Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
648 PM EDT Sat Jun 13 2020
Valid 12Z Wed Jun 17 2020 - 12Z Sun Jun 21 2020
...Overview and Weather Highlights/Threats...
For the forecast period /Wed-Sun/, the main feature will be the
developing area of low pressure and associated closed upper low
that stalls/slows over portions of the North Pacific, south of the
mainland. An area of low pressure is expected to track from south
of the Aleutians to the North Pacific by mid-week then slow/stall
with a large upper low setting up in the region. This will be
competed by an area of upper ridging over the eastern mainland and
northwest Canada that does begin to lift northward as the
aforementioned system over the North Pacific. Some periods of wet
weather could be possible early in the week with the
aforementioned low but widespread hazardous precipitation is not
expected. Across the mainland, the mostly ridging in place should
result in slightly above average temperatures and mesoscale driven
sensible weather characterized by showers and thunderstorms in the
afternoon.
...Guidance/Predictability Assessment...
Forecast confidence remains average to slightly above average
through the period, with the main focus being the developing
mid/upper level low expected over portions of the Aleutians and
North Pacific through the period. Areas of low pressure moving
through the flow are more unpredictable with wider variance seen
in the forecast guidance, but overall confidence is average even
through day 8. The GFS/CMC/ECMWF all show agreement at 500 mb with
the upper low mid to late week and generally upper ridging over
the mainland beginning to lift northward as the aforementioned
upper trough moves in. Typical model biases were seen with the GFS
being too progressive while the CMC was a bit too amplified with
the secondary area of low pressure developing. For the WPC blend,
a near equal blend of the ECMWF/GFS/CMC was used for day 4 but
quickly transitioned to a ECMWF heavy blend for day 5/6 followed
by increasing weights of the ECENS/GEFS.
Taylor
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:
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