFS verifies with aforementioned low
closer to the Pribilofs, there may be a few showers that track
across Southcentral on Thursday along its eastern periphery.
However, it is too early to determine, and in any case would be
non-impactful.

&&
.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gale 185
FIRE WEATHER...NONE.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...KM
SOUTHCENTRAL ALASKA...MO
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...AS
MARINE/LONG TERM...BL/AP


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