Graphical Hydro Meteorological Discussion

623
FXAK68 PAFC 141320
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
520 AM AKDT Sat Sep 14 2024

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

Main Points:

- Widespread moderate rain and breezy/gusty winds this weekend.

- Gusty southeast winds for the Hillside, south and west
Anchorage starting this afternoon, becoming south overnight and
continuing through Sunday throughout the Anchorage Bowl. Power
outages due to saturated soils and wet vegetation are
possible.

- Exercise caution near rivers as forecasted river conditions are
to be near bank-full for the Anchorage area and southern Mat-
Su. A Flood Watch remains in effect for Anchorage small streams
and urban areas through Sunday morning.

Active weather ensues for Southcentral Alaska this weekend with
breezy/gusty winds and widespread rain. A broad longwave trough
is currently over the Bering with a 120-140 kt jet streak
pointing towards the southern Mainland. The main surface low is
off of Nunivak Island with it`s warm front beginning to push its
way over Kodiak Island this morning, shortly followed by the Kenai
Peninsula and most areas of Southcentral by the afternoon. Mostly
south to southwesterly winds at mountaintop level and
southeasterlies at the surface will mean all areas should receive
a healthy dose of rain by Sunday morning, with the only dryish
spot being from Eureka to Glennallen. Moving later in the day on
Sunday conditions will become more showery in nature as colder air
wraps into the system, focusing most of the precipitation on the
west and southwest facing mountain ranges. This will more or less
continue through Monday, but to lesser extent as time goes on.

The wind forecast, particularly for the Anchorage Bowl, is
perhaps the most challenging aspect of this forecast package. This
is due to the balancing act in the pressure field between the
much deeper low moving into the Norton Sound over the next 24
hours, progged at ~976 mb, and a low that will form at the triple
point this evening at ~996 mb. The pressure gradients are not
supportive for the Turnagain wind to bend into Anchorage until
late this evening, by which the Whittier to Anchorage gradient is
subsiding. However, all of the high resolution models bring a
Turnagain wind into town this afternoon, with gusts between 30 and
50 mph. This forecast package reflects a Turnagain wind that will
effect the hillside and the south and west portions of Anchorage
where strong winds will often mix their way north of the Turnagain
jet and form turbulent eddies.

Winds for the rest of the region are more certain with a coastal
ridge initially bringing in the typical gap winds this afternoon
and through early Sunday morning. By this time, 90% of the model
guidance has the Gulf low pushing inland, which will produce a
gusty up-Inlet wind that will extend north into the Susitna
Valley, as well as a reinforcement of the Copper Valley Wind. All
of this wind will be very slow to subside through Tuesday due to
the slow occlusion and movement of the primary low far to our
north. Tuesday looks to be somewhat of a break in the weather but
then another Bering low looks to generate up a rinse and repeat
scenario with more wind and rain on the way.

-CJ

&&


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

Forecast remains on track for a stronger front pushing over the
Southwest Coast this morning and then spreading across the rest of
the Southwest Alaska through the afternoon. Widespread rainfall of
up to an inch is possible for most areas through Sunday morning
as the front progresses eastward. An initial push of south-
southeasterly gale force winds move along the Kuskokwim Delta
coast this morning before weakening to small craft and
transitioning to southwesterly by this afternoon. Winds will
increase again overnight tonight to gale force before diminishing
again late Sunday morning. The Coastal Flood Advisory remains in
effect for communities along the Kuskokwim Delta coast from the
mouth of the Kuskokwim River to Newtok this morning through late
Sunday night to address minor storm surge concerns and expected
minor coastal flooding. Also, a River Flood Advisory has been
issued for communities along the lower Kuskokwim River from Bethel
to the mouth of the river through Sunday afternoon.

Attention then turns to developing storms in the North Pacific and
near Kamchatka that will look to merge as they approach the Bering
Sea. The gale- force low in the North Pacific looks to send its
front into the Western and Central Aleutians Monday. The storm
then moves into the southcentral Bering Monday afternoon where it
will merge with the Kamchatka system. The storm will continue to
deepen as it moves farther into the central Bering with the front
reaching the Eastern Aleutians and Pribilof Islands by Monday
night.

