Graphical Hydro Meteorological Discussion

167
FXAK68 PAFC 181245
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
445 AM AKDT Tue Aug 18 2026

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3: Today
through Thursday)...

A complex longwave trough continues to drift over much of the
greater Alaska region this morning, with several embedded smaller
troughs slowly moving northeast along an axis between the
Aleutians and the Yukon. The leading trough in this series is the
one responsible for the blustery and wet conditions across
parts of Southcentral yesterday, now exiting across the AlCan
border into the Yukon. Gap winds are beginning to trend down as
the north-south pressure gradient slowly relaxes, and this
weakening trend should continue today into tonight. The next
shortwave disturbance to watch is now starting to lift from
Southwest into the western Alaska Range, and this feature will
likely become a key player in today`s outlook across Anchorage
and the Mat-Su Valleys. It`s looking like this trough will stay a
bit more intact as it crosses over into northern portions of
Southcentral today, increasing the threat for shower redevelopment
over both higher terrain and lower elevations this afternoon.

By late this evening, the shortwave poised to move into the Mat-Su
Valleys will shift into the Copper Basin. Lingering shower
activity will trend in the same direction, while the rest of
Southcentral temporarily dries out in between systems from tonight
into Wednesday morning. By the late morning to mid afternoon on
Wednesday, a weakening low moving along the AKPen will send its
occluded front into Southcentral. This will send renewed bands of
light rain quickly northeast, first reaching Kodiak Island and the
Kenai Peninsula, then shifting into the Mat-Su and Prince William
Sound later in the day. Models are struggling a bit to pin down
the location for the development of a new surface low at the
frontal triple point, but it looks most likely (around 70%
chance) to form close to Kodiak Island and the Barrens by
Wednesday night. As this new low forms, the front will sharpen
somewhat as it nears the Gulf Coast, with a weak barrier jet
likely to form along it as it approaches the northern Gulf
coastline late Wednesday night into early Thursday. Easterly winds
will peak at or near Small Craft range along the front early
Thursday morning, namely south of the Kenai Peninsula and Prince
William Sound.

Looking closer to the end of the week, the main low moving up from
the Aleutians and AKPen will shift northeast into Southcentral
through Thursday evening. Expect this to extend the cool, showery
and cloudy pattern for much of the region through at least
Thursday night.

-AS

&&


.SHORT TERM FORECAST SOUTHWEST ALASKA/BERING SEA/ALEUTIANS (Days
1 through 3: Tuesday through Thursday)...

The active pattern continues across Southwest Alaska, the Bering
Sea and Aleutians through the middle of the week as a series of
upper-level lows track across the region. Showers lingering across
Bristol Bay early this morning will continue to push off to the
north and east into the Kuskokwim Valley and along the western
Alaska Range throughout the day today as the first upper level
feature exits the region. Elsewhere across Southwest, low stratus,
patchy fog, and misty conditions continue through this morning
into this afternoon as the next system quickly follows by
Wednesday morning.

Farther west, the low currently centered over Nikolski continues
to track along the Aleutian Chain and Alaska Peninsula through
Wednesday before eventually pivoting south into the Gulf by
Thursday morning. Light rain associated with this system continues
across the eastern Aleutians and AKPen through tonight before
overspreading Southwest Alaska by Wednesday morning.

Looking ahead to the end of the forecast period, a strengthening
low entering the western Bering for Thursday into Friday will
bring the next round of widespread gusty winds and rainfall across
the Bering and Southwest Alaska.

&&


.LONG TERM FORECAST (Days 4 through 7: Friday through Monday)...

The long term begins with a strong zonal jet between Kamchatka
and western Alaska that will amplify into a broad trough over the
state on Saturday and Sunday. The jet streak over the Bering will
help to generate a fairly strong and broad low pressure system
that will impact southwest Alaska starting early Friday. Depending
on the track and timing of this system, which has a fairly large
spread, there are concerns regarding the potential for coastal
flooding, high surf, and/or erosion. It`s difficult to pinpoint
where this may occur at this time with guidance highlighting a
broad area of concern from the northern Alaska Peninsula all the
way to the Y-K Delta.

