Graphical Hydro Meteorological Discussion

358
FXAK68 PAFC 121301
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
501 AM AKDT Wed Aug 12 2026

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

An upper level ridge remains over the Gulf of Alaska and into the
Copper River Basin today. This ridge will remain largely
stationary the next few days which will allow an upper level wave
to move northward in the clockwise flow around its western
periphery. This wave can already be seen on GOES satellite south
of Kodiak Island early this morning. This upper wave will bring
rain today to Kodiak Island and then head up Cook Inlet. This is
where there is some increased uncertainty: this wave appears to be
moving farther to the east than it was previously, which opens up
the possibility for some rain showers for the western Kenai
Peninsula overnight tonight. As this wave propagates into the
Susitna Valley, there is an increasing chance for some rain
Thursday morning for the Anchorage and MatSu areas.

After this wave passes through, the ridge will reassert itself
over Southcentral for the remainder of the week. The result will
be for partly cloudy to mostly sunny skies over the region with
increasing temperatures for Friday into the weekend for most parts
of Southcentral. The northeastern Copper River Basin will be the
area most likely to see afternoon and evening showers and isolated
thunderstorms the next few days.

&&


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

High pressure over Southwest Alaska breaks down on Wednesday as
an area of low pressure lifts out of the North Pacific and over
the Western Alaska Range. With increasing clouds and limited
instability on Wednesday the threat for thunderstorms comes to an
end. Rain chances increase late Wednesday through Thursday with
Thursday looking like a wet day for much of Southwest Alaska.
Meanwhile, a broad upper low and front over the western Bering
will stall just short of the Pribilof Islands this afternoon. Rain
showers will impact the Aleutians from Adak to Atka, but should
go no farther than Nikolski. Showery conditions will overspread
the Eastern Aleutians and Alaska Peninsula throughout the day on
Wednesday before spilling into much of Southwest Alaska on
Thursday. Gusty winds, mainly at small craft speeds, will exist
across the Western Bering with the broad upper low, and also from
the Alaska Peninsula and Bristol Bay into the interior out of the
Kamishak Gap. Friday will see an improvement across Southwest
Alaska with decreasing winds and drier conditions as high pressure
tries to resume across the region, though the western Bering will
continue to be under the influence of a broad upper low.

-BL


&&


.LONG TERM FORECAST (Days 4 through 7: Saturday through
Tuesday)...

The general pattern going into the weekend will have an upper low
over the central Bering with a ridge over Mainland Alaska. On
Saturday, the upper low begins to move to the eastern Bering and
makes an attempt to push the ridge northeastward into the
Interior/Yukon down through the Alaska Panhandle. Temperatures
across the region will begin to cool as cloud coverage increases
from west to east. For most of Southcentral and the Kuskokwim
Valley, cloud coverage doesn`t increase until Saturday night.
Saturday will continue to be warm for these areas with highs in
the 70s at lower elevations with up to 80 degrees in spots of the
Copper River Basin and Kuskokwim Valley.

A surface low from the North Pacific will cross the eastern
Aleutian Chain Saturday and stall in the eastern Bering through
Tuesday. This low will also send a front eastward through the Gulf
and Southcentral Alaska Sunday into Monday. This will make
conditions conducive for rainfall across the Aleutians, the AKPen,
Southwest Alaska, Kodiak Island, and the Gulf Coast into early
next week. Some rainfall may be heavy, especially for the
Aleutians on Saturday, the AKPen, Kodiak Island, and portions of
Southwest Alaska Sunday into Monday, and the northern Gulf Coast
(particularly the southern Kenai Peninsula) Monday into Tuesday.
Though model agreement is fairly good, there are still slight
differences with the strength of the low and progression of the
low and front. Thus, while confidence is high with which areas
will receive the heaviest rain, confidence is still low on exact
timing and amounts of rainfall into early next week. The other
factor with the low moving through will be the potential for
southeasterly winds accelerating through favorable gaps and bays
of the AKPen (such as Cold Bay) Saturday into Sunday.

As the front progresses eastward Sunday into Monday, light
precipitation will spill over the mountains into the rest of
Southwest and Southcentral and linger into early next week. This
will result in cooler temperatures compared to this week. Though
the ridge is pushed east, it likely stays over the Copper River
Basin on Sunday before being pushed out to the Interior/Yukon.
There is also some model uncertainty on both when and how much
the front breaks the ridge down. The longer the ridge holds on,
the later precipitation will spill over into the Copper River
Basin. The Copper River Basin likely sees at least one additional
day of warm and dry conditions compared to the rest of
Southcentral Alaska. Any potential warm days past Sunday will be
determined by how much the front breaks the ridge down. Details
will become more clear in the coming days.

