Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
553 PM EST Thu Dec 26 2019
Valid 12Z Mon Dec 30 2019 - 12Z Fri Jan 03 2020
Upper troughing will dominate the southern portion of mainland
Alaska next week in between ridging over eastern Russia and off
the coast of Washington/British Columbia. The pattern will slowly
move eastward by the end of the period as heights relax a bit. The
models/ensembles showed good agreement overall with the synoptic
pattern but still differed on system timing/track/strength with
less than desirable run-to-run continuity.
Once again, the 12Z GFS did not cluster well with the 12Z
ECMWF/Canadian/UKMET with the lead system into Southwestern
Alaska. However, the 12Z GFS run from 12/25 (which was more or
less on its own then) was closer to today's consensus. With the
latest guidance, it has become more of a timing issue rather than
track issue, with the GFS being about 24 hrs slower than the rest.
Opted again to rely on the larger cluster of solutions including
the ECMWF ensemble mean. Thereafter, by Wed 1/1, the GFS developed
a sfc wave on a front south of 45N and moved it into the Gulf. The
ECMWF/Canadian (and UKMET through 144hrs) did not, similar to
continuity. Preferred to withhold this system for now. By next
Thu/Fri, system should push through the Aleutians from the west as
perhaps another shot of colder air circulates around the weakening
upper low over Southwest Alaska or Southcentral.
Cold air will moderate slightly early next week from a cold
weekend but remain below average. This may be reinforced later
next week. Rainfall (and snowfall) will be quite heavy across
parts of coastal Southcentral (southeastern Kenai to Prince
William Sound) eastward to the Panhandle given the storm track of
the lead system, with associated high winds possible.
Precipitation should decrease with time with weaker systems
through the area, assuming the Gulf system around Wednesday does
not materialize.
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
Hazards:
- Heavy precipitation across portions of the Alaska Panhandle and
mainland Alaska, Sun-Tue, Dec 29-Dec 31 and Wed-Thu, Jan 1-Jan 2.
- High winds across portions of mainland Alaska, Mon-Tue, Dec
30-Dec 31.
- Much below normal temperatures across portions of mainland
Alaska, Sun, Dec 29.
- High significant wave heights for coastal portions of the Alaska
Panhandle and mainland Alaska, Tue-Wed, Dec 31-Jan 1.
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