Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
747 PM EDT Sat Jun 08 2024
Valid 12Z Wed Jun 12 2024 - 12Z Sun Jun 16 2024
...Overview...
Guidance shows a fairly blocky pattern during the period. A
strong upper ridge over the Arctic as of early Wednesday should
settle over the mainland thereafter, likely persisting into the
weekend. This ridge may merge with the northern part of a
separate North Pacific into Bering Sea ridge, while a North
Pacific or Aleutians upper system and surface reflection (composed
of an initial feature and incoming dynamics from the west) should
evolve to the south of the mean ridge. Meanwhile, expect an upper
low well south of Kodiak Island early Wednesday to track steadily
eastward with time and far enough south to have minimal effect on
the Panhandle in terms of precipitation.
...Guidance Evaluation and Preferences...
Looking at some general trends from the past couple days for the
upper ridge settling over the mainland, the GEFS/ECens means have
become a little stronger with the ECens mean tending to be
somewhat ahead of the GEFS with the stronger trend. The
GEFS/ECens/CMCens means agree in principle toward merging the
mainland ridge with a strengthening ridge that initially extends
into the Bering Sea to yield a fairly broad area of upper ridging
by next weekend. However the dynamical models and 00Z
ECMWF-initialized machine learning (ML) models develop some
significant differences for how much ridging may develop over the
Bering Sea, with corresponding effects on the latitude of low
pressure to the south. Into Thursday-Friday, the 12Z GFS/CMC
bring the North Pacific system into the Aleutians due to less
ridging to the north while the ECMWF/UKMET are very suppressed due
to stronger/broader Bering Sea ridging aloft. The ensemble means
suggest a compromise idea while most of the ML models suggest the
system could get a little closer to the Aleutians, allowing for
some GFS/CMC inclusion as part of a blend. By next weekend the
12Z GFS in particular becomes more disagreeable in bringing its
upper low into the Bering Sea (leading to a band of southerly flow
between the low and upper ridge) versus ridging in the majority
cluster (and more low level easterly flow over the Aleutians). At
least the 12Z GFS does not have the suspiciously strong/wet system
tracking into the Aleutians on day 8 Sunday that the 06Z/00Z runs
depicted. Farther east, the ML models and ensemble means form a
majority cluster that is somewhat slower than the 12Z ECMWF/CMC
for the upper low tracking eastward across the Northeast Pacific.
Based on the full array of guidance, today's forecast started with
a blend of 30 percent each 12Z GFS/ECMWF and 20 percent each 12Z
UKMET/CMC during the first half of the period. Then the blend
steadily increased 12Z GEFS/00Z ECens input to reach half total by
day 8 Sunday, while eventually phasing out the GFS. The new 18Z
GFS has adjusted toward much more Bering Sea upper ridging than
past GFS runs, adding more support to the established majority
scenario.
...Weather/Hazards Highlights...
There may be localized enhancement of precipitation in the
southern part of the state as of midweek, followed by a lighter
trend as upper ridging settles over the mainland. Some scattered
and light activity may be possible at times farther north. With a
fair degree of uncertainty over specifics, the Aleutians may see a
trend toward easterly winds along with some light rainfall.
Clouds/precipitation will tend to keep highs below normal over the
south at the start of the period Wednesday, while the upper ridge
will likely promote a warmer trend to above normal levels over the
Interior later in the week through the weekend. The North Slope,
Panhandle, and pockets of Southcentral may remain below normal for
highs through the period. There should generally be greater
coverage of above normal lows, with most exceptions tending to be
over the aforementioned areas.
Rausch
Additional 3-7 Day Hazard Information can be found on the WPC
medium range hazards outlook 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