Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
659 PM EDT Sat Apr 17 2021
Valid 12Z Wed Apr 21 2021 - 12Z Sun Apr 25 2021
...Overview and Guidance/Uncertainty Assessment...
Latest guidance continues to depict a fairly 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 through
Thursday. Towards the end of the period, another upper low should
move towards/south of the Aleutians underneath the mainland ridge
which should also help shift the Gulf low eastward as well. Most
of the state should be fairly dry for most of next week and into
the weekend, with the best potential for precipitation along parts
of the Eastern Aleutians and Peninsula.
Most of the guidance does agree that upper ridging in some form
should dominate over mainland Alaska (and sliding westward into
the Bering) through the period. It is south of the Aleutians and
into the Gulf where models begin to diverge fairly rapidly after
day 5. The 12z GFS maintains a more blocky looking pattern (with
some support from the 12z CMC) with a defined ridge in between the
two upper lows mentioned above. The 12z ECMWF drags that north
Pacific/Gulf low more westward with time with lower heights/broad
elongated troughing south of the state which should act to break
down the ridge more than the GFS would try to indicate. Both of
the GEFS/ECENS means would support maintaining the blocky pattern
so after day 5, the WPC blend trended quickly in favor of the
ensemble means and the GFS. 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 Wednesday and Thursday, 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. The rest of the mainland should remain dry throughout the
entire week and into the weekend.
The vast majority of the state should be well above normal in
terms of temperatures through much of the period, with the warmest
anomalies over the North Slope region and western areas of the
Mainland (with even more anomalous warm morning lows). Lowering
heights across Alaska next weekend should help to moderate
temperatures a bit, especially for eastern areas. The exception to
all this warmth will be in the southeast quadrant and much of the
Panhandle temperatures should be near or below normal the entire
medium range period.
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