901
FXAK68 PAFC 091429
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
529 AM AKST Thu Jan 9 2025

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3/Today
through Saturday night)...

Satellite imagery this morning shows a large complex storm tracking
into the Gulf and toward Southcentral. The original low center is
tracking north-northeast toward the central Gulf. A leading warm
front wraps around the northern to western Gulf, with widespread
gale to storm force winds being observed ahead of it. A secondary
low has formed along the front to the southeast of Kodiak Island.
What is most notable is that the bulk of deep moisture (and
implied upward vertical moisture) is all moving over southern
Alaska, with a much more compact area of deeper moisture (and
precipitation) with the low centers. This is because the upper jet
helped drive an upper short-wave well out ahead of the low
center. Precipitation is in fact spreading onshore of
Southcentral, with low elevation rain and high elevation snow
along the coast. Snow is also spreading northward into the Copper
River Basin this morning. Precipitation is attempting to cross
the Kenai and western Chugach Mountains. However, a layer of
northerly winds from the Mat Valley to Anchorage and down Cook
Inlet and portions of the western Kenai Peninsula is maintaining
dry low levels (as seen in the 12Z Anchorage sounding). Thus,
precipitation is not reaching the ground in these areas.

Today`s forecast remains quite challenging. Model guidance is
split into two camps with placement of a deformation band which
forms in Cook Inlet today. The global models generally favor a
more south and west location (from the southwestern Susitna Valley
to Kenai/Soldotna and down the Inlet to Kachemak Bay/Homer) while
the hi-res models favor a more north and east location (from
Talkeetna south to Fire Island/west Anchorage and across inland
areas of the western Kenai). With steering flow favoring a general
south to north motion, the portion of the warm front over the
northern Gulf will push onshore while the portion over the western
Gulf will largely remain stationary until it is pushed north and
eastward later today by a short-wave trough moving in from the
Bering Sea. Based on this simple logic, the latest forecast favors
the hi-res guidance location of the deformation band.

The other big forecast challenge is precipitation type. An above
freezing warm nose remains in the Anchorage sounding. However, the
wet bulb temperature is at or below freezing. Thus, if you were to
saturate the atmosphere and there was no significant temperature
advection, the resultant precipitation type would be snow. The
northerly winds and dry air advection will rapidly diminish
midday into the afternoon hours which should allow the atmosphere
to gradually become saturated. In these borderline case,
precipitation type often comes down to precipitation intensity,
which is why the location of the band of heavier precipitation is
so critical to the forecast.

No matter where the band sets up, the upper level short-wave
coming in from the west will cause it to move north and east
across the Kenai Peninsula, Anchorage, and the Mat-Su tonight
before weakening/dissipating as it continues across the remainder
of Southcentral. Have trended toward more snow for these areas,
with a band of 2 to 4 inches from Talkeetna southward to Willow,
Big Lake, Anchorage, and the interior western Kenai. Any shift in
the band will affect precipitation type and total snow
accumulation.

The upper level flow will remain progressive as we head through
Friday and into the weekend. An upper level short-wave extending
from a storm moving into the Bering Sea tonight, will cross
Southcentral Friday bringing a quick shot of very light
precipitation to most areas. With little change in airmass,
expect mostly rain along the coast and snow inland. A much
stronger storm system will then track from the north Pacific to
the western Gulf/Kodiak Island Friday night. The ultimate track
of this low is very much in question, with some solutions
bringing it up Cook Inlet Saturday (very warm and windy) and
others bringing it further east (less warm and windy). In either
case, expect another round of moderate to heavy precipitation and
strong winds across the Gulf waters and coastal Southcentral with
a period of mixed precipitation likely inland. An even larger and
stronger storm system will follow late Saturday into Sunday. With
a track up across Southwest AK, this could bring high winds and
very warm temperatures to Southcentral, though it looks like much
colder air will wrap back around the south side of the low and
into Southcentral. Stay tuned to forecast the next several days,
as the weather pattern remains fast paced.

-SEB

&&


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

A very unsettled pattern is quickly taking shape across the
outlook area this morning as two strong low pressure systems begin
to impact parts of the region. The first of these lows is a
Hurricane force North Pacific low currently moving a ways south of
Amchitka, with a gale force front now extending north and east
from the low into the Aleutian Chain. Predominantly wet snow is
being observed as the frontal precipitation reaches Adak and Atka
early this morning, where surface temperatures are still hovering
at or just above freezing. However, snow should soon change over
to rain later this morning into the early afternoon as the front
continues north and as warmer air continues to stream in with the
approaching storm system. Looking out towards Southwest, another
low moving over the Gulf is spreading gusty north winds into
Bristol Bay and the northern AKPen. A band of rain and snow has
slowly been developing over Bristol Bay near a zone of deformation
and lift northwest of the low center, but it has taken time to
begin reaching the surface due to dry air feeding into the region
from the Kuskokwim Valley with the gusty north winds.

