Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
316 PM EDT Mon Mar 25 2019
Valid 12Z Fri Mar 29 2019 - 12Z Tue Apr 02 2019
Especially by way of ECMWF/ECMWF mean forecasts adjusting away
from some suspect solutions over the past couple days, model and
ensemble clustering has dramatically improved for the strong
ridge/upper high (behind a shortwave that crosses the mainland on
Fri) expected to build over the mainland during the weekend and
persist into early next week. The favorable guidance
agreement--minus the 00Z CMC that positions the ridge west of
consensus--now permits including more operational model input
through the period. Among the ensemble means the 00Z GEFS shows a
stronger ridge than the 06Z run so preference goes to the former
for GEFS input. The 00Z ECMWF mean brings the upper high a little
southeast of other means by late in the period but is still close
enough to other guidance to merit inclusion as part of a blend.
Teleconnections relative to the upper ridge's positive height
anomaly center, over southern or western mainland depending on the
day, maintain support for a fairly suppressed upper weakness to
the south. This is consistent with improving guidance consensus
toward dry conditions over the Gulf of Alaska region.
Corresponding to the upper ridge, expect strong surface high
pressure to prevail over much of the mainland and extending into
northwestern Canada. Flow around the high may bring a front into
the Panhandle during the weekend.
Details look more chaotic across the North Pacific, Aleutians, and
Bering Sea. Most guidance shows an initial regime of strong flow
around an upper low near Kamchatka pushing a series of
waves/fronts from the western Pacific into the western Bering Sea.
Then there should be a gradual elongation of upper troughing over
the North Pacific along with one or more surface lows tracking
south of the Aleutians. Through this entire evolution individual
model runs and ensemble members show poor clustering for
specifics, favoring a blended approach to reflect the more
agreeable large scale evolution and some periodic embedded
features. By day 8 Tue the ensemble means generally suggest that
strongest low pressure over the North Pacific should track close
to the western Aleutians.
Today's forecast started with a blend of the 00/12Z GFS and 00Z
ECMWF plus a little 00Z UKMET early in the period followed by a
model/mean blend consisting of the aforementioned GFS/ECMWF runs
and 40-50 percent total 00Z GEFS/ECMWF means.
Rausch
Bullet points from the WPC Days 3-7 Hazards chart can be found at:
https://www.wpc.ncep.noaa.gov/threats/threats.php
-No significant hazards for Alaska posted.
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