Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
615 PM EDT Mon Jul 04 2022

Valid 12Z Fri Jul 08 2022 - 12Z Tue Jul 12 2022

...Heavy Precipitation Threat for the Alaskan Southern Tier...


...Pattern Overview and Weather/Hazard Highlights...

Expect an active weather pattern will develop for Alaska over the
next week. The weather pattern into late this week will feature
closed lows/troughs centered over the Arctic Ocean and
southeastern Bering Sea on the periphery of a warming upper ridge
from western Canada to the Alaskan mainland. Guidance has trended
to transitioning more ample southeastern Bering Sea closed
low/trough energies toward Southwest Alaska/Alaskan
Peninsula/Kodiak Island then south-central Alaska into
Friday/Saturday where sustained and deepened Gulf of Alaskan
moisture feed offers a protracted threat for moderate to locally
heavy/terrain enhancing precipitation. Meanwhile, ejecting
impulses and moisture northward through Southwest Alaska and into
the Interior on the western periphery of the slowly eroding upper
ridge should meanwhile fuel local rain chances. Additional
downstream system progression with the main closed low/trough
position over the Gulf will tend to be inhibited by the main upper
ridge, so less certain upstream flow of additional Bering
Sea/Aleutians energies into the backside of this system should
tend next weekend into early next week act to reform a main closed
low position underneath over the west-central Gulf of Alaska. This
will focus a maritime threat, but large circulation proximity and
wrapping energies should also spread additional periods of
moisture and precipitation onshore across southern then southeast
Alaska. Meanwhile, the Arctic vortex should stay well to the north
of Alaska, but later period energies/boundaries underneath have
the best chance of focusing light to moderate precipitation down
from the North Slope to a potentially active Interior next
Sunday-Tuesday.

...Guidance/Predictability Assessment...

The 12 GFS/ECMWF solutions seem best clustered with the pattern
evolution aloft of the quite compatible GEFS/NAEFS/ECMWF ensemble
means through medium range time scales and a reasonable composite
from days 4-8 seems to also offset more evident surface system
differences, partially due to less certain smaller scale upper
impulse interactions over time. Some manual adjustments were
applied to ensure Gulf of Alaskan surface lows and wind flow were
not too weakened by the mean/blending process, consistent with
upper support and system specific uncertainties. This forecast
strategy maintains good WPC product continuity from yesterday in a
pattern with seemingly average to better overall predictability.

Schichtel

Hazards:
- Heavy rain across portions of southern coastal/higher elevations
of Alaska, Fri-Sun, Jul 7-Jul 10.
- Heavy rain across portions of southern coastal/higher elevations
of Alaska to the Alaska Panhandle, Sun-Mon, Jul 10-Jul 11.

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