-PA

&&


.AVIATION...

PANC...Fog and low stratus are expected to linger along Cook
Inlet this morning and intermittently push into the vicinity of
the terminal. Ceilings will predominately remain MVFR, but will
occasionally drop to IFR (and possibly even LIFR for a brief
period). Ceilings are expected scatter out by mid afternoon due to
radiational heating, likely causing VFR conditions to return. A
frontal system approaches from the south this evening, causing
more widespread cloud coverage and a slight chance for rain
showers tomorrow morning.

&&


$$

000
FXAK69 PAFG 122304
AFDAFG

Northern Alaska Forecast Discussion
National Weather Service Fairbanks AK
304 PM AKDT Wed Aug 12 2026

.SYNOPSIS...
A summer-like pattern will continue over most of Northern Alaska
as a ridge builds in from the south and stations itself over the
area through the weekend. On the west side of the ridge, scattered
showers and isolated storms will be prevalent through this
evening from McGrath northward to the Western North Slope. A weak
piece of energy from a low in the Pacific will race northward and
be the main driver of precipitation chances today. The Eastern
North Slope will remain dry due to a surface high north of
Kaktovik. Easterly winds along the Eastern Arctic Coast should
keep it cooler than the Plains and Chukchi Sea Coast. Otherwise,
the Central and Eastern Interior will be baking as highs remain in
the 70s/80s through the end of the week. There will be a chance
for isolated showers/thunderstorms, especially in the higher
terrain Thursday afternoon, but the most prominent time period
for some wet weather will be Friday as a weak upper level
disturbance provides moisture and enough lift to support showers
and thunderstorms across the Interior.

&&

.KEY WEATHER MESSAGES...
Central and Eastern Interior...
- Warm and dry with highs in the 70s/80s today, tomorrow and
Saturday. Friday will be a few degrees cooler, especially north
of Fairbanks with an increase of clouds and scattered showers.

- From Fairbanks south/east it should remain mostly dry, but there
will be a slight chance for a shower Friday morning into the
afternoon as a weak disturbance moves overhead.

West Coast and Western Interior...
- Warm today with scattered showers and isolated storms, mainly in
the Interior today as a weak disturbance moves from south to
north.

- Temperatures are warm today with highs in the 60s to near 70
along the coast, and in the mid to upper 70s inland. Tomorrow is
a few degrees cooler due to an increase of clouds and showers
but highs warm once again Friday through the weekend.

- After the showers/storms today and tomorrow, Friday through the
weekend will be much drier with increased sunshine.

North Slope and Brooks Range..
- Warm weather is expected across the Central and Western North
Slope with highs in the 60s along the coast, and mid 70s in the
Plains. Cooler temperatures from Deadhorse east with highs in
the 50s/60s. The Brooks Range will be in the 60s and 70s.

- Scattered showers and thunderstorms expected, particularly in
the Western Brooks Range/North Slope today and tomorrow.

- Shower coverage shifts over the eastern North Slope on Friday
with a chance for a thunderstorm in the Plains and Brooks Range
with drier and warmer weather expected on Saturday.

&&

.SHORT TERM...
Although we are seeing an increase in ridging, there are quite a
bit of moving pieces to this forecast and each one will contribute
to different types of weather across Northern Alaska. Getting into
the details, we`ll look at the general overview of the upper
levels. We are beginning to see our overarching pattern take
shape over the Interior as a 594 decameter ridge near 30N extended
northward through the Arctic Coast. A relatively weak 560
decameter low south of the Alaska Peninsula near 45N is being
sheared apart allowing for a shortwave to extend northward in the
Western Interior today, then towards the Brooks Range/North Slope
tomorrow. Accompanied by this shortwave is a 300mb jet streak,
around 50-80kt which will help support some wet weather in Western
Alaska today and tomorrow, the Eastern Alaska on Friday as it
shifts east.

Otherwise, the main ridge of high pressure will be getting choked
in the middle by two areas of lower pressure on each end. This
allows for an anomalous +2 sigma high to set up over Northern
Alaska by Friday. The high will gradually meander northwest this
weekend, then potentially east by next week. But that will be
spoken about more in the long range forecast.

