Small Craft Advisory 216, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
439 AM AKDT Sun Mar 12 2017

.ANALYSIS AND UPPER LEVELS...
The stout blocking high over the western Bering Sea remains the
dominant weather feature over the region this morning, yielding
continued dry northerly flow and predominantly clear skies over
the Alaska mainland. A positively tilted longwave trough
extending from the Yukon into the north-central Pacific is
beginning to shift slightly westward into the gulf. This is
helping to strengthen a surface trough across the north gulf
coast and aiding a corresponding increase in gap winds through
some of the favored areas. Farther west, the Bering remains locked
in a benign marine stratus regime beneath the ridge.

&&

.MODEL DISCUSSION...
Guidance remains in good agreement through early in the week as
the blocking high remains over the Bering and a series of arctic
shortwaves moving over the top of the ridge helps to dig a deeper
trough over the mainland. Given the good synoptic agreement, the
morning package primarily utilized a higher resolution NAM-based
solution to better depict localized wind features.

&&

.AVIATION...
PANC...VFR conditions will persist through Monday morning. Winds
will begin to increase out of the north later this morning,
becoming gustier in the 03-06z timeframe and lasting into Monday
morning as a weak upper level disturbance moves out of the
interior.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
More wind is on the way to Southcentral. A surface low will move
into the eastern Gulf today leading to tightening pressure
gradients while an upper level low and inverted trough shift
westward into the eastern Copper River Basin, leading to
strengthening flow aloft to the west of the trough axis. With
abundant sunshine there should be no problem mixing out surface
inversions and allowing gusty winds to reach the surface across
most of the region beginning this afternoon or evening. With flow
continuing to strengthen tonight and colder air stacking up
against mountains in the Copper River Basin, expect winds to
keep going all night long. A series of short-waves will then drop
down from the Arctic Monday through Monday night, leading to
another round of cold air advection and even stronger winds for
many areas.

As the short-waves from the north reach Southcentral, the upper
low and trough over the Gulf and eastern portions of Southcentral
will be forced to lift northeastward into the Yukon. Light snow
showers may make it into the eastern Copper Basin and eastern
Prince William Sound region as it does so, but with persistent
dry northerly flow in the low levels, expect little or no
accumulation. Elsewhere, expect no more than some mid and high
clouds.

&&

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

Some fog developed over Nunivak Island and the Kuskokwim Delta
coast this morning in response to a very strong nocturnal
inversion and a bit of increased moisture. In addition, some snow
flurries have also been observed falling out of the low
stratus/fog. This will likely continue through the morning hours
until daytime mixing allows for the fog to mix out with copious
amounts of dry air aloft (as evident on the 12Z PABE RAOB). The
rest of Southwest Alaska will look to remain on the dry side as
high pressure, both at the surface and aloft, become further
entrenched across the region. Expect near normal temperatures
through the weekend before temperatures begin to drop toward the
beginning of next week.

&&

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

A persistent Rex Block anchored over the Bering Sea will continue
to bring a period of docile weather throughout much of the region
through early next week. The high pressure over the western Bering
Sea will continue to stravage which may allow a few showers to
enter the coastal waters throughout the weekend. A decent shortwave
will round the eastern periphery of the upper level ridge in the
Bering Sea Monday afternoon through much of Tuesday. This will
help to enhance gap winds across the Alaska Peninsula and eastern
Aleutians with northerly gale force gusts possible through the
many gaps and passes across the aforementioned locations.

&&

.LONG TERM FORECAST (Days 3 through 7...Tue through Sat)...
Models continue to advertise a slow and steady pattern change. The
ridge over the western Bering will go from being more of a
negative tilt (oriented northwest to southeast) to a more neutral
orientation (north to south) as we go through the week. This will
allow cold air to move from the Interior into the southern half of
AK helping to carve out a trough in the Gulf of AK. Then by next
weekend, the Bering ridge is almost completely eroded as a broad,
warm low approaches the western Aleutians.

The net effect from this will be calm conditions over much of the
Bering, while cold returns to southern AK with some snow threats.
Seas will remain relatively low and winds light really until a
warm front moves towards the central Bering by Fri. A few
shortwaves driving over the ridge and into Southwest AK will usher
in much colder air starting Tue. This cold air could also bring
the chance for some very light snow, but not impressed with any
feature at this time as the column will be very dry. It will also
lead to some gusty winds mixing down to the surface. For South
Central, models remain in good agreement that low pressure will
make its way into the Northern Gulf of AK. However, there are
subtle differences in exactly how far north and west the moisture
makes it. For now, still looks like best snow chances stay along
the Gulf Coast. But we will monitor closely for any trends if the
low were to track further west towards the colder air. The GFS did
come in with a much stronger low near Southeast AK on Wed, but
since it was a big outlier, we did not incorporate this solution.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None
MARINE...Gale Warning 126 127 131 132

&&

SYNOPSIS AND MODEL DISCUSSION...CB
AVIATION...CB
SOUTHCENTRAL ALASKA...SEB
SOUTHWEST ALASKA/BERING  SEA/ALEUTIANS...MMC
LONG TERM...MO