Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
631 PM EST Sat Dec 19 2020
Valid 12Z Wed Dec 23 2020 - 12Z Sun Dec 27 2020
...Guidance and Uncertainty Assessment...
Model ensemble guidance today shows very good agreement on the
overall synoptic evolution relevant to Alaska for the medium range
period. A cyclone that is forecast to impact southwestern and
southern Alaska with high winds and heavy precipitation near the
coast should begin to weaken by next Wednesday. Remnant upper
troughing will then extend southeastward into late next week
across the Gulf of Alaska, as upper ridging over western Canada
gradually shifts eastward. There are decent model signals that a
couple of weaker cyclones will edge closer towards the Alaska
Panhandle during the Christmas holiday but uncertainty regarding
their speeds of motion and intensities remain high. By next
weekend, global model ensemble means continue to show decent
agreement that the next large-scale cyclone will be moving into
the Aleutians. The WPC Alaskan medium-range charts and grid
package were based on an even blend of the 06Z/12Z GFS, the 12Z
GEFS, the 12Z ECMWF, and the 00Z EC mean, with more weights given
to the ensemble means from day 7 to 8.
...Weather/Hazards Highlights...
High winds and heavy precipitation near the coast across
southwestern and southern Alaska should become less intense by
next Wednesday as the attendant large-scale cyclone begins to
weaken. Additional heavy precipitation is also forecast to affect
the Alaska Panhandle on Wednesday. The chance of heavy rain
should generally decrease during the Christmas holiday along the
entire stretch of the southern coastal sections but a couple of
smaller scale cyclones could bring periods of enhanced
precipitation near the Alaska Peninsula and Alaska Panhandle. By
next weekend, the next large-scale cyclone is forecast to move
from west to east across the Aleutians, where gale to storm force
winds and periods of heavy precipitation appear likely. Milder
than normal temperatures are forecast to overspread mainland
Alaska by next Wednesday under an upper ridge. The mild
conditions should continue through Christmas holiday, cooling down
slightly to near normal during next weekend along the Alaska
Peninsula.
Kong
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