Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
556 PM EST Wed Dec 25 2019
Valid 12Z Sun Dec 29 2019 - 12Z Thu Jan 02 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, with the trough axis
nearing 150W and ridging moving into the Bering. The
models/ensembles showed good agreement overall with the synoptic
pattern but still differed on system timing/track/strength.
Overall the 12Z GFS seemed to depart most from the otherwise
reasonable consensus of the 12Z ECMWF/UKMET/Canadian with the lead
system Sun-Tue. Did not favor taking any surface low across the
AKPEN into Bristol Bay though there remain about a dozen or more
ensemble members that do just that. However, trend in the guidance
was to bring the surface low NNE into/through Cook Inlet rather
than linger it just off the Kenai peninsula or south of Prince
William Sound. This could bring in significant precipitation to
coastal areas with southerly to southeasterly exposure.
Reinforcing cold front may bring in another round of colder air as
the upper trough axis moves eastward next Tue-Thu. Trended toward
nearly all ensemble means by next Wed/Thu as the ECMWF/Canadian
drifted well apart with the next system south of the Gulf --
either advancing it northeastward or stalling it in place. Either
way, it appears it may stay south of the Panhandle underneath the
weakening northern feature.
Cold air will moderate slightly early next week but remain below
average. This may be short-lived if the second surge spread
eastward next Tue-Thu. Rainfall (and snowfall) will be quite heavy
across parts of Southcentral to the Panhandle given the storm
track of the lead system, with associated high winds possible.
Future shifts in the track will determine the details of the
forecast.
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, Sat-Tue, Dec 28-Dec 31.
- High winds across portions of mainland Alaska, Mon-Tue, Dec
30-Dec 31.
- Much below normal temperatures across portions of mainland
Alaska, Sat-Sun, Dec 28-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