Small Craft Advisory 955, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
500 AM AKST Mon Dec 3 2018

.ANALYSIS AND UPPER LEVELS...

A negatively tilted trough whose axis extends from the Lower
Kuskokwim Valley southeastward across the Kenai Peninsula is
quickly lifting northeast this morning. Ahead of the trough,
an area of precipitation is overspreading much of Southcentral
north and east of Anchorage. The precipitation is falling into a
wedge of warmer air that has been remarkably persistent over the
Anchorage Bowl. Lower level winds based on the latest ACARS
soundings show that there were only a few hours early last evening
between when lower level winds briefly turned out of the west and
allowed lower level temps to fall near freezing, resulting in a
brief period where the rain mixed with snow, but after that the
southerly winds returned and temperatures continued climbing,
ensuring that rain would be the dominant precipitation type for
the lower elevations of the Anchorage Bowl for the rest of the
night. Further north into the Mat-Su Valleys, the event played out
much closer to what was expected in the forecast, with north to
northeast winds helping scour out that warm air so Wasilla only
briefly began as rain before switching to snow and Palmer was snow
for the entire event. Thus, needless to say, it ended up being
very localized differences around Anchorage that resulted in last
night's event resulting in mostly rain.

As that feature moves off to the east, shortwave ridging is
building into Southeast Alaska and over the eastern Bering, as a
strengthening very strong low churns south of Adak. This low is
likely to cause widespread storm force winds across much of the
Bering over the next 24 hours or so with hurricane force winds
likely through the western Aleutians. So far, the front to the
east of the low has been under-performing somewhat with Adak and
Atka only gusting to 42 knots. Buoy 46072 has had gusts to 55 kt
with wave heights of 25 feet.

&&

.MODEL DISCUSSION...

The models are in very good agreement this morning as the system
over Southcentral moves out today and the only game in town
becomes the powerhouse low over the Aleutians. As such, with
excellent timing between the models with the next front moving
into Southern mainland Alaska on Tuesday, forecast confidence is
high.

&&

.AVIATION...
PANC...With the overnight rain now having moved out of the area,
low clouds are likely to persist into the morning, gradually
clearing after sunrise back to VFR conditions. The next front and
chance of precipitation will be during the day Tuesday, but is
not yet included in the TAF.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
A front continues to move through Southcentral Alaska bringing
cold air behind it. As it pushes east the bulk of the
precipitation will be over eastern portions of Southcentral Alaska
through this afternoon. Ridging will then build in over the area
ahead of another front moving in from the southwest. This new
front will make it to Kodiak Island tonight and the rest of
Southcentral Alaska by Tuesday afternoon. This system will bring
warm air back to the area and although many locations will see
some snow at the onset of precipitation, most near the coast will
transition to rain. The majority of the precipitation from this
system will be along the north Gulf Coast with the coastal
mountains blocking areas further inland from any heavy
precipitation.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2...Mon and Tue)...
The pattern is going to be rather dynamic for Southwest AK for the
next 48 hours or so. A strong, very large low is moving across the
Bering. It will push a windy, warm, and wet front through the late
tonight into Tue. But first, we start off this morning with some
light snow showers exiting the YK-Delta. A shortwave ridge is
pushing these showers off to the east and allowing some more
stable air to move in. This is setting the stage favorable for fog
formation and we are now seeing some of that across parts of
Bristol Bay and the YK-Delta. This fog won't be able to last much
past sunrise as the front will start to cause the easterly winds
to increase later today.

As the front approaches, the first noticeable change will be the
winds shifting to an offshore direction. They will then become
progressively gustier through the overnight hours. This could
create some wind shear conditions for pilots trying to take off
and land during this time. Precipitation associated with the front
will slide from SW to NE and move into Bristol Bay by early Tue
morning. The cold air in front of this system is not especially
cold or deep. Thus, while the precipitation may fall briefly as
snow initially, it should quickly turn to mostly rain for just
about all areas.
By late Tue into Wed, the area will be in a "post-frontal"
environment. This means a rather unstable atmosphere complete with
rain showers and gusty winds. Warm air will remain in place, so
expect temperatures to remain above normal through mid-week.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2...Mon and
Tue)...
A monster upper 950 mb-range low is moving toward the Central
Bering. It is pushing a warm occluded front through the Central
Aleutians towards the Alaska Peninsula this morning. It is also
bringing wide-spread storm force winds, with even a small area of
hurricane force winds. The system will track along the chain today
and encapsulate nearly the entire Bering Sea by tonight.
On Tue, the low will effectively stall near Atka and Adak. This
will leave the entire area under the influence of showers and
gusty winds. This system will be rather warm for early Dec.
However, there will be some cold air advection on its western
flank. Its in this portion of the system we expect the gustiest
northerly winds and the best chance for snow showers (vs. rain
showers for the rest of the area).

