Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
659 PM EDT Wed Aug 03 2022
Valid 12Z Sun Aug 07 2022 - 12Z Thu Aug 11 2022
...Cold and wet pattern setting up over much of Alaska, with
rounds of heavy rainfall possible across the Southeast and the
Panhandle...
...Overview...
A shortwave into the Panhandle by Sunday will bring potentially
heavy rainfall to parts of the Panhandle through the weekend.
After this, the focus will shift to the north where a compact and
deep closed low will drive a cold front across western/central
Alaska and into the Gulf, with precipitation (possibly some snow)
likely across the Mainland, and another chance for heavy rainfall
into southern/southeast Alaska and parts of the Panhandle early to
mid next week. This system will usher in a much cooler regime
across Alaska lasting into at least the middle of next week.
...Guidance/Predictability Assessment...
The model agreement is improving compared to previous model runs,
but there are some key differences that remain, especially the
second half of the period. The models show relatively good
agreement on the initial shortwave into the Panhandle on Sunday,
as well as the upper low as it moves across the Bering Straight
and into western Alaska Monday-Tuesday. A general deterministic
model compromise seemed to handle any lingering timing differences
well. After this, the 12z GFS is a little faster than the
ECMWF/CMC but it does look ok compared to the (much weaker)
ensemble means. By days 7 and 8, the 12z CMC diverges from the
better consensus and doesn't have much support for bringing the
closed low more west into the Bering Sea and eventually across the
Alaska Peninsula. Meanwhile, the ECMWF/GFS show the main energy
moving into southern Alaska by that time, and possibly still as a
closed low. Given the differences, it seems most reasonable to
lean more on the ensemble means days 7 and 8 as a way to mitigate
some of these differences, although still able to incorporate
modest amounts of the ECMWF and GFS for some added definition to
the system. Compared to yesterdays WPC forecast, we are a little
bit faster with overall system progression.
The latest models seem to have a relatively good handle on about
the first half of the period through Monday, although the UKMET
and CMC were a little faster with the shortwave into the Gulf this
weekend. A blend towards the ECMWF and GFS was preferred and was
more consistent with the ensemble means for that system. After
this, models begin to diverge more especially concerning details
surrounding the deeper low across the Arctic. Initially, the 12z
GFS was noticeably quicker with a shortwave into western Alaska
compared to the rest of the deterministic guidance. Then around
Tuesday/day 7, some of the guidance (the 12z ECMWF and CMC) pull
the core of the upper low south and into mainland Alaska, while
the 12z GFS and the ensemble means (including the new 12z runs)
keep it farther north. This was a shift in the 12z ECMWF as the
00z ECMWF kept the low north like the GFS, so this will need to
continue to be monitored to see if this southward pull is a trend
or not. Of course, the evolution of this system and the details
will have strong implications for how cold it gets over Alaska and
also whether any, or none, of the associated precipitation is
snow. At such, the Alaska forecast for today trended strongly
towards the ensemble means late period to help mitigate these
larger and smaller scale differences.
...Sensible Weather...
Precipitation, heavy at times, will continue across the Panhandle
as the period begins Sunday, though may taper off by late Sunday
into Monday as the front/shortwave moves into western Canada.
Meanwhile, much of the mainland of Alaska looks to remain rather
unsettled next week as a strong system moves into western Alaska
and tracks east. This likely brings some gusty winds to the west
coast of Alaska and a maritime threat over the Bering Sea, as well
as widespread precipitation farther inland. Some of this
precipitation could fall as snow for areas that get cold enough,
particularly parts of northwest Alaska and higher elevations. The
heaviest precipitation should shift south and east with time next
week, with the potential for heavy rainfall once again returning
to parts of southeast Alaska and the Panhandle region. For the
most part, the Aleutians/Alaska Peninsula region should remain
mostly dry, with maybe some showers approaching by the middle of
next week as a system slides to the south across the northern
Pacific.
Chilly temperatures will overspread much of Alaska, including the
Panhandle by this weekend with daytime highs as much as 10 to 20
degrees below normal. The highest anomalies will feature across
the North Slope region though, where anomalies could be as high as
30+ degrees below normal and morning low near or below freezing
for some places. Temperatures should begin to moderate from west
to east by next Wednesday, though still much below normal across
the North Slope and eastern Alaska.
Santorelli
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
Hazards:
- Heavy rain across portions of the Alaska Panhandle, Sat-Sun, Aug
6-Aug 7.
- Heavy rain across portions of mainland Alaska, Mon-Tue, Aug
8-Aug 9.
- Much below normal temperatures across portions of mainland
Alaska, Sat-Wed, Aug 6-Aug 10.
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