The other aspect to this system is significant rainfall. Although
there isn`t a deep connection to the pacific and tropical
moisture, a decent slug of warm, moist air will accompany the
system. Models are indicating 1-2 inches of rain may fall on
Southwest Friday and Saturday. The storm will pass into
Southcentral and then the Gulf over the weekend, with a widespread
1-3 inches of rain possible. Given the wet environment,
particularly in the Susitna where flooding is currently occurring,
flood concerns will rise once again. Winds look strong through
the Bering, Southwest, and Gulf of Alaska/Kodiak Island.

&&


.AVIATION...

PANC...VFR conditions are expected to remain through the TAF
period, though periods of showers may cause ceilings to dip to
as low as MVFR range at times. Gusty southerly to southeasterly
winds will persist through the day, though will gradually diminish
this afternoon into tonight.

&&


$$

721
FXAK69 PAFG 181327
AFDAFG

Northern Alaska Forecast Discussion
National Weather Service Fairbanks AK
527 AM AKDT Tue Aug 18 2026

.KEY MESSAGES...
Central and Eastern Interior...
-Fire weather concerns remain elevated in the Upper Tanana Valley
due to low chances of wetting rains, near-critical temperatures/RHs,
and a non-zero chance for an isolated thunderstorm.

-Rain showers continue Tuesday (except for in the Upper Tanana),
with up to 0.5 inches possible in the valleys and 0.5 to 1.25 inches
of precipitation possible over terrain, with the highest amounts
west of Fairbanks.

-Temperatures will be below normal Tuesday, with highs in the
low/mid 60s throughout most of the region. Temperatures briefly warm
on Wednesday as ridging builds into the Central and Eastern
Interior. High temperatures are expected to be in the mid/upper 60s.

West Coast and Western Interior...
-A Hydrologic Outlook is in effect until 4 PM Tuesday for headwater
streams of the Koyukuk and Middle Yukon River Basins as 0.5-1.25
inches of rainfall has fallen so far, with another 0.5-1.25 inches
possible through Tuesday, which may cause significant rises in
smaller headwater streams. Showery conditions continue through the
weekend, though precipitation totals will be lighter (<0.5 inches a
day).

-Northerly winds continue in the Bering Strait through Wednesday
evening, with gusts up to 45 mph expected.

-Another low is set to enter the Bering Sea on Friday. Model
guidance is still not in agreement on location and specific
intensity, though there is agreement that it will be weak.

North Slope and Brooks Range...
-A Hydrologic Outlook is in effect until 4 PM Tuesday for headwater
streams of the Koyukuk Headwaters as 1 inch of rainfall has fallen
so far with another 0.5-1.25 inches possible through Tuesday, which
may cause significant rises in smaller headwater streams. Rain
continues in the Brooks Range and along the North Slope, with daily
totals ranging from 0-0.5 inches and 0-0.25 inches respectively.

-Temperatures cool off on the North Slope Tuesday and Wednesday,
with high temperatures in the mid/upper 50s from Point Lay south and
upper 30s/40s north of Point Lay Tuesday and in the upper 30s/low 40s
everywhere except for around Point Lay and Umiat (which will be in
the low 50s) on Wednesday. Temperatures then warm into the mid
40s/mid 50s on the coast and into the 60s inland to finish out the
week.

&&

.SYNOPSIS...
Weak troughing persists in portions of Northern Alaska before
another system moves into the Bering on Friday. The only region of
the CWA expected to avoid wetting rain is the Upper Tanana Valley,
though chances for an isolated thunderstorm or two are possible
Tuesday through Thursday. On the other end of the spectrum, the
Northwest Interior/Southwestern Brooks Range will stay consistently
showery. Other regions in Northern Alaska will be somewhere in
between. Temperatures slightly warm up in the Central/Eastern
Interior on Wednesday as high pressure briefly builds. Another low
system is set to arrive in the Bering at the end of the week,
bringing the potential for windy conditions and heavier
precipitation on the West Coast. However, there is too much model
uncertainty to say any specific other than that the system looks to
be weak. Troughing is expected to continue through at least the
weekend.