&&


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

Operational and ensemble guidance are in generally good agreement
with bringing a deepening upper low into the Bering late Monday
into Tuesday of next week. This low will be the focus for
potential impacts across Southwest and Southcentral Alaska during
the long term period. As the low overspreads the eastern Bering a
wet pattern with widespread showers is expected to persist from
Tuesday through at least Thursday from the Kuskokwim Delta coast
into Southcentral. At this time models are showing a deepening
trend with a robust front traversing the Aleutians and Bering into
interior Alaska. The thermal gradient along the front will favor
strong winds, even with the potential for some high winds through
the Eastern Aleutians into the AKPEN on Tuesday. The way the upper
low overspreads Southwest Alaska and then begins to meander
southeastward once finally undergoing some weakening by Wednesday,
suggests above normal shower chances will persist beneath the low
for much of both Southwest and Southcentral. Otherwise,
seasonably normal temperatures look probable through the period.


BL

&&

.AVIATION...

PANC...VFR conditions will persist through midday today as a front
from a system in the Bering moves over the area. Expect continuous
light to moderate rain through Sunday with MVFR ceilings and vis.
Vis may drop to IFR should heavy rain develop along the Turnagain
Arm convergence zone. Turnagain winds are likely with gusts up to
35 kts possible later this evening. Overnight winds will become
southerly and remain strong around 20 kts through the TAF period.

&&


$$

544
FXAK69 PAFG 140946
AFDAFG

Northern Alaska Forecast Discussion
National Weather Service Fairbanks AK
146 AM AKDT Sat Sep 14 2024

.SYNOPSIS...
A strong low pressure system will move north and east along the
West Coast this weekend bringing strong winds, high surf, and
heavy rainfall. As the low tracks towards the Interior, rain will
spread eastward. Strong winds develop in the Eastern Alaska Range
this afternoon and persist into Sunday morning.

&&

.DISCUSSION...
Upper Levels and Analysis...
Aloft, at 500 mb, a 526 dam (decameter) low over the Western
Bering Sea moves east northeast to be centered near Emmonak
Sunday morning. The low slowly moves northeast to be centered near
Kaltag Monday morning. As this low moves across northern Alaska,
pieces of energy will rotate through the flow. Meanwhile, a 531
dam low over the northwest Queen Elizabeth Islands tracks
northwest into the high Arctic and weakens through the weekend.

At the surface, a 982 mb low between St Lawrence Island and
Nunivak Island to near western Norton Sound Sunday morning and
near Kaltag Monday morning. A front associated with this low will
lift northeast across the Y-K Delta this morning to stretch from
near St Lawrence Island to near Stebbins to near McGrath this
afternoon. The occluding front continues north and east to stretch
from near St Lawrence Island to Huslia to Stevens Village to near
Chalkyitsik Sunday morning continuing north to stretch from
Norton Sound to Norvik across the Western and Central Brooks Range
to a 985 mb low near Kaktovik Sunday afternoon. The front
continues north offshore the Arctic Coast by Monday morning, as
the 985 mb low that was near Kaktovik moves to Mackenzie Bay.

Models...
The 14/00Z model suite initialized well aloft and at the surface.
Models are in good agreement with the overall synoptic pattern
through the weekend, but there remains some differences in the
details with the low moving out of the Bering. Inherited grid
package looks to be on track. Made only minimal changes to the
forecast to account for ongoing precip trends and winds. Leaned
towards the NAM for winds in the Alaska Range.

North Slope and Brooks Range...
One more day of quiet weather expected across the North Slope and
Brooks Range today. Areas of fog and low stratus persist along
the coast. Shower activity will be confined to the Brooks Range
today. Shower chances increase late Saturday night across the
Brooks Range, spreading north to the Coast Sunday as the Bering
low moves north along the West Coast, pushing a front north and
east. Southerly winds develop over the Brooks Range today and
continue into Sunday, allowing temperatures to warm into upper 40s
and lower 50s across the Arctic Plains. Along the coast, east
winds of 10 to 20 mph along the coast will prevail with east winds
of 15 to 20 mph along Central and Eastern Beaufort Sea coast
through Sunday. Winds diminish late Sunday into Monday as the
front pushes north of the coast.

