FXAK68 PAFC 060032
Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
432 PM AKDT Thu Aug 5 2021
.ANALYSIS AND UPPER LEVELS...
An upper level trough extending along an axis from Russia to the
Alaska Peninsula continues to dominate the weather pattern over
the Bering. On the south side of this trough, a short wave has
spun up a low center south of Kodiak Island. Farther east, an
upper level ridge remains over the central mainland, keeping much
of the central and northern part of the state under clear skies.
A decaying front extends across the entirety of the Southwest
coast, keeping a stagnant pattern of rain and cloud cover in place
over Southwest Alaska. A persistent low over the southeastern Gulf
is gradually pushing inland over the Alaska-British Columbia
Overall, model solutions are in good synoptic agreement. The main
forecast challenge over the next few days will be the development
of the low center south of Kodiak Island and its track into the
Gulf. By the weekend, another low spins up over the eastern Bering
and begins to track eastward. Models are currently handling this
system well, though there are differences in timing as the upper
level trough extends over Southcentral by Sunday. Overall, there
is moderate confidence in the forecast.
PANC...Expecting VFR conditions and light winds, though ceilings
may drop intermittently to MVFR with low level stratus.
.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3: Tonight
through Sunday afternoon)...
A low tracking into the western Gulf this evening will bring
moderate rain to Kodiak Island. Its associated upper trough will
weaken as it moves eastward and any lingering showers should end
by early Friday morning. Cloud cover is slowly breaking up over
Southcentral this afternoon which will lead to warming
temperatures before sunset. Mostly sunny conditions are seen
across the remainder of the region under a weak upper level ridge.
The same general pattern aloft is expected on Friday, with any
developing precipitation being confined to higher terrain over the
A broad upper low in the southern Bering will lead to a pattern
change into the weekend as it gradually displaces the
aforementioned ridge. An embedded shortwave will move over
Southcentral by Saturday afternoon, bringing light rain to the
area. The southwesterly flow aloft will continue to advect in more
moisture and thus the cooler, wet pattern looks to continue
through Sunday. Rain will overspread much of the mainland by
Sunday afternoon. Gusty winds are possible along Turnagain Arm
late Saturday through Sunday afternoon as the surface low moves
northward near Bristol Bay and weak high pressure develops over
Prince William Sound. Although this is reminiscent of a more
fall-like pattern, winds in Anchorage are not expected to be
significant at this time.
.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3)...
A quasi-stationary front over central Southwest Alaska will move
slowly east overnight while weakening. The main upper level energy
has separated from the front, moving south of the AKPen and
towards Kodiak Island. As a result, the system has lost much of
its upper level support, thus bringing an end to the rain by
Friday afternoon. The exception to this will be over the high
terrain where upslope flow will keep the precipitation going. On
Saturday, expect warmer conditions with pockets of sunshine. The
break in the weather will be brief however, as a strong low moves
from the North Pacific into the Eastern Bering. The mid to upper
level vorticity field from the system is expansive, resulting in
lift and onshore flow that will bring widespread rain to the
region on Sunday.
.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3)...
The broad longwave trough with transient shortwaves will persist
over the region through the forecast period. A system developing
in the North Pacific today will strengthen rapidly as it moves
into the area, tapping into the large temperature gradient between
the North Pacific and Bering Sea. Widespread small craft advisory
winds and rain will accompany the low as it moves over the
Central and Eastern Aleutians Friday night. The low is expected to
reach its minimum pressure Sunday morning over the Eastern
Bering. Expect showery conditions over the Aleutian Chain after
the low passage, becoming widespread rain over the AKPen on Sunday
as the low stalls out.
.MARINE (Days 3 through 5: Sunday through Tuesday)...
The main marine focus will be on a low moving into the Gulf of
Alaska Monday Night into Tuesday. There continues to be a large
amount of uncertainty with the track and strength of this low.
Overall, it looks increasingly likely that the strongest winds and
highest seas will move into the eastern Gulf of Alaska. It
remains possible for Gale force winds and seas to 20 ft to occur
across much of the Gulf on Tuesday so it is worth mentioning, but
this solution is looking less likely so forecast will show lower
winds and seas for the time being unless a reason to change
.LONG TERM FORECAST (Days 4 through 7: Monday through Thursday)...
A North Pacific low is still expected to trek toward the Gulf but
more along the path of Kodiak Island on Monday and Tuesday. It`s
not a surprise model solutions continue to differ with the
placement of the low and the arrival time of gales. Of all the
models, at least GFS and ECMWF invites gale winds near Kodiak
Island and portion of the Gulf between Monday evening and Tuesday
night. The bulk of tropical moisture associated with the low will
saturate the western and northern Gulf, including AK Peninsula
and the Alaska Range. At 500 mb, an upper low from the central
Aleutians will make its way through Bristol Bay by Tuesday,
causing clouds and increased rainfall to spread across the region
through at least Wednesday. This pattern combined with the
surface low will reinforced gusty winds especially along the gaps
and passes. Apart from the lows, a ridge of high pressure over
the Bering will transit from west to east through the midweek. As
a result, the forecast confidence remained moderate-high for the
first three days, Monday through Wednesday.
SYNOPSIS AND MODEL DISCUSSION...KO
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...CJ