Small Craft Advisory 8, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
456 AM AKST Wed Jan 2 2019

.ANALYSIS AND UPPER LEVELS...
The broad area of low pressure over the western Bering/eastern
Siberia continues. There is high pressure to our east over Canada
and zonal flow over the Aleutians which is beginning to push into
southcentral Alaska. Some weak upper level troughs are embedded in
this flow which are moving through the Bering Sea. They are not
producing much weather, just some snow showers with winds gusts as
they go and are not of big concern.

The low that has impacted our forecast area over the past day is
weakening and pushing north. It has diminished to a trough at
500MB, but is still reflected as a closed low on the surface. It
is also becoming pretty disorganized as it falls apart. We are
receiving some showery activity and weak cold air advection on the
backside of the low as it moves out of our area. The weak influx
of cold air has been just enough to switch precipitation type from
rain to snow overnight for some locations.

.MODEL DISCUSSION...
On the large scale models are in agreement with the overall pattern.
However, the issues with the smaller scale features mentioned in
the previous discussion continue. Models still have not been able
to lock onto the smaller low pressure systems moving through the
flow, so particulars of the forecast over the next couple of days
will be difficult to nail down. Past a couple of days models
continue to have disagreement even with the bigger features.

&&

.AVIATION...
PANC...Intermittent MFR conditions are expected to continue at
the airfield through the morning. This is due to low ceilings and
mixed rain/snow showers moving through the area. Conditions will
improve to VFR around noon but showers will remain in the area.

&&

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

After two days of widespread above-freezing temperatures around
Southcentral Alaska, today will see colder air beginning to move
into the region before the deep freeze arrives by Thursday night.
The big question will be whether there will be any additional
snowfall before the much colder temperatures arrives.

Widespread shower activity persists over Cook Inlet and the north
Gulf coast area. Most of this precipitation is rain early this
morning and the biggest forecast challenge is determining whether
the precipitation will mostly end before turning to snowfall or if
there will be some snow accumulation first. It is generally
difficult to get significant snow accumulation in the Cook Inlet
region in this set up as the cold advection tends to be a little
slower than often is expected and the rain ends before switching
to snow. The Susitna Valley is a bit of an exception as it is
easier to get snowfall there and the areas with the best chance of
snow today is from Palmer-Wasilla northward.

The showers in the Prince William Sound area will remain rain for
much of the day but should begin to turn over to snow late in the
afternoon and be all snow from this evening onward.

Another forecast question will be the Copper River Basin snow
chances tonight into Thursday. While it looks like 2 to 3 inches
of snow is likely, their is a chance (mostly advertised by the
NAM model) of snowfall closer to 6 inches around Glennallen with
more in the mountains. Going with the lower snow amounts at this
time but this will be something to keep an eye on.

&&

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

Because the low that caused the snow and rain over the area for
the past day or so continues to dissipate inland, improving
weather for this second day of the year is expected today.
Snowfall rates and winds continue to diminish over the Kuskokwim
Delta, where the Winter Weather Advisory has been cancelled.
The air mass behind this low is decidedly colder than Southwest
Alaska has experienced the past few days, so while most areas
should see some amount of sunshine today as the skies clear, it
will be a cold sunshine.

Enough about that low, the next front will move into the coast of
Southwest Alaska overnight and dissipate as it moves inland.
Comparatively speaking, this will be the weakest precipitation-
maker Southwest Alaska has seen in a number of days. As such, the
best chances for snow showers will be near the coast, with very
little precipitation expected to make it inland. Thus, most areas
will see mostly cloudy skies from it. A slightly stronger low and
front will approach the Kuskokwim Delta Thursday night, but it too
is only expected to produce some snow showers at times and make
for breezy conditions. All in all, quiet weather will be the
overarching theme to the forecast right into the weekend.

&&

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

Now that all of the strong systems have exited the area and a cold
air mass has settled over the Bering, the next two days will
mainly feature scattered snow showers over much of the Bering with
weak, small areas of low pressure forming and moving across the
Bering generally in a southwest to northeast motion. None of them
are expected to produce much more than brief periods with 25 kt
winds with light snow. The lows more or less consolidate into a
single one over the northwestern Bering Thursday, but once again
it is not expected to produce any hazardous weather. A stronger
low looks to move into the western and central Aleutians from the
Pacific around Friday morning.

&&

.LONG TERM FORECAST (Days 4 through 7)...

Southcentral:

Beginning the extended period forecast Thursday evening, there
will be a shortwave trough amplifying into a deeper longwave
trough as it moves east across Southcentral. This will be the
FIRST northerly offshore flow event of the entire winter. This
should promote much colder temperatures with a high likelihood of
below average temperatures developing by Saturday. Offshore winds
will enhance local gap winds, but this pattern will likely last
through at least Tuesday before the next front tries to undercut
the Bering blocking high and move into the Gulf of Alaska Tuesday
night into Wednesday. After this latest busy storm cycle, the
quieter weather will be appreciated by all.

Southwest/Bering Sea:

Thursday evening, there will be a weakening shortwave trough
moving onshore across Southwest Alaska, but the front will rapidly
deteriorate as it tries to move inland. Little to no
precipitation will be associated with this weakening front.
Attention then turns to a developing 960s mb low (high end gale
force, maybe low end storm force) over the far western Bering Sea
Friday. This will pump up a ridge over the eastern Bering Sea
which will eventually move into Southwest for the weekend, keeping
the region dry and colder. The general storm track looks to
remain over the western Bering Sea with weakening fronts falling
apart as they try to move into Southwest Alaska through Tuesday.
After this latest busy storm cycle, the quieter weather will be
appreciated by all.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Small Craft...119 125 127 129 132 136 137 140 150 155 160
                       172 174 175 176 177 178 179 180 185
         Gale...120 130 131 138 139 141
         Brisk Wind...181.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...BJB
SOUTHCENTRAL ALASKA...EZ
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...JPW
MARINE/LONG TERM...JRA