Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
314 PM EDT Wed Oct 16 2019
Valid 12Z Sun Oct 20 2019 - 12Z Thu Oct 24 2019
Model/ensemble guidance has similar ideas for the overall large
scale evolution during the period but there are significant
uncertainties with multiple embedded features. Consensus shows a
mean trough aloft (likely with an embedded low) over the Bering
Sea for most of the period while progressive flow prevails across
the North Pacific. From the start of the period early Sun the
operational models and individual ensemble members vary on the
location/strength of individual surface lows over the Bering and
especially the northeastern Pacific/Gulf of Alaska. There are
also divergent solutions for how a western Pacific wave may
interact with the northern stream dynamics--with the ensemble
means fairly agreeably consolidating low pressure near the Alaska
Peninsula-Kodiak Island around the middle of next week. Solutions
trend out of phase for upstream flow late in the period but there
are hints of a weak wave/frontal system that could reach the
Aleutians. At higher latitudes, evolution of an Arctic ridge
aloft should allow an upper low to approach the northeastern
corner of the mainland but with a fair amount of spread for
precise upper low position.
Overall the 06Z GEFS/00Z ECMWF means--with some operational input
and manual adjustment where the means could be enhanced--provided
the best initial starting point for today's forecast given the
diverse array of guidance and in a number of cases poor model
continuity. In particular this solution provided a good middle
ground for the potentially strong storm near the Alaska
Peninsula/Kodiak Island around midweek, with the 00Z ECMWF weak
and to the east versus the 12Z/15 run that was deep/westward like
the latest CMC runs. The new 12Z ECMWF has returned to a slower
version of yesterday's 12Z run. The 00-06Z GFS runs were closest
in principle to the ensemble mean scenario while the 12Z GFS
trended slower/southward. The means also offered an intermediate
path for the upper low that approaches the northeastern mainland,
between the 00Z ECMWF that was westward and latest GFS runs that
define the eastern side of the envelope. With uncertainty in the
specifics, the general pattern should favor highest precipitation
totals across the extreme southern mainland and Panhandle with
some potential for significant totals to extend somewhat westward
if the western side of the envelope verifies for the expected
midweek storm. Strong winds will also be a possibility based on
potential depth of the surface low.
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
Alaska Hazards...
- Heavy precipitation across portions of the Alaska Panhandle and
mainland Alaska, Tue-Wed, Oct 22-Oct 23.
- High winds across portions of mainland Alaska, Wed, Oct 23.
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