Graphical Hydro Meteorological Discussion

114
FXAK68 PAFC 290045
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
445 PM AKDT Mon Apr 28 2025

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

Remnants of a trough over Southcentral Alaska continue to promote
unsettled conditions across the region. Some breaks in the cloud
cover are allowing for areas of convective showers to develop over
the Western Kenai Peninsula, and pushed by the Southwesterly
winds up over the Anchorage and Mat-Su areas. Precipitation this
afternoon into tonight will be light, and with snow levels
sufficiently elevated, rainfall will be the prevailing
precipitation type leading into the workweek.

By Tuesday morning, the front of a North Pacific low pressure
system will swing into the northern Gulf of Alaska revitalizing the
rainfall over Kodiak, the Gulf Coast, and portions of interior
Southcentral. By later Tuesday afternoon, the orientation of the
winds will become more southeasterly, indicating a favorable
downslope pattern for Anchorage, diminishing the showers over the
city heading into Tuesday afternoon. As the low in the northern
Pacific shifts northeast, the pattern over Southcentral will hold
steady, maintaining a rainy pattern over the coast, with drier
conditions expected for more interior/sheltered locations such as
Anchorage, the Mat-Su Valleys, and the Copper River Basin through
Thursday. Overnight low temperatures are also expected to remain
above freezing for much of Southcentral for the next few mornings,
continuing our warming trend.

-CL

&&

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

A North Pacific low skirting south of the Aleutian Chain pushes
its front from the western/central Aleutians, where it is
producing easterly gales and light to moderate rain, north and
east through the eastern Aleutians and Alaska Peninsula, to reach
the Pribilof Islands and the Southwest coast. With colder air in
place over Southwest Alaska, precipitation with this front may
fall as snow during the early morning hours on Tuesday.

As the front tracks over the Alaska Peninsula, colder air filters
in behind across the Bering Sea, with a trough pivoting around
the low and centering over the Pribilof Islands. This allows for
precipitation to persist through Wednesday, primarily as snow with
temperatures at to just above freezing. Showery conditions will
continue across Southwest Alaska and the Aleutian Islands through
at least Tuesday. Showers may start as snow in the early mornings
when temperatures are cooler but are expected to transition to
rain in the afternoon as temperatures warm up. Northerly winds
bringing cooler air on the back side of the low on Wednesday may
lead to more widespread snow showers, with the best chances over
the western and central Aleutians.

&&


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

A large elongated trough with a NW - SE axis stretching from
Siberia to the Gulf of Alaska will keep the eastern Bering Sea and
most of western Alaska under low pressure for the start of the
long term forecast period. Broad cyclonic flow and excess moisture
will allow showery precipitation to persist for much of Aleutians
and Southwest AK. The embedded closed low that brought moderate
to high rates of precipitation to coastal Southcentral midweek
will slowly dissipate. However, continued damp onshore flow will
allow periods of rain and mountain snow through the weekend.

A shortwave trough swinging through the Aleutians will pivot the
Bering low pressure system into the Gulf of Alaska on Sunday.
Model guidance has been trending this system farther northwest,
slightly increasing north Gulf coast precipitation and wind
magnitudes for Sunday and Monday.

&&

.AVIATION...

PANC...Scattered showers will gradually taper off this afternoon
with MVFR ceilings rising and scattering out. Ceilings should
return to VFR this evening but may dip into MVFR at times. Rain
and lower ceilings spread back up the Cook Inlet Tuesday morning
with rainfall approaching the terminal between 13-16Z. As cross-
barrier flow increases over the Chugach and Kenai Mountains
Tuesday afternoon, ceilings will rise to VFR and precipitation
will become more hit-and-miss at the terminal.


&&


$$

705
FXAK69 PAFG 282328
AFDAFG

Northern Alaska Forecast Discussion
National Weather Service Fairbanks AK
328 PM AKDT Mon Apr 28 2025

.SYNOPSIS...A strong shortwave will bring locally heavy rain and
snow showers across the Interior Monday afternoon and overnight into
Tuesday morning. South winds through Alaska Range passes will gust
to 50 mph Tuesday and Wednesday.A few rain showers will persist on
the West Coast mainly south of the Seward Peninsula through
Wednesday. Blowing snow will continue near Point Lay with east winds
restrengthening Tuesday and persisting through the week.

&&

.KEY WEATHER MESSAGES...
Central and Eastern Interior...

-An organized shortwave will bring numerous rain and snow showers
across the area this evening through Tuesday. Expect most of these
showers to fall as rain, but some snow is possible at higher
elevations and overnight into Tuesday. Areas of the White Mountains
may see a quick 3 to 4 inches of snow. Total precip amounts between
a tenth and a quarter inch are possible, even in Fairbanks.

-Southerly gap winds through Alaska Range passes will increase again
behind the shortwave on Tuesday, leading to drier conditions across
the Tanana Valley. A Wind Advisory is in effect for Delta Junction
and the Eastern Alaska Range for gusts up to 50 mph from Tuesday
afternoon through Wednesday late morning.

