Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
634 PM EDT Tue Jun 02 2020
Valid 12Z Sat Jun 06 2020 - 12Z Wed Jun 10 2020
...Overview and Guidance/Predictability Assessment...
The best cluster of guidance shows an eastern Bering Sea upper low
gradually tracking across or near the Alaska Peninsula and into
the northeastern Pacific, in the process interacting with a
mid-latitude system forecast to be over the Central Pacific at the
start of the period. Farther north a compact upper shortwave/low
will likely track over the northeastern mainland underneath a
weakening upper high during the first half of the period. The
pattern aloft over the mainland should trend toward modest
east-west ridging by next Tue-Wed, between the Northeast Pacific
upper low and an Arctic upper low that comes into the picture
northwest of the mainland.
The primary forecast problem involves the eastern Bering to
northeastern Bering upper low and surrounding flow. Up to this
point there has been considerable variability for the specifics,
including among the last two ECMWF runs which were complete
opposites--keeping it over the Bering (00Z) or progressing into
the Pacific (12Z). Beyond that the 12Z GFS varied the details of
the low and surrounding flow such that it compared less favorably
to the means than the 06Z run over a sizable area. Before today
the GEFS mean had been faster with the upper low versus the ECMWF
mean but a slower trend in the 12Z cycle has brought it closer to
the ECMWF mean that has maintained continuity fairly well into the
new 12Z version. Also of note, the 12Z GFS was a bit on the slow
side with the mid-latitude Pacific system reaching the Northeast
Pacific. Over higher latitudes the 12Z CMC leaned to the extreme
side of the spread with height falls extending into the
northwestern mainland by next Tue-Wed.
12Z ECMWF/06Z GFS/12Z UKMET runs provided the initial basis of
today's forecast for days 4-5 Sat-Sun. Then the blend increased
12Z GEFS/00Z ECMWF mean weight as operational model details
diverged somewhat, reaching 50-60 percent by days 7-8 Tue-Wed.
Compared to continuity the new forecast reflects increased
definition of the initial eastern Bering upper low followed by a
somewhat farther north track of Pacific low pressure due to the
stronger upper dynamics. Over the mainland some precise details
at the surface changed but the tendency for thermal lows/troughs
will persist.
...Weather Highlights and Hazards/Threats...
Expect periods of convection over favored terrain from this
weekend into next week. The upper low tracking over/near the
Alaska Peninsula may also support some precipitation over and
southwest of the southwestern mainland during Sat-Mon. Activity
near the Peninsula may linger beyond Mon if low pressure ends up
tracking on the northwestern edge of the current envelope.
Otherwise the surface low should remain far enough south to keep
associated precipitation over water next week. For temperatures
expect a mix of above/below normal readings depending on
location/elevation. In general southern areas including the
Panhandle should see more below normal highs while the north will
likely see somewhat more above normal highs. There should be
greater coverage of above normal low temperatures during the
period.
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