Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
542 PM EST Thu Dec 12 2019
Valid 12Z Mon Dec 16 2019 - 12Z Fri Dec 20 2019
Models were relatively agreeable during the first portion of the
extended forecast period, and a blend of the ECMWF/GFS/CMC was
used as a forecast starting point during days 4-5 (Mon-Tue). These
solutions showed relatively small timing and structural
differences with a relatively deep low pressure system crossing
the Aleutians during that time, and the described blend should
resolve these differences favorably. From day 6 (Wed) onward, this
system is forecast to move eastward, passing near or just south of
the Alaska Peninsula and into the Gulf of Alaska. Timing
differences among the guidance increase substantially from Wed
onward, and a weighting of ECENS/GEFS ensemble means in the
forecast was increased to account for this increased spread.
Models/ensemble show some broad agreement that another relatively
deep low pressure system should enter the western Bering Sea by
day 7 (Thu), with guidance showing relatively large
timing/structural differences that are best resolved at this point
in time by going heavily toward the ensemble means. Some continued
use (about 30%) of deterministic solutions was warranted through
the end of the forecast period, however, to add a bit of
definition to features beyond that shown by the ensemble means.
In terms of sensible weather, this pattern should favor multiple
round of precipitation across the Aleutians, Alaska Peninsula,
southern mainland, and Southeast Alaska. Dry conditions should
prevail across the mainland interior, however. Temperatures are
forecast to be above average across southern mainland and across
the North Slope through the extended period, with a trend toward
slightly below normal temperatures across the interior by the
middle of next week.
Ryan
Additional 3-7 Day Hazard information can be found on the WPC
medium range hazards
https://www.wpc.ncep.noaa.gov/threats/threats.php
Hazards:
No significant hazards are expected over Alaska during this
forecast period.
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