The low will slowly drift east and fill by the end of the week.
This will open the door for some markedly weaker systems to
encroach upon the Western Aleutians.

&&

.LONG TERM FORECAST (Days 4 through 7)...
Beginning Wednesday evening, there will be an active weather
pattern in place as a very deep longwave trough sets up over the
Bering Sea and Pacific, extending to around 30N. The main moisture
stream will be directed at southern Alaska, with a continued warm
pattern in place as 850 temps will be around -1 to -3C, albeit
cold enough for some snow in parts of the interior such as the
northern Susitna Valley and the Kuskokwim Valley. Sometime
Thursday, all the global numerical models are strongly hinting at
a basal shortwave moving north toward the Gulf of Alaska, rapidly
deepening as it does so. Currently this low looks to be a strong
gale force and potentially low end storm force along the barrier
jet, but it will also be bringing another slug of warmer Pacific
air, enhanced by the above average SSTs. With that said, Thursday
and into Friday look warmer and wet, especially along the coast.
Heading into the weekend, the longwave trough slowly shifts east
so wetter weather will also shift east, and slightly cooler air
will filter into the mainland. Much uncertainty develops by
Saturday as the ECMWF disagrees with the colder Canadian GDPS and
18z GFS. With that said, ensembles do agree more in general that a
split trough may develop, allowing for arctic air to seep south
and interact with the warm moist Pacific air. Should this happen
increased snow threats will be possible. Stay tuned...

Over the Bering Sea, with the broad cyclonic flow associated with
the aforementioned trough moving east, expect northerly flow to
last through Saturday before a series of fronts and/or a stronger
low moves in Sunday as the next trough shifts east.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...
Hurricane Force Wind Warning: 178.
Storm Warning: 160 170-175 179 180 411-414.
Gale Warning: 130-132 138 150 155 165 176 177 181 185 352.

&&

SYNOPSIS AND MODEL DISCUSSION...JPW
SOUTHCENTRAL ALASKA...DK
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...MO
LONG TERM...JA

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE ANCHORAGE AK
306 PM AKST MON DEC 3 2018

..TIME...   ...EVENT...      ...CITY LOCATION...     ...LAT.LON...
..DATE...   ....MAG....      ..COUNTY LOCATION..ST.. ...SOURCE....
            ..REMARKS..

0800 AM     SNOW             10 NW MOOSE CREEK STATE 61.78N 149.28W
12/03/2018  M11.0 INCH                          AK   TRAINED SPOTTER

            SNOW WATER EQUIV - 1.0 INCHES

0800 AM     SNOW             2 E MATANUSKA GLACIER S 61.80N 147.77W
12/03/2018  M12.0 INCH                          AK   TRAINED SPOTTER

0921 AM     SNOW             1 S SUTTON              61.71N 148.88W
12/03/2018  M8.0 INCH                           AK   TRAINED SPOTTER

            TEMP 32F

1021 AM     SNOW             3 S RIDGEWAY            60.49N 151.08W
12/03/2018  M4.9 INCH                           AK   TRAINED SPOTTER

            SNOW WATER EQUIV - 0.51 INCHES

1130 AM     SNOW             7 N CASWELL             62.08N 150.07W
12/03/2018  M14.0 INCH                          AK   DEPT OF HIGHWAYS

1130 AM     SNOW             23 SW CANTWELL          63.14N 149.43W
12/03/2018  M5.0 INCH                           AK   DEPT OF HIGHWAYS

1130 AM     SNOW             6 NE TRAPPER CREEK      62.31N 150.29W
12/03/2018  M12.0 INCH                          AK   DEPT OF HIGHWAYS

1130 AM     SNOW             4 SE MEADOW LAKES       61.58N 149.53W
12/03/2018  M4.0 INCH                           AK   DEPT OF HIGHWAYS

1130 AM     SNOW             26 NNE CHASE            62.82N 149.91W
12/03/2018  M8.0 INCH                           AK   CO-OP OBSERVER

&&

KUTZ