Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
203 PM EST Wed Feb 20 2019

Valid 12Z Sun Feb 24 2019 - 12Z Thu Feb 28 2019

Highly amplified flow pattern expected across Alaska during the
extended period, with upper-level ridging from the Gulf north
across Alaska, and a mean trough across the Bering Sea. Confidence
in this general pattern is above average as models/ensembles show
very good consensus at the large scale. During the day 4-6 time
frame (Sun-Tue) models showed reasonably good consensus with
respect to a couple low pressure systems affecting the Bering Sea
and Aleutians. Thus, made fairly heavy use of deterministic
solutions in the forecast, the GFS and ECMWF in particular, for
that time period. Additional detail differences emerge after Tue,
both respect to additional low pressure systems traversing the
mean trough, as well as the exact strength/evolution of the upper
ridge. Models have generally trended toward a stronger/closed
upper ridge migrating north from the Gulf into the interior by
early next week. The one exception/outlier is the GEM global,
which continues to weaken/break down the ridge by the middle of
next week, allowing stronger westerly mid/upper-level flow across
mainland Alaska. Given strong ensemble support, continue to favor
a stronger and more persistent ridge as shown by the GFS/ECMWF.
This would keep the mean storm track across the Aleutians/Bering
Sea, with some potential affects in terms of precip/gusty winds
across the Alaska Peninsula and western mainland Alaska. Given
increasing differences among deterministic solutions from the
North Pacific to the Bering Sea by the middle of next week, went
with majority ECENS/GEFS ensemble mean weighting in the forecast
by days 7-8.

With 500 hPa height anomalies reaching at least +2 to +3 standard
deviations across Alaska and northwestern Canada by early next
week, highly anomalous temperatures are also likely. The greatest
temperature anomalies will occur across the North Slope, where
temperatures exceeding 40 deg F above average are possible by this
weekend into early next week. High temperatures in Utqiagvik may
even approach the freezing mark.


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