Small Craft Advisory 478, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
452 PM AKDT Sun Jun 17 2018

.ANALYSIS AND UPPER LEVELS...

The old low in Bristol Bay remains in place today and continues to
bring moisture into Southwest Mainland Alaska. A strengthening
low is moving along the left-front exit region of the jet stream
which is running due south-to-north in the North Pacific and
heading toward Kodiak Island. This will keep most of southern
mainland Alaska in the active weather pattern. High pressure over
most of the Bering Sea has produced stratus that extends over the
entire Bering Sea except for the far northern reaches of it.

&&

.MODEL DISCUSSION...
Models seems to all be locked on to the strong low toward Kodiak
Island tonight and then merging it with the low near Bristol Bay
tomorrow. There are some differences in rainfall amounts for the
north Gulf Coast and that is bringing in a little more
uncertainty to the river forecasts as a result. The other
important question is how much rain will downslope in the strong
southeasterly flow and the GFS is bringing in more rain than the
NAM. The GFS solution is reasonable due to the location of the jet
and associated upper level support will likely be enough to
mitigate the downslope.
The model trend of keeping the merged low in Bristol Bay from
late Monday through Friday, when it finally dissipates,
continues.

&&

.AVIATION...
PANC...Gusty southeast winds will become northerly at the surface
this evening bringing in some low level wind shear as winds aloft
remain southeast. Rain will also move into the area late in the
evening and persist into tomorrow. Tomorrow will see the southeast
winds increase again in the morning but the rain is expected to
continue in the winds. The southeast flow should keep ceiling
heights and visibilities above MVFR conditions.

&&
.SHORT TERM FORECAST SOUTHCENTRAL ALASKA...
The synoptic pattern of an upper level low over the eastern
Bering and ridging east of Southcentral Alaska will continue
into Wednesday. This will result in southerly flow aloft with
various shortwaves moving through. The strongest of which will
move in tonight with associated surface low and front. It will
bring rain to areas throughout Southcentral Alaska with the
heaviest amounts along the coast. This setup will also bring
strong winds to many channeled areas such as Turnagain Arm that
will see unseasonably high winds for this time of year, with the
highest winds on Monday. The Copper River will also see strong
winds on Monday. Rain intensity will diminish Monday night but
still linger into Wednesday while winds look to diminish through
Tuesday.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
A front remains across the Kuskokwim Valley and Delta as the
surface low currently along the eastern Bering is absorbed by a
fast tracking North Pacific low that crosses over Kodiak island
late tonight. This will bring widespread rain across Bristol Bay
as it pushes inland early Monday morning spreading north across
the Kuskokwim region late morning and afternoon. Gusty
southeasterly flow increases as the boundary moves through
tapering down late Monday with the frontal passage.

The surface low moves into the eastern Bering Monday evening and
slowly shifts from Nunivak Island to the Alaska Peninsula through
Wednesday afternoon. This will keep Southwest in a southerly flow
pattern under the influence of low pressure. Higher precipitation
chances remain in the forecast under this synoptic regime.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...

Low pressure currently over the eastern Bering is quickly replaced
by the next low pressure system moving up from the North Pacific.
Increased rain chances are expected with this pattern along with
varying winds as the next low pressure enters the eastern Bering
near Nunivak Island Monday evening, then tracks slowly toward the
Alaska Peninsula through Wednesday. To the west of this low,
ridging builds across from Kamchatka. A typical stable air mass
associated with this synoptic feature traps low level moisture
near the surface which keeps low clouds and areas of fog across
much of the western and central Bering and Aleutians through mid
week.

The Pribilof Islands, central Bering and Eastern Aleutians will
be under the influence of the low pressure system initially. Rain
wraps around the surface low on Monday spreading southward from
Nunivak Island. Precipitation chances were increased for the
aforementioned locations through Tuesday night, then a drier
pattern with clouds and fog become dominant on Wednesday.

&&

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

The long term forecast begins Wednesday evening with a sprawling
upper low over the eastern Bering Sea. This low will be in a
weakening phase, but with southerly onshore flow, rain and clouds
will remain in place across most of Southern Alaska. This pattern
will persist through Thursday with a gradual trend toward slightly
warmer and drier weather. However, the remaining moisture will
likely just turn to widespread showers given the strong diurnal
heating this time of year. This trend should continue into the
weekend with a switch toward more seasonable weather...meaning a
mix of sun and clouds and showers...but thankfully no cold or
overly wet weather.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Flood Advisory 125.
MARINE...Gales 119 120 125 351 352.

&&

SYNOPSIS AND MODEL DISCUSSION...EZ
SOUTHCENTRAL ALASKA...DK
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...KH
LONG TERM...JA