Area Forecast Discussion
Issued by NWS Anchorage, AK

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000
FXAK68 PAFC 200049
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
449 PM AKDT Mon Apr 19 2021

.ANALYSIS AND UPPER LEVELS...
A vertically stacked low is tracking westward to the south of
Kodiak Island and the Alaska Peninsula, producing areas of rain
along with high end small craft or gale force winds from Kodiak
Island to the Alaska Peninsula and Eastern Aleutians. While the
low is weakening as it tracks westward, northerlies are
strengthening across the central to eastern Bering Sea as this
storm system pushes up against a strong surface high over the
western Bering Sea. The remnants of an occluded front is lifting
northward across Bristol Bay and to the southern Kenai Peninsula
and north Gulf coast. This is mostly leading to an increasing
clouds, with very little in the way of precipitation. For interior
Southwest Alaska and most of Southcentral Alaska sunshine and
warm temperatures dominate once again.

&&

.MODEL DISCUSSION...
Model are in excellent agreement with large scale features and
forecast confidence generally remains high. All solutions have
trended a bit deeper and strong with the next low tracking south
of the Alaska Peninsula on Wednesday and forecasts have been
modified to reflect that. One of the bigger forecast challenges
today is the arctic trough which dips south across the Alaska
Range Tuesday afternoon, then exits across the Copper River Basin
Tuesday night. Southcentral is at the south end of the trough and
models have not been real consistent with exactly how far south
the trough digs. This will determine areal extent of precipitation
as well as how much arctic air makes it into Southcentral. There
is potential for rain and snow in the Copper River Valley, though
upper wave moves through quickly, so it wouldn`t amount to much.

&&

.AVIATION...
PANC...VFR conditions will persist. An upper level trough moving
up from the Gulf will pass by Anchorage tonight. This will help
bend Turnagain Arm winds into the terminal. There is quite a bit
of uncertainty in exactly when this will occur, but the most
likely time period is between 03Z and 07Z. The Turnagain Arm jet
won`t be very strong to begin with, so expect some southeasterly
gusts, but it should remain on the low end for these types of
events and the gusts could come in and out of the terminal.
Similarly, on Tuesday the terminal will be on the northern edge
of the Turnagain winds. Generally expect winds to be lighter, but
with daytime heating there is always a chance some gusts could
push into the airport.

&&

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

A vertically stacked low south of Kodiak Island will continue to
send a frontal system northward through the evening hours. High
clouds ahead of this feature will move into the Susitna Valley and
the Copper River Basin later this evening. As this front
continues moving northward, it will have limited moisture to work
with. Therefore, only a few rain/snow showers are expected across
the Eastern Kenai Peninsula to Prince William Sound as well as
Kodiak Island overnight and through Tuesday. Any snow showers will
mainly be confined to the higher terrain in all areas. One big
change this forecast package was to put all rain through Turnagain
Pass as snow levels look to stay between 2,000 ft and 3,000 ft
overnight. Also, as this front continues lifting northward through
the remainder of the day, it will push the Turnagain Arm wind
northward into West Anchorage and the airport with gusts up to 20
mph. These winds are expected to remain through late Tuesday
morning before diminishing and becoming variable. The Knik River
Valley wind is also expected to bring southeast/south winds into
Palmer through Tuesday morning.

Next, an upper level trough currently moving across the North
Slope is expected to move southeastward while digging as it moves
towards the ALCAN border. Some rain/snow showers are possible for
the Copper River Basin and Broad Pass area as this moves through
Tuesday evening/night. Any snow showers are mainly expected across
the Alaska Range, Wrangell Mountains, and the Talkeetna Mountains,
though, some snow may reach the valley floor and give Gulkana some
flakes. Basically, the only thing this upper level feature is
expected to do for the Matanuska Valley and Anchorage Bowl is
bring some increased clouds along with some cooler temperatures
for Tuesday night/Wednesday morning. Most locations are expected
to fall into the mid to upper 20s with low 30s for Anchorage and
the Matanuska Valley.

Wednesday, the Rex block pattern becomes established keeping much
of Southcentral quiet and dry and loads of sunshine. The only
game in town will be a strong gale force low that will send a
front towards Kodiak Island that will bring a decent amount of
rain. Right now it looks like Kodiak City will have a wet
Wednesday with generally 1 to 2 inches of rain expected. With the
pattern in place, there is the potential that this front stalls
over the area which will likely lead to persistent rainfall and,
therefore, heavier totals.

&&

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

A ridge of high pressure is keeping conditions relatively quite
and mostly clear over the Y-K Delta today. Further south, wrap
around moisture on the north side of a vertically stacked low is
streaming from the western Gulf into southern AKPEN. Rain showers
will persist along the AKPEN and coastal Bristol Bay with mountain
snow showers through the rest of today into Tuesday. The main
impact will continue to be gusty, easterly winds blowing through
the gaps and passes of the Alaska Range and across parts of
Bristol Bay. An upper level polar low is expected to move south
from the northern half of the state through the rest of today into
Tuesday with minimal effect.

As the polar low exits eastward, a ridge will dominate through
Wednesday with spring-like weather and fair, mild conditions over
the Y-K Delta. Another North Pacific low with an associated front
is expected to arrive late Tuesday into Wednesday. Much like the
previous storm system, the main impact will be gusty, easterly
winds blowing through the gaps and passes of the Alaska Range and
across parts of Bristol Bay during the forecast period.

&&

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

A westward propagating occluded front associated with a North
Pacific low moving toward the the southern AKPEN will continue
with scattered rain showers and high elevation snow along the
Eastern and Central Aleutians the rest of today through late
Tuesday. Additionally, gusty, easterly winds along the Aleutians
and northerly winds over the Bering will persist as well. As the
low weakens and moves southward, another frontal boundary
associated with a new North Pacific low and is expected to arrive
late Tuesday night into Wednesday. This storm system will have a
deep tropical moisture fetch and will bring widespread coverage of
rain showers along the Aleutians and the Bering with mountain
snow through the end of the forecast period. In addition to the
precipitation, expect periods of gusty, easterly winds much across
the forecast area on the backside of the low through the usual
gaps and passes and much across the Bering Sea.

&&

.MARINE (Days 3 through 5: Thursday through Saturday)...

Confidence remains high that another North Pacific low will move
just south of the Aleutian Chain Thursday. Easterly gale force
winds will accompany this low, though confidence is moderate that
south of the Aleutian Chain may experience low end easterly storm
force winds. That low will weaken through Saturday as another low
end gale force weather front moves in from the north pacific into
Sunday.

&&

.Long Term Forecast (Days 4 through 7: Friday through Monday)...

The block(y) pattern will continue into the longterm. The main
upper level ridge that rests across much of Alaska (and is
anchored across the northern half of the state) will be a
mainstay. As one north pacific low weakens on Saturday, another
builds in from the west. The blocking ridge will prevent most of
the mainland from being impacted by weather, though the Aleutian
Chain will be stuck the pattern of system after system. Much of
south central will benefit from the spring sunshine. Daytime
temperatures should be well above normal for this time of year
(mid to upper 40s) though overnight lows will be close to normal
(low 30s) when skies clear out. If we have a layer of clouds (even
thin), it will act like a cozy blanket, keeping overnight lows
elevated.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Heavy Freezing Spray 185
         Gale Warning 138 150 155 165 174 176 179 180 181 185 412-414.
FIRE WEATHER...NONE.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...SEB
SOUTHCENTRAL ALASKA...MV
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...MF
MARINE/LONG TERM...SS


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