Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
618 PM EDT Sat May 23 2020
Valid 12Z Wed May 27 2020 - 12Z Sun May 31 2020
...Guidance/Predictability Assessment...
Forecast predictability over Alaska remains above average due to a
relatively stable and blocky flow regime, but there has been more
uncertainty with offshore lows. A composite of well clustered
guidance from the 12 UTC GFS/ECMWF and GEFS/ECMWF ensemble means
now seems reasonable Wednesday into Thursday. However, forecast
spread quickly increases from that point forward offshore. The WPC
Alaskan medium range product suite was mainly derived from a blend
of best clustered guidance of the 12 UTC ECMWF and GEFS/ECMWF
ensemble means along with the 19 UTC National Blend of Models.
...Overview and Weather Hazards/Threats...
An amplified upper-level ridge is forecast to persist from the
Arctic Ocean across eastern Alaska and into northwest Canada. This
will result in above average temperatures with anomalies upwards
to +20 deg F over northern Alaska. This will enhance snow/ice
melt, so please refer to your local office for any seasonal river
ice flow issues.
A system well south of the state over the eastern Pacific
mid-latitudes should organize early next week. This system has
been difficult to track in guidance. However, latest models and
ensembles now agree to lift a deepened low northward into the
eastern Gulf of Alaska Wednesday/Thursday. Maritime wind/rain
impacts may also affect Southeast Alaska. The system should weaken
and meander over the northern Gulf of Alaska Friday into next
weekend, blocked underneath the upper ridge.
Meanwhile, an upper low and surface system will continue to weaken
while lifting northward on the western periphery of the upper
ridge from the Bering Sea midweek to the Arctic Ocean by Thursday.
This system offers some lingering winds and precipitation. Another
low in the wake of this system Wednesday-Friday is expected to
hold over the southwest Bering Sea where it should dissipate.
There is also an increasing guidance signal in support of
subsequent development of a deeper Pacific low that is slated to
work along with wrapping winds/rains toward the Aleutians into
next weekend that would also present an organized maritime hazard.
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