Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
635 PM EDT Sun Sep 06 2020
Valid 12Z Thu Sep 10 2020 - 12Z Mon Sep 14 2020
...Weather/Threats Highlights and Guidance/Predictability
Assessment...
An energetic upper trough and surface frontal system/weather focus
will exit the Interior Thursday. In the wake of this feature,
upper troughing underneath a closed Arctic Sea low will force a
cooling front across an unsettled North Slope and Interior.
Meanwhile, a separate and dynamic storm track will setup over the
northern Pacific and southern Bering Sea/Aleutians with ample
energy from an upper latitude closed trough/low. Details and
system transitions with lead system energies within this flow are
complex, lowering forecast confidence on the main weather focus up
into the Gulf of Alaska. There is also an uncertain signal with an
infusion of energy/moisture associated with the extratropical
evolution of current west Pacific Typhoon Haishen from the far
western Pacific then northeast Asia. This may lead to a late week
threat of high winds/waves and heavy wrapping rains for the Bering
Sea/Aleutians to then spread into southwest/southern Alaska next
weekend/Monday.
Models and ensembles offer a reasonably similar larger scale
pattern evolution, but differ with embedded system details and
offer less than stellar continuity. The 12 UTC GFS solution seems
overall the closest model fit with the 12 UTC GEFS/ECMWF ensemble
means and a composite blend of these was used for the basis of the
WPC medium range product suite along with the 19 UTC National
Blend of Models. Ensemble weighting in the composite blend was
increased by the weekend as per rapidly increasing forecast
spread.
Schichtel
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