000
FXAK68 PAFC 180056
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
456 PM AKDT Wed Apr 17 2024

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

A longwave trough axis remains parked over the Bering Sea into
the North Pacific. On the eastern periphery of this trough, a deep
moisture plume associated with a surface low just south of the
Alaska Peninsula continues to produce moderate to locally heavy
rain across Kodiak Island northward through portions of the
eastern Kenai Peninsula. This axis of moisture will remain fairly
stationary through Friday between the upper low over the North
Pacific and upper ridge over the Yukon, but is expected to move
slightly north tonight bringing a period of heavier precipitation
to the eastern Kenai including Seward northward to Portage and
Whittier. By Friday afternoon, this moisture plume moves back
south, shutting off precipitation in the western Prince William
Sound and possibly Seward as well, but bringing another round of
moderate to locally heavy rain to Kodiak Island. Everything
considered, an additional 1 to 3 inches of rain is expected
through Friday from Kodiak Island northward through the eastern
Kenai. With strong easterly flow off of the Gulf, snow will be
confined to the higher elevations of the Kenai Mountains and
Eastern Turnagain Arm.

In addition to the heavy rainfall, gusty easterly winds also
continue near Kodiak and portions of the Kenai Peninsula due to
a strong pressure gradient between the aforementioned low and high
pressure. Strong easterly gap winds also continue through Portage
and the Turnagain Arm. These winds are expected to slowly
diminish through Thursday night as the gradient begins to relax.

Periods of rain showers are likely to continue for these same
areas through much of the weekend as the upper level low remains
south of the Alaska Peninsula. High temperatures on Friday through
the weekend will rise into the 50s for much of Southcentral, with
Anchorage through the Mat-Su Valley remaining mostly dry over the
next few days.

-ME

&&


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

A high amplitude trough stretches across the Bering Sea with a
central low located south of the eastern Aleutians and western
Alaska Peninsula. East of the trough is southeasterly flow with
warmer, stronger winds, and ample moisture moving across Southwest
Alaska. With flow perpendicular to the mountains, some locations
such as Bethel are being downsloped this afternoon. Warmer air has
allowed some locations to transition from snow to a mix and even
over to rain for Southwest. Mekoryuk and coastal Kuskokwim could
see lingering snow and lower visibility. Strong, gusty winds will
continue for Kamishak Gap through tonight and gradually decrease,
though breezy still for Thursday. West of trough (primarily the
western Bering Sea from the Pribilofs and central Aleutians
westward) is cold northerly flow with convective pockets of snow
showers.

The front associated with the central low is stretching from the
Yukon-Kuskokwim Delta, across the eastern Bering Sea, and through
the western Alaska Peninsula. Precipitation is expected to linger
across this front through Thursday morning and is expected to lean
more west through Thursday. Snowfall in the eastern Aleutians is
expected to continue through Friday morning, though intensities
will gradually decrease by Thursday afternoon. There are
challenges with the forecast for identifying the extent and
duration that some locations will remain downsloped. Another
challenge is with how far west the trough will lean, promoting the
intrusion of midlevel warmth that could affect precipitation
type. At this time, Unalaska is expected to remain all snow. Run
to run consistency has been somewhat poor for the front moving
over the eastern Aleutians and although snow is expected to
decrease for Thursday morning, another forecast challenge we are
monitoring is how much precipitation could potentially increase
again for Unalaska Thursday night.

