Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
549 PM EST Mon Dec 16 2019

Valid 12Z Fri Dec 20 2019 - 12Z Tue Dec 24 2019

...Below average temperatures expected across the Alaska Interior
and portions of the North Slope later this week...

A blend of the ECMWF/CMC was preferred as a forecast starting
point during days 4-5 (Fri-Sat). These solutions were relatively
agreeable with respect to low pressure across the Gulf of Alaska
during that time frame. Farther west, models continue to struggle
with the exact track of a deep low pressure expected to develop
across the North Pacific Fri-Fri night, nearing the Aleutians on
Sat. The GFS was initially on the fast side of the spread with
this system, and also became a bit deeper than other deterministic
solutions at 500 hPa, causing the surface low to slow and wrap
northward into the Bering Sea. Meanwhile, the ECMWF kept the low
on a more east-northeast course south of the Aleutians, and the
CMC was roughly in between. Given these differences, the GFS was
not preferred and opted to lean toward the ECMWF/CMC (more
emphasis on the ECMWF). Farther north, upper ridging across the
arctic in the short range is forecast to migrate toward Siberia by
the extended period, allowing arctic shortwave energy to carve out
lower heights across the North Slope and the Interior, with some
solutions continuing to show an upper low developing 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
(Sun-Tue), deterministic solutions show another compact wave of
low pressure developing along an active North Pacific frontal
zone, perhaps nearing the Aleutians by Sun. Yet another such
system may follow by Mon night-Tue. Solutions vary widely on the
track, timing, and intensity of these systems - thus confidence in
the forecast specifics are 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
over the weekend, with the potential for gusty winds as well
(depending on the exact track) given the expected deep nature of
the system. 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
<a href="https://www.wpc.ncep.noaa.gov/threats/threats.php"><u>https://www.wpc.ncep.noaa.gov/threats/threats.php</u></a>

Hazards:

- High winds across portions of the Aleutians, Sun, Dec 22.
- Much below normal temperatures across portions of mainland
Alaska, Thu-Mon, Dec 19-Dec 23.

WPC medium range Alaskan products including 500mb, surface
fronts/pressures progs and sensible weather grids can also be
found at:

<a href="https://www.wpc.ncep.noaa.gov/alaska/ak_5dayfcst500_wbg.gif"><u>https://www.wpc.ncep.noaa.gov/alaska/ak_5dayfcst500_wbg.gif</u></a>
<a href="https://www.wpc.ncep.noaa.gov/alaska/akmedr.shtml"><u>https://www.wpc.ncep.noaa.gov/alaska/akmedr.shtml</u></a>
<a href="https://www.wpc.ncep.noaa.gov/alaska/ak_5km_gridsbody.html"><u>https://www.wpc.ncep.noaa.gov/alaska/ak_5km_gridsbody.html</u></a>