Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
338 PM EDT Tue Apr 09 2019
Valid 12Z Sat Apr 13 2019 - 12Z Wed Apr 17 2019
The ensemble means are fairly similar and consistent with the
general idea of low pressure tracking along the Aleutians during
the weekend and then settling into a position southeast or east of
Kodiak Island as mean troughing aloft becomes established near
150-160W longitude. Some ensemble mean runs have differed in
precise details of individual features making up the overall
trough. Not surprisingly individual model runs differ more
greatly with North Pacific details, between faster progression of
one or more features (as in 00-06Z GFS runs) or phasing that leads
to at least temporary slower motion (12Z GFS). Based on guidance
available through the 06Z cycle plus the 12Z GFS, the 00Z ECMWF
and 06Z FV3 GFS compare most favorably to the ensemble means so
preferences sided with those runs for emphasizing operational
model detail especially early in the period.
Arctic/Mainland details are of fairly small scale and not
consistent over recent runs, so confidence in this part of the
forecast is in the lower half of the spectrum. Currently there is
a a decent consensus showing a ridge over the Arctic and a more
modest cluster with a compact upper low over the northwest corner
of the mainland (part of an overall weakness aloft over the
mainland), with each feature lingering through the weekend into
early next week. Model behavior so far suggests that further
detail changes are likely in future runs.
Late in the period the 00Z CMC and recent GFS runs runs show a
stronger signal compared to the means for energy to round the
upper ridge over the Bering and then amplify into the 150-160W
mean trough. Lack of confidence in details at the late extended
time frame would argue for a conservative forecast closer to the
means for the time being.
Based on above considerations today's forecast started with a
blend of the 00Z ECMWF/ECMWF mean and 06Z FV3 GFS/GEFS mean. The
early part of the forecast placed greater emphasis on the
operational runs and the latter part focused more on the means,
with subsequent editing as appropriate.
Rausch
Bullet points from the WPC Days 3-7 Hazards chart can be found 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