Area Forecast Discussion
Issued by NWS Anchorage, AK

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000
FXAK68 PAFC 200002
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
402 PM AKDT Tue Sep 19 2017

.ANALYSIS AND UPPER LEVELS...
A trough over the northern Gulf in combination with a ridge
stretching north across Bristol Bay, is producing gusty outflow
(N-NW winds) across the western and north Gulf coasts. Patchy fog
formed under clearing skies and weak subsidence across Cook
Inlet, Anchorage Bowl, Mat-Su Valleys, Kenai Peninsula, and the
Valdez area. Rain, associated with a frontal trough moving east
across the Kuskokwim Delta, is spreading eastward to the western
Kuskokwim Valley/western Bristol bay. Variable cloudiness with
little rain was observed across much of the Bering Sea/Aleutians
this morning.

&&

.MODEL DISCUSSION...
The models are all in good agreement through the short-term. Only
real main difference is the NAM still appears to be the outlier
in solutions of a developing low south of the Aleutians. The
GFS/ECWMF solutions will be used out west and the NAM in the east.

&&

.AVIATION...

PANC...Light winds with VFR conditions will persist through the
day. There is a risk of some fog or low ceilings late tonight and
Wednesday morning, but not high enough to warrant adding to the
TAF yet.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
An upper level ridge building in from the west will continue to
influence our weather through the end of the day tomorrow. Dry
offshore NW flow will lead to mostly sunny skies over a majority
of the region tonight. The combination of clear skies, light
winds, and longer nights will allow temperatures to drop fairly
significantly overnight, especially for more inland locations.
Lows are expected to be in the mid to upper 30`s in the
Anchorage/Mat-Su areas, though typical cold spots like East
Anchorage could see lows approaching the freezing mark. Patchy fog
is also possible in the early morning hours over the Cook Inlet
and near the coast. A weak system moving in from the west will
bring increasing cloud cover tomorrow morning and light rain
extending down as far south as Palmer. This system will move
through fairly quickly and skies will begin to clear up by the
evening hours. Temperatures are expected to again drop well into
the 30`s for most location north of the Kenai Peninsula.

For Thursday, a frontal system associated with a strong low over
the North Pacific will push north into the region, bringing
widespread rain from Kodiak, north into the Kenai Peninsula,
Anchorage, and the Mat-Su by late morning to early afternoon
lasting through most of the day. Rainfall amounts with this
system do not look to be overly impressive along the coast as the
orientation of the upper level jet will be aimed more to the east,
keeping southcentral out of the core of heaviest precipitation.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
Scattered to numerous showers will continue across the northern
portion of the area through Wednesday as the system currently
tracking through the Yukon Delta is reinforced by a trailing
shortwave moving across the Kuskokwim Delta and Lower Kuskokwim
Valley Wednesday morning. More widespread stratiform rain will
then arrive late Wednesday evening along the Bristol Bay coastline
as the Bering front begins to push inland over Southwest AK
through Thursday morning. Rain looks to continue into Thursday
evening and beyond as the longwave trough extending from the
Arctic phases with the upper low south of the Aleutian chain and
helps to establish broad southwest flow over the region into the
latter half of the week.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
The front currently moving over the Aleutians will be the primary
feature of interest in the short term as rain and gale force
winds spread from the Central and Eastern Aleutians tonight to the
Alaska Peninsula Wednesday morning and the Pribilof Islands
Wednesday afternoon. The eastern half of the Bering will remain
in a wet and windy pattern into Thursday night as the parent North
Pacific low makes slow eastward progress from south of Adak to
south of Unalaska. Meanwhile, western portions of the Bering
including Shemya should remain on the drier side in northeast
flow on the back side of the evolving longwave trough.

&&

.LONG TERM FORECAST (Days 3 through 7)...
Beginning the extended period forecast Thursday night, there will
be an arctic trough merging with a North Pacific warm front over
the state. Broad southwest flow will bring rain to most of
Southern Alaska heading into Saturday as the upper trough remains
in place. Uncertainty develops on Saturday night with another warm
front moving north toward the Gulf of Alaska with the ECMWF
favoring a deep 978 hpa surface low tucked into the west side of
the Gulf. However, the 12z GFS and Canadian GDPS models are
notably weaker and much farther east with the surface low.
However, even with this uncertainty, there will still be plenty of
forcing for continued coastal rain and rain chances inland through
the weekend. Eventually, the upper low will move southward into
the North Pacific and Gulf of Alaska, which, in theory, should
result in less precipitation chances heading into mid/late week.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...NONE.
MARINE...Gale Warning 170 172>177 179.
FIRE WEATHER...NONE.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...RC
SOUTHCENTRAL ALASKA...KVP
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...CB
LONG TERM...JA



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