Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
322 PM EDT Thu May 30 2019
Valid 12Z Mon Jun 03 2019 - 12Z Fri Jun 07 2019
Flow over the high latitudes will feature a blocking pattern with
slowly moving features.
The majority of models have kept yet another upper low north of
Wrangel Island and retrograde the circulation west with time. The
model differences appear starting Monday with The 12z GFS and 00z
ECMWF showing much different behaviors. The differences fro the
06-12z GFS, GFS FV3, and 06-12z GEFS Mean in the trough
phasing/location/intensity underlie a low confidence forecast.
A blended solution giving more weight to the GFS/GEFS Mean was
used, with more weighting on the mean days 7-8.
The 00z ECMWF was most aggressive in moving height rises south
from the Arctic Ocean, in turn shunting the upper trough south
from northern to southern AK next week. The 00z ECMWF Ensemble
mean n was much slower to increase heights over northwest AK,
allowing the trough to move more slowly south like the GEFS Mean
and various GFS runs. The blended approach washed out the lower
heights aloft in the 12z run of the GFS, which was deeper than
each of the other models and broke continuity.
On next Tue 04 Jun the models mostly show a new cyclone developing
in the northern central Pacific to the southwest of the lower
Aleutians. There are latitude differences with the 06z GFS north
of the low positions/track vs the further south 00z ECMWF/ECMWF
Ensemble Mean/Canadian. The 12z GFS trended south, increasing
clustering of solutions. There is above average agreement on the
development of a low.
Given the typical fast GFS bias in moving closed lows too quickly,
greater weighting to the 06z GEFS/00z ECMWF Ensemble means should
bias correct the forecast.
Mon 03 Jun an upper low is forecast to be south of the central
Aleutians. The 00Z-06z suite of guidance (ECMWF/Canadian)
clustered fairly well together and close to the ensemble means
(00Z ECMWF ensemble mean and 06z GEFS Mean/00z Canadian mean) in
moving the low east, possibly reaching the coast of southwest
Canada 06 Jun. The consensus of these solutions stayed close to
the prior forecast/ continuity, so the consensus was used.
Early next week, Temperatures will average above normal in
northern AK, and cool in southern coastal areas. As the week
progresses, inland areas trend cooler if an upper trough develops.
The most likely area to stay above normal would be the Aleutian
Islands. Rainfall will generally be light but locally moderate in
favored areas in windward terrain, focused on the southern half of
mainland AK next Wed/Thu.
Petersen
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
No significant hazards are expected over Alaska during this
forecast period.
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