Small Craft Advisory 953, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
456 AM AKST Sun Dec 2 2018

.ANALYSIS AND UPPER LEVELS...

An area of low pressure located off the coast of Cape Newenham is
bringing a push of warmer air across southwest Alaska as showery
precipitation spreads across the area. Most stations around
Bristol Bay are above freezing, and most areas that are seeing
precipitation this morning are reporting rain. The low is being
supported by a negatively tilted trough which is enhancing the
lift out ahead of it, helping to cause the precipitation. This
feature is forecasted to push eastward today and cause tonight's
snow event across Southcentral. More on that below.

A strengthening, expansive low over the North Pacific well south
of Shemya will be the primary weather maker across the Bering for
the next several days.

The warming winds from yesterday that diminished overnight have
allowed temperatures to fall back into the 30s for most areas
around Anchorage, with 20s being reported further north.

&&

.MODEL DISCUSSION...

The models are in good agreement with the tracks of the low and
precipitation timing with the next snow event moving into
Southcentral this evening. However, differences that are causing
big challenges continue to be timing the changeover of
precipitation from rain over to snow, when the heaviest snow moves
into different parts of Southcentral, how quickly it ends, and
where and how strong the strongest winds will be around the low
moving into the Aleutians. Thus, while confidence is high on a
continuing active weather pattern, confidence in the
aforementioned details remains fairly low.

&&

.AVIATION...
PANC... The winds will increase again this morning out of the
southeast off of the mountains. While these are expected to remain
below wind shear criteria and above 2,000 ft, they may approach
the criteria at times today. This evening, the winds will taper
off as precipitation moves in. It appears most likely to begin as
a rain and snow mix this evening, then turn to all snow and
increase in intensity overnight before diminishing early Monday
morning. IFR to briefly LIFR conditions are possible during the
heaviest snow.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
A front associated with the low in the eastern Bering is tracking
toward Southcentral Alaska with it impacting the Kenai Peninsula
by this afternoon. Many of the southern areas of Southcentral
Alaska will start as rain when the front moves in. However, they
will gradually transition over to snow with coastal locations
holding on to warmer temps through much of tonight. The most
challenging part of the forecast is identifying when the rain will
fully transition to snow.

The track of the front makes for a good setup for potentially
heavy snow in areas from Anchorage north into the Susitna Valley.
The heaviest snowfall looks to be in the late evening but will
last into Monday morning before tapering off for these areas. Snow
will last through the morning for eastern portions of
Southcentral Alaska before ridging builds in from the west.
Clearing caused by the ridging will be short lived as another
front will push up from the southwest Monday night, when it will
bring rain to Kodiak Island.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2/Sunday and
Monday)...
Currently, the last low of the quick succession of lows is moving
through southwest AK, bringing rain showers and warmer temps with
it. Temperatures will cool down after the exit of this frontal system,
with highs back below freezing for inland areas tomorrow. This is
due to a shortwave ridge that will work its way across the region
later today and tonight, offering a break in the weather.

Monday will again see the influence of low pressure, with winds
becoming strong out of the southeast. Precipitation will also
move in, as the outer band of a large low pressure system moving
into the central Aleutians reaches the coast. Temperatures are
such that the rain/snow line will setup right along the coast,
with a chance of freezing precip in some coastal areas.
Temperatures will stay cold enough inland to keep precip as snow.
This low will be the dominant weather feature for early next week.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2/ Sunday
and Monday)...
The compact low moving through the eastern Bering will quickly
exit today. Behind it, a shortwave ridge of high pressure will
slide eastward across the Aleutians and Bering Sea the next couple
of days, offering some respite from the succession of lows that
has been passing over the eastern Aleutians.

However, a large and powerful low will be moving into the Bering
Sea the next couple of days. Its impacts will begin to be felt
later today in the western Aleutians, with storm force winds and
gusts to 75mph in the forecast for tonight. This storm will
slowly work eastward through Monday, with the low center tracking
right along the Aleutian Islands. The storm will slowly weaken as
it goes, but large swaths of gale force winds can be expected
through most of the Bering Sea and all along the Aleutian Island
Chain. This low will be the dominant weather feature for the next
several days.

&&

.LONG TERM FORECAST (Days 3 through 7)...
The forecast period commences with a longwave trough spanning
from the central Bering to the North Pacific and a high amplitude
ridge over the Gulf Of Alaska extending into the Yukon Territory.
The GFS/ECMWF and Canadian all ping into several potent
shortwaves embedded in the upper level trough. At the surface,
there is a deep mature low near the central Aleutians, however the
GFS has the surface low south of Nikolski at 12Z Wednesday and
the ECMWF has the surface low near St. Paul at 12Z Wednesday.
Additionally, to the west, the same models are out of sync with
the cyclone over the Sea of Okhotsk. As time elapses, expect this
eastern low to rapidly decay. The GFS continues to keep the
remnants south of the Chain and the ECMWF keeps it quasi-
stationary over the Bering. With the cyclone near Russia, the GFS
is more bullish bringing it into the Bering. By late
Thursday/Friday the next round of cyclogenesis is well under way
in the vicinity of the Gulf of Alaska. The intensity and the
track of this new low is present on both the GFS and ECMWF but the
timing is slightly off. Generally expecting a progressive and
active pattern.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Winter Weather Advisory 101 111 145
MARINE...Gale 150 155 160 165 170 171 179>181 185 411 412.
		  Storm 172>178 413 414.

&&

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