Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
350 PM EDT Sat Jun 01 2019
Valid 12Z Wed Jun 05 2019 - 12Z Sun Jun 09 2019
Over most areas north of 50N latitude the guidance shows a fairly
ill-defined pattern aloft with below average predictability for
specific details. Some common ideas prevail for most of the
period though, namely general ridging over the Bering Sea/Arctic
and a weakness (possibly containing one or more weak upper lows)
over the mainland. Corresponding surface features--Bering/Arctic
high pressure and mainland troughing--appear more agreeable than
details aloft. Some ridging aloft may try to build into the
mainland from the southeast by next Sat or Sun. A blend of
operational guidance early in the period (00Z ECMWF, 00Z GFS, 00Z
CMC, 06Z GFS in order of greater highest to lowest weight)
transitioning toward an even weight among models and means (06Z
GEFS/00Z ECMWF mean) by day 8 Sun provides a reasonable depiction
of agreeable features at the surface and aloft while downplaying
the lower confidence details.
The one defined system of interest during the period will be a
mid-latitude to northern Pacific system. In a broad sense there
is better than average model/ensemble clustering. However there
is still enough spread by the latter half of the period to provide
uncertainty over effects of the northern periphery of the system
(moisture and wind) on areas from the eastern Aleutians/Alaska
Peninsula to the Panhandle. Thus far ECMWF/ECMWF mean runs have
shown better stability versus the GFS/GEFS mean that have trended
somewhat northward toward the ECMWF cluster over the past 24-36
hours. Interestingly the new 12Z ECMWF has jumped a bit northward
while the 12Z GFS adjusted a little southeast. Stronger trends in
the means provide a more coherent signal that the system should
maintain its definition through the period. The starting point
described above with modest manual adjustment where appropriate
yields a good intermediate solution. This would bring potential
for some moisture and moderate wind enhancement to reach areas
from the Alaska Peninsula through the Gulf of Alaska next weekend.
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
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