Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
633 PM EDT Wed Jun 03 2020
Valid 12Z Sun Jun 07 2020 - 12Z Thu Jun 11 2020
...Overview and Guidance/Predictability Assessment...
Today's guidance maintains good continuity for the general
large-scale evolution during the period. The two primary features
of note will be the upper low initially near the Alaska Peninsula
and forecast to track across the Northeast Pacific--in the process
interacting with a North Pacific surface low--and a western
Pacific system that should affect the Aleutians during the latter
half of the period. In the wake of a compact shortwave/upper low
retrograding across the northeastern mainland early in the period,
the upper pattern over the mainland and the Bering Sea becomes
somewhat ill-defined but with a tendency toward ridging over the
mainland and a weakness over the Bering Sea by next Tue-Thu.
Within the agreeable and consistent mean pattern there are still
some significant detail questions yet to be resolved for the
initial upper low near the Peninsula and the surrounding flow.
The slow/northward 12Z runs of the GFS and ECMWF both differed
from their prior 6-/12-hourly runs and remaining model/ensemble
mean consensus so preference was to split GFS/ECMWF input between
the last two runs. For about the first half of the period the
blend also included the 12Z CMC/UKMET, with the result providing a
good intermediate starting point. Mid-late period inclusion of
the 12Z GEFS/00Z ECMWF means increased from 20 to 50 percent with
time. The operational model component maintained some 12Z/06Z GFS
and 12Z/00Z ECMWF input through day 8 Thu and 12Z CMC input into
day 7 Wed. The main trend of note is a moderate eastward
adjustment for the upper low and associated northeastern Pacific
surface low. Consensus continues to suggest the surface system
should not track farther north than 50-55N latitude. Meanwhile
the model/mean clustering for the system reaching near the
Aleutians late in the period has been fairly good over the past
day, providing better than average confidence relative to the
forecast time frame. The aforementioned model/mean blend provided
a good representation of this system through next Thu. Thermal
lows/troughs will continue to dominate the surface pattern over
the mainland.
...Weather Highlights and Hazards/Threats...
Southern and central portions of the mainland should see periods
of convection over favored terrain. The upper low initially over
or near the Alaska Peninsula may enhance activity in its vicinity
at least early in the period, with some uncertainty persisting
over how quickly it will move into the northeastern Pacific.
North Pacific low pressure will likely remain far enough south to
keep its rainfall south of the mainland but some leading moisture
could reach portions of the Panhandle. Expect the Aleutians to
see rainfall and somewhat stronger winds by around midweek with
the approach of western Pacific low pressure. Temperature
anomalies will depend on location and elevation. The best
potential for below normal highs will be over the south/southeast
including the Panhandle while above normal highs will be more
likely over the west and north. A greater percentage of the state
should see above normal lows.
Rausch
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
No significant hazards are expected over Alaska during this
forecast period.
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