Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
354 PM EDT Mon Jun 03 2019
Valid 12Z Fri Jun 07 2019 - 12Z Tue Jun 11 2019
The forecast once again follows the general strategy of depicting
an operational model blend early in the period (day 4 Fri into day
5 Sat) and then fairly quickly adjusts toward an even
model/ensemble mean weight mid-late period (through day 8 Tue) as
specifics become increasingly uncertain. The 06Z GFS/FV3 GFS and
00Z ECMWF/CMC/UKMET provides operational input while the ensemble
component consists of the 06Z GEFS/00Z ECMWF means.
One notable adjustment/clustering in the guidance relative to
yesterday is for the upper low initially north of Siberia.
Models/ensembles have been wildly divergent with the ultimate
track of this feature but the 00-06Z model/mean solutions are much
closer together today, showing northeastward progression and a
better defined leading surface front reaching the North Slope
region. The general idea of high pressure progressing eastward
across the Arctic during the weekend/early next week has better
continuity. The 12Z GFS has reverted to a farther westward path
for the upper low so confidence is still not particularly great.
Farther south the specifics continue to be ambiguous but
consensus/continuity show mean ridging aloft over the Bering Sea
and parts of the mainland. At the surface Bering Sea high
pressure and mainland low pressure/troughing prevail through the
period with fairly low sensitivity to exact details aloft.
Into about day 6 Sun the leading system drifting northeastward
from the mid-latitude Pacific has been reasonably well forecast in
principle but with typical differences in track/speed, favoring a
consensus approach. Today's guidance average is a bit slower than
24 hours ago. Ahead of this system expect an upper ridge to build
into the northeastern Pacific and then the Panhandle/western
Canada into the mainland. This general scenario has had fairly
good continuity over recent days.
Farther west individual models/ensemble members diverge
significantly for track and timing of individual systems. These
issues begin to affect the northeastern Pacific by days 7-8
Mon-Tue, such as determining whether the initial system will
persist through late period or dissipate in favor of one or more
trailing waves. Although the blend includes minority weight of
the 00Z ECMWF/CMC, preference reflects the ensemble means that
keep best-defined (though still fairly weak) low pressure westward
of the separate eastern waves depicted in those model runs by day
8 Tue.
Over and south of the western-central Aleutians the primary
observation is that the recent trend of ensemble members has been
to trim away the northern part of the spread for low
pressure/frontal systems. This would seem to provide less
confidence in some recent ECMWF runs that have tended to bring low
pressure and/or surface fronts at least as far north as the
Aleutians by the latter part of the forecast period.
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
- 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