Graphical Hydro Meteorological Discussion

000
FXAK68 PAFC 060032
AFDAFC

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
border.

&&

.MODEL DISCUSSION...

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.

&&

.AVIATION...

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
interior.

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
arises.

&&

.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.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...NONE.
FIRE WEATHER...NONE.

&&
$$

SYNOPSIS AND MODEL DISCUSSION...KO
SOUTHCENTRAL ALASKA...AP
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...CJ
MARINE/LONG TERM...MK/CB

000
FXAK69 PAFG 052148
AFDAFG

Northern Alaska Forecast Discussion
National Weather Service Fairbanks AK
148 PM AKDT Thu Aug 5 2021

.SYNOPSIS...
One more hot summer day is on tap for this afternoon across the
Interior ahead of a cooler and wetter pattern settling into the
area beginning tomorrow and lasting through the weekend. Showers
across the Yukon Delta continuing through tonight. An Arctic front
has reached the Arctic Coast keeping cloudy conditions with
occasional fog going into the weekend.

&&

.DISCUSSION...
The upper level ridging pattern that has been dominating over
northern Alaska and has resulted in multiple high temperature
records will hold on through today ahead of a transition to cooler
and wetter conditions. Firstly, an upper level trough, associated
with a strong closed low in the far western Bering Sea, will
stall across the Interior and West Coast tonight. However, this
feature will work in tandem with another strong upper level closed
low over Banks Island to break down the ridge over northern
Alaska through tomorrow.

The upper low in the western Bering Sea will move east be near
Bristol Bay, while the upper level low over Banks Island will move
east as well, with troughing stalling over the Brooks Range by
Saturday night. With weak ridging holding on in the far eastern
Interior and into Canada, a southerly flow pattern looks to
develop going into Sunday.

Due to the general troughing pattern over the state through the
weekend, expect increasing clouds and wet conditions headed into
next week for most areas of northern Alaska.

Central and Eastern Interior...
Another hot and dry day with temperatures reaching the low to mid
80s this afternoon. However, today is expected to be the final hot
day with this current pattern as increasing clouds and chances for
rain moves into the area for tomorrow and lasting into the
weekend. Isolated thunderstorms will encompass the southern
portions of the Interior today, tonight, and tomorrow afternoon.
High temperatures will fall to the 70s tomorrow and then the 60s
going into next week.

North Slope and Brooks Range...
An Arctic front has moved south of the Arctic Coast this
afternoon, which will usher in cooler temperatures going into the
weekend. Areas of the eastern Beaufort Sea Coast are receiving
rain with low visibilities, while areas to the west remain cloudy.
Northeast flow will persist going into the weekend, so expect
continued stratus and fog conditions.

West Coast and Western Interior...
A front stretched out across the Yukon Delta region this afternoon
will bringing rainy conditions through tonight. As this system
dissipates, showers will remain a threat across the area for
tomorrow and Saturday. Isolated thunderstorms will remain from
generally Galena east along with a small area of the western
Brooks Range through this evening. Temperatures will cool to below
climatological average by the weekend.

Coastal Hazard Potential Days 3 and 4...None.

&&

.FIRE WEATHER...
Another hot and dry day in the Interior today, but there will be
a transition to higher potential for wetting rains by tomorrow.
This will result in cooler temperatures beginning tomorrow, with
high temperatures reaching only into the 60s by Saturday. Slight
warming expected going into next week but will remain in the mid
to upper 60s across the Interior. Isolated thunderstorms will
remain a threat to the southern portions of the Interior for
today, tonight, and tomorrow afternoon.

&&

.HYDROLOGY...
The Kobuk and Noatak Rivers still have elevated water levels but
will continue to fall as no significant rain is expected across
the region going into the weekend. No other hydro issues expected
for the short term.

&&

.AFG WATCHES/WARNINGS/ADVISORIES...
Small Craft Advisory for PKZ210-PKZ220-PKZ230.

Gale Warning for PKZ225.

&&

$$

AUG 21

000
FXAK67 PAJK 052244
AFDAJK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
244 PM AKDT Thu Aug 5 2021

.SHORT TERM...One 500 mb closed low from from gulf move over the
southern panhandle tonight, as a new one breaks free from the huge
low over the Bering and into the wester part of the gulf. The
second low will track to Haida Gwaii by Saturday morning followed
by a positively tilted ridge. That will lead to the start of the
AR`s headed for the panhandle for next week.

Showers primarily over the southern panhandle tonight and the far
north panhandle near the boarder. Showers for the panhandle will
be scattered, but a weak easterly wave, will be headed towards the
northern panhandle Friday, and then fall apart Friday night.

Expect to see showers tapering off through late Friday into
Saturday, have lowered much of the area to 15 to 25 percent PoPs
so it would slight chance or Isolated showers. This could be to
much but was stepping back.

Next precipitation push will spread back into the Northeast Gulf
Coast Saturday night, then to the northern panhandle through
Sunday. It will continue to track south into the start of the
week.

Wind lighter winds through early Saturday, then expect Lynn Canal
to increase with a tighter gradient for Sunday and into Skagway
region, up to 20 to 25 kt.

.LONG TERM.../Saturday through Wednesday night/...As of 10pm
Wednesday. A low-amplitude upper level trough over the panhandle
Saturday moves into B.C. by Sunday and is replaced by a weak
transitory upper level ridge. The upper ridge is forced south by
Monday morning as a 140kt jet sets up over the top of the remains
of the ridge. There are model differences on exactly where the jet
max sets up, but flow at all levels is onshore. Models are also
showing a moisture source in the tropical Pacific, so confidence
is increasing in a potential atmospheric river event Monday into
Tuesday, possibly longer. Approximately 80% of GEFS ensemble
members are showing IVT values of 500 kg/m/s or greater aimed at
the northern / central panhandle by 18z Tuesday. To complicate
things, technical issues at the office limited the changes to the
forecast, so the latest model runs were not fully incorporated
into the forecast. This leaves plenty of things to look at for
tomorrow`s evening shift.

Getting back to the weekend, a ridge builds briefly, and models
have backed off on the easterly wave hints, so a diminishing
trend in the showers across the panhandle is expected, but the
cloudy skies and the chance of showers will not completely go away
with weak onshore flow. Temperatures are expected to remain
seasonal with no impactful winds through the weekend.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...None.

&&

$$

Bezenek/BFL

Visit us at http://www.weather.gov/Juneau