In terms of the forecast, most of the issues and impacts going
into the next day or so will stem from the currently Hurricane
force low moving south of the Aleutians. This low will weaken as
it crosses the Chain into the southern Bering, but it looks even
more likely to retain a more intense wind field compared to
earlier . Storm force winds will move south of the low near and
just south of the eastern Aleutians late this evening into
tonight. Gusts as high as 55 to 65 mph will be possible across
parts of Unalaska as the low passes to the north late tonight into
early Friday morning, particularly with winds funneling through
terrain out of Captain`s Bay. Meanwhile, the low`s front will
continue to lift northeast, spreading gusty winds and snow
changing over to rain into the Pribilof Islands this evening, then
into parts of Southwest late tonight into Friday morning.

As the low lifts north towards Nunivak Island during the
day on Friday, the wind field will weaken to gale force, but will
still stay strong enough to cause possible impacts to the
Kuskokwim Delta Coast. Onshore winds could gust up to 40 mph as
the low approaches to the west from Friday afternoon into Friday
night. While there is more sea ice in place along the coast
compared to what we had for the last coastal flood event, there
may still not be enough stronger, shore-fast ice to protect
coastal communities from a possible storm surge with this low.
Even where stronger ice exists, water could pool up through cracks
and cause localized flooding for communities along the immediate
coast near high on Friday evening. Confidence on the degree of
flooding is low, but concern is high enough to justify issuing a
Coastal Flood Advisory for the Kuskokwim Delta Coast, which is now
in effect starting midday Friday.

Attention from there quickly shifts to the next strong low setting
up along the active storm track continuing into the weekend. By
late Friday night, another potentially Hurricane force low will
approach Kodiak Island. The center could briefly head up into
Bristol Bay before it veers more northeast towards Southcentral on
Saturday. The main impact across Southwest will be another round
of gusty southwest winds moving in behind the low passage,
especially over southern parts of the region close to Bristol Bay
and the AKPen. Moderate rain and snow will also move north with
the low Friday night into Saturday morning, though temperatures
appear likely to remain too warm for significant snow
accumulation.

If all that wasn`t enough to handle, an even stronger, larger low
pressure system will begin to move up into the eastern Bering Sea
from the Pacific from Saturday into Saturday night. Very strong
southeast winds will spread into Southwest along with locally
heavy rain/snow moving back across much of the region as well.
Strong north winds up to Storm force could also move into the
eastern Aleutians and Pribilofs west of the low, where
temperatures could remain cold enough for mostly snow to fall,
especially up towards the Pribilof Islands. There is still some
uncertainty for the track and intensity of this next bigger
system, so stay tuned for updates as we continue to monitor this
very active pattern.

-AS

&&


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

Most of Southern Alaska will continue under a very active weather
pattern through the forecast period. The upper air longwave over
the Bering will be weakening, with the low centers moving into the
Arctic. A couple of significant shortwaves will support a
strengthening surface low in the Eastern Bering bringing heavy
precipitation and strong winds from the Central Aleutians to the
Canadian Border, and into most of Interior and Southwestern
Alaska. This low will push over Western Alaska as it tracks North.

Model guidance with the GFS and ECMWF hold decent synoptic scale
agreement through midweek, but some timing issues complicate the
locations and precipitation types expected due to strong warming
and the advection with the winds. Areas of moderate rains or rain
mixed with snow with gusty outflow winds are expected across
Southwest Alaska, and over Pribilofs and the Central Aleutians
Sunday. Most areas of rain are expected to change to snow by
Wednesday across Western Alaska. Heavy rains and high end gale
force winds are expected from the Eastern Aleutians over the
Alaska Peninsula and Kodiak Island Sunday. Higher elevations
across the Southcentral coasts will see heavy snow. These
conditions spread over the Kenai Peninsula into Prince William
Sound Sunday night before diminishing across the Southcentral
coasts and the Gulf of Alaska Monday afternoon. Another weak low
and front pushes over the Western and Central Aleutians Tuesday
and Wednesday.

&&

.AVIATION...

PANC...The precipitation forecast is quite difficult for today, so
forecast confidence in ceiling/vis forecast is low. Radar imagery
shows precipitation spreading toward the terminal early this
morning ahead of a complex storm system in the Gulf. However,
northerly winds in the low levels are maintaining a dry layer.
Expect this will remain the case as long as the northerly flow
continues. Thus expect some lowering of ceilings as precipitation
falls aloft this morning, but remaining VFR.

A band of precipitation will form somewhere in northern Cook Inlet
by early this afternoon, along an inverted trough extending
northward from the Gulf. Some models form this well west of the
terminal while some show the eastern edge of this setting up over
the terminal. The forecast leans toward precipitation developing
over the terminal. Winds will quickly diminish midday, so this
should allow saturation of the airmass, which should lead to snow
and ceiling/vis dropping to MVFR - or possibly IFR depending on
precipitation intensity.

No matter where the band of precipitation forms, it will move
north and east this evening, so confidence is higher in
precipitation over the terminal after 03Z with lower ceiling/vis.
If precipitation type ends up as rain or a rain/snow mix, then
ceiling/vis will not get as low.