.&&

.SHORT TERM /THROUGH FRIDAY NIGHT/...
The upper level low that has been moving across the state over the
last few days has moved into Canada, leaving weak troughing for most
of Northern Alaska in its wake. Post-frontal showers linger in the
Central and Northern Interior on Tuesday, with chances for a rumble
of thunder or two in the White Mountains/Fortymile Country where
temperatures have been warmer. Most lowland areas will see 0.5
inches of rain or less. Between 0.5 inches and 1.25 inches could
fall over higher terrain in the Central and Northern Interior
Tuesday, especially over southwest aspects. Northerly winds increase
in the Bering Strait with continued cold air advection in the
region, with the potential for gusts up to 45 mph.

On Wednesday, ridging builds into the Central and Eastern Interior
from Fairbanks East, while two weak lows arrive on the West Coast-
one over the Brooks Range and one over Bristol Bay. The low over
Bristol Bay stays our of our AOR for now, while the low over the
Brooks will bring another round of showers along the North Slope and
in the Northwest Interior. Totals will be lighter than earlier this
week, with 24 hour totals between 0.05 and 0.25 inches expected over
lower terrain, with 0.25 to 0.5 inches over higher terrain. Ridging
in the Central/Eastern Interior will briefly warm temperatures into
the mid/upper 60s. If shortwaves being advected from the low over
Bristol Bay arrive in the Upper Tanana Valley and/or Fortymile
Country around/after peak heating, isolated thunderstorms could
develop.

All 3 features shift east on Thursday. Isolated rain showers remain
primarily in the Northern/Western Interior and on the West Coast,
but few, if any, will be wetting. Another round of isolated
thunderstorms is possible in the Upper Tanana/Fortymile Country on
Thursday if the same conditions required on Wednesday are met.
Another trough associated with a weak surface low into the Bering
moves over Western Alaska on Thursday/Friday. There is disagreement
both among ensemble members and between ensemble means in intensity
and location, though the most aggressive members have the low
bottoming out at only 980 hPa. Coastal flooding concerns are minimal
to none at this time, since the system is quick-moving and wind
gusts will be relatively calm (50+ mph gusts don`t show up in the
NBM until the 90th percentile). This low will also bring more
widespread precipitation for the West Coast and Western Interior.
Given the uncertainty of the low placement/strength there is
considerable uncertainty in precipitation totals. This is especially
true for the southern Seward Peninsula, because if flow is more
southerly, orographic lift over the higher terrain in the middle of
the peninsula will be much more effective than if flow is
southwesterly/southeasterly. There is over 1 inch of spread between
the NBM 25th and 75th percentiles around Nome for 24 hour precip
totals on Friday.

&&

.LONG TERM /SATURDAY THROUGH MONDAY/...
At the start of the long term period the low pressure that will
bring moderate to heavy rainfall and gusty winds to parts of the
West Coast, will be moving southeast towards the Gulf of Alaska.
This low is paired with an arctic trough stemming from an area
of low pressure in the high arctic. As these features move
eastward it will bring isolated to scattered rain showers with
it across the Eastern half of Northern Alaska. Behind this
system a ridge of high pressure stemming from the North Pacific
Ridge is expected to build into the Bering Sea. This ridge will
help to influence the movement of lows in the North Pacific and
Arctic as we move into early next week.

Model Ensembles are in good agreement on the ridge axis
developing in the Bering Sea, and a strong Arctic low moving
towards Wrangel Island in the Chuckchi Sea. Where models begin
to diverge is how the low interacts with the ridge axis. This
arctic low could potentially flatten and shift the ridge axis
eastward. If this occurs we could see an atmospheric river
develop and move onto the West Coast. The flattened ridge would
allow for southwest flow to tap into tropical moisture and
advecting it onto the West Coast. The GFS ensemble is much more
aggressive in advecting this tropical moisture, but the ECMWF
ensemble still has this southwest flow. Regardless of how strong
the moisture advection will be, it could be a wet start for the
work week across the West Coast and Western Interior.

Coastal Hazard Potential...
No Coastal Hazards are expected in the forecast period.

