Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
720 PM EDT Wed Sep 16 2020
Valid 12Z Sun Sep 20 2020 - 12Z Thu Sep 24 2020
...Overview and Guidance/Predictability Assessment...
The extended period begins with a surface low and associated cold
front pass through the southern Mainland/panhandle into Canada
while a low over the Pacific/Bering deepens as it advances toward
the Aleutian Chain. While there is some timing and strength
differences, this system is forecast to be well-defined and
wrapped up as it tracks toward/over the Aleutians mid-to-late in
the forecast period. Stronger winds and additional focused rain
will accompany this system. High winds may impact parts of Kodiak
Island and Kenai Peninsula Monday and Tuesday, as well as, heavy
precipitation spanning from Unimak Island to Anchorage and the
surrounding area. The area of heavy precipitation will shift east
along the southern coastal area to Glacier Bay, with heavy rain
across the Southeast Tuesday and Wednesday.
There continues to be some spread in the timing of the low
pressure system that tracks across the Aleutians during the
mid/late period; however to a lesser degree than yesterday.
Persistence favored a combination of the 12Z ECWMF/GFS/CMC for
most periods with increasing weighting of the 00Z EC ensemble and
12Z GEFS mean by Tuesday and Wednesday.
...Weather/Threats Highlights...
Lingering clouds and showers are possible across parts of the
southern Mainland and panhandle as a front moves into Canada early
in the period. Increased cloudiness, heavy precipitation and
increasing gusty winds will accompany a fairly progressive low
pressure system as it tracks across the Bering, the Aleutians and
into the Gulf of Alaska next week. Much of the southern coastal
areas and the North Slope will have maximum daily temperatures
near or below average through at least mid week, while much of the
Interior will observe above average temperatures.
Campbell
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 mainland Alaska, Mon-Tue,
Sep 21-Sep 22.
- Heavy precipitation across portions of the Alaska Panhandle and
mainland Alaska, Tue-Wed, Sep 22-Sep 23.
- Heavy rain across portions of the Alaska Panhandle, Tue-Wed, Sep
22-Sep 23.
- High winds across portions of mainland Alaska, Mon-Tue, Sep
21-Sep 22.
- High winds across portions of the Alaska Panhandle, Tue, Sep 22.
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