&&


$$

385
FXAK67 PAJK 091415
AFDAJK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
515 AM AKST Thu Jan 9 2025

.SHORT TERM...Kept the forecast largely on track, with a storm
force front currently making its way over the panhandle. Winds and
rain will be increasing panhandle wide late tonight as the system
moves in. The highest winds are expected along the outer coast
and southern inner channels Thursday morning with gusts reaching
into the 50 mph range.

This system does have an atmospheric river associated with it,
however the front is moving through rather quickly so the heavier
precip will not linger over any area for an extended period of
time (less then 24 hours for most areas). Currently, between
around 0.5-1.0 inches have fallen. Rainfall through Thursday
night will be in the 1 to 2 inch range with the northern half of
the panhandle expected to get the higher totals. Freezing levels
are rather high right now (2000 to 3000 ft) and are expected to
rise higher (up to 4000 to 5000 ft) Thursday so precip type for
low elevations will be rain and some additional snowmelt may
contribute more runoff. The only place that will see snow is the
higher elevations of the Klondike Highway where a winter storm
warning remains in place. Current snotel observations indicate
that snowfall accumulations are around 1 - 2 inches per hour
currently, and will continue through the mid morning. After, snow
showers will consistently cause rates up to around 0.5-0.75
inches per hour through the day. Snow looks to become increasingly
wet before a transition to showers, so expect compacting on the
existing snowpack.

.LONG TERM...A period of active weather continues for the panhandle
through next week. After the front moves through Thursday, a brief
lull is expected before another front arrives Saturday. For this
Saturday system, a low moves northeast along the Aleutian Islands,
into the northern gulf. Yakutat and the northern panhandle will
have the heaviest and highest precipitation amounts. Winds in the
gulf will likely reach gale force changing to strong breezes as the
low weakens. The far northern areas may see strong winds with a
tightening pressure gradient. There is some uncertainty for where
the low will be located for this system. Winds may be stronger in
northern areas if the low moves farther east, closer to the
panhandle. This system will move quickly dissipating Saturday night.

A potentially stronger system will then reach the panhandle Sunday.
Gale force winds are expected throughout the gulf and along the
coast. Areas of storm force winds possible for marine areas.
Precipitation this time will be less localized with widespread
moderate rain with times heavy rain possible. With this system,
there are indications of IVT values reaching 500+.This show that
there is plenty of moisture heading toward the panhandle increasing
QPF amounts. We will continue to monitor each of these systems as
they head toward the gulf. This active weather pattern will continue
well into next week.

&&

.AVIATION...
Main aviation concern through mid day remains LLWS as front
pushes inland, with strongest LLWS expected for coastal and
southern TAF sites. AAWU forecast graphics continue to highlight
this across the panhandle moving into the afternoon. Otherwise,
predominate MVFR to IFR flight conditions with CIGS AoB 3000ft and
visibilities down to 1 to 3 SM within heaviest showers as a
strong initial front pushes through the Panhandle through Thursday
mid morning. Sustained winds will remain elevated the afternoon
with strongest gusts up to 40kts for southern panhandle TAF sites
through 00z Friday, gradually decreasing through the evening.

&&

.MARINE...Wide spread gales for the gulf waters and southern inner
channels are the main concern with the current front working its
way over the panhandle. Portions of the NE Gulf Coast are expected
to reach storm force as a barrier jet sets up. Meanwhile the
northern inner channels will mainly see 25 to 30 kt winds for the
most part. Seas in the gulf will also be rather high with wave
height possibly reaching 20 to 30 ft at times.

Behind the front is a secondary surface low that will move NW of
Yakutat Thursday night. This low will bring another burst of
severe gales from the south, primarily between Yakutat and Cape
Decision. Seas along the burst of higher wind speeds will reach
between 25 and 30 ft at times.

&&

.HYDROLOGY...Another atmospheric river moves over the panhandle
through Thursday afternoon. However, it will not stick around as
the main axis of the heavier precip will swing quickly through the
panhandle through midday Thursday. This fast movement is the main
limiting factor on how much rainfall various areas will receive
this time around and chances of areas breaking 24 hour return
intervals of 2 years or greater is less then 5 % for most areas.
Still total rainfall is expected to range around 1 to 3 inches
through Thursday night with the higher totals expected across the
northern half of the panhandle. Freezing levels will also be
increasing to around 4000 to 5000 ft today which could add more
snowmelt to area drainage basins. With all that, we are still not
expecting any flooding at the current time though we can not rule
out rapid rises to near or over bankfull in smaller drainage
basins or any localized flooding from blocked storm drains and
ditches.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Strong Wind through this afternoon for AKZ317.
Winter Storm Warning until 9 PM AKST this evening for AKZ318.
Strong Wind until 9 AM AKST this morning for AKZ323-328.
Strong Wind until 3 PM AKST this afternoon for AKZ330-332.
MARINE...Storm Warning for PKZ652-671-672.
Gale Warning for PKZ021-033-034-036-641>644-651-661>664.
Small Craft Advisory for PKZ012-013-022-031-032-035-053.

&&

$$

SHORT TERM...NC
LONG TERM....EAB
AVIATION...NM
MARINE...NC
HYDROLOGY...NC

Visit us at http://www.weather.gov/Juneau