Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
327 PM EDT Mon Apr 15 2019
Valid 12Z Fri Apr 19 2019 - 12Z Tue Apr 23 2019
Models/ensembles show broad consensus that upper ridging should
persist/expand across eastern Russia and the western Bering Sea
during the extended forecast period. A strong jet across the north
Pacific will undercut the ridge with a stream of shortwave energy
feeding into and reinforcing a mean upper-level trough extending
from mainland Alaska south into the Gulf of Alaska. Shortwave
energy spilling over the crest of the ridge will also move south
across the eastern Bering Sea throughout the period, interacting
with the mean trough as well as energy from the north Pacific,
introducing an additional degree of complexity/chaos to the
forecast and reducing predictability by the latter portion of the
forecast period.
Consensus has improved surrounding a low pressure system expected
to move north across the Gulf of Alaska on Sat. The ECMWF and GFS
solutions both lied within a fairly well-clustered consensus of
ensemble members through Sat. After this time spread begins to
increase gradually as arctic shortwave energy dives south and
enters the mean trough, reinforcing a deep upper low across the
Gulf. While models handle this evolution differently, they all
show a similar result with a highly occluded low remaining in the
Gulf as the front sweeps inland and weakens. The low should
persist in the Gulf in some form into early next week, with even
some degree of ensemble clustering evident around this feature
through day 8 (Tue), although the specific position of the feature
remains unclear, with members ranging from just of the Alaska
Peninsula to the eastern Gulf just off the Alaska Panhandle. Given
these considerations, the forecast was initially based heavily on
a blend of the ECMWF/GFS during days 4-5 (Fri-Sat), with a gradual
trend toward heavier weighting of ensemble means (ECENS and GEFS)
from day 6 (Sun) onward.
Ryan
Bullet points from the WPC Days 3-7 Hazards chart can be found at:
https://www.wpc.ncep.noaa.gov/threats/threats.php
- Heavy rain across portions of the Alaska Panhandle, Thu-Fri, Apr
18-Apr 19.
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