West Coast and Western Interior...
A low pressure system will move to St Lawrence Island and the Y-K
Delta this morning, tracking north and east across the West Coast
and Western Interior into Monday. Gusty southeast winds of 20 to
35 mph will develop with the passage of the front and the
associated low, with the strongest winds occurring over the Y-K
Delta and Eastern Norton Sound. On the backside of the low, winds
shift to the west southwest. In addition to the wind, elevated
water levels and high surf are expected to develop south of the
Seward Peninsula, and high Surf Advisories are in effect. The
highest water is expected early Sunday morning along the Y-K Delta
and during the day on Sunday in the Norton Sound Region. Rainfall
totals of half an inch to an inch and a half are expected through
Monday, with highest amounts south and west of a line from Kaltag
to Nikolai. High temperatures in the mid 40s to lower 50s.

Central and Eastern Interior...
Strong southerly winds develop in the Alaska Range this afternoon,
as the low in the Bering approaches the West Coast. Gusts up to
60 mph are expected in the passes of the Eastern Alaska Range,
while gusts up to 50 mph are expected in the passes of the Western
Alaska Range this afternoon into Sunday morning. A Wind Advisory
remains in effect for the Eastern Alaska Range. There will be a
break in shower activity for much of the Central and Eastern
Interior this morning and this afternoon before rain begins to
move in from the west this evening and overnight. Rain continues
Sunday with most of the area seeing a wet day. Rainfall
accumulations around a quarter of an inch expected in the
Fairbanks area Sunday, between a quarter and a half an inch from
Bettles to Tanana and in the Alaska Range, and less than a quarter
of an inch elsewhere. Additional rainfall Monday will drop an
additional tenth to a quarter of an inch west and south of a line
from Bettles to Delta Junction. High temperatures top out in the
50s and lows drop into the mid 30s to lower 40s.

Extended Forecast Days 4-7...Another low pressure system moving
across the Bering Sea early next week will approach the southwest
coast Tuesday afternoon and night. A front associated with this
low pressure system will bring heavy rain to the southwest
Interior midweek. Otherwise, overall troughing will maintain
unsettled conditions, seasonable temperatures, and mostly cloudy
skies.

Coastal Hazard Potential Days 3 and 4...Another strong low
pressure system will move to near St. Matthew Island Tuesday
afternoon. At this time, models indicate that the low will track
southeast from there into Bristol Bay. This track would not impact
areas from the Yukon Delta north with any type of elevated water,
but we will need to watch closely for changes in the forecasted
track.

&&

.HYDROLOGY...
Rivers across the Interior will rise over the next several days
as rainfall moves into the river basins. Heavy rain expected over
the west coast of 0.50 to 1 inch or more in some locations, that
will likely raise small rivers and streams.

&&

.AFG WATCHES/WARNINGS/ADVISORIES...
AK...Wind Advisory for AKZ849.
High Surf Advisory for AKZ822.
High Surf Advisory for AKZ824.
High Surf Advisory for AKZ825.
PK...Gale Warning for PKZ801-850.
Small Craft Advisory for PKZ802.
Small Craft Advisory for PKZ803-805-851-852.
Small Craft Advisory for PKZ804-806>810-816-817-854>856.
Small Craft Advisory for PKZ815.
Small Craft Advisory for PKZ853.
Small Craft Advisory for PKZ857.
Small Craft Advisory for PKZ860.
Small Craft Advisory for PKZ861.
&&

$$

480
FXAK67 PAJK 141308
AFDAJK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
508 AM AKDT Sat Sep 14 2024

.SHORT TERM...Diminishing rain and clearing skies through the day
on Saturday will be brought to an end by an advancing gale force
system Saturday night into Sunday.

