Small Craft Advisory 120, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
433 PM AKST Tue Feb 6 2018

.ANALYSIS AND UPPER LEVELS...
A broad negatively tilted upper trough extends from the Bering
Sea east to across the northern Gulf of Alaska. This feature split
the upper ridge allowing moisture to creep in to Southcentral. At
the surface are lows near Saint Matthew Island and one near the
North Gulf Coast. A weakening frontal trough extends between the
lows and extends across Southwest Alaska and eastward across the
North Gulf Coast. Snow is falling over much of the North Gulf
Coast/Western Kenai with light overrunning snow west of the
Chugach/Kenai Mountains from Cook Inlet/western Kenai Peninsula to
the Matanuska Valley. Easterly gales just north of the low center
were evident over the North Gulf Coast. Light snow, associated
with the frontal boundary stretching across the region, was
observed across Southwest Alaska. Areas of rain or showers were
evident across much of the Bering Sea/Aleutians.

&&

.MODEL DISCUSSION...
Models overall across the Gulf and Southcentral Alaska are in
relatively good agreement. Models are still struggling some over
the Aleutians/Bering Sea Wednesday and Thursday with the
placement of low centers. The silver lining however is that the
general position of the baroclinic zone is fairly consistent
across model solutions.

&&

.AVIATION...
PANC...Periodic MVFR/IFR visibilities in light snow will continue
into the evening hours. MVFR ceiling will likely continue
overnight tonight. Otherwise, light winds will prevail.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
The snow event is coming to an end across most of Southcentral as
the low in the Gulf of Alaska drifts east. Light snow will linger
through the evening before tapering off. Offshore winds along the
coast will continue tonight then strengthen Wednesday as a
shortwave trough moves through the Copper Basin. Inland locales
will dry out and with weak flow in place, except some low stratus
and/or fog development across favored areas like Cook Inlet.
Otherwise, expect temperatures to trend back down, especially at
night as high pressure settles in.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
A few showers continue to progress across middle portions of the
Kuskokwim Delta and southwest Alaska this afternoon, with this
activity being tied to a ribbon of vorticity (disturbance aloft)
that's trekking across the area. Although a brief period of
freezing rain may accompany the leading edge of the precipitation
across the interior, rapid warming/mixing down will allow for the
temporal window of this occurring brief enough to preclude
mentioning this in the forecast. Otherwise, this disturbance will
shear out overnight with moisture rapidly decreasing this evening,
as seen in area forecast soundings. Given the warmer air that
moved over the snowpack with some melting likely having occurred,
and a stout inversion seen for tonight, look for areas of fog to
develop overnight. The previous forecast package already accounted
for this and this looks good.

A ridge of high pressure will continue to build across the region
on Wednesday, which will reinforce the inversion with low clouds
and fog persisting. As high pressure continues to strengthen for
Thursday, increasing heights aloft and subsidence will allow for
a moderating trend to commence.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
A rather blocky pattern looks to develop over the next few days
as a high-amplitude ridge develops over the southwest mainland,
and a deep trough across the western Aleutians. In between these
features, a strong upper-level jet stream will take up residence
in a meridional fashion across east central portions of the chain.
A series of surface low pressure systems ejecting northward
through west central portions of the Bering/Aleutians will bring
increased precipitation and wind potential with them. This pattern
looks to hold for at least the next few days.

&&

.LONG TERM FORECAST (Days 3 through 7)...
Long term forecast starts in Friday with a ridge remaining over
mainland Alaska and a moderate low pushing into the eastern Bering
Sea from the south. This will set up a front with a tight
pressure gradient over Southwest Alaska and strong warm advection
which will bring temperatures into the 40s in parts of Southwest
Alaska coastal regions. Clouds will have a harder time moving into
Southcentral Alaska due to the strength of the ridge keeping the
front over Southwest Alaska at bay. This should allow colder
temperatures to persist into Saturday morning before temperatures
warm up later in the weekend as the ridge over mainland Alaska is
finally pushed eastward.

After this, things become a bit more uncertain. Due to the lack of
model consistency, ensembles were used to get an idea of the
general trend for next week with details remaining elusive. In
general it looks like a more progressive weather pattern is in
store for the area early next week with more mild temperatures. As
some fronts move through the region there is the chance for some
precipitation with each one, but nothing at this point looks very
certain so nothing more than 'chance of' POPs are being used in
that time frame over southern mainland Alaska from late in the
weekend onward.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Gale Warning 127 155 165 170>176 179 181 185.

&&

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