Getting into more of the specifics, there was a shortwave
mentioned before from a low in the Pacific. This wave of energy
will be coming with jet support and 700mb moisture. This energy
will be running into an atmosphere capable of producing
thunderstorms and will be the forcing mechanism. Isolated to
scattered showers and thunderstorms are likely to develop this
afternoon in the Western Interior, then gradually shift northward
to the Brooks Range this evening. The shortwave will lose some of
its punch as it slows and weakens over the Brooks Range tonight.
However, it will be over an unstable airmass, so thunderstorms are
still likely to occur north of the Yukon River with a bullseye
over the Northwestern Brooks Range and Western Arctic Plains
Thursday afternoon/evening. Moving into Friday, this energy will
be forced southeast by a weak cold front moving into the North
Slope, allowing for slightly cooler temperatures across the area.
With a degrading moisture source and less instability, a few
thunderstorms are possible in the Brooks Range, Central and
Eastern Interior Friday afternoon, but most of the area would only
see rain showers. This weekend, the ridge builds overhead with
very warm temperatures likely.

Getting into temperatures, something being monitored are the 850
mb temperatures which will be well above our normal values across
the area. For reference, the median 850 mb temperature for this
time of the year is around 5C. As this ridge builds in, we will be
seeing temperatures approximately between 10-12C across most of
Northern Alaska by Saturday. 850 mb temperatures this warm tend
to support surface temperatures in the 70s to low 80s for most
valley locations, disregarding cloud cover or any other
atmospheric features. Regarding cloud cover however, the ridge
will be pretty dry aloft, so there shouldn`t be too many clouds
except by any pop up shower or storm. So, there will be widespread
valley temperatures in the 70s and 80s, even on the North Slope
this weekend.

&&

.FIRE WEATHER...
Conditions will continue to warm today and tomorrow with many
valley locations expected to be in the 70s and low 80s, even in
the Arctic Plains. A shortwave will drift northward into an
unstable atmosphere over Western Alaska today through tomorrow
allowing for isolated to scattered thunderstorms from McGrath to
the Western Arctic Plain. the bulk of the activity will be north
of the Yukon River today, then in the Western Arctic Plain and
Brooks Range tomorrow. Isolated thunderstorms are then possible in
the Central/Eastern Interior on Friday. Temperatures will cool on
Friday, particularly on the North Slope with highs expected to be
5 to 10 degrees cooler, in the 60s and low 70s. Most of Interior
will also be approximately 3 to 5 degrees cooler due to an
increase in clouds and potential for showers and storms, but only
by a couple of degrees. The one exception will be in the Kuskokwim
Valley which remains in the upper 70s and low 80s while the
remainder of the Interior will be near the mid to upper 70s. This
weekend, the ridge builds in overhead allowing for a warming trend
over most of Northern Alaska.

Winds will remain fairly weak, but each afternoon there will be
variable diurnal wind gusts which may peak around 15 to 20 mph,
though they will be occasional and not widespread enough to
pinpoint exact locations. Min RHs will be low but mainly remain
above critical values with valley locations bottoming out near 30%
through the weekend. Isolated 25-30% values are possible in the
Tanana/Kuskokwim valleys, particularly this weekend. We will gain
more confidence in any critical values over the next couple of
days.

&&

.HYDROLOGY...
No concerns at this time.

&&

.LONG RANGE...
Throughout the extended period the stagnant high that has
remained persistent over Alaska will begin to progressively weaken
and be forced north and east by a closed low originating from the
Bering Sea that will travel towards the southwest coast of Alaska
on Sunday morning. Though there is low confidence, model guidance
suggests that by the end of the extended period, Alaska will be
divided by ridging along the Brooks Range and Interior and general
troughing towards southern portions of Alaska. Cooler
temperatures will likely be felt throughout the southwestern
portions of Alaska as soon as Monday when the state begins to be
divided between Northern ridging and southern troughing, with the
cooler conditions lasting through Tuesday. Generally drier
conditions will persist at the beginning of the extended period as
the ridge lingers through Saturday. As the Bering Sea low
approaches the southwest coast on Saturday wetter weather and
thunderstorm potential increases throughout the YK-Delta with
chances for scattered thunderstorms Saturday evening and isolated
storms in the Interior through Tuesday. Relatively calm winds are
expected throughout the extended time frame with the exception of
the Alaska Range Sunday to Tuesday, as the Bering Sea Low
increases the likelihood of both Isabel and Windy Pass
experiencing higher wind gusts throughout the end of this period,
although the peak strength and timing of these wind speeds are
still not certain.

