Graphical Hydro Meteorological Discussion

013
FXAK68 PAFC 201329
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
529 AM AKDT Tue May 20 2025

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

A weak shortwave can be seen on satellite imagery moving across
Cook Inlet and the Susitna Valley early this morning. So far, the
only precipitation caused by this wave has been some scattered
showers in the Susitna Valley. However, this will change as the
day goes on and this wave stalls out and becomes a boundary for
the development of showers for the central Kenai Peninsula
northward into the Susitna Valley. It looks like by later this
afternoon there will be showers that develop and train northward
and therefore could give some decent precipitation values in
narrow bands anywhere in the northern Cook Inlet through Susitna
Valley areas. Anchorage and the Matanuska Valley are on the edge
of this area and one of the big question for today is haw far east
the showers will fire up. It is possible that the southeasterly
Turnagain Arm wind later today will create a convergence area with
southwest winds moving up Cook Inlet and be the main point of
shower initiation.

There is a chance for an isolated thunderstorm in the northeastern
Copper Basin this afternoon before the increasing Copper River
winds start to usher in a little more stable airmass and shut off
any significant convective development. The Copper River,
Turnagain Arm, and Knik river winds will develop this afternoon
and persist well into the night. They should then briefly diminish
late in the night but then become even stronger tomorrow for all
those areas.

A front associated with a low in the Bering Sea will move into
the western Gulf on Wednesday which will bring rain to Kodiak
Island and parts of the north Gulf coast. The main low does look
like it will track into the Gulf of Alaska passing just south of
Kodiak Wednesday night and then eastward through Thursday. This
will keep the steady rainfall to the areas around the Gulf and
introduce some weak ridging aloft to the interior parts of
Southcentral. This ridging will be weak but should still bring in
some breaks in the clouds along with enough resultant warming in
an unstable environment for the afternoon and evening showers to
develop as well.

&&


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

A weak ridge lingers over the Southwest Alaska mainland, allowing
for calmer, drier conditions through the morning hours today.
Wind and precipitation chances increase again Tuesday afternoon
as a low tracks eastward across the southern Bering, arriving over
the Alaska Peninsula by Wednesday morning. Gale force gap winds
will be possible today along the Aleutian chain and AKPen. Winds
will be strongest on the Pacific side this afternoon, then
retrograding behind the low down across Unalaska and the
AKPen Wednesday morning before continuing south of Kodiak by the
afternoon hours. The low will draw moisture into the Southwest
mainland, allowing for widespread precipitation across all regions
late Tuesday into Wednesday.

This convoy-like pattern of lows will continue up to the weekend,
although there will be variation in the track and strength of
each system. As one system departs the region into the Gulf on
Wednesday, the next simultaneously enters the western Bering.
Winds decline across Southwest as another area of weak high
pressure builds from the interior mainland into Southwest.
Thursday`s system takes a more southerly route, dropping south
across Unalaska by Thursday afternoon. This will prospectively
keep the most intense wind and rain south of the Aleutians,
allowing for a longer break between systems and a more persistent
high pressure to develop over Southwest mainland on Friday.


&&



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

The overall synoptic situation continues its progressive pattern
and maintains generally good agreement through the forecast
period. The GFS and Canadian models carry the strengths and
development of all features with the ECMWF being a unsteady
outlier. On the upper level charts, an extended low stretches from
the Russian Far East across the Bering into the Gulf of Alaska.
This continues to support several surface features across the
region. Mostly showers dot the Southern Interior through the
weekend. The first surface low exits the Alaska Peninsula and
drifts along the Southern edge of the Gulf of Alaska before
turning Southeast through Sunday. Rain departs Southwest Alaska
and the AKPEN for late Saturday. In the West, a moderately strong
low and front move rain and locally gusty winds into the Western
Aleutians Friday, spreading across the AKPEN and Southwest Alaska
before exiting the Eastern Aleutians for Sunday. Another strong
low and front approaches from the North Pacific and bears down on
the Western Aleutians by Monday.

- Kutz

&&

.AVIATION...

PANC...VFR conditions and light winds will persist through this
morning. There will be a slight drop in cloud ceilings to 5000 ft
this afternoon and then just below 5000 ft this evening. Winds
will remain mostly southerly and increase with gusts to 25 kts
this evening and chance for rain showers increases.

&&


$$

851
FXAK69 PAFG 202118
AFDAFG

Northern Alaska Forecast Discussion
National Weather Service Fairbanks AK
118 PM AKDT Tue May 20 2025

.SYNOPSIS...
Showers in the Western and Central Interior. Isolated
thunderstorms in the Eastern Interior. Light snow showers along
the Eastern North Slope. Temperatures warm through the end of the
week.