-High temperatures will be in the 50s across the Tanana Valley with
mostly 40s elsewhere.

West Coast and Western Interior...

-A few rain showers will persist from the Seward Peninsula south
through this week with mostly clear skies to the north

-Northerly winds through the Bering Strait and over St. Lawrence
Island will persist at around 25 mph through next weekend with areas
of blowing snow, especially through Tuesday when there will also be
periods of falling snow.

-High temperatures will be mainly in the 30s near the coast and in
the 40s and 50s in the Interior.

North Slope and Brooks Range..

-A mix of clear skies and low stratus will persist across the Arctic
Coast with generally good visibility, except near Point Lay where
blowing snow continues and will likely continue through the week as
winds restrengthen Tuesday. A Winter Weather Advisory has been
extended for Point Lay.

-Lows will be mainly in the single digits with highs in the teens
along the coast and in the 20s in the Brooks Range.

-The Brooks Range will be mainly dry under partly cloudy to mostly
clear skies through Tuesday.

&&

.FORECAST ANALYSIS AND DISCUSSION...A strong shortwave is still on
track to move over the Interior later tonight, though models have
shifted precipitation to the east and show more uncertainty on
timing of precipitation than yesterday. Have adjusted the Special
Weather Statement to reflect that. Downslope flow over the Alaska
Range strengthens Tuesday as a vertically stacked low moves from the
southern Bering Sea to Bristol Bay, with showery conditions across
the West Coast. This will persist through Wednesday as the low
weakens before another low moves from the North Pacific into the
Gulf of Alaska and becomes the dominant feature. This will shift
flow aloft to southeasterly through the end of the week, weakening
winds through the Alaska Range and bringing in more moisture to the
Interior from the east. Significant precipitation is possible Friday
and Saturday from Fairbanks east to the Alcan Border as a low moves
to Prince William Sound. High pressure persists over the Arctic.

For the forecast today, we adjusted the strength and timing of gap
winds through Alaska Range passes, extended the Winter Weather
Advisory for Point Lay, and shifted precipitation with the shortwave
moving over the Interior tonight slightly eastward. We also adjusted
QPF to make to wettest areas the hills east of Fairbanks.


&&

.FIRE WEATHER...Wetting rains are expected across most snow free
areas of the Interior overnight tonight, then downslope flow kicks
in Tuesday morning with sustained south winds 20 to 30 mph and gusts
to 50 mph through Alaska Range passes. These winds will persist
through Wednesday mid-day, though latest model runs indicate they
could persist into the afternoon hours when RH will be at its
driest. The wetting rain overnight tonight combined with the amount
of moisture embedded within the southerly flow off the Gulf of
Alaska will keep RHs Tuesday afternoon fairly moist even in the area
of downslope winds. By Wednesday, RHs may dip down to near 25% from
Delta Junction across the Tanana Flats, with possible Red Flag
conditions near Delta Junction if south winds persist into the
afternoon. Will stick with a Wind Advisory for now and re-evaluate
Red Flag potential tonight and tomorrow. Flow turns southeast
Thursday and Friday with less wind across the area and more moisture
being advected into the Interior off the Gulf from the east, thus
fire weather concerns abate.

&&

.EXTENDED FORECAST DAYS 4-7...As a low pressure system in the Gulf
of Alaska moves east along the ALCAN border, a stronger low pressure
system builds in behind it. Models are in good agreement with this
low pressure system making its way into Prince William Sound by
Monday, allowing for the persistence of broad scale troughing across
the state. The current set up looks favorable for moderate rain/snow
showers to occur throughout the Central and Eastern Interior.
Showers are expected to be rain during the day, transitioning into
snow overnight. There is a chance for some showers to make their way
towards the West Coast however, confidence is low regarding the
exact timing and rain/snow amounts for this system right now.
Temperatures are expected to be below normal and precipitation
amounts above normal for both the Interior and West Coast through
the weekend. High pressure will remain along the North Slope with
minimal impacts expected.

Coastal Hazard Potential Days 3 and 4...None

&&

.AFG WATCHES/WARNINGS/ADVISORIES...
AK...Winter Weather Advisory for AKZ801.
Wind Advisory for AKZ837-849.
PK...Small Craft Advisory for PKZ806.
Heavy Freezing Spray Warning for PKZ806.
Brisk Wind Advisory for PKZ807.
Brisk Wind Advisory for PKZ810.
Gale Warning for PKZ811-857.
Brisk Wind Advisory for PKZ812-817-856-858.
Brisk Wind Advisory for PKZ814.
Small Craft Advisory for PKZ816-851-854.
Heavy Freezing Spray Warning for PKZ816-851.
Heavy Freezing Spray Warning for PKZ854.
&&

$$

Chriest/Santiago

719
FXAK67 PAJK 282257
AFDAJK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
257 PM AKDT Mon Apr 28 2025

.SHORT TERM.../through Tuesday night/...

