Small Craft Advisory 18, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
542 AM AKST Sat Jan 4 2020

.ANALYSIS AND UPPER LEVELS...

The core of the upper-level low is now moving into the southern
Gulf with an associated gale-force surface low positioned
southeast of Kodiak City. Mesoscale snow shower bands continue
along the eastern half of the island overnight and extend along
a front up to eastern half of the Kenai Peninsula. The snow
shower activity continues to wind down this morning for Kodiak
City as the main low drift southeast. Snow showers, however,
persist for places like Seward and Seldovia as a new low is
beginning to spin up south of the Kenai Peninsula along the
front.

Elsewhere along the southern mainland, conditions are relatively
clear, dry, and very cold (sub-zero temperatures across much of
the area) with a ridge firmly anchored over the interior of the
state. The clear conditions have been helped by an increase in
the northerly offshore flow between this ridge and the
aforementioned low. The exception to this has been within the
sheltered valleys of the Copper River Basin and along the Knik
Arm into Palmer where the northerly flow has been much weaker,
allowing for some low stratus and fog to persist. Fog and low
stratus also persist near Iliamna and west of King Salmon.

For the eastern half of the Bering, a cold, northerly flow
continues to produce bands of clouds and snow showers from the
Pribilofs south to the eastern Aleutians. A ridge is keeping
things quiet over the central Bering while the combination of a
decaying front and surface low lifting north toward Adak is
bringing some mixed precipitation and small-craft level winds to
the western Aleutians.

&&

.MODEL DISCUSSION...

While guidance continues to perform decently with the overall
synoptic pattern through Sunday, they are struggling in handling
the development and evolution of the smaller-scale convective
polar lows across the western and northern Gulf. This means an
added reliance on not only higher-res models, but also on radar
and satellite imagery and trends in the very short-term. This
includes forecasting the movement and timing of mesoscale snow
shower bands impacting places like Kodiak, the eastern Kenai
Peninsula, and eventually Prince William Sound.

Beginning Sunday, model consensus starts to break down concerning
a low tracking into Bristol Bay. Both the NAM and EC bring a
weaker system across over the AKPEN and redevelop a stronger low
in the western Gulf, steering toward Prince William Sound by
Monday. Conversely, the GFS and GEM both spin up a stronger low as
it moves over interior Bristol Bay. These models then spin up a
new low near the Barren Islands and lift the system close to
western Prince William Monday afternoon/evening. Given the
discrepancy, a middle of the road approach was taken for the
forecast package beyond Sunday.

&&

.AVIATION...

PANC...Fog continues to sit up in Knik Arm, and with weakening
northerly winds this morning through much of Saturday, there
remains the potential for fog and/or low stratus to move across
the terminal. Latest nighttime satellite imagery does show this
area of low stratus drifting south, therefore a tempo group has
been added for fog through 18z.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2...Sat and
Sun)...
The weather pattern will be slow to change for the next couple of
days. The biggest sensible weather makers will be a variety of
cold core compact lows moving over the warmer waters of the Gulf
of AK. A few of these features moved through Kodiak and Seward on
Fri and early this morning. Due to their convective nature, they
are capable of dropping a quick few inches of snow. The next
squall is just off the Southern Kenai Peninsula coast this morning
and should bring some more light accumulations to Seward. This
feature will then wrap up into a closed low by this evening. This
low is set to track towards the Eastern Prince William Sound and
the Cordova area. With as cold as this airmass is, it will not be
hard for this system to bring a few inches of fresh snow to these
areas. The low will then track inland through Sun morning bringing
the chance for some snow to the Copper River Basin, especially the
SE portions of that zone to include McCarthy along the Edgerton
Highway.

The other main story is the cold air. Many places will see their
coldest morning of the winter this morning with Ted Stevens
International Airport dropping as cold as -4F so far and Gulkana
reaching -38F. Some patchy fog and low stratus will continue to
lurk around parts of the Knik Arm and Cook Inlet. Otherwise, offshore
flow is leading to clear skies across nearly all inland areas.
The flow is being squeezed through some of the typical gaps, such
as Thompson Pass, and Whittier, creating gusty winds. A Wind Chill
Advisory remains in effect for Thompson Pass. If the previously
mentioned low in Prince William Sound arrives early enough, it
might bring some high clouds and actually allow temperatures to
warm in Thompson Pass. However, it could also make for a brief
period of blowing snow later tonight as the precipitation moves
in.

