Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
600 PM EDT Thu Oct 01 2020
Valid 12Z Mon Oct 05 2020 - 12Z Fri Oct 09 2020
...Overview and Guidance/Predictability Assessment...
Increasingly progressive pattern remains well-advertised by the
guidance, with a strong system plowing through the Bering Sea next
Tue-Thu. The 12Z guidance was fairly closely-clustered to start as
a departing system moves through the Panhandle early Mon. Trend
was a bit slower, so the front was slowed a bit as well but the
parent low position nearing Prince William Sound remained on
track. 12Z GFS/ECMWF again offered good agreement and formed the
majority of the blend. For next Tue-Fri, focus turned to the
Bering Sea. Trend continued to be just a bit quicker, giving
credence to the ECMWF ensembles from several days ago (seemingly
too quick compared to the rest of the guidance). Latitudinal
spread among the guidance between about 57-62N suggested a middle
ground track near 60N toward the central Bering Sea (12Z GFS was
most reasonable here) before the system likely sinks southeastward
across the AKPEN as triple point redevelopment takes place just
southwest of Kodiak by early Thu. Again the 12Z GFS/ECMWF were
remarkably close, but opted to blend in about 40% ensemble mean
weighting to temper the system for now. That low should push into
the Gulf as the old parent low slowly weakens in the Bering.
Better than average deterministic/ensemble agreement led to above
average confidence.
...Weather/Threats Highlights...
Lingering modest rain (perhaps locally heavy) on Monday will
diminish over parts of southern coastal areas to the Panhandle.
Some drying is forecast over the mainland Tue-Wed as height rise
in advance of the Bering system. Rainfall will increase over the
Aleutians late Tue into Wed as the cold front moves through, but
progressive flow should limit heavier rainfall. Once the triple
point redevelops east of the Aleutians, heavier rain may wrap
around the new low into Kodiak, southeastern Kenai, and the west
side of Cook Inlet.
Temperatures are forecast to be near to well above normal over
most of the mainland, especially north of the Alaska Range. Near
to below normal max temperatures are forecast for the Aleutians,
across portions of Southcentral, and over the Panhandle. Min
temperatures will be closer to normal over southern areas to well
above normal across northern areas.
Fracasso
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
Hazards:
- Heavy precipitation across portions of the Alaska Panhandle and
mainland Alaska, Sun-Mon, Oct 4-Oct 5.
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