Coastal Hazard Potential Days 3 and 4...None

&&


.AFG WATCHES/WARNINGS/ADVISORIES...
AK...Heat Advisory for AKZ816.
Heat Advisory for AKZ806-808.
PK...None.
&&

$$

SYNOPSIS...Bianco
KEY MESSAGES...Bianco
SHORT TERM...Bianco
LONG RANGE...Donner
FIRE WEATHER...Bianco

239
FXAK67 PAJK 121814
AFDAJK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
1014 AM AKDT Wed Aug 12 2026

.UPDATE...To the aviation section for 18Z TAF issuance as well as
an update to the Hydrology section...

.AVIATION.../Through Thursday morning/...The main aviation
concern for today will be the effects of the marine layer on the
outer coastal TAF sites lingering this morning and tomorrow
morning. Some southern sites struggled to break out of LIFR/IFR
conditions, though are now expected to persist in VFR through the
TAF period. The exception being PAKW, which could likely see the
return of low clouds tomorrow morning impacting both CIG/VIS.
Northern/central coast sites and into Cross Sound (Elfin Cove)
also seeing low clouds and MVFR/IFR conditions currently, with
higher confidence in CIGs AoA 2000ft until the afternoon. VFR
anticipated for these sites around 21Z to 00Z, breaking out from
south to north.Everywhere else in the panhandle is seeing VFR
conditions today with light winds to start, increasing through the
afternoon due to sea breezes. Highest winds will likely reach 15
to possibly 20 kts at most. Late tonight, offshore flow will
dominate the pattern so low clouds, possibly down to IFR or MVFR,
will keep mostly to the outer coast with all other areas remaining
generally VFR.

&&

.PREV DISCUSSION......ISSUED AT ...805 AM AKDT Wed Aug 12 2026

SYNOPSIS...

Key Messages:

- Suicide Basin is releasing. Major flood stage on Mendenhall Lake
and River expected to be reached Wednesday night.

- Warming trend for the week with highs in the 70s. Lower 80s
will be possible, especially across interior locations across
the south and far northern interior for mid to late week.

- The warm and dry conditions will bring elevated threat for fire
starts across much of SE AK. A few small fires have been
observed already over the past week.

SHORT TERM...Ridge of high pressure will build over the Gulf
through today, lingering through the rest of the week to the west of
the panhandle. Warm temperatures and dry weather is expected to
continue across the panhandle today through the end of the week,
with the warmest temperatures expected Thursday and Friday after the
ridging strengthens over the Gulf as westerly flow transitions to a
northwesterly offshore flow. Some marine layer clouds will still
develop in the Gulf with this ridge placement, however any low
stratus clouds are expected to stay just offshore and along the
outer coast.

The majority of the panhandle will see clearing skies
with the offshore flow, and by the end of the week most of the
panhandle is expected to see warmer temperatures with highs reaching
mid to high 70s Thursday and Friday. Inland areas along the Klondike
and Haines Highways may see high temperatures in the high 70s to low
80s through the end of the week with these clear skies. The southern
panhandle is also expected to see temperatures reach near 80 into
the low 80s Thursday and Friday, with areas further from the water
having potential to see daytime highs in the mid 80s.

There still is potential for some convective activity in the SE
corner of the panhandle Thursday and Friday afternoon/evening, with
the instability present and overall setup suggesting a very low
chance for easterly thunderstorms moving into the area. The moisture
still is not ideal however, and any development is likely to be
isolated over the SE panhandle and along the coastal range. Some
model guidance shows 60-70% RH at the low/mid levels with a bit of
westerly component to lower level winds to bring moisture into the
area, but confidence is still lacking as to if these ingredients
align for thunderstorm development.

LONG TERM...CORRECTED the right long term section / Friday
through Monday/...Ensemble models agreeing on an upper level ridge
dissipating and being replaced by a weak trough over the southern
panhandle by Friday, with the ridge rebuilding early next week.
This shift will bring positive vorticity advection and some
lifting, while moisture advection arrives via an easterly wave in
the 700mb level. Additionally, a surface maritime ridge forming in
the eastern gulf will generate northwesterly winds across the
panhandle which could work in conjunction with diurnally driven
sea breezes to promote weak onshore flow toward the end of the
week.

