Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
758 PM EDT Tue Oct 26 2021
Valid 12Z Sat Oct 30 2021 - 12Z Wed Nov 03 2021
***Heavy precipitation is expected for south-central Alaska this
weekend with atmospheric river event***
...Overview and Model Guidance...
The medium range period will begin on Saturday with an upper low
initially centered south of the Alaska Peninsula, and an upper
trough over eastern Siberia. An upper level ridge should be in
place across northwest Canada, and deep southerly flow between the
ridge and the upper low is expected to produce heavy precipitation
for portions of southern Alaska.
Model guidance begins in fairly good agreement with the deep
surface and upper-level low over the Gulf of Alaska, with some
minor differences regarding potential mesoscale features. There
are greater model differences upstream across the Bering with the
ridge axis, and the 12Z CMC shows significant phase differences as
early as Saturday and even more apparent by early next week, with
the CMC the only operational model suggesting a trough and closed
low over western Alaska, whereas the ensemble means strongly
support an extension of the ridge from western Canada. The WPC
forecast was primarily derived from a GFS/ECMWF/UKMET blend along
with some previous WPC continuity, and gradually increasing
contributions from the ensemble means by the second half of the
forecast period.
...Weather/Hazard Highlights...
Precipitation is forecast to increase substantially over the
weekend from the Alaska Peninsula to western portions of the
southeast Panhandle, with the deep low pressure system over the
Gulf of Alaska providing a prolonged moist onshore flow to the
region. The rain will be quite heavy for windward terrain, with
the potential for 3 to 6 inches over the weekend, and very heavy
snow for the higher terrain. Some strong southerly winds are also
possible in those areas, while gusty northerly winds are expected
on the backside of the low for the Aleutians on Saturday.
Precipitation should continue into early next week, albeit abating
in intensity. Farther north, light snow is likely to spread
across much of the western and central parts of the state with the
moist inflow from the low pressure system. By the weekend into
early next week, temperatures should gradually warm as upper level
ridging sets in as the upper low shifts away from the state. Low
temperatures are currently expected to be 10-15F above normal for
much of the interior, with highs generally 5-15F above average.
Hamrick
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
Hazards:
- Heavy precipitation across portions of mainland Alaska, Sat-Mon,
Oct 30-Nov 1.
- High winds across portions of mainland Alaska and the Aleutians,
Fri-Sat, Oct 29-Oct 30.
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