Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
314 PM EDT Mon Jun 04 2018

Valid 12Z Fri Jun 08 2018 - 12Z Tue Jun 12 2018

A persistent and anomalous upper ridge over Siberia (500 hPa
heights around +2.5 standard deviations) will favor lower heights
generally along 50N from the Aleutians into the Gulf of Alaska.
The flow along this corridor will be fairly progressive, with a
couple systems traversing near the Aleutians and toward the Gulf
of Alaska during the medium range. A weakening low pressure system
should be in place across the Gulf on Fri, with another passing
near/south of the Aleutians and the Alaska Peninsula Fri- Sun, and
yet another entering the picture across the Aleutians by next Tue.
Farther north, a relatively weak upper ridge axis is expected to
persist across mainland Alaska through much of the period. Models
have shown a relatively poor degree of run-to-run consistency,
especially with the system passing south of the Aleutians Fri-Sun.
The 00Z ECMWF seemed to be an outlier among the deterministic
guidance, taking the low north across the Aleutians into the
Bering Sea - a solution that was discarded based on the better
consensus on keeping the low farther south among the
GFS/CMC/UKMET. The latest 12Z run of the ECMWF has now shifted in
line with this farther south consensus. In general, a bit more
run-to-run consistency was noted in the GFS/GEFS throughout the
forecast period, and these solutions played a central role in the
forecast this cycle. A multi-model deterministic blend was used
for days 4-5 (Fri-Sat) including the 06Z GFS and 00Z UKMET/CMC,
along with the 06Z GEFS mean. For days 6-8 (Sun-Tue) weight was
shifted heavily toward the GEFS mean, with a minority component of
the deterministic GFS included through the period.

In terms of sensible weather, the Aleutians, southern mainland
Alaska, and Southeast Alaska will see occasional precipitation
through the period as systems pass to the south.

precipitation chances will initially be relatively high across
southern mainland Alaska and Southeast Alaska, ahead of the first
Gulf system. Rain chances will increase for the Aleutians Sat-Sun
as the system passes to the south. The interior will also see
daily scattered precip due to diurnal instability. Temperatures
will generally be near to above average.

Ryan


WPC medium range Alaskan products including 500mb, surface
fronts/pressures progs and sensible weather grids can be found at:

http://www.wpc.ncep.noaa.gov/alaska/ak_5dayfcst500_wbg.gif
www.wpc.ncep.noaa.gov/alaska/akmedr.shtml
http://www.wpc.ncep.noaa.gov/alaska/ak_5km_gridsbody.html