Area Forecast Discussion
Issued by NWS Anchorage, AK

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000
FXAK68 PAFC 161335
AFDAFC

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
435 AM AKST Thu Nov 16 2017

.ANALYSIS AND UPPER LEVELS...
Widespread light snow is poised to return to Southcentral AK this
morning as an upper level ridge overhead is displaced eastward by
a weak trough and associated surface front currently crossing the
western Alaska Range. Snow associated with this system is ongoing
from the Lower Kuskokwim Valley southward through Lake Clark
National Park and eastern portions of Greater Bristol Bay. Fairly
benign showery conditions prevail across the remainder of Southwest
AK in the wake of this system and in advance of a trailing
shortwave poised to drop into the region from the northwest later
today. The Bering Sea region is largely quiet in moderate westerly
flow as high pressure builds south of the Aleutian chain.

&&

.MODEL DISCUSSION...
Models remain in good agreement for the short term portion of the
forecast, first with the system moving through Southcentral today
and then also with the trailing shortwave trough which will
quickly dive southeastward across Kodiak Island and into the Gulf
by late tonight. This will usher in a return of drier offshore
flow through the end of the work week as the pattern once again
becomes more amplified by the trough digging into the Gulf and
another ridge building over the Bering. Given the strong
agreement, mainly utilized Hi-Res guidance for the morning
package to better capture local wind effects.

&&

.AVIATION...
PANC...Generally light snow will move into the Cook Inlet region
this morning and drop conditions to MVFR, with a brief window of
IFR conditions possible from roughly 17-20z as snowfall peaks in
intensity. Snow will taper off around 21z, with conditions
returning to VFR by 00z as light northerly winds return to the
region.

&&

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

A fast moving weather front approaching the Cook inlet to Susitna
Valley corridor this morning clears the Copper River Basin by
late this evening. Snowfall amounts overall should be on the
light side with most areas not receiving much more than a couple
of inches. Values should be somewhat greater though, but sub
advisory, along higher elevations and across the Copper River
Basin where colder air will allow for higher snow to water
ratios. Strong outflow/gap flows are expected to develop over the
western Gulf and North Gulf Coast after frontal passage
today/tonight and continue through Friday. Cold advection and an
upper wave dropping south across Kodiak Island this evening will
enhance the surface wind flow and generate storm force winds
with higher gusts over marine zones near Kodiak. Some locals
across Southern Kodiak Island could approach wind gusts near 70
mph tonight.

&&

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

A busy stretch of weather is in store for Southwest Alaska. This
morning, scattered showers are ongoing across portions of the
Kuskokwim Delta and Lower Kuskokwim Valley. For the most part,
temperatures are warm enough across the delta for all rain.
Meanwhile through the Kuskokwim Valley, snow showers are ongoing.
This afternoon into tonight, another wave of moisture moves into
Southwest Alaska ahead of some slightly cooler air from off the
Bering. The showers should remain as rain for the Delta, perhaps
mixing with some snowflakes at times. For the Lower Kuskokwim
Valley, a few inches of snow are possible, with the highest totals
along the foothills of the Alaska Range. Gusty northwest winds
will keep the upslope snow going for the Kuskokwim Mountains and
Alaska Range into the day on Friday. For the rest of Southwest
Alaska, Friday will be windy and dry with colder air moving in
keeping temperatures for most areas away from the immediate coast
below freezing. The winds will be strongest through bays and
passes where the mountains may further enhance wind speeds due to
funneling. The dry weather in Southwest Alaska will be short-
lived as the next much stronger, potent, and dynamic storm system
begins moving into the Kuskokwim Delta coast by early Saturday
morning. A hodgepodge of winter weather is expected this weekend,
with some portions of the area getting rain with a driving wind,
while others have the potential of seeing plowable snow. Stay
tuned.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...

The primary weather story this morning concerns the next wave of
moisture in the wave train diving southward out of the Arctic
across the eastern Bering and Alaska Peninsula this afternoon and
tonight. It is the leading edge of much colder air streaming out
of Siberia. As that wave and associated cold air slams the Alaska
Peninsula and eastern Aleutians, very strong winds will be seen
through the bays and passes, and also across the marine areas
south of the Alaska Peninsula between Kodiak Island and the
Shumagin Islands especially. Hurricane force wind gusts are
possible through this area.

The next front and associated rainfall move into the western
Aleutians tonight on the west side of a strong area of high
pressure centered south of Adak. This moisture will feed into the
warm pre-storm environment over the Bering. It will slowly push
eastward across the central and northern Bering Friday night.
Meanwhile, a very strong shortwave trough will approach the
western Bering late Friday and set the stage for powerful
cyclogenesis across the eastern Bering by Saturday.

&&

.LONG TERM FORECAST (Sunday through Thursday)...

The upcoming weekend will feature a fast-moving and rapidly
intensifying storm dropping from the northern Bering Sea across
the AKPEN and into the western Gulf. Unfortunately the models
still are not in great agreement on the track of this low, with
the GFS and now the GEM much further south than the more northerly
ECMWF solution. The ECMWF solution would bring a few inches of
snow to much of southcentral Alaska, with potentially higher
amounts of the Kenai Peninsula. Meanwhile, the southerly solutions
would bring no snow to Anchorage, and minimal snow to the Kenai
Peninsula. For now, the afternoon forecast is right down the
middle with a chance of snow as far north as Anchorage, but
suffice it to say as we get closer to the event the chances for
snow around Anchorage will get either much higher or much lower
depending on the ultimate storm track. What we can say with higher
confidence is that this low will be moving very quickly and
strengthening very rapidly - both of which will help winds behind
and to the west of the low center really ramp up. The strongest
winds will develop somewhere over the eastern Bering/Aleutians
before crossing into the north Pacific, and these winds will need
to be watched closely in the next day or so in case a high wind
Watch is necessary.

Once this low drops into the Gulf for the start of next week, a
reinforcing shot of cold air and "outflow" winds along the Gulf
Coast will develop. This should bring a renewed period of sunny
skies and cold northerly winds to most of southern Alaska that
continues through the Thanksgiving holiday as the storm track will
steer storms from the Bering Sea into the southern Gulf.

&&


.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Storm 130 131 132 150 155. Gale 127 138 160 165 172 178
180 181 185 351 352 414.

&&

$$

SYNOPSIS AND MODEL DISCUSSION...CB
SOUTHCENTRAL ALASKA...RMC
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...JW
LONG TERM...PS



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