Graphical Hydro Meteorological Discussion

349
FXAK68 PAFC 210034
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
434 PM AKDT Sun Jul 20 2025

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through
3: Tonight through Wednesday)...

Southcentral Alaska remains on the northern periphery of a North
Pacific ridge this afternoon. Meanwhile, a broad longwave trough
sits out over the Bering Sea, ejecting a series of shortwave
troughs up and over the top of the ridge, across Southcentral.
One shortwave is presently tracking across Southcentral, promoting
showers from the Kenai Peninsula, up through Anchorage, into the
Matanuska Valley. As the shortwave quickly exits to the east,
there will likely be a lull in shower activity this evening before
a second wave lifts quickly from the Aleutians toward Southcentral
tonight. This will reinvigorate shower activity, with the heaviest
precipitation shifting to the western slopes of the Chugach Front
Range and the south and west of the Talkeetna Mountains. These
locations could see a tenth of an inch or two, meanwhile lower
elevations around Cook Inlet are likely to remain less than a
tenth of an inch, and most likely only see a few hundredths
through Monday morning.

The second wave exits the area on Monday, leaving the Copper Basin
mostly dry. The Cook Inlet region looks at a warmer and drier day,
but temperatures are likely to be hindered by lingering cloud
cover hanging up along the mountains potentially through midday.
Thereafter, expect a mostly sunny afternoon, with highs in the
upper 60s for most low elevation locations, with the exception of
the Copper Basin where temperatures reach into the mid to upper
70s.

Beyond Monday, a pattern shift starts to take place with the
Bering trough shifting east over the mainland and flattening the
ridge over the Gulf. Prevailing flow turns more westerly and then
northwesterly by Tuesday as another more potent trough moves
across the Alaska Range and digs into Southcentral. Gusty offshore
gap winds are expected to pick up along the Gulf coast as early
as Monday evening, especially across the eastern Kenai Peninsula
and through the Kamishak Gap into the Barren Islands. The
strongest sustained west to northwest wind could reach gale force
by Tuesday morning.

Cooler temperatures aloft brought by the troughing increases
instability over the Copper Basin, which will lead to showers and
may even contribute to some isolated thunderstorm development in
the southern portion of the valley Tuesday afternoon/evening.
Precipitation becomes increasingly likely for the Copper Basin by
Wednesday. While the Copper Basin cools and becomes wetter, the
Cook Inlet region remains mostly dry, with high temperatures
reaching around 70 degrees by mid-week.

&&


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

Southwest Alaska is currently in a region of southwest flow
between a north Pacific ridge and a low near St. Matthew Island.
This is allowing for relatively light winds for inland areas and
breezy winds for the Bering. A small region of small craft winds
will affect the Pribilof Islands through early Monday morning. A
weak wave passing through the Southwest mainland is bringing
rainfall, particularly to the Kuskokwim regions. In the Bering,
widespread low stratus and fog with some breaks in cloud cover is
prevalent. Low stratus and fog will drift into the Southwest
coast by the nighttime hours. By Monday, the low will track
north toward the Seward Peninsula, allowing for the ridging to
extend northward. Rainfall chances in the mainland will decrease
as a result. The Bering will be similar to today with low stratus
and fog lingering. These conditions in the Bering will remain for
the entire forecast period and potentially the whole week. The
coastal regions of the southwest mainland will similarly have low
stratus and fog push in as long as the southwesterly flow remains.
Meanwhile, a shortwave trough will push into the mainland on
Tuesday, allowing for increased rain chances, lasting through
Wednesday. Wind speeds however, will remain on the light side.

-JAR

&&

.LONG TERM FORECAST (Days 4 through 7: Thursday through
Sunday)...

Little change from previous discussion. Models show the low
currently over the Bering Sea slowly progressing northeast toward
the Chukchi Sea. This causes a flattening of the ridge and a turn
to northwest flow over all of Southwest, South Central, and the
Aleutian Chain by the the middle of the week. Embedded shortwaves
are likely in this pattern, however moisture availability may be
somewhat limited. We`ll be watching for the low over the Chukchi
to drop south, potentially bringing higher precip chances to much
of the region through the weekend.

-DD


&&


.AVIATION...

