Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
640 PM EDT Sun May 09 2021
Valid 12Z Thu May 13 2021 - 12Z Mon May 17 2021
...Guidance/Predictability Assessment...
Latest 12 UTC GFS/ECMWF/Canadian model solutions seem reasonably
well clustered and consistent days 4-6 (Thu-Sat) and enjoy ample
ensemble support. A composite blend seems to produce a good
forecast starting point consistent with a pattern with above
normal predictability and maintains great WPC product continuity.
The ECMWF/Canadian and to a lesser extent ECMWF ensemble solutions
remain best clustered into day 7/8 and bring a much deeper low
into the Aleutians day 7/8 than the GFS. The GFS does not match
well with GEFS ensembles either at these longer time frames,
lowering forecast confidence. Used a composite blend of the 12 UTC
ECMWF/Canadian and ECMWF ensemble mean to show a reasonably deep
low as there seems to be an established/dynamic storm pattern out
from eastern Asia.
...Weather/Threats Highlights...
Upper trough energies and lead/complex precipitation focusing
surface lows/frontal weather systems will work across the Gulf of
Alaska to southern/southeastern Alaska into later this week,
undercutting a warming and stabilizing interior upper ridge.
Meanwhile upstream, amplified/closed upper trough energy is slated
to track over the southern Bering Sea/Aleutians and deepening low
pressure will support increasingly unsettled maritime conditions
and inland feeding enhanced rains and winds across the region.
Activity is expected to translate downstream into Southwest
Alaska, the Alaskan Peninsula, Kodiak Island, the Gulf of Alaska,
the southern interior and then southern and southeast Alaska
through next weekend with steady main system progression and lead
triple point low developments and inflow. A less certain second
main low with enhanced rains/winds may reach the Aleutians next
Sun/Mon.
Schichtel
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