Small Craft Advisory 944, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
434 AM AKST Mon Dec 7 2020

.ANALYSIS AND UPPER LEVELS...

A longwave trough remains the dominant feature over Alaska, with
two embedded areas of low pressure. One north of the central
Aleutians and another just east of Kodiak Island. These upper
level dynamics are bringing precipitation to the Kuskokwim Delta,
Bristol Bay, the Alaska Peninsula, the Kenai Peninsula and across
Prince William Sound. Precipitation type continues to be a
challenge this morning, with snowfall across the Kuskokwim Delta,
Bristol Bay and the Alaska Peninsula. For the Kenai Peninsula,
however, what started as freezing rain seems to have transitioned
to rain as temperatures have increased above 32 degrees. For the
Prince William Sound area, it looks to be that all areas have
transitioned to rain with the exception being Valdez, with
temperatures in the mid 20s continuing snowfall there.

Over the Bering Sea, conditions remain relatively quiet as an
upper level ridge continues to usher in polar air over warm sea
surface temperatures. This is presenting precipitation as all snow
for the area, with high winds out of the north. This has set up
the potential for blowing snow across the YK Delta coast and the
Alaska Peninsula, including Cold Bay and Sand Point.

&&

.MODEL DISCUSSION...

Models are in good agreement with synoptic features lending to
moderate to high forecast confidence. Smaller scale details, like
precipitation type, continue to be a challenge for this forecast
package.

&&

.AVIATION...

PANC...VFR conditions and light winds will persist. This evening
there is a chance for freezing rain at the terminal, switching
over to a freezing rain/snow by tomorrow morning.

&&

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

The large low in the southern Gulf is moving slowly northward and
weakening. Due to the way the low was quite strong and weakening,
and due to another low that will develop in Bristol Bay by
tomorrow, there is not much 'follow through' with the warm air
moving inland from this system. That is keeping inland surface
temperatures below freezing in the northerly surface flow. Aloft,
there is warmer air above freezing which has produced a vertical
temperature profile conducive to freezing rain through this
evening for the western Kenai Peninsula, Anchorage, and the Mat-Su
Valleys. While the temperature profile is what is needed for
freezing rain, there continues to be significant downsloping which
is removing most-or-all of the precipitation from the lee side of
the mountains where the freezing rain threat exists. This is
likely to be the case into the evening, so there is only a chance
of freezing rain due to low POPs. As the weakened low moves
inland tonight, colder air from the southwest will follow turning
all precipitation in the Cook Inlet region and Mat-Su Valleys to
snow.

Coastal areas such as Kodiak, Seward, and Cordova will remain
rain through tonight. Valdez may stay tucked away in the cold air
enough to remain mostly or all snow for this event as the warm air
is having difficulty displacing the cold air at the surface there.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3: Monday
morning through Thursday morning)...

An upper level trough in place over Southwest will continue to
bring active weather this week. An upper level shortwave embedded
within this trough is currently moving south over the eastern
Bering. Meanwhile, a surface low currently forming over the
Bristol Bay area will retrograde westward through the day today.
As it does so, snow will spread across much of the interior
Bristol Bay area as well as the Kuskokwim Delta. Gusty northerly
winds, accompanying this system, will bring blizzard conditions
to the Kuskokwim Delta coast, thus a Blizzard Warning has been
issued. Areas across the Lower Kuskokwim Valley will also see some
snowfall, though winds are not expected to be as high across
interior locations. As this low moves initially toward the
southwest tonight through Tuesday, snowfall will taper, but winds
are expected to remain elevated across the coast before tapering
by Tuesday afternoon. By Tuesday night, the weakened surface low
will track eastward, bringing additional snow showers to the
interior Bristol Bay area. Clear conditions are expected across
Southwest for Wednesday as cold northerly flow will fill in across
the area. An upper level ridge over the eastern Bering will build
in early Thursday, ahead of an approaching front over the central
Bering.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3:
Monday morning through Thursday morning)...

