Small Craft Advisory 471, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
600 PM AKDT Mon Jun 8 2020

.ANALYSIS AND UPPER LEVELS...
SW Alaska is quite similar to the past couple of days while
Southcentral has seen a major shift. Out west, the day started
very similar to the weekend. Patchy fog and low stratus plagued
many of the population areas. This has nearly all burned off
allowing for some heating and developing instability. There was
also some "leftover" convection from Sun afternoon that continued
through the YK-Delta this morning. Now, everything has
transitioned over to a convective mode with showers popping up on
the King Salmon and Bethel radars. Over the Bering, a gale-force
low is exiting south of Dutch Harbor while another a weak occluded
front lies across the Western Aleutians.

Instead of sunny skies and developing cumulus clouds over
Southcentral, a broad mass of clouds and rain has been moving from
the Copper River Basin through the Cook Inlet all day. This has
led to widespread wetting rains, with some spots seeing more than
0.50" over the past 12 hours. It is all courtesy of a weak low in
the Northern Gulf directing all of the remaining energy from
Sunday's convection and moisture down from NE to SW. This
widespread cloud cover and cooler, more stable airmass will
severely limit any thunderstorm chances for this afternoon and
evening.

&&

.MODEL DISCUSSION...
Models have come into better agreement in the past couple of runs,
but there remain some key differences. For tonight, there is quite
a variance in how they handle the rain moving from the Copper
River Basin down through the Mat Valley and into Anchorage. This
forecast package has utilized hi-res guidance to increase PoPs
further. Due to some of these errors early on, it makes it very
hard to trust the evolution of the pattern into Tue. The day will
start quite cloudy and rainy for Southcentral, but exactly what
time conditions begin to improve remains in question. Convection
will remain the theme over Western AK and as per the usual, this
is tough for the models to pinpoint. In general, forecast
confidence in some of these important details is low to moderate.

&&

.AVIATION...
PANC...Conditions will vary from VFR to MVFR through the afternoon
and evening depending on how steady the rain will be. The
Turnagain Arm winds look to develop and bend into the airfield for
a brief period again this evening. The timing could vary by an
hour or two once again. Overnight, more steady rain will return to
the area causing ceilings and vis to lower. By late Tue morning,
conditions should slowly improve as offshore flow starts to take
over.

&&

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

The rain will continue across Southcentral overnight tonight
before tapering off in the afternoon on Tuesday. Isolated
thunderstorms are possible Tuesday afternoon along the Alaska
Range and over the Talkeetna Mountains. A brief period of offshore
flow will allow for some drier conditions and clearer skies
Tuesday night. Meanwhile, an upper level low over the Gulf will
move toward the southwest, allowing several upper level waves to
track across Southcentral from east to west on Wednesday. This
will introduce additional chances for precipitation, especially
across the Copper River Basin and foothills of the Alaska Range.
Chances for isolated thunderstorms return for Wednesday afternoon,
specifically along the northern part of the Copper River Basin
and over the Susitna Valley and Talkeetna Mountains.

&&

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

An active weather pattern will continue with showers and scattered
thunderstorms on Tuesday and Wednesday. Wednesday will see fewer
storms as instability moderates some and the main source for lift
will be elevated areas adjacent to the Alaska Range. The broad
nature of the upper level pattern with several smaller
disturbances moving through along with daytime heating effects
makes this a very ambiguous forecast. Coastal areas should see
enough cooling overnight with dissipating clouds to initiate some
fog development in the Kusko Delta and Bristol Bay on Monday
night. Thursday looks to be quiet with a weak area of higher
pressure parked over southwest Alaska for most of the day.

&&

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

An upper low is exiting the Aleutians and Western Alaska Peninsula
this afternoon and a ridge of high pressure is building in behind
this feature in the central Bering. Another frontal boundary is
lifting into the Western Aleutians tonight and will bring some
gale force winds and rain to the Western Aleutians on Wednesday.
This semi-stationary low will bring a frontal boundary through
the remainder of the Aleutian Chain and Pribilof Islands Wednesday
afternoon. Thursday looks to remain wet and cloudy with scattered
showers on the east side of the low with steady southerly winds
in the eastern Aleutians.

&&

.MARINE (Days 3 through 5...Thu through Sat)...

Generally weak flow is expected over the Gulf of Alaska for the
end of the week. By Friday morning, easterly winds will pick up
to small craft levels south of Kodiak Island as a weak low forms
and gradually drifts eastward across the Gulf through the weekend.

A low centered over the western Aleutians will bring small craft
winds across much of the western Bering Thursday afternoon. Winds
weaken significantly by Friday night as the low weakens and moves
southward. Weak northerly flow will persist across the Bering
through the weekend.

&&

.LONG TERM FORECAST (Days 3 through 7...Thu through Mon)...

The general idea in this period will be afternoon convection
(showers/thunderstorms) across the southern mainland with a trend
towards warmer and drier. On Thu, the 3 primary weather features
will be 1) a weakening low over the Central Aleutians 2) a low
shifting away in the Gulf of AK 3) a high-latitude low over the
northern portion of AK. Working from west to east, the system over
the Aleutians will slowly weaken as it slides eastward along the
chain. It will bring steady rain and some gusty winds to the area
before it dives into the North Pacific over the weekend. For the
low over the Gulf of AK, this feature will pull away from the
state. This will create a brief period of offshore flow and allow
for some induced ridging to continue over Southcentral. The 3rd
feature over the Seward Peninsula was initially handled very
poorly by the models, so confidence is still not great with it.
However, it does look like it now stays well north of the area and
should move away through the Arctic over the weekend.

Most of Southern AK will see seasonal temperatures to start this
period. Mostly clear mornings (patchy fog over SW will remain
possible) will yield to afternoon showers and thunderstorms,
especially over the higher terrain. By early next week, models are
starting to hint at a fairly robust area of ridging building over
the state. The evolution of this ridge is still up in the air, so
confidence in the details remain low to moderate. However, the
trend is certainly towards a warming and drier pattern. The
biggest element of uncertainty surrounds if there would be enough
stability to shut off the afternoon convection.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gale Warning 176 177.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...MSO
SOUTHCENTRAL ALASKA...KO
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...LB
MARINE/LONG TERM...KO/MSO