Overall, the general synoptic pattern is expected to change very
little for the next couple days and even somewhat through the end
of the week as unsettled weather continues. Model consensus begins
to diverge later on Friday but guidance hints at the central low
nudging northward and weakening as lobes of easterly waves flowing
cyclonically around the low and supporting that westward movement
of the front and weakening of the trough. An arctic low sinking
through Kamchatka toward the end of this week will also help to
guide the synoptic pattern and shift flow to moist and southerly
for the western Aleutians.

rux

&&


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

An upper level ridge extending from a Northwest Canadian high
center continues its hold across Mainland Alaska through the
forecast period. Over the Gulf of Alaska, a closed low South of
the Alaska Peninsula and Kodiak Island is weakening and beginning
its movement away from the Gulf Monday. In the Far West, a well
developed low out of Siberia moves across the Northern Bering
before weakening and sliding back into the Arctic late Tuesday. A
Western North Pacific low picks up some cold air from across the
Russian Far East strengthening as it moves over the Central
Aleutians by Wednesday. This scenario appears to set up a longer
term duration over the Bering beyond the forecast period.

The remnants of a front extending into Western Alaska from the
Gulf low continue periods of heavier rainfall over Kodiak Island
and the AKPEN through early Monday. Some rain mixed with snow
should occur around Bristol Bay, with areas of new snow further
North along the West Coast. The approach of the Western Bering low
and its front will spread gusty winds and precipitation across
the Aleutians late Sunday, into the Pribilofs late Monday and
continue over the AKPEN through Wednesday. A second North Pacific
low moving East along the Southern Gulf brings another round of
heavier precipitation and gusty winds over Kodiak Island and the
AKPEN late Monday into Tuesday.

Kutz

$$


.AVIATION...

PANC...VFR conditions will persist. There is still some uncertainty
with the winds coming out of Turnagain Arm and whether they will
continue to bend down Cook Inlet or be able to make it into the
airport. It is looking more likely that these winds will continue
to turn down the Inlet through the night with surface winds
remaining northerly. However, with these northerly winds there
will also be some wind shear over the airport with winds aloft
being from the east to southeast.

&&

$$

000
FXAK67 PAJK 172246
AFDAJK

Southeast Alaska Forecast Discussion
National Weather Service Juneau AK
246 PM AKDT Wed Apr 17 2024

.SHORT TERM...Through Thursday night...Ridge of high pressure over
the region will maintain dry weather with mostly sunny skies
through the period. Another round of optimal radiational cooling
will allow temps to drop again overnight with lows similar to Wed
morning with guidance continuing with slightly warmer max temps
Thu. Minimal changes to inherited forecast to adjust toward
persistence.

.LONG TERM.../Friday through Wednesday/...The end of the week
brings about an end to the dry and warm weather for SE AK as the
gulf high pressure ridge shifts east. A trough from 500 mb low
over the Western AK Gulf extends over the SE Gulf then rotates
over the Panhandle from S to N Saturday night into Sunday. At the
surface the stalled front that was over the Western Gulf moves
east then pushes over the Panhandle. Cloud cover increases and
temps return to seasonable normals with a narrower diurnal range.
The front will shear apart as it loses upper level support so not
expecting much in the way of rainfall amounts. Operational models
have fair amount of spread on if this front will produce any
precip but ensembles have been consistent keeping in some light
precip. As the front rides over the ridge another short break in
precip occurs Monday as another low moves in from the west.
Northerly winds diminish as pressure gradient weakens with a
directional shift occurring through Saturday into Sunday. Active
weather continues into next week. More spread in operational model
solutions due to the break down of the ridge but ensembles keep a
broad low in place with precip for most of the time, so overall
lower confidence in forecast details next week

&&

.AVIATION...

VFR conditions will persist across the panhandle with clear skies
and little wind aside from localized afternoon sea breezes
through the TAF period.


&&

.MARINE...High pressure over the region will stall an advancing
front over the gulf. Strong to near gale southeasterly winds will
persist over the gulf through the week before high pressure moves
E of the region. Over the inner channels, generally light to
gentle winds prevail with moderate to fresh NE to E outflow winds
out of Taku Inlet, back side of Douglas Island and S Lynn through
Cross Sound.

&&

.AJK WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Small Craft Advisory for PKZ022-053-642>644-651-652-661>664-671-
672.

&&

$$

SHORT TERM...BC
LONG TERM....PRB
AVIATION...NM
MARINE...BC

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