Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
647 PM EDT Sun Mar 29 2020
Valid 12Z Thu Apr 02 2020 - 12Z Mon Apr 06 2020
A relatively progressive weather pattern appears set to evolve
across Alaska and the North Pacific during the extended forecast
period. A strong upper-level jet along the northern periphery of a
building upper-level ridge axis near the date line and along the
southern periphery of a broad region of cyclonic flow across
eastern Siberia will result in an increasingly active storm track
across the Bering Sea. A leading frontal system should bring
precipitation and gusty winds to the Alaska Peninsula on Thu (day
4), while surface high pressure weakens and retreats across the
Interior. Deterministic solutions showed quite a bit of
variability and inconsistency throughout the extended forecast
period, making it difficult to prefer a single model solution for
the forecast across Alaska and surrounding waters. The ECMWF was a
bit of an outlier in terms of its intensity for a wave of low
pressure across the Bering Sea on Thu. With the next, much
stronger low pressure system expected to enter the Bering Sea
Fri-Sat, the GFS becomes an outlier in terms of track, which is
much farther south than almost all other guidance as well as
ensemble means. The one solution that seems to be somewhat
reasonable across the board is the 12Z UKMET, which was weaker
(like the GFS) with the leading Bering low, but then much closer
to the ECMWF and overall consensus with the track of the more
intense low pressure system in the Bering Fri-Sat. Thus, opted to
lean heavily on the UKMET early in the forecast period (days 4-5).
The Fri-Sat Bering Sea system is forecast to weaken as it
approaches western mainland Alaska on Sun. The system should
bring the potential for a round of precipitation to the Aleutians
and western mainland Alaska through next weekend, with the
potential for gusty winds near the coast. The overall pattern
looks to persist, with the potential for another significant low
pressure system to enter the Bering Sea late Sun into Mon.
Model/ensemble spread gets quite large by days 7-8 (Sun-Mon), with
the ECENS mean almost entirely out of phase with the GEFS/CMCE
means. The ECMWF/ECENS were substantially slower with this system
than other guidance. Given the fairly progressive pattern, and a
somewhat more consistent solution in the GEFS, opted to lean
heavily toward the GEFS (and to some degree the NAEFS) by late in
the forecast period. Given the large degree of spread, forecast
confidence by days 7-8 was well below average.
Ryan
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