Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
311 PM EDT Wed May 30 2018

Valid 12Z Sun Jun 03 2018 - 12Z Thu Jun 07 2018

Upper flow continues to look quite blocked across Alaska (and much
of the northern hemisphere) through the medium range. An upper
ridge is expected to persist across eastern Asia into next week,
and downstream of the ridge, negative height anomalies are
expected to persist (in the form of an upper low) across the
Bering Sea and the Aleutians, perhaps working east into the Gulf
of Alaska by the middle of next week. Meanwhile, upper ridging
will initially be dominant from eastern Alaska/northwestern Canada
north to the Arctic Ocean. Models/ensembles show some degree of
weakening of this feature during the forecast period, although it
remains a bit unclear to what degree this will occur.

Models/ensembles initially showed decent consensus Sun-Mon, with a
deep upper low and associated surface cyclone in place across the
Bering Sea. The 00Z ECMWF and CMC solutions seemed most tightly
clustered within consensus and a blend of these solutions served
as a starting point for the forecast during days 4-5. From Wed
(day 6) onward is when model solutions begin to show some more
significant differences. The ECMWF has been the most consistent in
keeping the Bering upper low a bit more consolidated as it drifts
southeastward across the Aleutians. Previous runs of the GFS and
CMC showed the feature becoming more elongated roughly along a
northwest-southeast axis, but the 12Z runs of these models both
trended toward the ECMWF in this area. Farther north, models have
shown significant variability with potential shortwave energy
originating in the Arctic later in the forecast period. The 00Z
ECMWF showed a vigorous shortwave diving southeastward across the
Arctic Ocean toward northern Alaska by next Tue-Thu, even cutting
the system off into an upper low (this was a sharp change from the
previous run which held the upper ridge in much stronger, allowing
southeasterly upper flow with shortwave energy propagating through
it. The latest (12Z) run of the ECMWF seems to have backed off the
00Z solution and is now back to resembling the run from 12Z
yesterday. Given the significant variability over the Arctic, and
with the upper ridge, the forecast during days 6-7 was much more
ensemble based, with most weight placed toward the 00Z ECENS/NAEFS
ensemble means.

In terms of sensible weather, the medium range will initially be
unsettled with frequent showers and gusty conditions across the
Aleutians. Higher probabilities for precipitation should gradually
migrate eastward as the upper low moves southeast, with the Alaska
Peninsula and southern mainland Alaska seeing potential for more
widespread precipitation from Tue onward.

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