Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
651 PM EDT Sun May 16 2021
Valid 12Z Thu May 20 2021 - 12Z Mon May 24 2021
...Overview...
Troughing near the Aleutians late this week will translate
eastward into the Gulf and weaken as ridging builds to its north
into the Interior. A new system will dig into the Bering Sea this
coming weekend into next week. This promotes an unsettled pattern
over the southern coastal areas with more scattered showers and
convection north of the Alaska Range. Temperatures will trend
warmer over interior areas as heights build.
...Guidance/Predictability Assessment...
The deterministic models appear to be slowly coming into better
agreement as the pattern becomes a bit more defined. However, the
12Z UKMET/Canadian diverged rather quickly from the consensus of
the 12Z GFS/ECMWF/GEFS mean/Canadian mean and 00Z ECMWF ensemble
mean. Though agreement was not tightly-clustered, that grouping
fared quite well into next weekend with the system just south of
the Aleutians Thu-Fri (ECMWF on the northern side) and the
incoming system(s) into the Bering next weekend (broadly
speaking). With upstream ridging forecast to build to +2 sigma in
the ECMWF ensemble mean over the Sakhalin Oblast next Sun/Mon, the
robust solutions of the ECMWF/GFS seems plausible. However, given
the inconsistent recent runs even in the ensembles, trended toward
a deterministic/ensemble split and then tilt toward an ensemble
consensus by the end of the period.
...Weather/Threats Highlights...
Weak troughing over the mainland will promote scattered showers
(snow over higher elevations) across the Interior/North Slope for
the first part of the forecast, with isolated convection as
temperatures aloft remain cool (850T near 0C to start). A defined
system around the Aleutians on Thursday will bring widespread
light to modest rain for the island chain as the occlusion skirts
eastward. Enough moisture could get drawn northward toward Kodiak
and the southern/coastal area of Southcentral to bring a couple
inches of rain to those areas with southern exposure. Temperatures
will be within several degrees of normal over much of the state,
warming into next weekend over the Interior to near 70F, but near
to below normal along coastal areas of the Gulf where clouds/rain
are more likely.
Fracasso
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