Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
747 PM EDT Sat Jun 10 2023
Valid 12Z Wed Jun 14 2023 - 12Z Sun Jun 18 2023
...Overview...
Overall a stalled and blocky pattern is likely to remain in place
next week across much of the Northern Hemisphere. This will
include a northeast Pacific ridge/high (with varying amplitude
over time), while to the west troughing is likely to prevail
across the Bering Sea into at least western Alaska as high
latitude energy drops south to reinforce energy already in place.
The troughing should keep much of Alaska cooler than normal while
also directing moisture into the state for widespread rain
chances, but light to modest amounts. The overall storm track
including recurving current Typhoon Guchol should stay south of
Alaska over the midlatitudes much of next week, though by next
weekend there is a chance for the post-tropical cyclone to
approach the Aleutians that will continue to be monitored.
...Guidance Evaluation/Preferences...
The bulk of recent model guidance indicates that energy from the
far northern latitudes is likely to create an upper low around the
Bering Strait/Chukchi Sea for the latter half of next week, with
north-south oriented upper troughing extending across the Bering
Sea. The 12Z GFS spilled this energy farther south and west into
the Bering Sea compared to other guidance including its 06Z run,
which seemed less likely since other guidance was more agreeable
on a more northeastern position. Models show fair agreement that a
couple of troughs/lows south of the Aleutians and Alaska Peninsula
as the forecast period begins on day 4/Wednesday will track east
across the northern Pacific and could affect southeast Alaska with
a surface low by late week. GFS/ECMWF/UKMET runs show this
potential, though with some variations in position and depth. This
continued trend of energy in this area should suppress the
northern extent of the northern Pacific ridge for late next week.
Farther west, the Joint Typhoon Warning Center forecast for what
is currently Typhoon Guchol indicates the storm will recurve east
of Japan and across the mid-latitude north Pacific as it
transitions to post-tropical. Most model guidance agrees with its
track eastward around 40N or so, reaching the Dateline around
Thursday. The CMC is a significant exception though. It has the
post-tropical cyclone as much weaker and farther north, affecting
its 500mb pattern as well for some odd phasing with the Bering
trough. Other than the CMC, recent models now have Guchol's low
restrengthening late week, but perhaps weakening by next weekend.
The low may take a turn northeast or northward by next weekend,
potentially influenced by the Bering Sea troughing. Deterministic
models keep the low south of the Aleutians through next Sunday,
but some ensemble members show it approaching or crossing the
Aleutians, so will continue to watch this potential. With this
Guchol low/trough south of the Aleutians, downstream there may be
a restrengthening of the northeast Pacific ridge farther north,
perhaps with ridging even coming into Southcentral after a troughy
pattern for weeks.
The WPC forecast was based on a blend of the 06Z and 12Z GFS and
the 12Z ECWMF and UKMET early in the period. No CMC was used today
given its disagreement with Guchol. Transitioned to a blend of
over half GEFS and EC ensemble means by days 7-8 given the
increasing uncertainty with multiple features, but the fairly
agreeable ensemble means for the overall pattern.
...Sensible Weather and Potential Hazards...
The persistent troughing over the Bering Sea (and beyond) will
allow for some moist inflow into the state, but not too high in
terms of precipitable water anomalies. Thus mainly diurnal showers
are likely, with broad coverage of rain chances but with amounts
generally staying light to moderate. Across the Brooks Range
though, lingering moisture may help to promote more modest
rain/snow. There is somewhat better agreement today for a front to
move through the western Alaska mainland Wednesday-Thursday ahead
of the upper low, for some possibly enhanced precipitation totals
there as well. Southeast Alaska should have increasing rain
chances/amounts late week with a surface low or two coming
through, and then by the weekend the Aleutians to Alaska Peninsula
could see some rain potential depending on the track of Guchol.
Meanwhile temperatures will be near to well below normal over the
bulk of the state given the presence of the upper trough.
Tate
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