Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
646 PM EDT Mon Oct 26 2020
Valid 12Z Fri Oct 30 2020 - 12Z Tue Nov 3 2020
...Guidance/Predictability Assessment...
The forecast period begins on Friday with a strong storm system
passing just south of the central Aleutians and a compact low
approaching the Arctic Coast region. The deterministic guidance
indicates above average mass field agreement for Friday and into
the weekend, given the increasingly amplified pattern in place.
The 00Z ECENS becomes more progressive overall compared to the
generally slower 12Z model guidance suite, with the 12Z ECENS
slower and closer to the other guidance. By Sunday and Monday,
another system is forecast to approach the western/central
Aleutians, with the 12Z ECMWF slower than the GFS/GEFS, and the
CMC to the southeast of the consensus. There has been an overall
slower trend in the past 48 hours of model runs with the storm
systems across the north Pacific. The WPC fronts and pressures
forecast was primarily derived from the 12Z GFS/ECWMF/CMC for the
first half of the forecast, and with time increasing the weighting
of the GEFS mean and some of the EC mean. Some previous WPC
continuity was also incorporated into the forecast.
...Weather/Threats Highlights..
Heavy rain and mountain snow will likely be making weather
headlines across the southeast panhandle region as a potential
atmospheric river event sets up to the east of a northern Gulf
low. The potential exists for several inches of rain for the
lower elevations as a result of the onshore flow, and at least a
foot of snow for the higher elevations in this region. A
wind-driven rain is looking more likely for portions of the
Aleutians for Friday as the strong oceanic storm passes near or
just south of this region, and again early next week in
association with the next occluded surface low that passes south
of the islands.
The weather should also be noteworthy for the Arctic region with a
well-developed polar low passing near the Arctic Coast through
Saturday afternoon. There will likely be a period of gusty
northwest winds over mainly ice-free water, and this may lead to
some coastal flooding and heavy freezing spray. In addition,
colder weather is expected across the northern and eastern
portions of the Interior, with more sub-zero high temperatures
likely by the second half of the forecast period.
Hamrick
Hazards:
- Heavy precipitation across portions of the Alaska Panhandle and
mainland Alaska, Fri-Sat, Oct 30-31.
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