Small Craft Advisory 197, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
341 AM AKST Mon Mar 5 2018

.ANALYSIS AND UPPER LEVELS...
Mostly clear skies prevail across Southcentral Alaska this morning
as a transient upper level ridge moves across the mainland, with
patchy fog lingering over the Upper Cook Inlet region. A slow
moving front is tracking through the Kuskowim Valley and Bristol
Bay, bringing light snow to parts of Southwest Alaska and rain
showers to the Akpen. Onshore flow behind the front is keeping
extensive stratus and fog over the Kuskokwim Delta. Benign cloudy
conditions prevail across much of the Bering within westerly flow
beneath a low amplitude ridge. Meanwhile, the next front is
entering the Western Aleutians accompanied by rain and strong
southerly winds.

&&

.MODEL DISCUSSION...
Models are once again in good agreement for the duration of the
short term as a progressive pattern remains in place over the
region. There are only minor differences in the timing of the
front/upper trough as it moves into Southcentral later today
accompanied by generally very light QPF as depicted by the 00/06z
guidance suites. The handling of the next system has also been
pretty consistent as it races across the Bering to the Southwest
coast by late tonight and then into Southcentral by Tuesday
afternoon. This lends above average confidence to the short term
forecast.

&&

.AVIATION...
PANC...Patchy fog over Upper Cook Inlet will linger at the
terminal through late morning, keeping the threat of IFR/LIFR
conditions with some occasional breaks of VFR possible. An upper
level disturbance moving from west to east across the area this
afternoon will bring the potential for a few snow showers to the
terminal in the 19-00z window, however VFR conditions are expected
to prevail through Monday evening once the morning fog
dissipates. Fog potential will then increase again after midnight
as the disturbance moves off to the east and temporary ridging
builds overhead.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
Areas of fog persist in Anchorage and vicinity early this morning,
but expect it to quickly dissipate as clouds arrive ahead of the
next upper level short-wave. Precipitation falling over Southwest
Alaska ahead of this trough is extremely light, with generally one
to two hundredths of snow water equivalent. As this crosses the
western Alaska Range into Southcentral today, low level flow will
be primarily out of the west-southwest, which usually maintains
dry low levels. Since the vertical motion is already unimpressive,
backed off the already meager PoPs and snow amounts, keeping
measurable snow confined mainly to the mountains. Lowlands may see
an isolated shower while the mountains may see a dusting to half
inch. A separate upper wave will drop into the back side of the
trough late this afternoon and evening, resulting in
amplification as it crosses the Copper River Basin, so expect some
more widespread light snow there - once again with half inch or
less accumulation.

Fog will likely develop in Cook Inlet, Anchorage, and portions of
the Mat-Su tonight as skies clear and a short-wave ridge moves
overhead. This will be fairly short-lived as another stronger
short-wave reaches Southcentral Tuesday morning, with another
round of widespread light snow on tap for the region. In this
case there will also be a surface frontal system tracking from
west to east and expect a weak triple point low to develop over
the northern Gulf. This will produce a brief period of easterly
winds down Turnagain Arm and a little bit of cross barrier flow
across the mountains on Tuesday afternoon. Light snow may stop for
a bit in Anchorage and the Mat Valley, but will quickly start up
again as the low continues eastward Tuesday evening. A jet streak
and short-wave moving down the back side of this trough may keep
light snow going all night long for Anchorage and vicinity.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
The front that swept across Southwest Alaska yesterday has now
moved into Southcentral. There is cold advection behind the front
in the west to southwest flow. Areas of fog persist especially
in the Kuskokwim Delta region. With the cold advection there is at
least a chance that there will be some partial clearing in the
Bristol Bay area by this afternoon. The next system will reach
the Kuskokwim Delta coast late this evening and bring some snow
and gusty south winds. There will likely be some areas that get
some blowing snow with this system but the fact the winds are from
the south to southeast in warm advection usually keeps a damper
on the very low visibility in snowfall. Therefore, expecting some
places to see occasional one mile in blowing snow by not really
less than that except possibly in bursts of heavier snowfall where
the snow rate is the main factor.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
A strong front moving through the Western Aleutians today will
bring storm force winds to the Attu to Kiska area. These winds are
southerly and bringing in warmer temperatures therefore rain is
the expected precipitation type as long as winds are south to
southeast. By this afternoon the winds will begin to shift toward
the southwest and usher in cold advection which may bring in some
mixed rain and snow showers. Farther east along the Eastern
Aleutians and Alaska Peninsula there will be some breaks in the
cloud cover. However, as is typically the case, there are also
large areas of stratus lurking around the region as well, but some
sunny breaks today will be seen over most of the area.
The progressive pattern will continue for the next few days which
will bring the next front into the central Bering Sea tomorrow.

&&

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

Beginning the extended period forecast Tuesday evening, the
region will be under the influence of a continued progressive wave
pattern as another trough moves across the state. This system
will be moving east across the Alaska Range, and this looks to
bring widespread light snow to Southcentral Tuesday evening into
Wednesday morning. That system moves east Wednesday, then
attention shifts to a much stronger and dynamic low moving east
across the Bering Sea. This powerful low will track an occluded
front into Southwest Wednesday, bringing widespread rain and snow
to the region. The forecast becomes trickier Wednesday night and
Thursday as a triple point low forms in the Gulf of Alaska along
the left exit of a powerful North pacific jet stream, and along a
rather sharp warm front/baroclinic zone. The general consensus is
that a powerful low will form in the Gulf, but placement is rather
disparate at this time. Regardless, this low has the potential to
bring widespread snow to Southcentral, including strong winds
along and near the coast, but until the placement of the low is
better known, this forecast will remain more general until details
can be hammered out. The upper jet will move south again behind
this strong low, so winter will maintain it's grip as colder air
settles in again over all of Southern Alaska.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None
MARINE...Storm Warning 178 411
		 Gale Warning 173 175 177 179 180 185 412 413 414

&&

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