Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
641 PM EDT Fri Apr 16 2021
Valid 12Z Tue Apr 20 2021 - 12Z Sat Apr 24 2021
...Overview and Guidance/Uncertainty Assessment...
Latest guidance continues to depict a blocky regime during the
extended range period. This pattern will be highlighted by upper
ridging that covers most of the mainland into the western Bering
Sea/eastern Siberia, while a consolidating Pacific mean low aloft
should settle into a position south of the eastern Aleutians and
Alaska Peninsula. Shortwave energy within progressive flow around
the north side of the upper ridge may push a cold front/lower
heights into the northern/eastern mainland by Tuesday-Thursday.
Most of the state should be fairly dry for most of next week, with
the best potential for precipitation along coastal locations
shifting west to east from the Aleutians to Southern Coast to
Panhandle.
Overall, the 12z GFS and 12z ECMWF and respective ensemble means
shows fairly good agreement on the large scale through much of the
period and continues to trend towards a stronger ridge aloft. The
12z CMC (along with the 00z ECMWF) was the outlier with bringing
stronger shortwave energy into the Bering Sea by mid-week and
faster to break down the ridge. The 12z ECMWF came in much closer
to that of the GFS, which advertise being less aggressive to break
down the ridge across the mainland/Bering/eastern Siberia and
suppressing energy/low pressure systems south of the Aleutians.
Models do show pretty good agreement with lowering heights into
northern/eastern Mainland early to mid week as well. The WPC blend
favored the deterministic guidance (GFS/ECMWF) for the first half
of the period. After this, increased influence from the ensemble
means to account for some smaller scale timing and detail
differences. Leaned a little heavier towards the 12z GFS over the
12z ECMWF just given the GFS has been the most consistent with
showing the stronger ridge and is the deterministic solution which
best supports the ensemble means. This approach fits well with
yesterdays WPC continuity as well.
...Weather/Hazards Highlights...
Most precipitation should be confined to the Aleutians/Alaska
Peninsula and vicinity, with a fairly persistent flow of moisture
carried in the gradient between one or more Pacific lows and high
pressure well to the north. Light to moderate amounts are most
likely but some locally higher totals could be possible depending
on exact strength and track of Pacific systems. By the end of the
week, lighter precip may begin shifting east towards the Southern
Coast region and the Panhandle. The rest of the mainland should
remain dry throughout the entire week.
A vast majority of the state should see above normal temperatures
at the start of the period Tuesday, with the warmest anomalies
over the North Slope region and western half of the Mainland (with
even more anomalous warm morning lows). A cold front should
deliver a near or even slightly below normal air mass during the
middle of next week to parts of the eastern Mainland and
especially the southeast and Panhandle. Temperatures may also
begin to moderate a bit across the rest of the state by next
weekend.
Santorelli
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