Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
540 PM EST Sun Dec 15 2019
Valid 12Z Thu Dec 19 2019 - 12Z Mon Dec 23 2019
...Below average temperatures expected across the Alaska Interior
and portions of the North Slope later this week...
A blend of the ECMWF/GFS was preferred as a forecast starting
point during days 4-5 (Thu-Fri). These solutions were relatively
agreeable with respect to low pressure moving east across the Gulf
of Alaska during that time frame. Farther west, model consensus
has improved with respect to a relatively deep low entering the
western Bering Sea on day 4, and the aforementioned blend should
resolve this system favorably. Farther north, upper ridging across
the arctic is forecast to migrate toward Siberia during the early
extended period, allowing arctic shortwave energy to carve out
lower heights across the North Slope and the Interior, with many
solutions continuing to show an upper low developing across the
North Slope by Fri. Solutions continue to show a fair degree of
run-to-run variability with this chaotic arctic flow, however, and
it may take some time for this to be resolved favorably by the
guidance. By days 6-8 (Sat-Mon), deterministic solutions show
another wave of low pressure developing along an active North
Pacific frontal zone, perhaps nearing the Aleutians by Sat
night-Sun. While models agree on the potential for this system,
solutions vary widely on the track, timing, and intensity
(although a number of solutions suggest the potential for a deep
system). Spread among ensemble members suggests that uncertainty
with this system is even higher than would be indicated by spread
among the deterministic solutions - thus confidence in the
forecast specifics surrounding this system is low. Given increased
spread during days 6-8, went heavily toward ECENS/GEFS ensemble
means during that time frame.
This pattern should favor persistent wet conditions across the
Panhandle/Southeast Alaska from the middle of the week onward.
Precipitation should become more widespread across the Aleutians
by next weekend, with the potential for gusty winds if some of the
deeper deterministic solutions were to verify (confidence is low
at this time, however). Farther north, the growing arctic
influence will result in dropping temperatures later this week,
with a period of well-below average temperatures expected across
the Interior and portions of the North Slope away from the coast.
Max temperatures as much as 20 deg F below average are forecast by
mid to late this week. Relatively dry conditions should prevail
across these regions, however.
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
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