Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
753 PM EDT Wed Jun 22 2022
Valid 12Z Sun Jun 26 2022 - 12Z Thu Jun 30 2022
...Overview...
Today's guidance is fairly agreeable and consistent in showing the
center of an eastern mainland/northwestern Canada upper ridge
gradually drifting more into Canada by the middle of next week.
This ridge will support multiple days of above to much above
normal temperatures over a majority of the state. Farther west an
upper trough with embedded low should persist over the Bering Sea
and Aleutians for most of the period. An initial dissipating
surface front anchored by Bering Sea low pressure should help to
focus rainfall over parts of the Alaska Peninsula on Sunday, with
some moisture extending farther north through the western
mainland. Then the Bering Sea upper low may encourage a North
Pacific wave to track into the Aleutians/Bering Sea and another
system emerging from the western Pacific may start to influence
the Aleutians after midweek. A deep upper low initially north of
Siberia is still likely to remain well northwest/north of the
mainland but some differences persist for how surrounding flow
could influence the northern mainland.
...Guidance Evaluation/Predictability Assessment...
The best guidance convergence noted over the past 24 hours or so
has been with the Bering Sea upper low, which as of early Sunday
is forecast to be in the process of replacing a leading
trough/upper low from the short range. Some GFS runs had been
well west with the main low but latest runs cluster well with the
ECMWF/UKMET/CMC. Toward the end of the period the 00Z ECMWF mean
brought it a bit east of consensus but the new 12Z run adjusted
westward. Even with this improved agreement for the upper low
(aside from spread for how close it may get to the Aleutians at
some point), the surface evolution over and north of the North
Pacific is still fairly ambiguous. GFS/ECMWF runs still suggest
that the upper low will encourage a Pacific wave to track into the
Aleutians/Bering Sea, albeit faster than yesterday, while the
UKMET/CMC are less defined at the surface. As expected the means
are also ill-defined but the new 12Z ECMWF mean is starting to
hint at similar wave. There may be a weak leading wave as well,
while a system emerging from the western Pacific may begin to
influence the western Aleutians by next Thursday. This latter
feature appears to be somewhat larger in scale and hopefully has
better predictability than the potential waves to the east.
Around the western/northern side of the mean ridge, latest
consensus suggests that some combination of ejecting Bering Sea
energy and/or an impulse swinging around the southeast periphery
of the Arctic upper low may brush the far northwestern mainland
early in the week. Then for the rest of the period solutions
still vary somewhat for heights aloft across the North Slope and
vicinity, due in part to differences in track/progression of the
Arctic upper low. Overall preference was to put greater weight on
solutions with relatively higher heights given consistent ensemble
mean support. In particular this would favor underweighting the
12Z GFS around Tuesday and Thursday.
Guidance comparisons supported starting with a 12Z operational
model composite from Sunday into early Tuesday. Preference to
maintain good definition of the Bering Sea upper low through the
latter half of the period, given current model agreement, favored
only modest incorporation (up to 20-30 percent) of the 12Z
GEFS/00Z ECMWF means by next Wednesday-Thursday.
...Weather and Hazard Highlights...
The strong upper ridge drifting over the mainland and northwestern
Canada should promote a broad area of above to much above normal
temperatures during the period. Currently expect the most
notable/impactful anomalies to be over the Interior and southern
Panhandle. The Panhandle may see the greatest departures from
normal and best potential for a few locations to challenge daily
records. Some pockets of below normal highs may exist close to
the southern coast and over the northwestern mainland, while the
Aleutians will tend to be on the cool side under mean troughing
aloft. A weakening front anchored by Bering Sea low pressure
should produce some focused rainfall over parts of the Alaska
Peninsula into Sunday with some of this moisture extending farther
north through the western mainland. Expect precipitation to be
lighter and more scattered over most areas to the east given the
prevalence of upper ridging. The North Slope may see episodes of
light precipitation if a front to the north gets close enough to
the region. North Pacific waviness could bring some moisture into
the Aleutians next week but confidence in the specifics is still
fairly low. Another system emerging from the western Pacific may
begin to have some influence on the western Aleutians by next
Thursday.
Rausch
Hazards:
- Much above normal temperatures across portions of the Alaska
Panhandle and mainland Alaska, Sat-Wed, Jun 25-Jun 29.
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