PANC...MVFR ceilings are expected by late afternoon as a
shortwave trough advancing from the west ushers in another round
of scattered showers. The shower activity may taper off for a time
this evening; however, a trailing wave moving from Bristol Bay
into the lower Susitna Valley tonight will likely bring additional
rain showers to the terminal late this evening through early
Monday morning. Ceilings may continue to lower to IFR during this
time as the southwesterly flow near the surface weakens in
conjunction with lingering low-level moisture. Rain chances
diminish greatly by mid to late Monday morning as a developing
near-surface westerly flow acts to drive any lower clouds away
from the terminal, banking up against the foothills of the
Chugach. Winds through the period will remain variable and light.

&&


$$

687
FXAK69 PAFG 202029
AFDAFG

Northern Alaska Forecast Discussion
National Weather Service Fairbanks AK
1229 PM AKDT Sun Jul 20 2025

.SYNOPSIS...
The last warm and mostly dry day is upon us in the Interior.
Expect highs in the 70s and low 80s with a couple of isolated
showers or storms in the higher terrain. Isolated showers and
storms are also expected in the Brooks Range and North Slope this
afternoon and evening from a front approaching from the southwest.
This front also brings more widespread rain to the Interior with
the slightest of chances for a thunderstorm tonight in the White
Mountains. Heading into the new work week, rain chances remain,
especially along the West Coast and in the Western Interior.

&&

.KEY WEATHER MESSAGES...
Central and Eastern Interior...
- A front moves through tonight with the widespread rain and
chances for storms, especially in the higher terrain of the
Interior, west of the Dalton.
- Widespread rainfall totals of 0.10 to 0.25" with localized
0.50"+ possible in the most persistent showers/storms.

- A cooler and wetter pattern persists through much of the week
with shower chances and cooler temperatures in the 60s/low 70s.

West Coast and Western Interior...
- A low over the Bering is bringing numerous rounds of rain
through the remainder of the week.
- 0.50 to 1.50" in the W. Brooks Range and from the Seward Pen
south, with up to 0.50" in the Interior through Wednesday.

- Isolated thunderstorms in the Northern Western Interior this
afternoon.

- Additional rain is likely through the end of the week as the low
drops south over SW AK.

North Slope and Brooks Range..
- While the wind has subsided, the fog has lasted a bit longer
than initially anticipated. The fog will be exiting this
afternoon as the coastal stratus deck erodes.

- Isolated thunderstorms in the Western Brooks Range and across
much of the North Slope this evening, then numerous showers.

- Widespread rain showers likely along the coast by late tonight
and continuing through tomorrow.

- 0.25 to 0.50" of rain expected tonight through Monday night with
areas over an inch likely in the Brooks Range.

&&

.FORECAST ANALYSIS AND DISCUSSION...
A low in the Bering Sea is the driving force of Northern Alaska`s
weather through next week. This low is gradually moving north over
the Bering Strait today, then sit for a few days before dropping
south and east over the Western Interior and into the Gulf towards
the end of the work week. The impacts from this will be numerous
rounds of rain, especially along the West Coast and Western
Interior which may be enough to end most of the fire weather
concerns. The Central and Eastern Interior will be wet as well,
but not as much. The only exception may be in the SE Interior and
Eastern AK Range towards the end of the week as heavy rain
becomes possible. The low currently in the Bering will drop south
into the Gulf Thursday/Friday bringing wrap around moisture and
upslope flow and this is something to monitor.

&&

.FIRE WEATHER...
A warm and dry day across the Central and Eastern Interior with
highs in the 70s to low 80s and min RHs largely in the 30s/40s.
There will be a couple of spots with RHs near the upper 20s,
specially near the Ptarmigan Complex. There will be isolated
thunderstorms from the Fortymile Country, through the White
Mountains and to the Western Brooks Range. Most of the
thunderstorm activity will be in the Western Brooks Range and N.
Western Interior as a front moves from southwest to northeast.
Most of the activity will be late afternoon (after 4PM) through
about midnight. Wetting rains are likely for many locations in the
Interior as the front moves through. Even the Yukon Flats will
get some rain out of this late tonight into tomorrow morning.
Cooler and wet conditions look to persist through the end of the
week across much of the state.

