Area Forecast Discussion
Issued by NWS Anchorage, AK

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000
FXAK68 PAFC 140118
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
518 PM AKDT Mon Aug 13 2018

.ANALYSIS AND UPPER LEVELS...
There is a vertically stacked low over southwest Alaska, centered
over the lower Yukon River. Plenty of moisture is spinning around
this low into all of the southern Alaska Mainland. This low is
slowly filling (weakening). There is an upper level low centered
over the northern Bering Sea, with fairly fast upper level zonal
flow over the central and southern Bering. Fairly strong surface
high pressure is located south of the Aleutians. Fairly breezy
conditions exist across most of southern Alaska as well as much of
the Bering Sea. The strongest winds are over the far eastern
Bering and Bristol Bay, as well as through Shelikof Strait and
Cook Inlet.

&&

.MODEL DISCUSSION...
The numerical models are struggling a bit with how they handle the
transition of the low currently centered over the lower Yukon
Valley into an open wave, and how it interacts with a low
currently over the northern Bering. The GFS in particular is
handling things a little different than the other models, keeping
the Bering low further west on Tuesday night, and then pushing it
into the western Gulf faster on Wednesday. The NAM and ECMWF keep
the low in Bristol Bay, while the Canadian GEM is in between
these solutions. Therefore the forecast confidence is lower than
normal.

&&

.AVIATION...
PANC...VFR conditions are generally expected through Tuesday
afternoon. Some MVFR conditions are possible in rain and showers
through Tuesday morning. Gusty south winds should diminish this
evening.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Tonight through Thursday)...
A wetter pattern continues through mid week as an upper level
trough remains over the mainland. There is high uncertainty on
timing for the individual short waves spinning around the broad
low center; therefore, kept the inherited forecast intact which
captures the highest chances for rain along the ranges. A few
thunderstorms are possible this evening as some clearing of the
sky set up a weakly unstable air mass along the eastern half of
the Alaska Range as well as over the Wrangell Mountains. To the
west of this area, the air mass is quite stable and will allow
areas of fog to persist overnight as a saturated air mass advects
up from the inlet.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Tonight through Thursday)...
The low currently causing the rainfall over nearly all of
Southwest Alaska today will continue drifting into interior Alaska
and weakening on Tuesday. Gusty winds will continue throughout
the day, but the steadiest rainfall will slowly move north with
time, following behind the surface low. Thus, the second half of
the day should be relatively dry across Bristol Bay, but onshore
winds should keep the region on the damp side. A weak area of low
pressure associated with a stalled out front along the Bering
coast develops Tuesday evening along the Kuskokwim Delta. While
most of the models show the low developing, they each do something
different with it. The NAM and GEM quickly shunt most of the
energy south to the Alaska Peninsula, the GFS keeps it as a
diffuse low nearly stationary between Kuskokwim Bay and Cape
Newenham, while the EC shows a stronger compact low in the same
area. The main impacts of this low will be the wind directions and
whether the winds are closer to 10 or 20 mph along the coast.
Precipitation associated with the low, regardless of the solution
that pans out, will be limited to some shower activity that
develops along the mountains along Bristol Bay from King Salmon
south. While the remainder of Southwest Alaska stays under mostly
cloudy conditions, elsewhere most of the day should be dry on
Wednesday. Wednesday will also feature much lighter winds area-
wide. Much of the same conditions persist into Thursday, with most
areas staying dry. Any steadier precipitation will be limited to
areas impacted by the aforementioned low, with large model spread
keeping specifics associated therewith highly uncertain.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Tonight through Thursday)...
A series of weak lows are expected to impact the eastern Bering
into Wednesday, keeping conditions cloudy and unsettled. There is
a lot of model spread on the exact position and timing of those
lows, so uncertainty is high, but in general the winds and chances
for hazardous weather will continue to diminish from Tuesday and
beyond across the eastern Bering. High pressure centered south of
Adak right now will build northward across much of the central and
western Bering through Wednesday, allowing that area to alternate
between some sunshine and the typical stratus. The next low and
associated front move into the far western Bering towards Shemya
and Attu on Wednesday, which will evolve to consolidate with a
developing weak low that will track south of the Aleutians on
Thursday, as the aforementioned high pressure persists over the
western Bering.

&&

.LONG TERM FORECAST (Thursday night through Sunday night)...
The extended forecast begins with the remnants of the upper low
pressure, which is currently in the northern Bering Sea.
Deterministic models are ranging in solutions from the northern
Gulf through the tip of the Alaska Peninsula, but eventually
consolidate a low center somewhere south of the Alaska Peninsula.
The upper low and it`s front will be the focus for active weather
through the weekend. No matter the position of the surface low,
guidance agree on it being a relatively strong system. Most of the
mainland will be dry and seasonable as far as temperatures go,
until the front reaches the area. The front will approach Kodiak
Island on Saturday, likely a solid small-craft front, with a
chance to reach into the gale-force range. The front and more
and it`s precipitation should spread up to the north Gulf coast on
Sunday along with a round of gap-driven winds in the same area.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Gale 138 139 140 160 180.

&&

$$

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


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