Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
633 PM EST Wed Nov 10 2021
Valid 12Z Sun Nov 14 2021 - 12Z Thu Nov 18 2021
...Overview and Guidance Evaluation/Preferences...
Early next week, model guidance agrees that the pattern over
Alaska will be characterized by slow-moving troughing aloft
extending over the central/eastern mainland and into the
northeastern Pacific (including an initial closed upper low Sunday
in the Gulf of Alaska), while upper ridging moves in behind. At
the surface, low pressure over the Gulf of Alaska and a low
tracking through the northeastern Pacific are forecast to
consolidate Sunday into Monday, while a surface high is forecast
to persist over the central/northern part of the mainland. Farther
upstream, negatively tilted troughing and surface low pressure
will move across the Bering Sea Monday-Tuesday. These features
appear to be coming into somewhat better agreement in model
guidance compared to previous cycles, though some track and timing
differences remain, along with differences in whether or not
energy splits to create two shortwaves/surface lows--GFS runs have
a split by Tuesday while ECMWF runs do not. Then, there remain
questions as to how that Bering Sea troughing merges with another
trough stemming from a deep upper low northeast of the state
around Wednesday, though regardless this should maintain the
surface low in the Gulf of Alaska. Uncertainty also abounds with
the possibility of additional energy coming from upstream
(Kamchatka) and track of a surface low associated with it.
Overall for the early part of the period, was able to use a
multi-model blend of the 12Z deterministic guidance (ECMWF, GFS,
CMC, and UKMET), though phased out the UKMET quickly as it seemed
to get out of phase by next Monday-Tuesday. This maintained a
stronger low across the Bering Sea and differences between models
were phased out somewhat. With the increasing uncertainty by the
latter part of the period, gradually phased in the GEFS and EC
ensemble means and ended with 60% means/40% deterministic models
for the blend by next Thursday/day 8.
...Weather/Hazard Highlights...
Generally dry conditions are likely for most of the mainland
through next week, other than a few possible snow showers. Some
light to moderate precipitation is possible for the Panhandle for
the early part of the week, with the best precipitation chances
over southern parts of the Panhandle with the surface low in the
northeastern Pacific. Then as a front tracks across the Aleutians
with the Bering Sea surface low, precipitation and gusty winds
could spread eastward Sunday into Tuesday. Precipitation could be
enhanced by next Wednesday-Thursday for the southeastern mainland
into the Panhandle, but model guidance varies with forecast
amounts at this point.
Below normal temperatures will be most pronounced in terms of
anomalies over the southwestern mainland, and the cold
temperatures (especially in terms of highs) should spread eastward
into the central/eastern mainland and the Panhandle by
Monday/Tuesday and persist through the week. Meanwhile, the North
Slope should see above normal readings (especially for lows)
through the forecast period.
Tate
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