Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
604 PM EST Wed Nov 04 2020
Valid 12Z Sun Nov 08 2020 - 12Z Thu Nov 12 2020
...Guidance/Predictability Assessment...
Successive troughing is forecast to push through much of the state
in progressive flow next week, squashing upper ridging at times
nosing out of the northeastern Pacific into eastern/southeastern
areas. The 12Z guidance offered reasonable clustering to start the
period Sunday as a system out of the north central Pacific moves
across the AKPen/southwestern areas. Guidance still diverge on
where to track the parent low before the triple point low takes
over into the Gulf and how quickly the front will progress
eastward, perhaps slowed by a surface wave on the southern portion
(per the GFS). Opted to form a consensus of the models, though
varied, which maintains the general continued thinking that the
parent low will weake across western coastal Alaska and the triple
point takes over near Kodiak to move eastward into the Panhandle
around early Monday. To the north, a boundary should linger/waver
astride the North Slope and Brooks Range as the old upper trough
weakens ahead of the next Bering system.
Late Sun into early Mon, next Bering system will move in from the
west toward the Bering Strait. Models/ensembles remain rather
diverse with embedded features within and around the larger
trough/upper low leading to low confidence in details. Preferred
to maintain the more simplified depiction of the system taking the
parent low toward the Bering Strait, the cold front into western
areas, and the triple point redeveloping near the Kenai peninsula
around late Tue into early Wed. Trended to solely an ensemble mean
blend between the 12Z GEFS mean and 00Z ECMWF ensemble mean with
only a small minority 12Z ECMWF weighting as it was the closest of
any model to the means. At the least, this was again close to
continuity from 24 hrs ago. Troughing may carry a weak cold front
around its southwest/south side at the end of the period.
...Weather/Threats Highlights...
Modest to locally heavy coastal rain and inland snow will
accompany the lead system Sunday over southwestern portions of the
state. Precipitation may be heavy especially in terrain-favored
areas with several inches (liquid) possible. Heavy snow is also
possible in some areas that stay cold enough. In-house
bias-corrected QPF shows 2-4 inches over southeastern Kenai
eastward toward Yakutat and some locally higher amounts into Mon
(4-6"). Next system over/near the western to central Bering Sea
Mon-Tue should spread another area of precipitation and strong
winds across the Bering Sea/Aleutians. This will move into
Southcentral by mid week next week but perhaps with less
precipitation than the lead system Sunday. However, this may bring
significant precipitation to western areas from the Y-K Delta
northward to Kotzebue as milder air surges north-northeastward in
advance of the cold front.
Above normal temperatures are forecast to remain over much of the
Interior (generally west and north of the Alaska Range) next week.
By contrast, below normal temperatures are expected over the
Panhandle and southeastern 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, Nov 8-Nov 9.
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