&&

.KEY WEATHER MESSAGES...
Central and Eastern Interior...
-Showers continue this afternoon across the Central Interior.

-Isolated thunderstorms expected in the Eastern Interior,
particularly over elevated terrain in the Fortymile Country and
near the Upper Tanana Valley.

-Moderate southerly gap winds through the Alaska Range passes
tonight through Wednesday night. Gusts up to 35 mph possible
through Isabel Pass and gusts up to 30 mph possible through Windy
Pass.

-A warming trend is expected through the end of the week with
highs in the mid to upper 60s this weekend.

West Coast and Western Interior...
-Northerly Winds 25 mph mph through the Bering Strait and 20 mph
through the eastern Norton Sound.

-Light showers return to the Western Interior this afternoon and
remain through Thursday. Mostly scattered today and then becoming
isolated Wednesday.

North Slope and Brooks Range..
-Light snow showers persist across the eastern North Slope this
afternoon. Additional accumulations an inch or less.

-Northeasterly winds increase across the North Slope to 10 to 20
mph by Wednesday night. Winds get stronger further west.

&&

.FORECAST ANALYSIS AND DISCUSSION...
A stalled front sits over the Central Interior and Brooks Range
between broad troughing along the West Coast and a building ridge
along the Canadian border. Isolated thunderstorms expected today
in the Fortymile Country as the ridge and front interact.
Scattered showers expected across the Interior along the front
this afternoon. A 533 dam low moves through the trough pattern
tonight and causes the trough to dig south into the Gulf of Alaska
by Wednesday afternoon. This weakens the trough along the West
Coast causing the front to fall apart as ridging strengthens in
the Interior. The strengthening ridge will bring a warming and
drying trend through the end of the week. Another 535 dam low
moves through the pattern Thursday and interacts with the previous
low that moved into the Gulf. At this point models begin to have
difficulty determining how these two lows interact with each other
which will change how ridging across the Interior behaves. The
most likely solution is that the second low wraps into the first
one as a shortwave feature, which will strengthen it enough to
potentially break free of the Arctic low pressure at the top of
the trough. Should this occur the ridge will be able to build in
much stronger than previously expected which will strengthen the
warming and drying trend possibly bringing temperatures in the
upper 60s to low 70s to the Interior. A 594 dam high in the north
central Pacific will try to extend a ridge into the Bering Sea
late Friday, but a 521 dam low moving into the Western Bering at
the same time will prevent a ridge from fully forming. These
features will further complicate the mess of lows over southern
Alaska leading to poor forecast confidence on the finer details of
the forecast after Friday. Generally though, ridging will keep the
Interior warmer and drier with afternoon convection possible each
day Friday through the early part of next week.

&&

.FIRE WEATHER...
Showery conditions continue for the Central Interior today.
Showers move into the Southeast Interior this afternoon and will
help to moderate the dry conditions of the past several days.
Another area of showers moves into the Western Interior overnight
tonight. This results in decent chances of wetting rain across
much of the Interior through Wednesday. Showery conditions
diminish Wednesday into Thursday as ridging builds into the
Eastern Interior. This will cause a steadily warming and drying
trend through the end of the week with Interior highs in the upper
50s to lower 60s today rising to into the mid 60s by Friday.
Minimum RHs fall from the mid 30s to low 40s today into the mid
20s to 30s Wednesday and remains steady through Friday. Generally
weak flow aloft will limit winds in the Interior, but some weak
southerly gap winds are possible through the Alaska Range passes
tonight through Wednesday night. Elsewhere northerly winds along
the West Coast slowly diminish through Thursday.

Thunderstorms are expected in the Fortymile Country and Upper
Tanana Valley this afternoon. Mostly isolated, but there is
potential for widely scattered Thunderstorms near Northway and
Eagle. Thunderstorms will be generally confined to elevated
terrain, but may drift north after forming. Isolated thunderstorms
are expected Wednesday afternoon as well, generally confined to
elevated terrain in the Fortymile Country, but may reach into the
Yukon Flats later in the evening.

&&

.HYDROLOGY...
Degraded ice remains in place at the mouth of the Yukon River.
Breakup has yet to begin along the Porcupine, although some of the
upper tributaries are beginning to respond to snowmelt. Enhanced
snowmelt in the Chena Basin will lead to gradual rises in water
levels, although there are no immediate flooding concerns.

