Area Forecast Discussion
Issued by NWS Anchorage, AK

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FXAK68 PAFC 160242 CCA

Southcentral and Southwest Alaska Forecast Discussion...CORRECTED
National Weather Service Anchorage AK
642 PM AKDT Mon Oct 15 2018

Correction to long term forecast

The large low in the Eastern Bering Sea near the Alaska Peninsula
is becoming vertically stacked and will slowly weaken over the
next few days. It will, however remain the region as an anchor
low with the jet stream running around it to the south and then
bend back to the north-northeast over the north Gulf coast. this
pattern is tapping into some deep subtropical moisture and moving
it over Cook Inlet to the Prince William Sound area. A strong
Barrier Jet is also developing along a front as it approaches the
north Gulf coast.


Models remain in good agreement for the next day or two and the
adjustments made by them yesterday seem to be panning out well at
this time. By Thursday they start to show a large disparity with
the development of what will become a strong low in the Gulf of
Alaska. They all agree on the current anchor low in the Bering Sea
persisting until then and weakening which keep the region of
active low development swinging into the Gulf and then into
Southern Alaska. At this time the GFS model looks to have a very
reasonable track and strength for the Thursday through Saturday
time frame, but with a dynamic system such as this there are often
rapid changes in strength and track that occur so this system will
need to be watched closely.


PANC...Ceilings and visibility will likely drop to marginal
conditions this evening as the rain becomes more steady. While the
rain will persist into Monday afternoon, it will become more
showery in nature by tomorrow afternoon and ceilings and
visibility will improve back to VFR conditions by then.


Tonight through Thursday)...

An atmospheric river of subtropical moisture is being drawn
northward into Prince William Sound and Southcentral Alaska this
evening. Heavy rain is ongoing across Prince William Sound,
including Cordova. The "nozzle" of the river will shift westward
overnight, allowing the heavy rain to spread into the western
Prince William Sound. As this happens, the cross-barrier winds
over the Chugach will relax somewhat, which will allow some of the
rain to move into Anchorage and the Matanuska Valley tonight.
Overnight rainfall totals will approach 1 inch in these areas. 3
to 5 inches of rain are expected around Seward, which is likely to
exacerbate flooding concerns in that area. A Flood Advisory is in
effect for the Seward area. The highest rainfall totals will be
along Prince William Sound, where the rain is expected to continue
through the day Wednesday, with storm totals over 6 inches likely
in Cordova over to Whittier by Wednesday night.

The other major weather story tonight will be very strong winds
along the Gulf Coast and into Prince William Sound. As the
aforementioned atmospheric river pushes mass into the coast, a
barrier jet will form tonight which will increase southeast winds
to 55-65 mph with higher gusts along the coast into Prince
William Sound. Waves will exceed 25 feet in the strongest winds on
the Gulf, with waves exceeding 15 feet in Prince William Sound
itself. Once the front forcing the jet pushes inland early
Wednesday morning, the winds will very quickly diminish back to
around 20 mph, which will persist for the next several days.

Tuesday through Thursday will be very steady state weather-wise
across nearly all of Southcentral. Steady onshore winds will keep
cloudy conditions with scattered to numerous showers ongoing
across much of the area. Rain will continue all along the Gulf
Coast through Thursday, though it should be significantly lighter
in intensity than the areas currently seeing the atmospheric
river. Another strong low moves into the Gulf Thursday night into
Friday. More on that to come.


Low pressure over the Alaska Peninsula lifts slowly north over
the eastern Bering tonight and fills through Tuesday afternoon.
Gusty easterly flow and rain continues through late tonight, then
tapers down rapidly Tuesday morning as low pressure kicks the
ridge anchored across the Panhandle further east. The low center
remains nearly stationary Tuesday through Wednesday night, then
slowly moves south of the Alaska Peninsula late Thursday. Light
rain and periodic gusts persists in the forecast through the end
of the week as energy rotates around the core of the low.



An active weather pattern keeps a persistent wet and windy
pattern across the Bering through the end of the week. Low
pressure moves across the Alaska Peninsula to the eastern Bering
tonight with gusty southerly flow ahead of this system and
northerly flow to the west. Gale force northerly flow increases
through the evening as a cold air mass advects toward the Central
Aleutians on the backside of the low. Wind strength tapers down as
the low begins to shift southeast late Wednesday into Thursday.
The exception to this is for the Western Aleutians/Bering, as
winds taper early Wednesday ahead of the next North Pacific front
which moves up late Wednesday night.


.LONG TERM FORECAST (Days 4 through 7)...

At the onset of the forecast period, the synoptic pattern
features a low near Kenai, a second low south of the Aleutian
chain and a low near Kamchatka. Anticipate a very wet and progressive
pattern. There is good general consensus between the
GFS/EC/Canadian but the best performing model is thought to be the
GFS for this forecast period. Expect back to back lows to bring a
hefty amount of precipitation to Kodiak, Prince William Sound,
and the Anchorage Bowl. Even though the third week of October is
considered to be part of the cold season for Alaska, the
temperatures with both storms will remain well above freezing in
the low elevations. Higher elevations on the Kenai and other
portions of South Central can expect a fresh blanket of snow this
forecast period bu significant accumulations not expected. The
entire forecast period, the GFS has above normal temperatures at
500 mb from Kenai to the Yukon Territory to Juneau.


PUBLIC...Flood advisory 125.
MARINE...Storms 119 125. Gales 129 173-177 185 351 352 412 413.



LONG TERM...PS is the U.S. government's official web portal to all federal, state and local government web resources and services.