Satellite imagery shows a decaying low moving out of the northern
gulf and off to the SE. A low stratus deck has built over some
parts of the panhandle, alongside fog for other locations, as the
pressure gradient has collapsed and winds have subsided. Some
rain showers will linger through the morning hours and even
potentially the afternoon hours, though by the late afternoon or
early evening, anticipate dry weather across the panhandle.

The source of the brief round of drying weather is a ridge which
will briefly rebuild through the day as the decaying low in the
gulf disintegrates entirely. The situation will begin to rapidly
change through Saturday night, as a gale force system advances
into the Gulf and approaches the panhandle. Winds will begin to
increase across the area, with precip chances increasing across
coastal communities - and to a lesser extent the northern half of
the panhandle, by late Saturday night. Sunday will see small
craft conditions across many of the inner channels, with elevated
winds across land-based locations and widespread rain reaching
across SE AK as the system fully moves into the panhandle. For
additional information, see the long term-forecast discussion.

Primary changes to the forecast focused on wind. Increased winds
across both the inner channels and land-based locations,
especially on Sunday as the system arrives fully in the area. Made
some minor changes to precip, diminishing chances through
Saturday afternoon more quickly, and bringing somewhat greater
chances in across the northern panhandle by late Saturday night.


.LONG TERM.../Sunday through next Sunday/...In short: Active
pattern will continue through days 3-10. While there may be
breaks of 12-18 hours of little to no rain, the main story is
multiple systems will push into the panhandle through next
weekend.

In long: Several fronts of various strength will move through the
panhandle with short breaks in between beginning this Sunday. The
Sunday system will feature a gale force front, mainly impacting
the NE gulf coast with this highest rain rates and sustained wind
speeds. The front will successfully push through the panhandle
Sunday and exit to the southeast Sunday night. As it progresses,
up to 20-25 knots in the inner channels will follow the front.
Eldred Rock and Taiya Inlet look to be the main hold out points
with leeside troughing keeping wind speeds enhanced in those
areas.

The big question mark for today`s forecast is a developing low in
the northern Pacific Ocean aimed at the southern panhandle.
Uncertainty in the forecast is in track of the developing low,
with many deterministic models indicating that as the low deepens,
it will push southward hitting Haida Gwaii. However, if strongest
winds aloft are further north (an unlikelier solution), then a
developing system bringing heavy rain rates to the southern
panhandle will hit Monday night.

Behind the Sunday/Monday systems, a dry period is shortly expected
with the low feature pulling southward. Wednesday sees another low
in the northern gulf with an associated front extending across the
northern half of the panhandle and NE gulf coast. Rain rates do
not look impressive, maximizing around moderate, with no flooding
expected.

Ultimately, what is currently on the radar as the next impactful
rain event could possibly be next weekend. There are early
indications of a long duration rain event. At this time, there is
40-60% chance of IVT values exceeding 250 kg/m/s for three days.
Unfortunately, details are scarce, but it will be monitored
closely.


&&

.AVIATION.../until 12z Sunday/

Near calm winds and saturated low levels have compounded to a create
LIFR to VFR CIGS and VSBY flight conditions across the panhandle
this morning. Anticipating patchy fog and LIFR/IFR decks to slowly
dissipate through 20z into the afternoon. Drier conditions
expected today as brief surface ridging will develop prevailing
VFR flight conditions through 00z this evening with CIGS generally
AoA 5000ft. Variable light winds this morning will increase
through afternoon to 10kts or less with an isolated gust up to
20kts possible for Haines and Skagway.

Approaching system in the Gulf will affect PAYA first by early
Sunday morning, anticipate light rain developing after 06z with
increasing LLWS by 12z Sunday morning as front pushes into the NE
Gulf coast.

//Aviation Forecast Confidence...
-High confidence on precipitation, winds, and afternoon VFR
flight conditions
-Medium confidence on CIG and VSBY improvement timing this
afternoon and LLWS timing for PAYA

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Dense Fog Advisory until 9 AM AKDT this morning for AKZ326.
MARINE...Gale Warning for PKZ652.
Small Craft Advisory for PKZ012-022-642>644-651-661>664-671-672.

&&

$$

SHORT TERM...GFS
LONG TERM....NC
AVIATION...NM

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