&&

.FIRE WEATHER...
Fire weather concerns will be quickly dropping over the next
few days across much of Northern Alaska. Temperatures will be
cooling across the Interior and Arctic Plains to the 50s/60s.
These cooler temperatures will be accompanied with cloud cover
and isolated to scattered rain showers. We will continue to see
moderate rainfall up to an inch across the Koyukuk Valley and
Central Brooks Range. Across the rest of the Western/Central
Interior we can expect 0.10" to 0.40" of rainfall. This rainfall
will steadily become more isolated as we move into Wednesday.
There is a non zero chance that we could see a thunderstorm or
two Tuesday afternoon across the Central/Eastern Brooks Range
and in the higher terrain from Eagle Summit to Eagle.

The exception to fire weather concerns dropping will be the
Upper Tanana Valley as downsloping will be able to persist
Tuesday and Wednesday. Conditions will not be at the critical
threshold like they were Monday afternoon, but over the next few
days they will be near critical. Temperatures will slightly
cool to around 70, and with downsloping the minimum RHs will be
in the upper 20s. Winds in the valleys will generally be from
the southwest and light, but during peak heating we could see
some mixing occuring allowing for gusts of 20 mph to mix down
into the valley. Overnight if the southwesterly winds persist
similar to Tuesday morning there will not be that much recovery.
As of now we dont expect these southwesterly winds to mix down
into the valley for the next couple of nights, so the overnight
RH recovery should be in the 70s. Rain chances don`t return to
the region till around Thursday afternoon, but they would come
in the form of thunderstorms if they do develop. These chances
are going to heavily rely on a wave of upper-level energy and if
it moves through the region during the daytime. There is not a
lot of model agreement on the timing, and we are continuing to
monitor the feature.

&&

.HYDROLOGY...
0.5 to 1.25 inches of rainfall has fallen across the Central
Interior and Brooks Range in the past 24 hours. A stalled front
will allow for an additional 0.5 to 1.5 inches of rainfall over
the next 24 hours across the region. This could lead to river
rises across the Koyukuk and the Middle Yukon Rivers headwaters.
While no flooding is anticipated, some smaller creeks and
streams could become bankfull.

&&

.AFG WATCHES/WARNINGS/ADVISORIES...
AK...None.
MARINE...Small Craft Advisory until 4 PM AKDT this afternoon for PKZ806-
807.
Small Craft Advisory until 1 PM AKDT this afternoon for PKZ808-
855-856.
Small Craft Advisory until 10 AM AKDT this morning for PKZ809.
Small Craft Advisory until 10 AM AKDT this morning for PKZ854.

&&

$$

KEY MESSAGES...Schlezinger
SYNOPSIS...Schlezinger
SHORT TERM...Schlezinger
LONG TERM...Dennis
FIRE WEATHER...Dennis

175
FXAK67 PAJK 181728
AFDAJK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
928 AM AKDT Tue Aug 18 2026

.UPDATE...Updated the aviation section for the 18z tafs. Also did
a small update to Lynn Canal and Skagway winds. While the general
message is that winds will be on the diminishing trend today,
keeping them elevated through the morning hours from daytime
heating in Canada, keeping the thermal trough alive and well.

&&

.SYNOPSIS...

Key Messages:

- More seasonable conditions will prevail through the end of the
week with mostly cloudy skies and periods of rain, especially
across the north, as multiple systems traverse the region.

- The marine layer and weak onshore flow will keep high temps in
the upper 50s to lower 60s across the north. Breaks in clouds
across the south could bring high temps into the mid to upper
60s and possibly low 70s.

- Marine conditions will improve through the day. The next system
looks to bring increasing Gulf winds and seas by Wednesday
night.

&&

.SHORT TERM.../through Wednesday night/...
The front has weakened and cleared the panhandle overnight.
Pockets of low stratus and fog are present across portions of the
central and southern panhandle this morning. A Dense Fog Advisory
is in effect for Kake. High pressure is building back over the
eastern Gulf into the southern panhandle today. Expect lighter
onshore flow bringing marine layer into the panhandle today, with
mostly cloudy skies and periods of light rain across the northern
and central panhandle. Late tonight into Wednesday, a weak
disturbance will ride over the ridge and into the panhandle,
bringing an increased chance of light rain. A frontal boundary
will then straddle the central and northern panhandle Wednesday as
the next low lifts towards the Kenai Peninsula. The low and front
will bring increasing rain potential across the northeast Gulf
coast and into the northern panhandle through Wednesday night,
with moderate to heavy rain at times possible. The cooler, but
seasonable, temperatures will continue across the north, with
highs in the upper 50s to lower 60s. Across the south, some breaks
in cloudiness and slightly warmer temperatures with highs in the
mid to upper 60s, possibly reaching the low 70s.

