Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
631 PM EDT Thu May 28 2020
Valid 12Z Mon Jun 01 2020 - 12Z Fri Jun 05 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
western 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 rise
into the 70s for some locations. 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.
A relatively deep low pressure system is forecast to pass
near/south of the Aleutians though Mon/early Tue before entering
the Gulf of Alaska. Persistent onshore flow is expected ahead of
the system, with rain and mountain snow expected across southern
mainland and Southeast Alaska. Areas of showers will also cross
the Aleutians in association with the incoming system. As the low
pressure system reaches the Gulf, precipitation across southern
mainland Alaska should become more widespread, with moisture (and
scattered precipitation).
...Guidance/Predictability Assessment...
Deterministic models have continued to struggle with the timing of
the Aleutian/Gulf low pressure system, with the ECMWF/GFS both
showing a relatively large degree of variability and inconsistency
today after seemingly better consensus yesterday. Ensemble means
continue to show a bit more consistency, and the 12Z UKMET was the
deterministic solution (through early day 6) that fit best with
the ensemble means and within the center of the overall ensemble
spread. Thus, a blend of the UKMET along with ECENS/GEFS ensemble
means was used during days 4-6 (Mon-Wed), with the blend for days
7-8 (beyond the time range of the UKMET) comprised entirely of
ensemble means.
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 western Alaska,
Sun-Mon, May 31-Jun 1.
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