Area Forecast Discussion
Issued by NWS Anchorage, AK

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FXAK68 PAFC 191257

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
457 AM AKDT Fri Apr 19 2019


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.


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.


PANC...Light snow will persist at the terminal for the next few hours,
before improving CIGS and visibilities are expected. Gusty south
winds will continue through the evening, before dropping to less
than 10 knots. Given the fresh snow cover, with afternoon
temperatures climbing into the mid to upper 30s, sublimation
should allow some light fog to persist, likely in the MVFR range.


The potent upper level low is tracking through Bristol Bay this
morning. It is allowing an impressive shortwave to lift from south
to north across the northern Gulf Coast this morning. This will
keep widespread snow falling across the Cook Inlet up through the
Matanuska and Susitna Valleys this morning. Temperatures should
remain at or below freezing through the morning, so we are
expecting most of the inland precipitation to fall as snow.
Instability is already present on the 12z upper air sounding at
Anchorage and should only increase as we go through the day today.
This could aid in another quick couple of inches of snow to fall
at sea level this morning with higher amounts at elevations above
1,000 feet. The Special Weather Statement remains in effect to
address this.

The upper level low itself will move overhead this afternoon. This
will bring the peak of instability with 500 mb (18,000`)
temperatures dropping to near -40C. There is even some jet support
at 30,000` to further support shower development. Thus, we have
added a slight chance of thunderstorms over the Northern Gulf of
AK and gulf coast this afternoon. There will also be some gusty
south-southeast winds across the area in our post-frontal
environment. As usual, these will be strongest in the usual places
such as the Turnagain Arm and the Copper River Valley.

More active weather is in store as we head into the weekend.
Strong southerly flow/upslope over the Northern Gulf will bring a
return to steady precipitation across much of the Prince William
Sound by late tonight. The one area of particular interest in this
pattern is Seward. They typically see fairly high precipitation
amounts with southerly flow and strong instability. While they
could see some snow mix in at times and possibly even some
accumulation, we do expect the April sun and warmer air off
Resurrection Bay to result in mostly rain. A new large low will
develop over the Central Gulf Sat. This system will reinforce the
precipitation along the Gulf Coast (with no perceivable break for
most) and bring another shot of snow to inland areas such as the
Cook Inlet and Mat-Su Valleys.


through Sunday)...

An upper level low currently centered near Bristol Bay will
continue to bring isolated snow showers across the region through
this evening. This low will track northward and merge with a
second upper level low on Saturday creating a broad upper trough
over all of western Alaska. Cool temperatures and isolated snow
showers (particularly along the coast) are likely to continue
through the day.

A surface low will track into the Gulf this weekend. It is still
difficult to say exactly how much this will affect Southwest. It
will depend on how much the ridge upstream will amplify due to the
series of shortwave troughs in the Bering. Nonetheless, confidence
is at least moderate that some areas could see accumulating snow
starting early Sunday morning.


through Sunday)...

The overall pattern experienced over the past several days is
expected to continue under an upper level trough. This combined
with light northerly flow (though gusts will be stronger in
channeled areas) will consistute onshore showers and/or flurries
and cooler temperatures over the Aleutians through the weekend.


.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.





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