Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
630 PM EDT Wed Sep 22 2021
Valid 12Z Sun Sep 26 2021 - 12Z Thu Sep 30 2021
...Guidance and Predictability Assessment...
The synoptic pattern for the extended period generally is an
upper-level low that drifts southward from the Arctic Circle with
spokes of upper troughing pinwheeling within the flow across the
state and the Gulf of Alaska. Initially, a potent surface low will
have already spread heavy precipitation across the Southeast just
prior to the beginning of the extended forecast and there will be
some lingering precipitation to start. Another surface low is
forecast to track across the northeastern Pacific and cause
another round of precipitation for the Panhandle early next week.
Then, another low that could be reasonably deep for this time of
year is currently expected to move from the Bering Sea
southeastward across the Aleutians into the Gulf of Alaska, which
could cause increasing precipitation chances for southern Alaska
and the Panhandle dependent on the low track.Additionally of note,
the Joint Typhoon Warning Center has begun issuing advisories for
T.D. Twenty that will be strengthening while tracking over the
western Pacific-- is forecast to be near 140E by the 27th.
There continues to be timing and depth differences among the
guidance that decreases confidence on exactly where and when the
moderate to heavy precipitation will occur; however this pattern
is favorable to keep much of the state cooler and the Southeast
wet. WPC continued to prefer the slower solutions since they
clustered well with the ensemble means. Therefore to maintain a
since of continuity from the previous forecast, the blend utilized
12Z ECWMF/GFS along with the EC ensemble and the GEFS means-- with
increasing weighting of the means through the middle and later
periods.
...Sensible Weather...
Some precipitation is expected to linger while the Southeast gets
another round of precipitation early in the coming week as a
strong low approaches in the Gulf. Gusty winds will accompany this
low for areas offshore. Farther north, central/eastern parts of
the mainland could see moisture and increased precipitation (some
falling as snow) chances this weekend. A secondary low, just as
potentially strong as the initial one, could bring gusty winds and
precipitation to the Aleutians and toward South-central Alaska and
eventually the Panhandle again by midweek. The exact track and
strength of this low remains uncertain. The upper trough
persisting over the mainland will keep temperatures below normal
over much of the state through the extended period. Coldest
anomalies should be over the southern parts of the state and
across higher elevations of the Brooks and Alaska Ranges. Daily
maximum temperatures are expected to range from the 40s and 50s in
coastal areas, while highs could remain in the 30s or lower across
much of the mainland.
Campbell
Hazards:
- Heavy precipitation across the Alaska Panhandle, Wed, Sep 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