Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
702 PM EDT Mon Jul 26 2021
Valid 12Z Fri Jul 30 2021 - 12Z Tue Aug 03 2021
...Heavy rainfall possible for parts of western and northwestern
Alaska...
...Guidance/Predictability Evaluation...
The medium range period over the Alaska region looks to feature a
couple of shortwaves moving through the Bering Sea into far
northern Alaska/the Arctic before a much deeper low becomes
established over the Bering Sea by late weekend or early next
week. Meanwhile, an upper low will drift only slowly westward
through the period in the Gulf/Panhandle region while upper level
ridging holds on across southern and eastern Alaska. The latest
ensemble means remain reasonably compatible with each other on
this pattern, while the deterministic GFS, ECMWF, and CMC show
typical differences in the smaller scale, lower predictability,
features. The WPC Alaska grids leaned more on the deterministic
models days 4-6, with increasing contributions from the ECENS/GEFS
means days 7-8. Favored the 12z GFS slightly more than the 12z
ECMWF late period because it was more compatible with the means on
placement of the Bering Sea low.
...Weather/Threats Highlights...
The main areas of precipitation and unsettled weather will be
focused across the western and northwestern mainland throughout
the period as southerly flow ahead of the Bering Sea cyclone
interacts with stalled frontal boundaries. A reinforcing trough
from eastern Siberia could ingest moisture from T.S. Nepartak and
is forecast to reinvigorate the Bering Sea low next weekend into
early next week to sustain the general rainfall across western
Alaska. Heavy rain is possible especially across the wind-facing
upslope terrains of Lisburne and Seward Peninsulas where rainfall
amounts may approach climatological extremes. Temperatures should
remain below normal for western and northern parts of Alaska but
they should trend warmer over eastern parts of the state as upper
level ridging builds in aloft.
Santorelli
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
- Heavy rain across the southern portions of Lisburne and Seward
Peninsulas in mainland Alaska, Thu-Mon, Jul 29-Aug 2.
- Heavy rain across portions of southwestern Alaska, Sat-Mon, Jul
31-Aug 2.
- Heavy rain across portions of southwestern Alaska, Fri-Mon, Jul
30-Aug 2.
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