Small Craft Advisory 284, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
449 AM AKDT Tue Apr 4 2017

.ANALYSIS AND UPPER LEVELS...
Upper level ridging over the Southeast coast and across the AlCan
border continues to keep the upper level low tracking northward
over toward the Gulf, and hindering any easterly progression for
now. Meanwhile to out west, a flattening upper level ridge over
the Bering is beginning to give way to low pressure from both the
east and west.

At the surface, a strong and fully wrapped up low is in place
over the far southwestern Gulf, with an associated front producing
strong gusty winds and rain along the Northern Gulf coast, Cook
Inlet region, and parts of the Southwest mainland. Relatively weak
high pressure is in place over much of the western half of the
Bering and Aleutians, with gusty northerly flow over the eastern
portion of the Bering and Aleutians.

&&

.MODEL DISCUSSION...
The models remain in good synoptic agreement on the track and
positioning of the Gulf low over the next couple days. There are
some minor differences by mid week as to where any associated
fronts will be and their strength. Due to the small scale of those
differences, however, high resolution versions of the NAM/GFS
were used to help iron out small scale wind effects. The changes
in the winds through southern Alaska's many bays and passes
remains the primary forecast challenge in this environment. Thus,
overall forecast confidence is high with less confidence in local
effects.

&&

.AVIATION...
PANC...VFR conditions and light winds will persist. Generally
light northerly winds are expected to continue into Tue
afternoon. Weak wind shear over the anchorage area should
continue though this morning, as winds around 2000 ft remain gusty
and out of the southeast.

&&

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

A front continues to drive much of the weather across Southcentral
this morning and is currently pushing against the north Gulf
Coast. As a result it is supporting an impressive low level jet
which has been bringing storm force gusts overnight to Middleton
Island. However, due to the orientation of the front and
associated pressure gradients, the majority of the gusty winds
have remained south of Prince William Sound. The Anchorage
sounding this morning reveals steep lapse rates above the surface
inversion, which indicates this morning why precipitation on the
radar is convective in nature. However, the sounding also reveals
a deep layer of dry air near the surface, which is limiting the
amount of precipitation that is making it to the surface. The
sounding this morning also indicates a dramatic warming in mid-
levels from the afternoon sounding yesterday, which indicates the
potency of this front.

The front will slowly weaken throughout the day, and its
associated low will weaken south of Kodiak. A second, more potent
low follows quickly on its heels and pushes into the eastern Gulf
of Alaska by late this evening. This will help to re-intensify the
low level coastal jet by early Wednesday morning, and will
reinforce the warm air advection across Southcentral. While this
system will bring a round of more intense precipitation, this will
mainly occur in coastal regions, while the Anchorage Bowl, Kenai
Peninsula and Matanuska Valley will remain mostly downsloped.

&&

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

Persistent cyclonic flow around a Gulf of AK low will keep much
of the Kuskokwim River and Delta dry into Fri. Moisture
circulating around the low will bring a mix of overnight rain and
snow, and then daytime rain to the Bristol Bay region through the
same period. Gusty winds are also expected through channeled
terrain of the Aleutian Range.

&&

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

Northerly flow will continue across the eastern Bering and Alaska
Peninsula into Fri. Snow showers combined with the wind will bring
areas of blowing snow, mainly east of Cold Bay through the period.
Weak ridging will diminish snow shower activity across the eastern
and central Aleutians until a fast moving low from Kamchatka
reaches the area with some snow later on Wed. The next front will
enter the western Bering Wed night with wind and rain for the
western Aleutians. This will spread to the central Aleutians Thu
and Fri.

&&

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

The extended forecast period beginning Wednesday evening will
feature a continued active Pacific Jet stream in the vicinity of
40N with a high latitude blocking high over the North Slope. There
will be weakening near gale force low near Kodiak Island with
rain along the coast. This will set in motion another rather
quiescent weather pattern as the low near Kodiak Island weakens
slowly and the storm track shifts south again. Rain and snow
shower threats will be possible inland, but right now, they look
rather meager since the low will be falling apart as some moisture
aloft moves inland. Otherwise, this pattern will feature slightly
above normal temperatures with a continuation of the slow spring
thaw through the weekend.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Gale Warning 119 120 130 131 155 351.

&&

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