Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
757 PM EDT Thu May 05 2022
Valid 12Z Mon May 09 2022 - 12Z Fri May 13 2022
...Overview...
A potent upper trough is forecast atop much of the mainland as the
workweek begins, and this trough should shift eastward and deepen
through around midweek along with some moisture and a low
pressure/frontal system, supporting showers across much of the
state. Then an upper-level ridge/high is expected to set up over
the Bering Sea, north of a persistent upper level and surface low
in the Pacific well south of the Aleutians. Additional troughing
may come into the mainland during the latter part of the week with
some chances of additional precipitation, but with uncertainty in
the details.
...Guidance/Predictability Assessment...
As the medium range period begins Monday, most guidance is in
fairly good agreement with the overall pattern, continuing with
considerably strong energy diving into the western mainland to
create troughing that continues to deepen Tuesday and possibly
split off an upper low in the Gulf of Alaska near the Panhandle by
Wednesday. The 12Z CMC seemed a bit south and aggressive with
forming the upper low earlier than consensus. Meanwhile recent
guidance shows an upper high incoming stationed a bit farther east
than the previous forecast, centered to the north of the Aleutians
with surface high pressure near Bristol Bay. An upper low and an
associated surface low show good consensus hovering well south of
the Aleutians (around 40N and just east of the International Date
Line). The WPC forecast utilized a multi-model deterministic blend
but favoring the ECMWF and GFS for the early part of the medium
range period.
The latter half of next week becomes more uncertain with the
overall flow over Alaska, as possible shortwaves moving into the
northwestern part of the state could impact the extent of the
ridging from the Bering Sea upper high. The GFS runs have been
persistent in showing some suppression of the ridge due to
shortwave energy, and the 12Z ECMWF and CMC did start to trend
toward stronger shortwaves as well. However, there are ample
differences in the timing and strength of such shortwaves that
grow to be pretty significant by Thu-Fri. Gradually increased the
proportion of the GEFS and EC ensemble means through the period to
about 60 percent by day 8 given the model differences.
...Weather and Hazard Highlights...
Increasing precipitation chances are likely across interior Alaska
Monday into Tuesday as troughing and a surface front/trough pass
across the area, with perhaps some moderate amounts. Given the
trough movement, precipitation should spread into southeastern
Alaska and the Panhandle Tuesday and Wednesday, but heavy totals
are generally not expected. Another round of light precipitation
is possible for the interior Wednesday and beyond next week.
Another concern during the period will be for flooding, as above
freezing temperatures atop a significant snow pack could lead to
river flooding and ice jams could develop in parts of interior
Alaska. One short to medium range flooding concern is an ice jam
along the Kuskokwim at Crooked Creek.
Much of interior Alaska can expect cooler than normal high
temperatures through the period, with low temperatures more of a
mix of somewhat below and above normal. The Alaska Peninsula could
gradually warm through the week as ridging builds in. Meanwhile,
the Panhandle has the best chance of seeing below average
temperatures for both highs and lows.
Tate
Hazards:
- Flooding possible across portions of mainland Alaska, Sun-Thu,
May 8-May 12.
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