Small Craft Advisory 277, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
433 AM AKDT Mon Apr 2 2018

.ANALYSIS AND UPPER LEVELS...
Early this morning an upper level blocking ridge is centered near
the Bering Strait. A sprawling trough pattern encompasses much of
Canada to its east with a low center closing off along the
northern panhandle. An established closed low continues to spin
south of the Aleutian Chain with an associated surface low
bringing rain and gusty winds along a weak front that moved into
the southern Bering late Sunday. Gusty offshore flow, which
increased along the Thompson Pass and Valdez on Sunday, developed
across the remainder of the typical gap locations overnight.

&&

.MODEL DISCUSSION...
Models are relatively in good agreement through midweek with the
general synoptic pattern. There is some uncertainty on how fast
the low over the panhandle retrogrades west as strong short waves
dive through the flow along its western side. A new low center
develops over Southcentral Tuesday night as energy swings down
from the Brooks Range. Models are struggling with the evolving
synoptic pattern; therefore, only minor edits were made Tuesday
night into Wednesday. The highest precipitation chances are
expected across the Gulf and surrounding coast along with gusty
winds as a weak front develops.

&&

.AVIATION...
PANC...VFR conditions are expected through Tuesday morning. North
winds will gust through late today then taper down
tonight...however there is some uncertainty on when the pressure
gradient slackens which may cause prolonged wind gusts into
Tuesday.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
Today will be very much like yesterday over most of Southcentral
Alaska. The notable differences will be stronger winds over the
Matanuska Valley and down Cook Inlet.
The upper level low digging southward along the Alcan border will
begin to retrograde westward Tuesday which will start to increase
clouds over the region. Along the north Gulf coast there may be
some snow showers that develop tomorrow with some snow likely
along the coast by Wednesday with this new system.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
The large upper level ridge centered over the eastern Bering and
western Alaska shifts north today leading to breezy northeast
winds, sunny skies, and very dry conditions across Southwest
Alaska for the beginning of the week. Beginning tomorrow
afternoon, a cold upper level trough will drop southwest from
interior Canada/Alaska into the Kuskokwim Valley bringing
increased cloud cover and colder temperatures. A tightening
pressure gradient between the departing high and incoming low will
mean continued breezy northeasterly winds across the Delta. As
the low pushes further west towards Bristol Bay, moisture will
wrap around it from the gulf leading to increasing chances of snow
for the later half of the week.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
A surface low south of the Aleutians with an associated front
draped across the western half of the island chain will stay
mostly stationary today as a large blocking high to the north
impedes any significant movement of the system. Thus, a narrow
plume of moisture aided by a southerly jet aloft will continue to
focus rain over the Dutch Harbor area with lighter showers seen
further west. As the high and low pressure systems slowly drift
apart today, winds will die down some and rain will lighten and
the frontal system decays. By Wednesday, the upper level low over
Southwest Alaska will begin spreading cold air aloft over the
eastern Bering as the upper level ridge which had been centered
over the Bering is pushed well north of the area.

&&

.LONG TERM FORECAST (Days 4 through 7...Thursday through Sunday)...
The forecast period commences with an upper level low centered
over the Yukon Kuskokwim Delta, and the span of the cyclonic flow
basically covers the Last Frontier. There is also a second upper
level low just south of Attu Island, and a dome of high pressure
over Siberia. As the forecast period unfolds, the low that had
been over the mainland will continue to move west towards the
Pribilof Islands. An easterly wave this time of year is very
uncommon. Definitely expecting a pool of cold air aloft to cross
both the East and West domains. But there is a high amount of
uncertainty regarding the sensible weather impacts for this period
purely based rarity of these types of events in the cold season.
By Friday, the low south of the Western Aleutians will begin to
push eastward across the chain bringing gusty winds and rough seas
to the region. By Saturday, a ridge axis will begin to build into
Southcentral.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...None.

&&

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