Area Forecast Discussion
Issued by NWS Anchorage, AK

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000
FXAK68 PAFC 190102
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
502 PM AKDT Thu Apr 18 2019

.ANALYSIS AND UPPER LEVELS...

An upper level low which had been over Norton Sound has moved to
the Kuskokwim Delta. Broad cyclonic flow continues around the
center and dominates much of Southcentral Alaska. A weak
deformation zone extends north across the Kenai Peninsula to
across the Anchorage Bowl is producing some light snow or mix or
rain and snow. Cold air entrenched over Southwest Alaska is
starting to drop across the western Gulf and likely will return
north across Southcentral tonight with favorable low and mid level
flow. The remainder of Southcentral is under cloudy conditions
with showers and gusty north winds.

&&

.MODEL DISCUSSION...
Synoptically, models are in general agreement through Friday, but
due struggle some with the placement of snow bands across
Southcentral, which if convective, will be difficult to resolve.
Models still struggle with the movement and placement of the gale
center moving into the Gulf Saturday and Sunday. For now will
lean toward the GFS/NAM western most position.

&&

.AVIATION...
PANC...Steady MVFR-IFR conditions should develop this evening and
continue through the overnight hours and snow spreads across much
of the Anchorage Bowl. These conditions will likely hold into the
early afternoon hours on Friday.

&&

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

A cold upper low remains in place over Western Alaska with a
shortwave trough extending eastward into the North Gulf Coast.
Ahead of the trough axis, southerly flow aloft is advecting
moisture northward, with a more widespread area of precipitation
over the north coast. Westerly cold air advection is occurring
from Kodiak Island and across the Gulf, with some of that longer
fetch west wind moving up into Kachemak Bay. Overnight, the trough
axis will move north, and snow will move into inland areas from
the northern Kenai to the Susitna Valley, including Anchorage.
Accumulating snow will will likely impact the morning rush hour,
with heaviest accumulations in the higher elevations where temps
are much colder. However, wet snow accumulations will be possible
(1-3") in low elevation areas west of the Chugach and Talkeetna
Mountains.

The main upper low center will move north through Saturday, with
southerly cold air advection favoring snow along the coast and
inland snow shower threats, thus keeping a prolonged wintery
pattern in place.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 through 3/Tonight
through Sunday)...

An upper level low along the Kuskokwim Delta coast will drop
south to Bristol Bay tonight, then lift back northward across the
Kuskokwim Valley Friday night. This will maintain mostly cloudy
and cool conditions across the region, with isolated to scattered
snow showers.

A low will develop over the North Pacific Friday and track to the
western Gulf on Saturday. The exact track of this low will greatly
affect whether Southwest Alaska sees snow later this weekend. A
series of short-waves dropping south across the eastern Bering Sea
will amplify the upper trough, which should help pull the surface
low westward. Thus, the forecast favors a more westward track of
the low which would be favorable for snow to spread westward from
the Gulf into Bristol Bay and the Kuskokwim Valley Saturday night
into Sunday. A few inches of snow accumulation are possible, but
until have a better idea of storm track, it is tough to say which
areas will see accumulation.

Meanwhile, with the short-waves digging across the eastern bering
Sea, the Kuskokwim Delta will see a resupply of arctic air
Saturday through Sunday. This will maintain the chilly (below
normal) temperatures. Also expect some locally gusty winds and
snow showers along the coast.

&&

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

The pattern of the past few days will persist over the next few
days, so expect continued cool temperatures, with occasional
showers and locally gusty winds. With a strong blocking ridge over
the western Bering Sea, a series of short-waves will drop south
across the central to eastern Bering Sea. These waves will help
focus shower activity and usher in a resupply of arctic air. Thus,
most precipitation will be in the form of snow, with a mix of rain
and snow possible along the Aleutians.

&&

.MARINE (Days 3 through 5)...The forecast still looks likely for a
low pressure system to make its way up into the Gulf of Alaska on
Saturday, then move northward and linger there through Monday. A
relatively large swath of gales is expected through the Gulf of
Alaska on Saturday and Saturday night. The higher winds will
become confined to the North Gulf Coast by Sunday, but will remain
at gale strength possibly as late as Sunday afternoon. Northerly
winds on the west side of this low will also bring gale force
winds to Cook Inlet Saturday and Sunday. In the Bering Sea and
Aleutians, northerly flow is expected to continue through Monday.
Overall, this will be less than gale force, except for Bristol
Bay and south of the Alaska Peninsula, where winds will reach gale
force mainly on Sunday.
&&

.LONG TERM FORECAST (Days 3 through 7)...
High pressure continues to hold strong in the Western Aleutians on
Sunday, meaning that most of the weather action will be happening
east and south of the Alaska Range through early next week. The
low that moves into the Gulf of Alaska on Saturday will bring a
front onshore on Sunday, then linger, bringing generally unsettled
weather for Southcentral and the Copper River Basin throughout
the long term period. This system will initially bring some
warmer air into the state, but by Monday, cooler air will
infiltrate from the west and temperatures closer to average or
slightly below will return. On Tuesday it starts to become less
clear as to how this pattern will break down across the region.
Some forecast solutions show a low pressure system developing
south of the Aleutians and then moving into the Gulf. Other
solutions show the high pressure system moving eastward and
bringing better weather to the mainland, while a storm develops in
the western Aleutians and tracks northward. Expect change in the
long term forecast over the next several days as things start to
shake out.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Heavy Freezing Spray 181 185.
FIRE WEATHER...NONE.

&&
$$

SYNOPSIS AND MODEL DISCUSSION...BC
SOUTHCENTRAL ALASKA...JA
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...SEB
MARINE/LONG TERM...LF


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