Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
755 PM EDT Fri Oct 23 2020
Valid 12Z Tue Oct 27 2020 - 12Z Sat Oct 31 2020
...Guidance/Predictability Assessment...
The forecast period begins on Tuesday with a lingering surface low
over the northern Gulf of Alaska, and a surface high building over
the Interior by the middle to end of the week. Deterministic
guidance indicates reasonable mass field agreement through
Wednesday, and then normal levels of model spread become apparent.
This holds true with the next and stronger storm system to pass
south of the Aleutians, with the CMC and GEFS mean closer to the
Alaska mainland, in contrast to the GFS/ECMWF that are a bit
slower and farther offshore. By the end of the forecast period
next Saturday, a third system may approach the western Aleutians,
with surprisingly better model agreement regarding location of the
surface low, and greater model spread over the Gulf region. The
WPC fronts and pressures forecast was primarily derived from the
12Z GFS/ECWMF/EC mean, and with time increasing the weighting of
EC mean along with some of the NAEFS mean.
...Weather/Threats Highlights..
Heavier rain and mountain snow is expected across the southeast
panhandle and portions of the southeastern Mainland on Tuesday as
the surface low over the northern Gulf meanders slowly and
gradually weakens, with onshore flow to the east of the low. Some
snow showers will also be possible across the Arctic Coast region
as a couple of disturbances pass north of the region. Very little
in the way of snow is expected for the Interior as high pressure
will govern the overall weather pattern. The coldest temperatures
are expected to be across the east-central portion of the state,
especially for the latter half of the forecast period where some
sub-zero high temperatures will be possible. Depending on the
track of the Aleutian storm system towards the middle to end of
next week, strong winds may materialize across this region,
although confidence in this remains limited for now.
Hamrick
Hazards:
- Heavy precipitation across portions of the Alaska Panhandle and
mainland Alaska, Mon, Oct 26.
Additional 3-7 Day Hazard information can be found on the WPC
medium range hazards 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