Area Forecast Discussion
Issued by NWS Anchorage, AK

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000
FXAK68 PAFC 211711 CCA
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
341 AM AKDT Tue Aug 21 2018

.ANALYSIS AND UPPER LEVELS...
An upper level trough extends through southwest Alaska and into
the western Gulf with an embedded low southeast of Kodiak island.
This trough is one of the factors that is helping drive a long
fetch of precipitable water up from the Pacific Ocean into the
north Gulf coast as shown by satellite imagery. The result is rain
throughout Southcentral Alaska with the heaviest amounts around
Prince William Sound. Further west, another system is over the
western Bering with its front extending through the central
Aleutians.

&&

.MODEL DISCUSSION...
The models are in good agreement through the mid term with the
main synoptic features. The struggles are with localized concerns
like downsloping with the southerly flow. Because of this the high
res models were preferred.

&&

.AVIATION...
PANC...Light winds will persist. VFR conditions will last through
the early morning before ceilings drop later this morning as a
trough moves over the area from the south. After the trough
passes, ceilings will rise again this afternoon.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
The upper level trough over the Gulf this morning will push
through Southcentral during the day today. The very moist jet
stream will weaken and push northeast of the area in the
afternoon. Conditions should then begin to slowly improve from
southwest to northeast. Weak cyclonic flow aloft however will
allow for clouds and showers to continue tonight. On Wednesday an
upper level ridge will build over the area, but low level
conditions will still be quite moist, and considerable clouds will
linger. Some fog could develop Wednesday morning as well. The
ridge will then slide east Wednesday night, with southwesterly
flow aloft bringing increasing chances of showers.

&&

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

The weather pattern will stay generally wet and cool for Southwest
Alaska for the next couple of days. An upper level trough
currently rotating onshore will continue to bring rain and
showers to the area through Tuesday. A flat transient ridge will
build in from the west Tuesday night and Wednesday tapering off
showers but bringing a fog and low stratus concern to the area.
The leading edge of the next frontal system will reach the Kuskokwim
Delta early Wednesday with additional troughs following Wednesday
afternoon through Thursday.

&&

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

The large vertically stacked low centered east of the Kamchatka
Peninsula will track slowly east to the central Bering through
Wednesday with a variety of troughs rotating around it. The low
will remain in this general location and gradually fill through
Thursday. The next developing low pressure system will approach
the central Aleutians from the south Thursday night.

&&

.LONG TERM FORECAST (Friday through Monday)...

An active pattern will start off the long term period on Friday as
a vigorous short wave trough slides east across the southern
mainland bringing another round of widespread rain to the region.
An upper low over the Bering will follow closely behind the first
system Friday evening into Saturday morning and track across
western and southcentral Alaska bringing more rain to the area.
There are some timing discrepancies regarding how fast the system
exits the region, with the EC being a bit quicker, but regardless
there should be a drying trend across the southern mainland by
Saturday afternoon as an upper level ridge builds in from the
North Pacific.

By the end of the weekend models are coming into better agreement
as a strengthening low enters the Western Bering, aided by energy
from a tropical system being entrained up from the South Pacific.
The low looks to be supported by a strong southerly jet that will
tap into subtropical moisture bringing a decent plume of
moisture, or atmospheric river, across the Aleutian Chain, into
the Bering, and eventually into Southwest Alaska by the beginning
of next week. There is still a fair amount of uncertainty in how
far east this system will push, which is dependent on the location
of the downstream ridge axis.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...Flood Advisory...135.
MARINE...None.

&&

$$

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


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