Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
647 PM EST Thu Dec 30 2021
Valid 12Z Mon Jan 03 2022 - 12Z Fri Jan 07 2022
...Overview...
Guidance is continuing to show a blocky pattern as initial Bering
Sea into Arctic upper ridging likely closes off a high early in
the week, with the high center drifting over or near eastern
Siberia through the rest of the week. The Arctic portion of the
ridge may rotate southward into and through the mainland enough to
yield more northerly flow over the mainland by next Friday.
Meanwhile there is steadily improving agreement that energy over
the southeastern mainland/northeastern Pacific as of Monday should
consolidate into an upper low that retrogrades along the Aleutians
around Wednesday-Thursday. Cold temperatures supported by strong
surface high pressure tracking from the northern mainland into
northwestern Canada should moderate slowly with time while a
strong gradient south of the high will support brisk to strong
winds over the southern mainland and Panhandle. Most
precipitation next week will be confined to the Aleutians and
Alaska Peninsula/Kodiak Island.
...Guidance Evaluation and Preferences...
Today's guidance exhibited tendencies similar to recent days, with
the operational models generally ahead of the ensemble means in
depicting the strength of the upper ridge/high as the means
continue to trend stronger in the direction of the models. At the
same time the ECMWF/CMC and their means have tended to lead the
GFS/GEFS with the ridge's strength/evolution/location, though
sporadic GFS runs have been relatively close to the model
consensus. Most guidance has gravitated to having the high center
meander over the vicinity of eastern Siberia for most of the week,
for a time achieving a 564dm contour before weakening somewhat
late in the week. By the latter half of the week the 12Z GFS
becomes a little slower than consensus with the Arctic ridge that
rotates into the mainland. Meanwhile to the south there has been
a noticeable trend in the models over the past day or so for
deeper and faster retrogression of an upper low near the Aleutians
by Wednesday-Thursday. In the 12Z cycle the ECMWF/UKMET/CMC ended
up in very similar positions for the retrograding low through
early Wednesday while the GFS was a little farther east. Details
diverge thereafter. There is a decent signal in the models/means
for a western Pacific system to come into the picture and track
far enough east by late week for the northern side of the
circulation to affect the Aleutians.
As was the case the past couple days, various aspects of
continuity and trends again favored an operational model blend
through the entire period to maintain the best definition of the
upper ridge and surrounding features as well as the surface
features/gradients over the mainland and Panhandle. The
divergence in the models for some of the less confident aspects of
the forecast, in particular the details south of the upper ridge
after midweek, provided some smoothing where appropriate. The
forecast started with the 12Z ECMWF/GFS/CMC/UKMET from day 4
Monday into early day 6 Wednesday and then trended to half total
ECMWF weight (split between the 12Z and 00Z runs) with the
remainder tilted a little more to the 12Z CMC relative to the 12Z
GFS. In most respects the new 18Z GFS provided some favorable
trends toward the preferred solution.
...Weather/Hazard Highlights...
Most of the mainland will see dry weather next week as strong high
pressure over the northern mainland on Monday settles into
northwestern Canada while a weaker surface ridge likely persists
over the northern half of the mainland into late week. Far
northern/northeastern locations could see a little light snow
toward Thursday or Friday. Much below normal temperatures over
the southeastern half or so of the mainland will slowly trend less
extreme with time while readings should stay well below normal
over the Panhandle the entire week. On the other hand the North
Slope will see a pronounced warming trend with temperatures
reaching well above normal by mid-late week. The western
Aleutians will see enhanced precipitation/wind extend into at
least Monday. Developing easterly flow at the surface and aloft
should spread moisture from Kodiak Island and parts of the Alaska
Peninsula through the Aleutians. Low-confidence surface low
details will determine if there may be some localized enhancement
of precipitation/wind. A separate system emerging from the
western Pacific could increase moisture/wind over the Aleutians by
late week.
Rausch
Hazards:
- Heavy precipitation across portions of the Alaska Panhandle,
Sun, Jan 2.
- High winds across portions of the Alaska Panhandle and mainland
Alaska, Sun-Mon, Jan 2-Jan 3.
- High winds across portions of the Aleutians, Mon, Jan 3.
- Much below normal temperatures across portions of the Alaska
Panhandle and mainland Alaska, Sun-Thu, Jan 2-Jan 6.
Additional 3-7 Day Hazard Information can be found on the WPC
medium range hazards outlook 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