Regarding severe weather potential for end of week/early weekend,
guidance is keying in on seasonably high CAPE values in parts of
the central and southern regions, though forecaster confidence
remains low due to drier conditions in many of the atmospheric
pressure levels and a lack of support for sustaining storms
moving in from Canada. Cumulus fields are more likely than storms,
as a lack of a cap and significant moisture inhibits potential
convection. While westerly flow on Friday might drive some
localized convection through upsloping, marine influences will
likely stabilize the surface layer and choke off development.
Meanwhile, light winds and clearing skies are expected to boost
temperatures, with Friday and Saturday continuing this warm spell
as temperatures reach the upper 70s to low 80s, before cooling
returns Sunday into Monday as the surface high pressure weakens.
There is still a lot of spread in the track of a low pressure
center moving into the central gulf next week, and if lingering
high pressure will block precipitation from moving in. We will
continue to monitor this next system and associated rainfall
accumulation.

MARINE...
Outside: Marine forecast remains on track. High pressure over the
Gulf will strengthen and shift eastward, tightening the gradient
over the eastern Gulf. Gentle to moderate northwest breezes will
become fresh for the outer coastal waters from near Cape Spencer
down to Dixon Entrance. Wave heights of 3 to 4 ft will increase
to 4 to 6 ft by midweek and remain through the end of the week.
Winds will diminish by the weekend as the high weakens. Main
marine concern for outer and coastal waters will be nightly return
of marine layer, with fog and low stratus impacting visibility.

Inside: High pressure out in the Gulf is expected to linger
through the week, with light to gentle W/NW-ly winds overnight
shifting to a NW-ly moderate to fresh breeze for the inner
channels by this afternoon. Localized wind shifts due to sea
breezes are possible, alongside elevated gusts to 15-20 kt, but
overall wind direction is expected to be from the NW. Strongest
inner channel winds up to 15 to 20 kts are expected for the
afternoon and evening hours. Winds across the inner channels will
also diminish Thursday and Friday as the ridge begins weakening,
however N-ly winds of 15 to 20 kt are expected for northern Lynn
Canal from a tightened N-S gradient remaining across the northern
panhandle the end of the week.

FIRE WEATHER...High pressure continues to sit over the area with
no real signal of a pattern change likely until the upcoming
weekend. With the persistent dry weather, we have started to see
temperatures rise into the 70s with some pockets of 80s for the
inland areas with warm temperatures expected to continue through
the week. Looking at the past few days, relative humidities have
fallen down to the 30s to 40s for some areas during the daytime
hours with rebounding during the overnight hours into the 90s.
With the continued lack of rain, fine fuels such as grasses will
continue to dry. Models continue to suggest the potential for
isolated thunderstorms along the Panhandle border with Canada as
well as the SE panhandle on Thursday and Friday. However, due to
the lack of low/mid level moisture the chance of thunderstorms is
only around 15% or less.

Overall, expecting the dry and warm trend to continue through the
week with fire weather conditions continuing to develop, the main
variable to watch for will be daytime winds. As of now, expecting
the worst fire weather conditions to be Thursday and Friday
afternoon, however given the persistent pattern can`t rule out
this extending further into the weekend.

HYDROLOGY.../Flood Warning in Effect/

Mendenhall Lake gauge levels, along with USGS imagery from
Suicide Basin and water levels within the basin, indicate that
a glacial lake outburst flood is ongoing into Mendenhall Lake and
River.

As of 10am AKDT, the Mendenhall River is at 5.85 ft and rising.
It usually takes around 2 days from when the basin release starts
to when you see the highest water levels. Water levels on the
Mendenhall Lake and River will rise through today as the release
continues, with a forecast crest between 16.1 to 16.6 feet
expected early Thursday morning. Compared to previous years this
is slightly below last year`s high water mark, and above the high
water marks of 2023 and 2024.

Visit weather.gov/ajk/SuicideBasin for the latest updates on the
Glacial Lake Outburst Flood for Mendenhall Lake and River. The
weather.gov/ajk/SuicideBasin web page is currently updated every
two hours by the NWS Juneau office and as we move further into the
event, this cadence will increase to hourly updates.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Heat Advisory until 7 PM AKDT Thursday for AKZ318-319.
Heat Advisory from noon Thursday to 7 PM AKDT Friday for AKZ328-
330>332.
MARINE...None.

&&

$$

SHORT TERM...Contino
LONG TERM...BAS
AVIATION...BAS
MARINE...Contino
HYDROLOGY...SF

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