Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
658 PM EDT Sat Sep 05 2020
Valid 12Z Wed Sep 09 2020 - 12Z Sun Sep 13 2020
...Weather/Threats Highlights and Guidance/Predictability
Assessment...
Stormy upper troughing and short range focusing unsettled weather
over the Bering Sea moves inland over the Interior
Wednesday-Thursday, pushing robustly through an ambient amplified
upper ridge. In the wake of this heading into the weekend, Arctic
stream upper troughing and a frontal push works into the North
Slope. Meanwhile, a separate and dynamic southern storm track sets
up across the Pacific. Details and system transitions with lead
system energies within this flow are more complex, lowering
forecast confidence on the main weather focus up into the Gulf of
Alaska. However, there is a decent guidance signal for flow
amplification in this stream in tandem with some infusion of
amplified northern stream energy. This occurs with the slated
approach of the deepened extratropical low associated with
northward lifting Typhoon Haishen from a current position to the
south of Japan/Korea. This deep low may reach the Aleutians next
weekend and produce quite a threat of high winds/waves and
enhanced wrapping rains.
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 ECMWF 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.
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