Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
639 PM EST Thu Jan 16 2020
Valid 12Z Mon Jan 20 2020 - 12Z Fri Jan 24 2020
The large scale pattern across Alaska during the extended forecast
period is forecast to be strikingly different than that seen
during the short range. A mean trough/upper low is forecast to
develop/persist across the Arctic Ocean north of Alaska and
Siberia through the extended forecast period, with an active storm
track across the North Pacific, generally south of the Aleutians,
and into the Gulf of Alaska, and upper ridging shifting eastward
into west central Canada.
Throughout much of the extended forecast period, the 12Z GFS
seemed to be the piece of deterministic guidance most
well-centered within the spread of ensemble members. The first
such system is forecast to be moving north across the Gulf of
Alaska on Mon, with another deeper system passing south of the
Aleutians Mon into Tue. For the latter of the two, the ECMWF was
quite a bit slower even when compared to the ECENS mean (which was
closer to the GFS). This system is forecast to move into the Gulf
of Alaska on Wed, with yet another low following a similar track
in its wake, passing south of the Aleutians on Wed. Guidance
generally agrees on a somewhat slower progression for this system
as it deepens and becomes more wrapped up. As with the prior
systems the GFS was reasonably close to the ensemble means.
Farther north, a stream of relatively weak upper-level shortwaves
are forecast to progress across the Interior and the North Slope
as energy traverses around the Arctic trough/upper low. Models
showed some inconsistencies with these features among each other
as well as run to run, but the GFS was reasonably representative
of the ensemble consensus here as well.
Based on the described factors, the WPC forecast was based heavily
on the 12Z GFS, with increasing weight placed on GEFS/ECENS
ensemble means going farther out in time. The general agreement of
the GFS with the ensemble means allowed for its used to add detail
to features/systems through the end of the forecast period.
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
- Heavy precipitation across portions of the Alaska Panhandle,
Sun-Tue, Jan 19-Jan 21.
- Much below normal temperatures across portions of mainland
Alaska, Sun-Mon, Jan 19-Jan 20.
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