Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
321 PM EDT Sun Jun 02 2019
Valid 12Z Thu Jun 06 2019 - 12Z Mon Jun 10 2019
Guidance continues to show persistent surface high pressure over a
majority of the Bering Sea as well as portions of the Arctic (one
center northeast of the mainland late in the week and early
weekend possibly followed by one or more centers building north of
the mainland by next Sun-Mon) associated with general ridging
aloft, while surface troughing remains over the mainland. Exact
details aloft are still somewhat ambiguous though. One trend of
note is for the mean ridge aloft over the Bering to extend its
influence farther eastward into the mainland compared to
yesterday's consensus. There is also a fair degree of uncertainty
over an upper low north of Siberia. Most guidance keeps it well
away from the mainland but the past couple ECMWF runs bring it
farther southeastward.
Across the Pacific there is still decent clustering among most
models and ensemble means for a leading system to drift closer to
the Alaska Peninsula and Kodiak Island late in the period with a
leading ridge aloft building over the Panhandle/western Canada
into the mainland. The situation farther westward is much more
chaotic with a wide spread of model/ensemble solutions for one or
more lows whose influence could extend as far northward as the
Aleutians--or remain well suppressed.
Today's guidance preference maintains the approach of starting
with an operational model blend early in the period and then
transitioning to a model/ensemble mean blend (60 percent means by
day 8 Mon). Latest consensus shows higher heights aloft over the
mainland versus yesterday early-mid period and yields a slight
northward adjustment for the Pacific system. By next weekend this
system should bring some enhanced winds/precipitation to areas
from the Alaska Peninsula and Kodiak Island eastward through the
Gulf of Alaska with moisture also reaching the Panhandle.
As for specific considerations by area/system: The forecast
reduces 00Z ECMWF weight after day 4 Thu as its upper low north of
Siberia strays farther southeast than most other guidance. The
new 12Z ECMWF still shows this southeast scenario though.
Ensembles as a whole are all over the place with the low, leaving
the ECMWF within the full spread, but that model is far enough
from the majority to favor downplaying its forecast until
supported by other guidance. For the primary Pacific low of
interest, the 12Z GFS is favorably slower than the 06Z run and
northward of the questionably suppressed 00Z run so the new run
provides the GFS input (along with the 06Z FV3 for about the first
half of the period). Spread over the western Pacific favors a
conservative blend/ensemble mean approach. By day 8 Mon an
overwhelming majority of ensembles favor a more suppressed pattern
than depicted by the 00Z ECMWF that tracks strong low pressure
close to the western Aleutians. The ensemble component of the
forecast leans more to the 00Z ECMWF mean relative to the 06Z GEFS
as the former has better definition across most of the North
Pacific.
Rausch
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