Small Craft Advisory 479, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
438 AM AKDT Mon Jun 18 2018

.ANALYSIS AND UPPER LEVELS...

A strong low moving north out of the Pacific is currently centered
over the waters of southern Shelikof Strait between Kodiak Island
and the Alaska Peninsula. The low has a feed of moisture
originating straight out of the tropics, and as such is producing
steady rainfall over nearly all of Southcentral, including some of
the Copper River Basin. Light rain is also ongoing throughout much
of Southwest Alaska except for a small area in the Kuskokwim
Delta.

The winds remain gusty through many of the gaps, including
Turnagain Arm and the Knik River Valley as the large amount of
mass moving out of the Pacific into the Chugach and Kenai
mountains then has nowhere to go except to be funneled through
those gaps. The downsloping component continues for parts of the
Matanuska Valley and northern Kenai Peninsula, but more areas than
usual are getting rain, indicating the drying is relatively weak.
Temperatures area-wide remain seasonable with little variation
due to the widespread cloud cover over the area.

The story continues to be the same in the upper levels as a nearly
stationary upper low persists across the eastern Bering. To its
west, from the Pribilofs west, northerly flow continues with
widespread stratus. To its east, broad, very moist southerly flow
continues, as previously mentioned, keeping the whole of southern
Alaska under overcast skies.

&&

.MODEL DISCUSSION...

The models are handling the low moving into Shelikof Strait and
the Alaska Peninsula all in lockstep through Tuesday, with minor
differences arising thereafter. Beyond that, most of the models
track an upper level wave approaching the southern Gulf early
Wednesday morning, which the GFS seemingly has the best handle on
being one of the stronger solutions. This also agrees with the
ensembles as well. The NAM was used early on for better high
resolution definition, followed by the GFS on Wednesday. Forecast
uncertainties are primarily concerning the strength of the gap
winds and how much precipitation falls across Southcentral through
Wednesday. Forecast confidence is average.

&&

.AVIATION...
PANC...LLWS with mostly steady light rain will remain the primary
hazards affecting the area for the rest of the morning. The
Turnagain Arm wind will return around midday with rainfall
tapering off. LLWS was removed from the TAF after midday, but SE
winds to 50 kts at 2,000 ft will continue into the afternoon, then
diminish through the evening and overnight. Ceiling heights and
visibility are both expected to remain VFR throughout the TAF
period.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
The synoptic pattern of an upper level low over the eastern
Bering and ridging east of Southcentral Alaska will continue.
This will result in southerly flow aloft. A strong weather system
embedded in this flow is moving through Southcentral Alaska
this morning. Rain will change to showers this afternoon as the
front moves inland. Tonight through Tuesday night several weak
upper level short waves will push through the area, keeping some
shower activity going, especially along the coast. Unseasonably
high winds in many channeled areas such as Turnagain Arm will
continue through this afternoon, then slowly diminish tonight as
the surface gradient weakens. The Copper River will also see
rather strong winds today as the front moves inland.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
A north Pacific low will track across the Bristol Bay and
Kuskokwim Delta today while weakening, then remain nearly
stationary over the eastern Bering through Wednesday. This will
keep widespread rain over much of the southwest Mainland through
the middle of the week. Mildly gusty southeasterly flow will
persist through Tuesday night, with the strongest gusts through
channeled terrain along the Alaska and Aleutian Ranges. Winds will
also become gusty along the southwestern coast Tuesday, as the
low tracks into the Eastern Bering.

&&

.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 through the
southwest Mainland today. Increased rain chances are expected with
this pattern along with varying winds as the next low pressure
enters the eastern Bering overnight tonight, then tracks slowly
toward the Alaska Peninsula through Wednesday. The Pribilof
Islands, central Bering, and Eastern Aleutians will be under the
influence of the low pressure system initially. Precipitation
chances were increased for these locations through Tuesday night,
then transitioning to a drier pattern with clouds and fog by
Wednesday.

To the west of this low, ridging builds across the western half
of the Bering and Aleutians from the Kamchatka peninsula through
Wednesday. Expect continued stable conditions under this ridging
pattern, with widespread low stratus and fog persisting over the
area through Wednesday morning.

&&

.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...Gale: 119 120 125 130 351 352.

&&

SYNOPSIS AND MODEL DISCUSSION...JPW
SOUTHCENTRAL ALASKA...BL
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...TP
LONG TERM...JA