Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
745 PM EDT Wed Jun 09 2021
Valid 12Z Sun Jun 13 2021 - 12Z Thu Jun 17 2021
...Overview and Guidance Evaluation...
The main system of interest in the medium-range remains across the
Aleutians. Since yesterday, there has been more of a split
decision among the major model guidance on this system. The ECMWF
switched quite abruptly to separate the upper trough dropping into
the western Bering Sea with the southern wave that is forecast to
pass to the southeast of the Aleutians. The CMC supported this
split as well but the GFS still tended to merge the two systems.
The ensemble means basically continue to advertise a main low
moving across the Aleutians early next week. Therefore, the
decision was to include more of the ensemble means starting on Day
5 to better agree with continuity for today. This solution keeps
a double-barrel low moving eastward across the Bering Sea and the
Aleutians Sunday and Monday, followed by gradual elongation of the
system toward the Gulf of Alaska, with residual vortices near the
Aleutians through next Thursday. This scenario is supported by
the latest (12Z) EC means (not incorporated in this forecast
package).
A general model compromise among the 12Z ECMWF/00Z EC mean, 12Z
CMC/CMC mean, and 12Z GFS/GEFS trending toward the ensemble means
was used to compose the current medium-range forecast package.
This yielded a more elongated low pressure system across the
Aleutians to the Gulf of Alaska than yesterday's WPC forecasts.
Elsewhere, a stationary front should remain draped across the
northern portion of Alaska through the medium-range period.
...Weather/Threats Highlights...
Precipitation associated with the upper shortwave edging in from
Siberia should overspread the northern portion of Alaska on
Sunday, and especially along the Brooks Range. The precipitation
is expected to linger through midweek near a stationary front but
is expected to slowly diminish with time. Meanwhile, the
strengthening system that tracks into the Aleutians/Bering Sea
will spread a broad area of moisture across the Aleutians and into
much of the Alaska Peninsula early next week. The Aleutians
should see a period of enhanced rain/winds on Monday as the
occluded cyclone is forecast to reach peak intensity. Some
enhanced rainfall will then shift eastward along the south coast
of the Alaska Peninsula Tuesday and possibly Wednesday. Along the
Alaska Panhandle, chance of precipitation will tend to increase
through midweek.
High temperatures will tend to be cooler than normal for the
western half of Alaska through the medium-range period. For lows,
expect slightly below normal readings over parts of the Interior
and western mainland, while remaining areas should be above
normal. The coverage of above normal lows should increase through
midweek.
Kong
No significant hazards are expected over Alaska during this
forecast period.
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