Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
535 PM EDT Sat Sep 14 2024

Valid 12Z Wed Sep 18 2024 - 12Z Sun Sep 22 2024

...Dynamic Storm to Impact Southwest through Southern/Southeast
Alaska into midweek...


...Guidance Evaluation/Preferences...

Guidance still highlights a pattern with highly energetic and
progressive flow with dynamic storms impacting Alaska. A composite
of reasonably well clustered guidance of the 12 UTC
GFS/ECMWF/UKMET/Canadian shows good system detail consistent with
above normal system predictability and WPC product continuity for
Wednesday/Thursday. Switched to a models/ensemble means blend
Friday/next weekend. The models offer much deeper systems
clustering in position around a more stable center point provided
by the ensemble means. Manual edits will be applied to further
deepen offshore storms.

...Weather/Hazards Highlights...

Forecast confidence continues to rise through above average levels
regarding the details for yet another major storm slated through
the early through middle part of next week. Expect a
deepened/potent low track through the Aleutians and southern
Bering Sea into with earnest Southwest Alaska will also with
downstream energy transfer reform over the northern Gulf of Alaska
and track near/offshore the Alaskan southern tier, eventually and
actively crossing Southeast Alaska later Wednesday into Thursday.
This would focus the majority of precipitation to the southwestern
mainland and southern to southeastern Alaska. This storm will
again also produce widespread maritime threats of high winds and
waves. Onshore, the WPC Hazards Outlook depicts an associated risk
of high winds and coastal impacts from the Aleutians to Southwest
Alaska and the Alaska Peninsula given dynamic system strength and
speed. The pattern seems to remain favorable for additional storm
systems upstream in this flow along with the potential tapping of
Pacific system energy and longer fetch moisture inflow leading
into next weekend. Predictability lowers to average for details,
most the bulk of guidance agrees in the
development/re-developments of a complex and deep/moist storm to
work potently up into the Gulf of Alaska. This seems to favor
widespread threats of enhanced winds/waves/rainfall and coastal
impacts from the southern Bering Sea/Aleutians/northern Pacific
into especially the Gulf of Alaska/Alaska southern/southeast tier
for next Friday/weekend to monitor. 

Meanwhile to the north, lingering low pressure centering over the
Interior along with the uncertain passage and digging of shortwave
energies aloft over the mainland may support persistence of
scattered light precipitation into next week in the wake of a
highly energetic leading short range storm. Activity on the
northern periphery of the next main Bering Sea storm through next
midweek may also lead to some locally/terrain enhanced gusty winds
and precipitation with passage.

Schichtel

Additional 3-7 Day Hazard Information can be found on the WPC
medium range hazards outlook chart at:
https://www.wpc.ncep.noaa.gov/threats/threats.php

WPC medium range Alaskan products including 500mb, surface
fronts/pressures progs and sensible weather grids can also be
found at:
https://www.wpc.ncep.noaa.gov/alaska/ak_5dayfcst500_wbg.gif
https://www.wpc.ncep.noaa.gov/alaska/akmedr.shtml
https://www.wpc.ncep.noaa.gov/alaska/ak_5km_gridsbody.html