Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
247 PM EST Sun Nov 10 2019
Valid 12Z Thu Nov 14 2019 - 12Z Mon Nov 18 2019
Models show reasonably good consensus on a deep but gradually
weakening low pressure system passing south of Kodiak Island and
moving into the Gulf of Alaska Thu-Fri. The ECMWF and CMC
solutions were best clustered with the current model/ensemble
consensus (and the forecast for days 4-5 was based heavily on
these solutions), while the GFS was a bit southeast of consensus
with the low (especially on Thu). Otherwise, the flow pattern
across Alaska through the remainder of the extended period will be
a chaotic one, with a train of shortwave energy traversing the
westerlies across the North Pacific, and additional Arctic
shortwave energy diving southwestward across mainland Alaska -
with the potential for interactions between the Pacific/Arctic
waves. The GFS is the most aggressive solution with one of these
potential interactions, developing a deep upper low and associated
surface low across the eastern Bering Sea Thu-Fri, a solution
which seems too strong based on the consensus of model/ensemble
data. Model run-to-run variability is relatively high (and thus
predictability is relatively low) during days 6-8 (Sat-Mon). Thus,
trended quickly toward the ECENS/NAEFS ensemble means by later in
the forecast period. There was some consensus evident among the
ensembles that another low pressure system should enter the Gulf
and approach mainland and southeast Alaska Sat-Sun, with another
quickly following in its heels by Sun night, and yet another
approaching the Alaska Peninsula by Mon. Confidence in the
specific details and timing of these systems decreases quickly
through time.
Ryan
Additional 3-7 Day Hazard information can be found on the WPC
medium range hazards 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