Small Craft Advisory 180, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion...UPDATED
National Weather Service Anchorage AK
544 AM AKST Sat Feb 22 2020

.ANALYSIS AND UPPER LEVELS...

An upper level low is situated west of the Bering Strait this
morning, with its trough extending southeast over western Alaska.
Out west, a stacked 988 mb North Pacific low lifting northward
still resides just south of the western Aleutians. The main
jetstream still resides south of the Aleutians.

A surface low positioned just northwest of Homer this morning is
responsible for bands of snow showers across much of Prince
William Sound and the Kenai Peninsula.

&&

.MODEL DISCUSSION...

Model discrepancies of concern are mostly with the North Pacific
low and its trajectory as it merges with the other low spinning
up in the North Pacific on Sunday afternoon. Solutions are quite
divergent Sunday night and will warrant closer looks in subsequent
model runs.

&&

.AVIATION...
PANC...Snow showers are expected to increase through the afternoon
with visibilities possibly dropping into the MVFR range briefly.
Otherwise, look for light windsw to continue with ceilings around
1500 feet.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
(Today through Sunday night)

A low sitting just northeast of Augustine Island early this
morning will move ashore and weaken during the late morning hours.
Meanwhile, a trough moving in from the west will be accompanied by
fairly decent cold air advection aloft. The incoming trough with a
few disturbances crossing the area ahead of it should be
sufficient to maintain some snowfall from the western Susitna
Valley southward towards the Kenai Peninsula, Anchorage
Bowl, and southern Matanuska Valley. Southerly flow ahead of
these features will also allow for fairly robust precipitation to
continue in a onshore flow/showery type regime.

As the trough crosses all of Southcentral, the drier and colder
air advecting into the region will put the kibosh to any
precipitation, while helping to decrease cloud cover as well.
With this in mind, kept temperatures below guidance given the
fresh snow cover and clearing skies through the weekend. This will
also allow the pressure gradient to kick up the winds for Passage
Canal, the Valdez Narrows, and the southern Copper Basin (mainly
near Thompson Pass) into the Copper River Delta.

Thompson Pass is an area where we'll need to keep an eye on to see
if observations and the newer model guidance suggests the
possibility of lower visibilities due to blowing snow and the
potential for a winter weather advisory issuance.

&&

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

Few snow showers linger across Southwest Alaska this morning as
an upper level ridge begins to build in over the western coast. A
quick moving upper level wave will brush along the Southwest coast,
bringing a chance of snow showers for a brief period this morning
from Toksook back to Pilot Point. However, any remaining snow
showers across interior locations will taper off through the
afternoon.

As the high pressure moves in over the region, weak winds will
persists across most areas, along with sunny and dry conditions
throughout the weekend. Cold temperatures will continue across
the Southwest today and into tonight. Low temperatures overnight
will drop near 10 to 20 below zero for most inland locations, with
the coastal locations only slightly below zero as colder air
continues to move in. However, temperatures will be on a warmer
rebound late this weekend into Monday as cloud cover and the
chance for precipitation returns to the southern Bristol Bay
region and Alaska Peninsula with the next front approaching.

&&

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

A strengthening upper level ridge over the eastern Bering and
Aleutians will persists through Sunday, resulting in relatively
quiet and dry conditions. This ridge will push eastward over the
mainland Sunday afternoon as a strong gale-force low approaches
the western Aleutians. The position of this low is farther north
than previous models runs, which means a small area of gale-force
winds will stay just south of the western and central Chain today
before shifting back into the North Pacific late this evening.
Rain and show showers will accompany this system, but any snow
accumulation will be minimal.

Strong winds will quickly shift to the eastern Aleutians and
Alaska Peninsula for Sunday morning as a North Pacific low lifts
northward. This system will be stronger than the previous one,
with solid gales south of the Chain and possible storm-force
gusts. This low, much like the one today, will also stay south of
Aleutians and Bering as it quickly dives southward back into the
North Pacific by Sunday night into Monday morning. The active
pattern remains across much of the Bering through Monday as
another round of gale force winds and precipitation move over the
western Aleutians.

&&

.MARINE (Days 3 through 5 Mon through Wed)...
The main low will be in the Gulf of Alaska region or just a little
south of there during this period. Gales are expected with this
low with a decent chance of storm force winds. There is a bit of
uncertainty with this system as its projected track and strength
remains uncertain.

The Bering Sea region is a bit more settled as generally westerly
winds will be over the area with the potential for occasional
gales.

&&

.LONG TERM FORECAST (Days 3 through 7)...
Next week will start off with well below normal temperatures over
most on southern mainland Alaska with high pressure over the state
and a low to the south of the Gulf of Alaska. This low will make
some headway northward through the middle of next week which will
bring most temperatures back to seasonal levels for the middle to
late parts of next week. There may be some periods of snowfall in
Southcentral with this low monday through Wednesday timeframe, but
at this time and snow should not make it much farther west than
just west of the Alaska Range. However, there is a bit of
uncertainty to the track of this low so the areas of snowfall are
subject to change.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Storm Warning 130.
         Gale Warning 127 131-32 138 155 172 174 176-77.
         Heavy Freezing Spray 130 138-39 160 165 179 185.
         Brisk Wind Advisory 180 181.
FIRE WEATHER...NONE.

&&

SYNOPSIS AND MODEL DISCUSSION...LB
SOUTHCENTRAL ALASKA...PD
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...ALH
MARINE/LONG TERM...EZ

PRELIMINARY LOCAL STORM REPORT
NATIONAL WEATHER SERVICE ANCHORAGE AK
259 PM AKST SAT FEB 22 2020

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

0255 PM     SNOW             UPPER POTTER VALLEY     61.05N 149.78W
02/22/2020  E2.1 INCH        ANCHORAGE          AK   PUBLIC

            SPOTTER REPORTED 2.1 INCHES OF SNOW IN LAST
            24 HOURS.

&&

MV