Key Points:
-Some breaks in the showers through the short term but with
continued onshore flow, rain showers will continue to dot the
landscape.
-Strong wind gusts upwards of 40 to 50 mph are likely in Skagway
and the Klondike highway, some potential for 55 to 60 mph wind
gusts.
-Above normal overnight low temps, below normal afternoon high
temps.

Details:
Surface low pressure is tracking eastward this Monday afternoon.
This low has been keeping the rainy and cloudy weather over the
panhandle today. As this low moves east, the rain and rain showers
will continue through Tuesday, though some breaks in the rain is
likely, especially for those closer to the coast. The farther
inland you are, the fewer the breaks.

As the previously mentioned area of low pressure exits the
panhandle, a ridge of high pressure will build over Southeast.
This ridge will start increasing the pressure gradient in the
northern Lynn Canal area. To the west of this expected ridge, will
be a front that will tighten the pressure gradient even more as
it approaches Tuesday into Tuesday evening. This tightening of the
pressure field will cause the wind speeds and wind gusts to
increase. The pressure field looks to relax Tuesday night, which
would decrease the wind gust speeds.

For now, confidence is high that wind gusts will reach 40 to 50
mph but this weather pattern has produced wind gusts upwards of 55
to 60 mph in the past. Right now, there is about a 30% chance of
wind gusts being at or above 55 mph. So there is some concern for
high wind gusts near 60 mph but confidence is not high enough to
issue an official product at this time. We`ll continue to assess
the weather data and update as needed.


.LONG TERM.../Wednesday through Monday/ The first days of May are
expected to be rather unsettled in terms of expected weather
conditions courtesy of multiple low pressure systems and moist
onshore flow from the Gulf. Cool wet weather pattern SE AK weather
for the long range. Aloft, a broad upper low is expected to be in
place across the Bering for the middle to end of the week, and then
pivoting to the Gulf by next weekend and next Monday. While there
are short periods of ridging tracking in there are just no
foreseeable long or substantial breaks in the next week, and from
CPC outlook likely the next two weeks. Low/front moving in early
Wednesday with gale force winds developing along the Eastern AK
Gulf. Some model differences on position and timing so but some more
confidence details for the front position and reaching the NE Gulf /
Northern panhandle first. EFI puts more heavy precip into the region
with long fetch of moisture from the south. Hydrology concerns with
this next batch of heavy rain, especially due to the earlier systems
causing some rivers rises and the record and or record rainfall for
the month of April. Periods of rain lasts into the weekend as the
parent low reaches the Central AK Gulf but rates and overall
coverage diminishes. Updated previous forecast with some more detail
on front for Wednesday but overall it either remained in line with
new model runs or there is still enough spread in operational model
that a national blend still covers the gist of the long range.

&&

.AVIATION.../Through Tuesday afternoon/...Marginal visual
conditions will continue unabated for this short term period with
instrument conditions at times. There`s no getting around the
fact that this is not the normal Spring flying weather SEAK is
accustomed to experiencing. Freezing level is still well below
normal and an ongoing issue for departing and arriving instrument
traffic, as indicated indicated in PIREPS today. Mountain
obscuration across all or Southeast Alaska will not be going away
soon either. LLWS persists into the evening for the outer coast
and is reflected in the Sitka and Klawock TAFs.

&&

.MARINE...
Outside: For tonight, the recent gale force low will continue to
track eastward. This puts wind direction in the gulf in an onshore
pattern with the strongest winds, upwards of 25 to 30 kts, in the
far southern outside zones. Lighter winds of 10 to 20 kts will be
found elsewhere. Tuesday, another front will move west to east
through the gulf, swinging winds to the south at 15 to 25 knots.

Seas are up to 10 to 15 feet, as of Monday afternoon, with a near
10 second swell in the southern gulf with those higher waves
moving east, bringing wave heights down to to around 5 to 8 feet
with a 2 to 4 second swell by Tuesday morning. As the next front
approaches tomorrow, waves will slowly build to near 10 feet with
a 3 to 4 second swell.

Inside: Inner channel marine concerns can be broken up into two
sections: tonight in the south and tomorrow in the north.

For tonight, as the recent gale force low tracks east, the
westerly winds will be rushing through the inner channels at a
decent clip, upwards of 15 to 20 knots from a general west
direction. But as the low exits the area, a ridge will build,
which will swing winds to the south at around 10 to 15 knots.

For the north, as the ridge builds, it will tighten the pressure
gradient in Lynn Canal. So southerly wind speeds upwards of 20 to
30 kts are likely beginning Tuesday morning and lasting through
Tuesday evening. Afterward, wind speeds will decrease.

The next round of elevated winds in the inner channels will be
late Wednesday into Thursday as the next gale force front moves
through, increasing winds to 15 to 25 knots.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Strong Wind from Tuesday morning through Tuesday evening for
AKZ318.
MARINE...Small Craft Advisory for PKZ012-022-036-641>644-651-652-661>664-
671-672.

&&

$$

SHORT TERM...GJS
LONG TERM....PRB
AVIATION...Fritsch
MARINE...GJS

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