&&

.HYDROLOGY...
No concerns at the moment, but numerous rounds of rain will allow
for rivers across Northern Alaska to gradually rise. We are not
anticipating any flooding, but some gravel bars may be covered,
especially in the Western Interior.

&&

.EXTENDED FORECAST DAYS 4-7...
The low near the Bering Strait is ejecting a shortwave into the
Gulf Wednesday into Thursday with heavy rain possible in the SE
Interior and Eastern AK Range. Over 1 inch of rain is possible.
The low will move out of the Bering Strait Region and drop into
SW AK late on Thursday, with another round of rain for Western AK.
Then the low drops into the Gulf and south of our area by the
weekend. After this, there is high uncertainty in what happens
next. Right now, there are hints of upper level ridging returning
towards next Monday (the 28th) with a low in the Gulf providing
easterly waves. We`ll have to monitor this as it could mean
increased fire activity again.


Coastal Hazard Potential Days 3 and 4...
West to southwest flow will bring some high water to the West
Coast about 1 to 4 feet above the normal high tide line Monday
through Wednesday. The highest water looks to be in Eastern
Norton Sound. Items on the beaches may be washed away if they are
close to the normal high tide line. There may be localized coastal
erosion as well.

&&

.AFG WATCHES/WARNINGS/ADVISORIES...
AK...None.
PK...Small Craft Advisory for PKZ801-802-850.
Brisk Wind Advisory for PKZ860.
&&

$$

794
FXAK67 PAJK 210609
AFDAJK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
1009 PM AKDT Sun Jul 20 2025

.UPDATE...After 06 TAF issuance except for some coastal airports
have clouds, but interior one are generally clear over night and
into Monday. Lower clouds possible for Yakutat area, Sitka and
Klawock.


&&

.PREV DISCUSSION....ISSUED AT 251 PM Sunday 20 July...

SHORT TERM.../Through Monday night/ Low to mid level cloud cover
is clearing out nicely this afternoon based on satellite imagery
due to more offshore flow across most of the panhandle. The hold
outs as of 1 pm are around Cross Sound, Glacier Bay, and along
the NE gulf coast. Temperatures have consistently been warmer as a
result this afternoon with more areas reaching into the upper 60s
so far.

Into Monday and Monday night the clearer weather is expected to
continue with the exception of the marine layer clouds along the
outer coast and in Icy Strait moving in and out (these clouds
could reach as far inland as Angoon and southern Lynn Canal
tonight and Monday night). Warmer weather is expected tomorrow as
a result with more wide spread 70s for highs likely. Some area of
the southern panhandle will likely hit 80 with the most likely
regions being inland areas away from the cooling effects of any
sea breezes that develop. Heat advisories have been issued for
Monday afternoon as a result. Annette Island has been excluded as
the marine influence will likely be too much for most of the island
to warm to 80 or higher.

The higher temperatures Monday afternoon will also promote
stronger sea breeze winds in localized areas. Some of these could
reach 20 kt and will likely cool down areas near the channels when
they develop.

LONG TERM.../Tuesday through Saturday/...The ridging that has
brought clear and dry weather earlier this week begins to
straighten into a more westerly flow from the surface all the way
up to 500 mb. Onshore flow and an approaching system will begin to
increase cloud cover for the northern panhandle through Tuesday.
A tightening pressure gradient will increase sustained winds in
the gulf to at least 20 kts, with speeds peaking Tuesday evening
around 25 kts off the southern coast of PoW. Gusts may reach 30 to
35 kts in Dixon Entrance. Westerly flow across the gulf will
funnel between Kodiak Island and the Kenai Peninsula and
drastically increase. From these gap winds, the central gulf can
expect to see up to 30 kts of wind with significant wave heights
reaching 10 to 12 ft through Wednesday. This is not expected to
reach the outer coastal waters.

High temperatures of between 14 to 16 degrees C at 850 mb
indicate warm surface temperatures continuing into Tuesday, though
not to the same caliber as Monday. The northern panhandle will
cloud over throughout the day which will lower max temps. Southern
interior regions of the panhandle will experience the highest
temperatures, with highs reaching the mid to high 70s and lows in
the mid 50s. Max temp EFI values are still 1 for Tuesday. NBM
probabilities have consistently indicated a very high potential of
reaching 80 degrees in areas of the southern panhandle. These are
areas of known temperature biases for the NBM, and other models
are only estimating around a 30% chance for the southern
panhandle, so confidence is still low on temperatures actually
breaching 80 Tuesday.

