Area Forecast Discussion
Issued by NWS Anchorage, AK

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000
FXAK68 PAFC 271228
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
428 AM AKDT TUE SEP 27 2016

.ANALYSIS AND UPPER LEVELS...

A rather quiet weather regime encompasses southern Alaska this
morning as the region remains under the influence of weak
troughing. One trough can be seen digging into Southcentral from
interior Alaska with a second shortwave trough tracking into the
Gulf of Alaska. Shortwave ridging is building into the eastern
Bering Sea ahead of a larger eastern Siberia trough. Very weak
surface pressure gradients exist across the mainland which is
allowing for efficient diurnal cooling this morning across cloud
free locations. With time, the ridge will move east over southern
Alaska which will allow for continued quiet weather and clearing
skies.

&&

.MODEL DISCUSSION...

The numerical weather models are in excellent agreement with the
large scale pattern through the weekend. There are some
discrepancies that arise with the timing/strength of gale force
warm front moving into the Bering late week, but the overall
depiction is rather similar. Forecast confidence is very high
through the short term period.

&&

.AVIATION...
PANC...VFR conditions will prevail throughout the day. Mid-level
clouds have limited radiational cooling this morning which will
likely inhibit fog development. However, a few patches of fog may
develop throughout the morning but confidence in this is quite
low. Any fog that does develop will quickly dissipate after sunrise.

&&

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

Temperatures are dropping across Southcentral this morning in
partly clear skies. While temperatures are approaching dew points,
fog is currently limited to the Copper River Basin. The Anchorage
sounding this morning reveals relatively dry air over the first
several thousand feet of the atmosphere, along with light
northerly and northwesterly winds. This mixing is just enough to
keep fog from being widespread across the area as temperatures
plummet. In addition, some mid level clouds ahead of an upper
level trough are helping to keep some locations from completely
radiating out overnight. Although the trough covers much of the
state, it is too weak, and there is too much dry air in place for
any type of widespread shower activity as it moves eastward across
Southcentral today.

After the upper trough passes eastward today, a broad ridge will
begin to establish itself across much of Southcentral over the
next several days. As surface high pressure becomes established
across the interior, broad northwesterly offshore flow is expected
to increase through Thursday.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
High pressure ridging has moved in over southwest Alaska where it
will remain through much of Tuesday as the ridge axis moves east.
This ridging will aid in fog formation overnight tonight and
Tuesday night. An upper level trough pushes a front across the Kuskokwim
Delta Tuesday night bringing rain to the area, with rain become
more broken as it moves further east toward the Alaska Range
Wednesday as amplifying ridging at the surface and aloft moves
rapidly north behind the front late Wednesday into Wednesday night.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
Ridging will dominate much of the Bering through early Wednesday.
The exception will be a trough that will push through northern
portions of the Bering from west to east today into the overnight.
The ridging will also help pull up warmer air (and plentiful low-
level moisture for low stratus and fog) from the North Pacific to
the southwestern quarter of the region tonight into Wednesday. A
pair of low pressure systems, one from the North Pacific and the
other from Kamchatka, will begin to move into the Bering and
Aleutians bringing rain and mainly small-craft and some gale-force
winds by Wednesday night.

&&

.LONG TERM FORECAST (Days 3 through 7)...
The extended forecast begins on late Wednesday with a flat upper
ridge over the southern mainland. Some light rain (or snow at
upper elevations) is possible in western areas of the
Alaska/Aleutian range, but little precipitation if forecast at
this time. The ridge will continue to build to the east on
Thursday bringing clear sky and light wind to most areas. The
southwest mainland will begin to see some influence from the low
pressure system and front developing over central Bering at this
time, including strong southeasterly winds. The forecast hereafter
will depend on the interaction of that low complex and the ridge
to the east. Currently guidance has a wide range of solutions for
both the development of the low and how it interacts with the
ridge. However, there is much confidence in the development of
both features. It looks like the most likely scenario is the front
running into the ridge over the southwest mainland then falling
apart, while the ridge gets shunted to the north. Expect very
seasonable conditions as far as temperatures go through the
period.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Gale Warning...178.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...JA
SOUTHCENTRAL ALASKA...EN
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...CC
LONG TERM...MTL/MMC



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