/Thursday through Sunday/...
Active weather continues into the long term period, especially
over the northern panhandle. To end the work week, an area of low
pressure moves into the northern gulf continuing to bring onshore
flow, rain, and slightly increased winds to the northern and
central panhandle. An area of high pressure southwest of the
panhandle with a positively tilted ridge axis will remain near
Prince of Wales Island. This ridge will likely keep the far south
drier, but a few periods of light showers may occur. That ridge,
southwest of the area, breaks down Friday into Saturday as a
stronger low pushes into the northern gulf. There is still some
uncertainty on how strong this low will be. The strength of the
low will really help to indicate what weather hazards to expect,
like how much rain we may receive and how strong winds may get.
Confidence on the location and timing of this low has slightly
increased, but it is still a ways out.

Temperatures through the long term period remain near average
with high temperatures in the mid to high 60s. There are
indications that areas near Hyder will see temperatures into the
mid to high 70s on Thursday and Friday. The main indicators of
this is continued dry weather along with 850 temperatures between
12 to 15 C. The limiting factor will be the amount of cloud cover
that they receive as the low pressure system moves into the gulf
bringing more moisture into the area.

&&

.AVIATION...

Improving flight conditions through the morning hours today, with
mostly MVFR conditions in the inner waters and IFR to LIFR just
offshore, predominantly in the NE gulf coast. Not expecting these
conditions to last too long in the inside waters, as daytime
heating, ridging and drying aloft looks to raise CIGS to high MVFR
to VFR for most locations. An incoming front tonight is expected
to bring conditions back down to MVFR, with CIGs between 1500 and
2500 ft for the central and northern panhandle. There is the
possibility for IFR conditions, even if they do not strictly
happen at TAF sites, for the outer coast. Additionally, weak
forcing will at least bring a few light showers to drizzle for the
aforementioned areas. The southern panhandle does look to get
these lower conditions, specifically Ketchikan and Wrangell, but
this looks to occur just outside of the TAF issuance.

As for winds, relatively light winds overall, with no LLWS
concerns. Skagway continues to be a sore spot for winds, however,
winds do look to lax tonight as upper level support shifts out of
the area.

&&

.MARINE...
Outer waters: Building high pressure in the gulf contributed to
decreasing winds overnight, and this trend will continue through
Tuesday. Waters near Cross Sound are the exception here, with
isallobaric winds (rising pressures) increasing near this area,
channeling into Cross Sound up to 15 knots. Similar story for
wave heights, but with a predominantly southwest swell up to 6 ft,
wave are expected to be slow to diminish. Buoy 083 off Cape
Edgecumbe is reporting 8 ft seas dominated by a westerly swell
with a wave period around 10 seconds. Waveheights up to 10 feet
were observed up to 3am. Looking ahead in the week, a system
moving up along the western gulf late Wednesday into Thursday
morning will develop a barrier jet bringing increased seas and
winds to the coast near Cape St Elias.

Inside waters: While some increased southwesterlies near the
mouth of Glacier Bay and Cross Sound from the aforementioned
isallobaric winds are present, they are expected to gradually
weaken through the day today. With the gradually increasing high
pressure over the panhandle and lower pressure over the interior,
Lynn Canal is expected to hover between 15 and 20 kt through the
day with gusts up to 30 kt, particularly near Taiya Inlet. Other
than the winds up north, the primary hazard for marine travel will
be persistent low clouds, mist, and fog potential, primarily for
the central and southern panhandle through the morning hours.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Small Craft Advisory for PKZ642>644-652-662>664-671-672.

&&

$$

SHORT TERM...DS
LONG TERM...EAB
AVIATION...NC
MARINE...STJ

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