Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
748 PM EDT Sun Jun 06 2021
Valid 12Z Thu Jun 10 2021 - 12Z Mon Jun 14 2021
...Overview and Guidance Evaluation...
There are still stray solutions that differ but today's model and
ensemble guidance is generally better clustered for the large
scale pattern. Over the past day consensus has finally converged
toward the idea of the short-term upper low over/near the far
western mainland ejecting to the north-northeast in response to
upstream troughing. The majority of guidance shows this mean
trough amplifying and eventually interacting with a western
Pacific feature that should track into the Aleutians--most likely
yielding an upper low over the eastern half of the Bering Sea by
the start of next week.
Today's forecast blend started with a blend of 12Z operational
models, ECMWF/GFS/UKMET/CMC in order from most to least weight,
for the first two days of the period to depict the most agreeable
aspects of guidance while blending lower confidence details. Then
the forecast trended to 40-60 percent total weight of the 12Z
GEFS/00Z ECens to provide a slightly enhanced ensemble depiction
of the system tracking into the Aleutians/Bering Sea while staying
close to the means over the mainland where models differ
significantly over some details.
Even with the outcome of the short-term western mainland upper low
closer to being resolved, there are still other detail
uncertainties in the guidance. The majority shows shortwave
energy that reaches near the southwest corner of the mainland as
of early Thursday dropping well southward into an eastern Pacific
mean trough/low. However there is still some spread for the
character of this energy and the new 18Z GFS has a particularly
low-confidence evolution of it closing off an upper low that
remains over the mainland for most of the period. From late week
into the weekend the ensemble means provide a good middle ground
between the offsetting 12Z ECMWF cyclonic flow (around a Bering
Strait upper low) and 12Z GFS ridge. The means agree that flow
should evolve toward a western Canada into mainland mean ridge
late in the period as the upper trough/low reaches the eastern
Bering Sea.
The North Pacific into Bering evolution still has a fair degree of
uncertainty for specifics. Recent ensemble means have been
trending toward more stream interaction which the operational
models had been suggesting, thus nudging the main surface low a
bit eastward. Otherwise the means have been fairly stable. In
contrast, consecutive GFS runs have been particularly inconsistent
lately. Today's 06Z/18Z runs are quite progressive and suppressed
for the leading wave which pushes into what the remaining
consensus says will be a mean ridge. The 12Z GFS was just close
enough to other guidance to include in a compromise with the
ECMWF/CMC to enhance the ensemble low depth a bit.
...Weather/Threats Highlights...
Precipitation from the eastern Alaska Peninsula to the Kenai
Peninsula and vicinity may extend into Thursday before a brief
drier trend. Meanwhile shortwave energy of uncertain strength
could help to produce scattered areas of precipitation farther
north over the mainland. Confidence is low in the details of
coverage and intensity due to significant model spread for
specifics of flow aloft. The system expected to track into the
Aleutians and Bering Sea should spread moisture into the Aleutians
late this week into the weekend and then the southwestern mainland
and vicinity by next Sunday-Monday. Some areas could see a period
of brisk winds/enhanced rainfall depending on the strength and
track of the system.
Below normal highs over much of the state as of Thursday should
gradually moderate from the southwest with time, yielding various
areas of above/below normal highs by early next week. Low
temperature anomalies should be fairly modest on either side of
normal from late week into the weekend. Interior and western
areas along with parts of the Panhandle are most likely to see
below average readings with remaining areas near/above normal. By
Sunday or Monday there may be greater coverage of above normal
lows and with somewhat higher anomalies.
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
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