Small Craft Advisory 326, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
452 AM AKDT Sat Apr 11 2020

.ANALYSIS AND UPPER LEVELS...
Another day of mild weather is expected for Southcentral. However
a frontal boundary is closing in on the region, so expect
increased cloud coverage today. A weak finger of the jet stream
is flowing at 100 kts near Kodiak this morning. On satellite
imagery, there is a front approaching the Gulf, a front bisecting
the eastern Bering/Aleutians and an occluded front southwest of
Attu Island that is producing gale force winds. Merrill Field
reached 40 degrees Fahrenheit yesterday afternoon while Wasilla
reached 41F and the melting continued.

&&

.MODEL DISCUSSION...
Models are in good agreement through Monday. Which is seconded by
the tight clustering of the GFS ensemble members through early
Monday. There are some minor differences in the timing of the
precipitation. However, all the models point towards a dynamic
pattern in the North Pacific and system moving into the Gulf
riding over the back side of the ridge.

&&

.AVIATION...
PANC...VFR conditions and light north winds will persist through
the afternoon before becoming variable overnight.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...

The pattern is shifting today as a low in the north Pacific will
move to near Kodiak Island Saturday night. This will bring
increasing clouds back into Southcentral by this afternoon. The
front associated with this low will move along the north Gulf
coast tonight increasing winds and bringing in some precipitation.
At this time, it looks like most of the precipitation will remain
along the coast and over the coastal mountain ranges without
spilling over into the lee side of the mountains. However, there
is a chance for some light snow or rain to make across tonight
into Sunday. Sunday night looks like the best shot overall for
precipitation inland. Due to the time of year, the time of day the
precipitation falls is critical to precipitation type.
Temperatures should warm into the upper 30s to lower 40s for most
inland areas so all rain (or at least a rain/snow mix) is
expected for daytime hours. However, it will still get cold enough
for snow for the nighttime precipitation so the timing of the
precipitation is important. Even if everything comes together for
a nighttime snow event, the amounts are not expected to be very
much with just a couple of possible exceptions.

The Susitna Valley could see a number of inches of snow Sunday
night into Monday should everything come together right. The other
areas is right around Kenai which is being highlighted by models
as a place that could see more snowfall. However, temperatures are
getting warm enough that even if snow can maintain for longer, it
will likely melt as it reaches the ground. All that said, there is
enough uncertainty to warrant keeping an eye on this system the
next few days.

&&

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

Scattered mixed precipitation will track from south to north
through today, likely changing to all snow once it reaches the
Kuskokwim Delta. After a brief lull overnight tonight, heavier
precipitation will develop across all of western Alaska by Sunday.
While it may briefly begin as snow over the Kuskokwim Delta in
the early morning hours, most of it will fall as rain, as
temperatures in the low 40s are expected across much of the area.
A strong upper level trough will lead to the quick departure of
associated front, with most rain tapering off by Monday morning.
Although only about half an inch is generally expected (with
localized higher amounts possible), this combined with rapid snow
melt may cause issues in poor drainage areas.

&&

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

Rain will persist across the central and eastern Bering/Aleutians
through Sunday under a warm front. Partial clearing is expected
Monday morning under weak high pressure, with rain redeveloping in
the afternoon north of a low. Scattered showers will continue
today across the western Aleutians as an upper level low departs
to the north. Quiet conditions are likely Sunday under a weak
ridge. Showers will again develop Sunday night and persist through
Monday under a warm front.

&&
.MARINE (Days 3 through 5/Saturday through Monday)...

Bering Sea/Aleutians:

The theme for this extended forecast will be warmer and wetter air
masses as a period of southerly flow begins thanks to a broad
area of high pressure over the Gulf of Alaska/Mainland Alaska. As
a frontal boundary lifts north out of the north Bering on
Saturday, high pressure over the eastern half of the Bering begins
to break down as a 1007 mb low in the north Pacific pushes a warm
front north into the eastern two thirds of the Aleutian Chain on
Saturday morning. This wave will push north of the Pribilofs
Saturday afternoon and keep western Alaska, Bristol Bay, and the
Alaska Peninsula in a wetter pattern through Monday morning.
Another warm front lifts into the Western Aleutians Sunday
afternoon, with its 995 mb parent low in the north Pacific set to
cross the chain late Monday night.

Gulf of Alaska:

The forecast period will start with dominant high pressure pushing
off to the northeast Saturday and a warm front lifting across
Kodiak Island Saturday afternoon as a north Pacific low pushes
into the Aleutians. This frontal boundary will maintain a presence
across the north Gulf Coast through Sunday night and then fade
Monday morning as high pressure builds back in from the east.

&&

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

Model guidance has come into much better agreement for the Sunday
through Tuesday time period showing an upper level ridge in place
across much of Alaska with confidence very high. With this upper
level ridge in place, the warming trend will continue every day
into the middle of next week. For the mainland, expect
temperatures warming to near normal on Sunday and then to above
normal early next week. Unsettled conditions are also possible on
Sunday as a weak system from the North Pacific south of Dutch
Harbor moves northward toward Bristol Bay with high confidence for
this system. A different closed off system west of the Aleutians
Sunday will move east towards the Bering Monday due to the upper
level trough in place over eastern Russia and the North Pacific.
This may bring another period of unsettled weather to Southwest
and Southcentral Alaska Tuesday to Wednesday time frame next week
as it continues east but gets pushed north due to the blocking
ridge to the east. Confidence is average for this system.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gale 131.

&&

SYNOPSIS AND MODEL DISCUSSION...PJS
SOUTHCENTRAL ALASKA...EZ
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...AP
MARINE/LONG TERM...LB/MV

SPECIAL WEATHER STATEMENT
National Weather Service ANCHORAGE AK
154 PM AKDT Sat Apr 11 2020

AKZ145-121400-
Susitna Valley-
Including the cities of Talkeetna, Willow, and Cantwell
154 PM AKDT Sat Apr 11 2020

...April Snow Storm Possible Sunday Night into Monday...

A very moist system will make its way into Southcentral AK Sunday.
This system will bring a swath of warm air to most areas, allowing
daytime temperatures to rise well above freezing. Precipitation
will generally start out as a rain/snow mix on Sunday afternoon.
However, as temperatures cool Sunday evening in the Susitna Valley,
precipitation will change over to all snow and increase in
intensity. Surface temperatures will be critical to determine how
much snow will be able to accumulate. In general, we are expecting
between 4 to 8 inches of heavy, wet snow before the system winds
down late Monday. However, there remains potential for colder
locations to see even higher amounts.

Please continue to monitor the forecast for updates at
www.weather.gov/Anchorage