The consistent upper-level winds help to pull a broad upper-level
trough across the gulf and over the panhandle by Wednesday. This
will assist the associated surface shortwave trough in
strengthening into a disorganized, yet closed low moving east over
the northern gulf coast. The northern panhandle can expect light
rain Wednesday with minor accumulations of 0.25 inches or less in
24 hours. This will spread to the entire panhandle Thursday, with
light rain persisting through Friday before the next system brings
more impactful precip Saturday morning. As this troughing shifts
east over the border, NW winds push another deep upper-level low
into the gulf where it looks to stall through the weekend. The
associated surface low has potential to bring increased rain and
winds with most impacts in the southern panhandle. The 12Z GFS
runs are pushing for much stronger impacts than the rest of the
models, with frontal winds bordering on gale force, therefore it
is currently being considered less. Stay tuned through the week as
we will continue to update the forecast as guidance becomes more
consistent.

&&

.AVIATION.../ 00z issuance /Most areas in the inner channels have
cleared out with a nicely developed marine layer. Kruzof Island
has successfully held back the ongoing marine layer from both
Sitka and the western front of Prince of Wales Island. Expecting
to see the mostly low MVFR CIGs currently out on the outer waters
to move back inland tonight into Gustavus, western PoW Island,
Sitka, and possibly as far as Kake, Angoon, and Juneau. Yakutat
looks to take a brunt of the low clouds yet again, with LIFR CIG
conditions developing early tomorrow morning from descending
clouds overnight. Will most likely see some IFR to borderline LIFR
conditions move into Sitka and Klawock overnight as well, but not
looking lower than that at this time.

&&

.MARINE...Inside waters: Afternoon and evening sea breezes remain
the main concern for the inside waters for the next few days.
Winds currently are around 15 kt or less with 3 ft or less seas,
but with the warmer temperatures expected on land over the next
few days some of these sea breezes could reach 20 kt in localized
areas. Otherwise lighter winds and low seas expected for the next
few days.

Outside waters: W to NW winds of 15 kt or less are the order of
the day across the gulf. Highest winds are along the outer coast
from Cape Fairweather southeastward. These winds are expected to
strengthen this evening to 20 to 25 kt off of Baranof and Prince
of Wales Island as the ridge in the gulf strengthens. The rest of
the gulf will see winds strengthen to 20 kt Monday into Monday
night as a weak shortwave moves through flattening the ridge. Seas
remain low at 6 ft or less (S to SW swell of 3 ft at 16 sec), but
are expected to start building up to 7 to 8 ft as winds
strengthen. First off of Prince of Wales Island tonight and then
across the rest of the gulf by Monday night. This will mostly be
from wind wave as swell remains mostly 2 to 3 ft or less.

HYDROLOGY...The warmer temperatures across the northern panhandle
expected from Sunday afternoon through Tuesday will increase melt water
runoff from glaciers and any remaining snow at higher elevations
over the next few days. River levels on the Chilkat did not rise
as high as expected Sunday morning likely from increased cloud
cover and cooler temperatures over the Chilkat Valley on Saturday.
This lower starting point for river levels today has delayed the
possible time that the Chilkat could reach minor flood stage over
the next few days. The revised timing now has the Chilkat River
most likely reaching above minor flood stage by late Monday night
(a good 24 hours later), and while there will be daily
fluctuations, the river may stay at or above minor flood stage
possibly into Wednesday morning. The flood watch for the Chilkat
Valley has been pushed back 24 hours to reflect the new
information and is now in effect from late Monday night into
Wednesday afternoon. However if the Chilkat Valley sees cooler
temperatures than expected Sunday or Monday, that could delay
this even further if there is not as much melt water runoff as
expected on either day.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Flood Watch from late Monday night through Wednesday afternoon
for AKZ319.
Heat Advisory from 1 PM to 8 PM AKDT Monday for AKZ328-330-331.
MARINE...Small Craft Advisory for PKZ641-642-661-662.

&&

$$

SHORT TERM...99
LONG TERM....99

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