Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
543 PM EST Mon Nov 02 2020
Valid 12Z Fri Nov 06 2020 - 12Z Tue Nov 10 2020
...Guidance/Predictability Assessment...
Troughing is forecast to push through much of the state in
progressive flow, bounded by upper ridging anchored in the
northeastern Pacific but at times nosing into southeastern areas.
The 12Z guidance offered good clustering to start the period
Fri-Sat with a weakening Bering system into western Alaska and
high pressure near the Panhandle in western/northwestern Canada.
Tail-end of the Bering system will linger south of the Aleutians
as a mid-latitude/subtropic system lifts northward toward the
eastern Aleutians late Sat. By early Sun, 12Z GFS slips the
surface low east of the other models (closer to Kodiak) which was
a shift westward from its 06Z run. Preferred to side with the
larger ECMWF-led consensus that included both the Canadian and
UKMET that take the surface low across the AKpen and into Bristol
Bay, then into southwestern areas before translating eastward
across the Interior. Triple point low should develop into the Gulf
late Sun and head into the Panhandle Mon per the consensus.
Next system of interest will enter the western Bering around late
Sun, moving eastward next Mon/Tue. 12Z ECMWF/Canadian paired
better with the ensemble means than the GFS, and again preferred
that cluster of solutions. However, ECMWF/Canadian outpaced the
ensemble means which was certainly plausible given the quicker
flow, but how quickly the system may develop into the western
Bering to begin with remains in question. Therefore, trended
toward a mostly ensemble mean solution by the end of the period.
...Weather/Threats Highlights...
Weakening system in the Bering Fri will bring lingering coastal
rain and inland/northern snow to the region with breezy conditions
as milder air attempts to push northeastward. Reforming boundary
astride the North Slope will support well above normal
temperatures near the Brooks Range southward over much of the
Interior. By contrast, below normal temperatures are expected over
the Panhandle and southeastern areas Fri with high pressure over
Canada. That may persist for several days thereafter until it
slips southeastward late in the weekend. Back to the west,
approaching Pacific system will bring increasing coastal rain and
inland snow to southwestern portions of the state late Sat into
Sun on southerly to southeasterly flow. Precipitation may be heavy
with several inches (liquid) possible in favored areas. In-house
bias-corrected QPF shows 3-5 inches over southeastern Kenai
eastward toward Yakutat and some locally higher amounts into Mon.
Next system over/near the western to central Bering Sea next week
should spread another area of precipitation and strong winds
across the Bering Sea/Aleutians.
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, Nov 8.
- Heavy precipitation across portions of the Alaska Panhandle,
Mon, Nov 9.
- High significant wave heights for coastal portions of mainland
Alaska, Thu, Nov 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