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 24 25 26 27 28 29 30 31 32

575
FXAK68 PAFC 100115
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
515 PM AKDT Wed Oct 9 2019

.ANALYSIS AND UPPER LEVELS...

A broad upper long wave is continuing to move eastward and
is now extending south across the Kuskokwim Delta. Cooler more
unstable air associated with this system is evident by the
presence of showers over Southwest Alaska, eastern Bering Sea, and
Alaska Peninsula. The main frontal band, under broad southwesterly
flow aloft, is bringing widespread precipitation (rain at lower
elevations and snow at higher elevations) across Southcentral.
Gusty southeasterly winds are also noted across Turnagain Arm and
western Anchorage, as well as along the Copper River. An eastward
moving front brought strong southerly winds and rain across the
western Aleutian Islands.

&&

.MODEL DISCUSSION...

Overall models have a similar broad synoptic pattern. The details
on positioning of low centers and QPF patterns however differ
significantly at times during the next couple of days. So the
brunt of the forecast adjustments will be fairly minor and will
consist of mainly hand edits.

&&

.AVIATION...
PANC...Gusty southeast winds will continue across the airport
complex through about midnight tonight. Low VFR to MVFR CIG/VSBY
are expected through tonight.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 through 3:
Tonight through Saturday)...

Areas of rain and higher elevation snow will continue across
Southcentral as an area of low pressure develops along a
front inching closer to the Kenai Peninsula. Gusty south to
southeasterly gap winds will continue through the evening in
advance of the front, before winding down as the surface low spins
up. Rain and mountain snow will persist into Thursday as the first
low moves onshore and a secondary area of low pressure develops
and lifts northeast toward the Copper River Delta. The heaviest of
the precipitation will fall over Prince William Sound, Copper
River Delta, and Chugach Mountains, ahead of the center of
circulation. Rain over the Copper River Basin Thursday is then
expected to switch over to snow Thursday night and Friday morning
as the low tracks to the Alaska Peninsula and pulls colder air
south. Accumulations of 2 to 5 inches are expected across the
Copper River Basin Thursday night. There is still some uncertainty
concerning how quickly the colder air arrives and just how much
moisture moves over the Copper River Basin, and any change in
these ingredients will impact snow totals. Therefore, this will
continue to be monitored as the event draws closer.

For the Mat-Su Valleys, Anchorage Bowl, and Kenai Peninsula, the
rain and higher elevation snow will taper off to scattered
rain/snow showers through the day Thursday as colder and drier
air arrives on the backside of the low. Although snow levels will
drop late Thursday, most of the moisture will have exited the
region by then. This will keep any additional snow accumulations
rather light (less than an inch) and confined to the higher
terrain (Turnagain Pass and the Upper Hillside of Anchorage
included).

Gusty northerly, outflow winds will also develop late Thursday
into Friday, especially along the coast, in the wake of the
departing low.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1-3: Wed-Fri)...

An upper level trough will continue to bring showers this
afternoon, tapering off this evening into tomorrow across
Southwest Alaska. Friday should see mostly clearing conditions,
with less cloudy conditions as the trough continues to slide out
of the region. Onshore flow this afternoon will switch over to
northerly flow for Friday before the next system approaches on
Saturday. A new front approaches the the Southwest by Saturday
afternoon, which will bring another round of rain to coastal
regions and the Alaska Peninsula.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1-3: Wed-Fri)...

Ridging centered over the central Aleutians will shift eastward
and move south of the eastern Chain by Friday afternoon, with
possible patchy fog beneath the ridge. Strong north-northwesterly
winds continue over the eastern Bering through Friday afternoon,
bringing small craft winds in Bristol Bay and out of gap areas
along the Alaska Peninsula. The largest feature for today`s
forecast is the gale force front starting to cross over the
western Aleutians this afternoon. Southerly winds will weaken to
small craft advisory levels by Thursday afternoon, stretching
across much of the central Bering and continuing to slightly
weaken through Friday.

&&

.MARINE (Days 3 through 5)...

...Bering Sea and Aleutian Coastal Waters...

General low pressure is expected to remain over the Bering
Friday, bringing small craft conditions. The real story for the
Bering is the arrival of a storm force low over the western
Aleutians by Sunday night. There is moderate to high confidence
that Typhoon Hagibis will undergo an extratropical transition and
will enter the Bering early next week as a strengthening area of
low pressure. This will bring strong winds, heavy rain, and high
seas to the western and central Aleutians Sunday into Monday.
There is still low confidence on the exact track of the low,
however regardless of where the low center moves, we are confident
that sustained storm force winds will impact the western and
central Aleutians early next week.

...Gulf of Alaska...

A strong area of low pressure centered in the northeastern Gulf
will produce gale force northwesterlies over the northern Gulf
Friday into Saturday. Pockets of storm force winds are possible
for a short duration of time on Friday, especially over Kamishak
Bay, the Barren Islands, and Sitkinak. As the low weakens and
exits the Gulf to the southeast, winds and waves are expected to
decrease for Saturday evening. By Sunday, another low enters the
Gulf from the North Pacific, bringing easterly gales to the
northern Gulf coast waters for early next week.

&&

.LONG TERM FORECAST (Days 4 through 7)...

An active weather pattern is still expected for early next week as
Super Typhoon Hagibis undergoes an extratropical transition and
enters the western Bering by late Sunday. There is high confidence
that the western and central Aleutians will see storm force winds
and heavy rain with this low for the start of the workweek next
week, however where the low tracks is less certain. At this time,
deterministic models seem to agree on a more southerly route
along the ALeutians while ensemble solutions are keeping the low
in the central Bering. By midweek, another low enters the western
Bering.

Meanwhile farther east, there is moderate confidence in a North
Pacific low entering the Gulf of Alaska Sunday night. Gale force
winds are likely with this low along the northern Gulf coast
through Monday. Beyond that, there is a lot of uncertainty in the
weather pattern by midweek, as a lot will depend on the path of
the extratropical system (remnants of Typhoon Hagibis).

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gale Warning 119 130 131 132 150 177 178 351 352 411.
FIRE WEATHER...NONE.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...BC
SOUTHCENTRAL ALASKA...TM
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...AH
MARINE/LONG TERM...KO



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