Area Forecast Discussion
Issued by NWS Anchorage, AK

Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23

000
FXAK68 PAFC 120159
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
459 PM AKST Sat Jan 11 2020

.ANALYSIS AND UPPER LEVELS...
The general pattern consists of a deep upper low over the western
and Central Bering Sea, a sharp ridge centered along about 155
degrees west longitude, and a trough over the northeast Gulf
extending east into western Canada. There is a frontal system
extending from the central Bering across the eastern Aleutians and
western Alaska Peninsula moving towards the northeast. Clouds
from this system are already moving into southwest Alaska. Most of
Southcentral is clear, with just some high clouds starting to move
in from the southwest. Temperatures in Southcentral remain cold,
with weakening offshore flow through gaps in the terrain.

&&

.MODEL DISCUSSION...
The numerical models are in good agreement for the short term
portion of the forecast. There are some timing differences with a
developing surface low in the Gulf Sunday and Sunday night as it
races eastward, but due to the high speed of this low it has only
a minor impact on the forecast. Forecast confidence is a bit
higher than normal today.

&&

.AVIATION...
PANC...VFR conditions and light winds will persist into Sunday
afternoon. Late Sunday afternoon conditions should drop to MVFR in
snow as a weak front moves into the area.

&&

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

Very cold, clear conditions continue over much of Southcentral as
an Arctic air mass over western Canada maintains general northeast
flow. A low moving eastward through the Gulf is enhancing the
pressure gradient between the coast and inland areas. Hence, the
persistent strong offshore gap winds out of the usual bays and
passes: Resurrection Bay, Whittier, Valdez waters and the Copper
River Delta. Tonight, a vertically stacked low in the northwestern
Bering Sea will steer a shortwave trough towards the Southwest
Alaska coast. Expect increased cloud cover from west to east
overnight into Sunday, and a round of light overrunning snow over
Kodiak Island tonight into early Sunday. Increasing cloud cover
will moderate temperatures some tonight, particularly for the
western areas (Kodiak, western Kenai Peninsula). Snow will spread
to the Kenai Peninsula by midday Sunday. The western Kenai may
initially be shadowed due to down sloping. But, precipitation
should eventually reach the ground as a closed low forms south of
the peninsula and slows the progression of the system, allowing
the column to saturate. For most of Southcentral, temperatures
will trend a good 10 degrees warmer than today. Expect snow to
reach the Anchorage Bowl Sunday night... the devil is in the
details. The track of the low will be important and there`s still
enough disagreement to maintain some level uncertainty with snow
amounts. Right now, expect around an inch of light, fluffy snow Sunday
night in the Anchorage Bowl. With widespread cloud cover by
Sunday night, most of Southcentral will have overnight lows above
zero. The Copper River Valley will remain 20 to 30 below zero.
Precipitation will clear up Monday and offshore winds will begin
to ramp back up as the Gulf low drifts east out of the area and
surface high pressure builds over the Alcan.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3: Tonight
through Tuesday)...

A front over Bering is moving ashore into Southwest Alaska this
evening. As it moves into the area, snow is beginning to break
out from the coast of the Kuskokwim Delta south through Cape
Newenham. It is helping transport warmer air into the area. For
almost everyone, it will not be warm enough for rain. The gusty
winds and falling snow will lead to blowing snow conditions along
the coast tonight. Thus the Winter Weather Advisory for the
Kuskokwim Delta remains in effect, though now primarily for
blowing snow along the coast. Once the snow moves inland from the
coast, conditions will improve. Since it will shift inland from
the coast earlier, the Advisory time has been shortened to end at
9am tomorrow. Meanwhile, further inland, several inches of snow
are expected, but amounts have been lowered somewhat due to weaker
lift, warmer temperatures, and slightly less moisture. 3 to 6
inches are expected over the Kuskokwim Delta.

The snow will overspread the rest of Southwest Alaska tonight.
With better lift further south and east, the Winter Weather
Advisory remains in effect through 3pm Sunday. Blowing snow will
be the primary concern at the coast, with snowfall amounts of 4 to
8 inches expected generally along a Dillingham to Port Alsworth
line. The lift is weaker further north, so sub-advisory snow
amounts remain in the forecast for the Lower Kuskokwim Valley,
where 3 to 6 inches of snow are expected. It is over the Lower
Kuskokwim Valley, in the foothills of the Alaska Range, that the
snow will persist longest, likely not ending until after sunset on
Sunday.

Broad onshore flow off the Bering will persist into Monday, with
scattered snow showers possible along the coast. Elsewhere,
clouds will persist through Monday, with the most notable clearing
beginning Monday night into Tuesday as a strong area of high
pressure builds in. This high pressure and clear skies will allow
temperatures to drop, so this period will feature a cooling trend,
with lows by Tuesday night back in the zero to 10 above range.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 through 3: Tonight
through Tuesday)...

A strong occluded low moving into the Kamchatka Peninsula this
evening is dragging its leading front across the Eastern Bering.
The front moves completely ashore in Western AK by Sunday morning,
making for strong westerly flow with somewhat colder air allowing
widespread snow showers to form over much of the Bering. This
will persist through Monday across the eastern Bering. Meanwhile,
a developing low will move into the western Aleutians late Monday
night. It will track north towards Kamchatka as well, leaving its
storm force front dragging much warmer air north across the
western Bering, in addition to soaking rains. Strong ridging and
associated surface high pressure ahead of it will keep the front
moving only slowly eastward. This will create strengthening
southeasterly winds ahead of the front over the central Bering and
Pribilofs by Tuesday night.

&&

.MARINE (Days 3 through 5...Tue through Thu)...
The western gulf will see gusty northerly flow continuing through
Wednesday of next week as the pressure gradient tights between
low pressure near the Gulf and a ridge moving to the Southwest
mainland. Small craft to gale force winds will taper down for a
short time Monday night; however, gusty winds return by late
Tuesday morning. Across the Bering...relatively quiet weather on
Monday is followed by a gale force front moving to the western
Bering Monday night. This front moves slowly across to the
central Bering on Wednesday. There is still high uncertainty on
the strength of the front on Wednesday and it should be monitored
as it has the potential to be stronger than currently forecast.

&&

.LONG TERM FORECAST (Days 3 through 7...Tue through Sat)...
Dry and colder than normal conditions are on tap for much of the
southern mainland in the extended forecast Monday night through
Saturday. A few snow showers will be possible across the
southwest as several weak fronts push inland. The Bering will see
the most active weather pattern as a North Pacific storm sends a
front across the western Aleutians late Monday night. This front
moves slowly east bringing strong gusty winds and rain from the
Eastern Aleutians to Pribilof Islands. There is still some
uncertainty on the strength of this system and should be monitored
for updates. A ridge will build over the eastern Bering and force
the jet to reorient from north to south across the southern
mainland. This could result in a stronger than normal offshore
wind pattern for many favored locations. Otherwise, the forecast
for Wednesday night through Saturday will generally be a
persistent forecast with dry, cold conditions over the southern
mainland and active weather over Bering and Gulf.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Winter Weather Advisories 161 155
         Wind Chill Advisory 131
MARINE...Heavy Freezing Spray Warning 119 127 128 130 139
 Gale Warning  411 412 165 170 172 185 351 352 130-132 139.
FIRE WEATHER...NONE.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...BL
SOUTHCENTRAL ALASKA...MM
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...JW
MARINE/LONG TERM...KH



USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.