&&

.EXTENDED FORECAST DAYS 4-7...
A broad trough extends from the high Arctic through the West Coast
and into the Gulf of Alaska. Models are in good agreement on this
broad pattern. Ridging builds into the Eastern Interior which
will allow for warmer and drier conditions in the Central and
Eastern Interior early next week. Afternoon showers and isolated
thunderstorms are possible most days under this pattern in the
Central and Eastern Interior.

Coastal Hazard Potential Days 3 and 4...None

&&

.AFG WATCHES/WARNINGS/ADVISORIES...
AK...None.
PK...Small Craft Advisory for PKZ806.
Heavy Freezing Spray Warning for PKZ811.
Small Craft Advisory for PKZ811.
Heavy Freezing Spray Warning for PKZ812.
Small Craft Advisory for PKZ854.
Brisk Wind Advisory for PKZ856.
&&

$$

Stokes

036
FXAK67 PAJK 202213
AFDAJK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
213 PM AKDT Tue May 20 2025

.SHORT TERM...Somewhat dreary day, with a nearly fully saturated
atmosphere for the panhandle from the surface up to 500 mb. A
weak, progressive shortwave aloft moving over the panhandle looks
to provide the most modest amount of lift to ensure most areas of
the panhandle remain wet for this Tuesday. Looking at water vapor
satellite, a dry slot in the southern panhandle is clearing some
clouds in Ketchikan with mostly clear conditions in the Metlakatla
area. Wednesday sees the weak shortwave be replaced by a transient
ridge aloft, which will provide some clearing from dry air
advecting into the inner channels, but due to widespread surface
moisture, not looking to see widespread clear skies.

.LONG TERM...Looking towards late week, guidance have begun to
converge on a less progressive pattern, with increased cold air
descending down from the Arctic. This cold air will intensify the
trough, increasing the amplitude, and directing the moisture flow
towards SE AK. The result will be multiple waves of moisture
moving over the panhandle beginning this Saturday. Exact details
of this evolving system are hazy, but what can be said is long
duration moderate rain with periods of heavy rain will move into
the southern panhandle. What is uncertain is how far this moderate
to heavy rain producing moisture will move northward. Currently,
the more likely solution is the heavier moisture will be directed
at the southern panhandle with lighter precipitation from
Petersburg up to Juneau. However, trends in ensemble guidance has
probabilities increasing for these much higher than normal
precipitation totals up into the Juneau area. In the southern
panhandle, there is around an 80% chance for 2 inches of rainfall
in 24 hours, while the same percentage chance exists for 1 inch of
rainfall for areas like Juneau, Gustavus, Angoon, and Sitka.
Regardless of either solution, with the current state of rivers,
no flooding is currently expected.

&&

.AVIATION...Through Tuesday a layered sky has caused varied
VFR/MVFR conditions, with towering cumulus mainly south of
Frederick Sound. By and large the most concerning cloud base is
2000ft to 3000ft, with FEW/SCT AoB 1500ft. Expect -SHRA to
continue through the evening with VIS dropping to 4SM at times
with heavier showers. Early Wednesday morning expect MVFR CIGS
from a shallow cloud deck to settle in across the region,
improving to VFR showers in the afternoon. Winds at major
airfields remain below 15 knots with the exception of Skagway,
expect 15 to 25 southwesterly summertime breezes by Wednesday
afternoon.

&&

.MARINE...

Eastern Gulf of Alaska: Surface ridging over the
panhandle will give general onshore-to-southerly flow in the Gulf.
Wind speeds will be generally 5 to 15 knots through Thursday,
little closer to 15 to 20 knots in the central gulf. Friday into
Saturday, an area of low pressure will track southeast through the
western and southern gulf. Ahead of this low, southerly wind
speeds will increase to around 15 to 25 kts with the higher
speeds, 20 to 25 knots, in the southern marine areas and in Dixon
Entrance.

Wave heights will be mainly less than 5 feet until that low pressure
approaches, then wave heights will build ahead of the low to upwards
of 8 to 10 feet.

Inner channels: Inner channel wind speeds look to be pretty light
overall through most of Friday - generally out of the south at
around 5 to 10 knots. The main exception to this is Icy Strait and
Lynn Canal, where speeds will be upwards of 15 to 20 knots tonight
and tomorrow, with speeds decreasing tomorrow night.

Late Friday into the weekend, wind speeds will increase in response
to the next approaching area of low pressure. While confidence in
speeds greater than 20 kts is high, confidence is speeds greater
than 35 knots is low. So for now, capped wind speeds at 25 to 30
knots. But as confidence in the track and strength of the low
increases, gales may need to be introduced. Stay tuned.


&&

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

&&

$$

SHORT TERM...NC
LONG TERM....NC
AVIATION...AP
MARINE...GJS

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