A developing low over the eastern Bering this morning will bring
gusty northerly winds to the eastern Bering waters, Alaska
Peninsula, and central and eastern Aleutians. A Winter Weather
Advisory for the Alaska Peninsula remains in effect beginning this
evening as snow and blowing snow will limit visibility. There is
still some uncertainty regarding where the heavier snow bands
will occur, but current thinking is up to 5 inches is likely with
some higher amounts possible in localized areas. As the low center
weakens and tracks slightly southwest through Tuesday morning, it
will continue to advect cold northerly flow across the Alaska
Peninsula, keeping snow in the forecast for much of the day on
Tuesday. By Wednesday morning, the low lifts toward the northeast
allowing a much colder and drier air mass to fill in on the
backside over the eastern Bering for Wednesday. Meanwhile farther
west, attention shifts to a developing storm force low south of
the western Aleutians. As the parent low lifts northward and
extends a front eastward across the Bering Wednesday morning,
models are advertising the formation of several additional lows
spinning up along the front. By Wednesday night, a large complex
low will be in place over the western Bering while its front
extends over the eastern Bering. This system will keep the active
weather pattern in place through the end of the week.

&&

.MARINE (Days 3 through 5)...

Bering: Low pressure will be centered just south of the western
Aleutians on Wednesday. It will be sending a front through the
western and central Aleutians/Bering through Thursday. There is
still disagreement in the models, but we do have increasing
confidence that those areas will see gale force winds with this
system. Storm force winds are not out of the question either. The
position of this low pressure system looks like it will cause
strong northeasterly winds to continue through late next week for
the Bering and Aleutians. Overall, with guidance doing a little
better with this low, we have moderate confidence with this
forecast.

Gulf of Alaska: The Gulf of Alaska will generally be under low
pressure Wednesday through late next week. Models have come into a
little better agreement, so we can anticipate a couple weak lows
moving through the Gulf, but discrepancies exist with the track
of each. We can say both look like weak systems compared to what
we have been seeing, with the strong winds being small craft
advisory level. So, active weather but with little marine impact.

&&

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

The long term continues to present a challenge to establish some
sort of upcoming weather pattern. Solutions from our more heavily
used guidance like the GFS and ECMWF have markedly different
outcomes on movement of low pressure systems. This makes it
difficult to ascertain the movements of key features like fronts
and to be able to start getting an early look at the forecast.
Therefore, specific features will have to wait for the short term.

What we do know is that the weather pattern will continue to be
active, with unsettled weather in the Gulf of Alaska and along the
Aleutians. There is some increasing confidence in a gale to
possibly storm force low existing just south of the Aleutians and
sending weather into the Chain. It will induce northeasterly
winds through the Bering as well. Yet another series of lows will
be in the Gulf of Alaska, but where they will go remains a
question. High pressure with perhaps some off-shore flow in
Southwest AK still looks to be the case for mainland AK. All in
all, the long term guidance looks to be establishing a pattern of
active weather along the coasts and quiet inland. However, we will
need some more consistency in model runs before we can start
really increasing our confidence in the forecast for later this
week.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Blizzard Warning: 155
		 Winter Weather Advisory: 181
MARINE...Heavy Freezing Spray Warning: 160 180 181
		 Gale Warning: 119 130 155 165 180 181 185 351 352 414
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...CRK
SOUTHCENTRAL ALASKA...EZ
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...KO
MARINE/LONG TERM...BB

SPECIAL WEATHER STATEMENT
National Weather Service ANCHORAGE AK
1259 PM AKST Mon Dec 7 2020

AKZ101-111-081900-
Anchorage-Matanuska Valley-
Including the cities of Anchorage, Eagle River, Indian, Eklutna,
Palmer, Wasilla, Sutton, and Chickaloon
1259 PM AKST Mon Dec 7 2020

...A WINTRY MIX EXPECTED TODAY WITH A CHANGEOVER TO SNOW TONIGHT
INTO TUESDAY...

An occasional light wintry mix of snow and patchy light freezing
rain will impact the Anchorage Bowl and Matanuska Valley today
into early tonight. No snow or ice accumulation is expected during
this timeframe. However, drivers should be alert for patchy slick
spots during the evening commute.

Precipitation will change over to all snow after midnight
tonight. Periods of light to moderate snow are then expected for
the morning commute continuing into the early afternoon Tuesday.
Snow totals of 1 to 3 inches are anticipated. Motorists should
allow extra time for their Tuesday morning commute and use
caution while driving.

For the latest road conditions call 5 1 1 or visit
511.alaska.gov.