&&

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

Cold high pressure is continuing to remain dominant across
Southwest Alaska as temps remain well below across the region.
More cloud cover moves in tonight, so temps will still be cold,
but slightly warmer than this morning. A compact low will move
into the Alaska Peninsula Sunday afternoon. The northward extent
of this low is not very certain, but light snow accumulation will
impact the Alaska Peninsula, with a chance that locations farther
north across interior Bristol Bay also see light snow Sunday
evening and Monday morning.

&&

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

A low is developing across the Central Aleutians this morning,
bringing a mix of rain and snow to Adak and Atka. The rest of the
Bering remains under the influence of cold arctic air with
convectively driven snow showers. A weak low is centered over the
Pribilof Islands and this is also supporting more organized light
snow showers. Over the next 36 hours, these lows will move east,
bringing snow along the Chain before moving east across the AKPEN
Sunday night.

A storm force warm front will move into the far Western Aleutians
late Sunday night and Monday.

&&

.MARINE (Days 3 through 5)...
On Sunday, a surface low across the central Gulf brings small
craft gusty winds across much of the gulf, then tapers down by
Monday morning as the Low exits east. The next strong storm
organizes over the north Pacific and pushes a front to the western
Aleutians Sunday night. This storm system moves slowly northeast
spreading gales across the southwest Bering through Monday night.
Winds were increased across a broader area along the front for
the afternoon package.

&&

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

Southcentral:
Dry and cold conditions will persist for inland Southcentral
Alaska Saturday through next Thursday night. Gulf coastal
locations will see snow through Sunday as low pressure tracks
east...tapering off Sunday night with the low moving to the
eastern Gulf. Another weak low tracking east from the Bering
could bring additional snow to Kodiak between Sunday and Tuesday,
however there is still a bit of uncertainty on the track and
timing of this next system.

Southwest:
Dry and cold conditions are expected for Sunday; however, snow
chances increase Sunday night along the coast and across Bristol
Bay as a weak low from the Bering pushes east toward the Gulf.
Drier conditions are expected on Tuesday and Wednesday, however
another Bering front approaches Tuesday night. There is high
uncertainty with the progression of this front, but the general
model trends keep the dominant ridge influence across the
Southwest through Thursday night.

Bering:
Across the Bering, active weather persists through the extended
forecast Sunday through next Wednesday night. The next strong
storm develops across the North Pacific and lifts north to the
Western Aleutians late Sunday night. This is a warmer gale force
system that moves to the southern Bering on Monday with re-
enforcing energy sending this front farther north and east into
Tuesday. Precipitation around the core of this system will mainly
be rain for the central Aleutians with mixed precipitation for the
western and eastern Aleutians. The front moves across the
Pribilof Islands Tuesday night and then across the Alaska
Peninsula on Wednesday. Precipitation along the front across the
central eastern Bering will likely stay snow; however, a rain and
snow mix is possible as the atmosphere modifies slightly warmer
Wednesday afternoon.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Wind Chill Advisory 131.
MARINE...Heavy Freezing Spray Warning 121 127 129 130 160 180 185 414.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...TM
SOUTHCENTRAL ALASKA...MSO
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...JA
MARINE/LONG TERM...KH

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE ANCHORAGE AK
1147 AM AKST SAT JAN 4 2020

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

1000 AM     SNOW             KODIAK                  57.80N 152.39W
01/04/2020  E12.0 INCH       KODIAK ISLAND      AK   LAW ENFORCEMENT

            TROOPERS REPORTED 12 INCHES OF NEW SNOW AS
            OF SATURDAY MORNING IN KODIAK.

0900 PM     SNOW             KODIAK                  57.80N 152.39W
01/03/2020  E6.0 INCH        KODIAK ISLAND      AK   PUBLIC

            6 TO 8 INCHES OF NEW SNOW REPORTED AT KODIAK
            AS OF 9PM FRIDAY EVENING.

&&