Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
638 PM EDT Wed May 27 2020
Valid 12Z Sun May 31 2020 - 12Z Thu Jun 04 2020
...Overview and Weather Hazards/Threats...
A mid/upper-level ridge centered across the arctic just north of
Alaska is expected to slowly weaken through the extended forecast
period. The ridge will promote well above average temperatures for
much of mainland Alaska (especially western mainland and the
Interior) through early next week - with forecast highs ranging
from 5 to as much as 20 deg F above average. Temperatures may
approach 80 deg at a few locations across the Interior. Meanwhile,
an active and somewhat blocked pattern farther south will keep
persistent negative height anomalies in place across the North
Pacific from near/south of the Aleutians, gradually migrating east
into the Gulf of Alaska. As the upper low moves into the Gulf of
Alaska, with a weakened upper ridge persisting in the Arctic,
easterly flow is expected to develop across much of the Interior.
This easterly flow will spread deeper moisture into the Interior
as well, with precipitation chances increasing early next week.
A weakening barotropic low in the Gulf of Alaska on Sun is
expected to dissipate as another low pressure system passes
near/south of the Aleutians Sun-Mon and enters the Gulf of Alaska
on Tue. The leading system in the Gulf of Alaska will keep onshore
flow in place, with rain and mountain snow expected across
southern mainland and Southeast Alaska. Areas of showers will also
cross the Aleutians in association with the next system. As the
system reaches the Gulf by early next week, precipitation across
southern mainland Alaska should become more widespread, with
moisture (and scattered precipitation).
...Guidance/Predictability Assessment...
A blend of the 12Z ECMWF/GFS was used as a basis for the forecast
during days 4-6 (Sun-Tue). Overall model consensus during the
first half of the extended period was improved relative to 24
hours ago. Despite appearing as an outlier yesterday with a faster
eastward progression of the low pressure system into the Gulf of
Alaska, the overall guidance consensus has now shifted in toward
that idea. Starting on day 7 (Wed) and continuing through day 8
(Thu), weighting of ensemble means (ECENS and GEFS) was gradually
boosted to comprise a majority of the forecast weighting.
Ryan
Additional 3-7 Day Hazard information can be found on the WPC
medium range hazards chart at:
https://www.wpc.ncep.noaa.gov/threats/threats.php
Hazards:
- Much above normal temperatures for portions of mainland Alaska,
Sat-Tue, May 30-Jun 2.
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