Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
655 PM EDT Thu Jul 22 2021
Valid 12Z Mon Jul 26 2021 - 12Z Fri Jul 30 2021
...Guidance/Predictability Evaluation...
A stagnant cutoff low in the Gulf of Alaska to begin the period
next Monday, should gradually shift east and weaken as a weaker
low drifts south across the Aleutians into the North Pacific (or
possibly eastward into the Gulf) and upper level ridging builds
across mainland Alaska. By the middle of next week, models suggest
more pronounced upper troughing should develop over the Aleutians
and extending into the Aleutians. The latest guidance shows good
agreement on this pattern for days 4-5, but thereafter the pattern
becomes increasing uncertain. The 12z GFS is an outlier is
dragging the initial weak upper low over the Aleutians into the
Gulf, as well as later period rapid development of energy out of
the base of the Bering Sea trough into a deeper low again over the
Aleutians. The 00z/12z ECMWF runs are more consistent with the
means which is noticeably weaker with late period energy over the
Aleutians and the main core of the vortex remaining farther north
over eastern Siberia. As such, WPC relied on a rapidly increasing
blend towards the ECENS/GEFS by days 7-8 with smaller
contributions from the ECMWF for added system definition.
...Weather/Threats Highlights...
The main areas of precipitation and unsettled weather will be
focused across the western the northwestern mainland throughout
the period in the vicinity of a nearly stationary surface boundary
draped across the region. Waves and precipitation may increase
slightly mid week as stronger energy reaches the area, but still
rainfall amounts don't appear to be too significant or hazardous
at this time. Troughing extending into the Bering Sea and
Aleutians later in the week could lead to some higher waves and
more precipitation as well. Otherwise, generally below normal
temperatures are expected across the mainland for much of the
week, particularly in the far North, but values across the central
part of the state should gradually trend warmer underneath of
upper level ridging.
Santorelli
Hazards:
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 outlook 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