Area Forecast Discussion
Issued by NWS Anchorage, AK

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162
FXAK68 PAFC 270013
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
413 PM AKDT MON SEP 26 2016

.ANALYSIS AND UPPER LEVELS...
There is an upper level low just south of the Alaska Peninsula
moving rapidly southeast into the Gulf of Alaska. There is a weak
upper level trough over western Alaska, also moving toward the
southeast. There is a high amplitude north-to-south oriented ridge
over the bering sea with its axis around 177 west longitude. A
deep trough is over northwest Russia with an associated strong
jet in excess of 150 knots pushing across the Kamchatka Peninsula.

&&

.MODEL DISCUSSION...
The numerical models are in good agreement through the short term
portion of the forecast (Wednesday afternoon). There are some
minor differences in the speed and strength of a low that shoots
across the northern Bering Tuesday and Tuesday night, but this
does not significantly impact the forecast. The forecast
confidence is a little above normal today.

&&

.AVIATION...
PANC...There is some potential for fog and/or low stratus in the
morning due to lingering moisture and the offshore flow being
weak, but confidence is not very high.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
A progressive pattern setup over much of Southcentral Alaska will
persist through the middle of the week, transitioning between wet
and dry regimes over the next few days. The upper level trough
currently stretching over Prince William Sound and the Northern
Gulf will continue to weaken and track eastward as some brief and
weak shortwave ridge builds in from the west through tonight.
Clear and drier offshore flow conditions will continue through
this evening as the weak ridge passes over Southcentral, then
transitioning to a more cloudy and showery (mainly along the
Mountains surrounding the Copper River Basin) regime as the next
trough drops down from the Northwest interior Tuesday morning.
This trough will quickly clear the area Tuesday night, with some
stronger ridging building over much of Southcentral Alaska by
early Wednesday morning. The stronger ridging moving over the area
Wednesday will bring stronger offshore flow, resulting in more
clear and drier conditions over the area through Wednesday
Afternoon.

With guidance showing the offshore flow being weak enough over
much of the area and decent stabilization with cooler air passing
over warmer waters, there remains potential for fog to develop
again overnight tonight into Tuesday Morning ahead of the next
approaching upper level trough. However, confidence remains low
with regards to fog development, as the weak Northwesterly winds
are marginal and could potentially keep conditions mixed in the
lower levels.

&&

.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. A trough will swing through the Kuskokwim Delta
Tuesday night bringing rain to the area and then it will push into
the rest of southwest Alaska Wednesday.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
Ridging will dominate much of the Bering through the forecast
period. The exception will be a trough that will push through
northern portions of the Bering from west to east through Tuesday.
The ridging will also help pull up warmer air from the North
Pacific to the area.

&&

.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...None.

&&
$$

SYNOPSIS AND MODEL DISCUSSION...BL
SOUTHCENTRAL ALASKA...TP
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...DK
LONG TERM...MTL



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