Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
623 PM EST Wed Jan 19 2022
Valid 12Z Sun Jan 23 2022 - 12Z Thu Jan 27 2022
...A wet pattern with heavy precipitation possible will continue
into the first half of next week for Alaska's southern coast and
Panhandle...
...Overview...
Guidance continues to show a very warm and wet pattern for early
next week, as a strong eastern Pacific mean ridge extends
northward into Alaska's mainland and northwestern Canada while a
mean trough axis persists farther west, with an embedded initially
fairly deep upper low over eastern Siberia that should drift
northward with time. This pattern and a shortwave and surface low
affecting the Alaska Peninsula and southwest mainland
Sunday-Tuesday will direct moist flow into the state and cause
precipitation for western and southern parts of the state
spreading eastward with time, with the highest totals likely over
the southern coast and Panhandle. Weak upper troughing and
cooler/drier surface high pressure is forecast to push west to
east across much of the mainland around midweek onward as the
ridge axis relaxes and shunts eastward into Canada.
...Guidance/Uncertainty Assessment...
Model agreement at the beginning of the period is fairly good with
the overall pattern described above. The upper low and associated
surface low/frontal system initially located west of the state has
a slightly slower trend compared to yesterday's model guidance and
WPC forecasts as they track northwest while weakening, but there
is good agreement for the upper ridge axis farther east across
much of the mainland and Panhandle through the early part of the
week. For the most part, guidance has also come into fairly good
agreement with a mid-upper shortwave and a surface low track near
the Alaska Peninsula around Monday, though there remain
differences with the exact timing of the low and whether it will
track north of the peninsula into Bristol Bay or south. The main
outlier with these features was the UKMET, which was farther west
than the consensus of other guidance, so the early part of the
medium range forecast was based on a blend of the deterministic
ECMWF/GFS/CMC.
For days 6-8 (Tuesday-Thursday), troughing should weaken but press
into the northwestern parts of the mainland, but other than that
the details are quite nebulous regarding shortwaves and the track
of surface lows especially for the western part of the state and
the fairly progressive northern Pacific flow. Thus the medium
range forecast blend quickly ramped up the proportion of GEFS and
EC ensemble means for days 7-8 given the deterministic model
differences and no perfect solution at this point.
...Weather/Hazard Highlights...
The deep layer southerly flow will bring in significant moisture
(precipitable water values generally +1.5 to +2.5 standard
deviations above normal) into Alaska for the first half of the
week. The highest precipitation totals are likely from the Alaska
Peninsula into Southcentral Alaska and spreading eastward into
mainly northern parts of the Alaska Panhandle, with a possible
period of gusty winds. Some snow is forecast to spread into the
western part of the mainland as well in conjunction with a frontal
system. A drier trend is likely by Thursday as high pressure
builds in.
Much above normal temperatures are predicted early next week
underneath the upper-level ridge, with widespread temperatures
15-30F above average (locally higher) for much of the mainland
except the far western part. Temperatures will moderate closer to
normal and even shift to below normal from west to east on Tuesday
through Thursday as the ridge moves away from the state.
Tate
Hazards:
- Heavy precipitation across portions of the Alaska Panhandle and
mainland Alaska, Sat, Jan 22.
- Heavy precipitation across portions of the Alaska Panhandle and
mainland Alaska, Sun-Mon, Jan 23-Jan 24.
- High winds across portions of the Alaska Panhandle and mainland
Alaska, Mon, Jan 24.
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