Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
608 PM EST Tue Jan 07 2020
Valid 12Z Sat Jan 11 2020 - 12Z Wed Jan 15 2020
...Guidance/Predictability Assessment...
The latest runs of the 12z GFS/ECMWF show fairly good agreement on
a deep low pressure system moving into the Bering Sea this
weekend, weakening as it moves into northwest Alaska by Monday.
Behind this, another shortwave will slide south of the Aleutians,
showing potential strengthening as it moves into the Gulf of
Alaska next Tuesday and Wednesday. The 12z GFS remains on the
faster and deeper side of the solution envelope with this system,
especially after day 6. The 00z ECMWF seemed totally out of line
with much of guidance as it brought this system northward into the
Bering Sea. The 12z ECMWF however came into better agreement with
the GFS and ensemble means and is very much usable. The next
possibly deep surface low moves into the far western Aleutians day
7/8 time frame with again, growing uncertainty amongst the latest
deterministic runs.
The WPC blend for today leaned heavily on the deterministic GFS
and ECMWF for days 4 and 5 given the agreement, with increasing
contributions from the ensemble means day 6 and beyond. The means
tended to wash out the shortwave moving into the Gulf early next
week so the blend used about a third of the 12z ECMWF through day
8 to bring back some definition of both the upper system and the
resulting surface low. The blend for today fits well with
yesterday's forecast as well as the forecast downstream over the
CONUS.
...Weather/Hazards Highlights...
A building upper ridge over the North Slope and much of the
Interior will partially ease the current cold snap, with lingering
much below normal air held over the eastern Interior/Southeast and
Panhandle region as post-frontal high pressure spreads in from
Canada.
The main weather threat upstream will be from the Aleutians to the
Bering Sea associated with a major low pressure system. This
brings along with it the threat for some locally heavy
precipitation, along with high winds and waves to mainly the
western Aleutians. Precipitation should also work its way into the
western and southwestern mainland this weekend. The shortwave
moving into an already unsettled Gulf of Alaska early next week
should bring more modest effects for maritime interests and
onshore to the southern Alaskan tier. The next deep low for the
Aleutians may bring a period of gusty winds and heavy
precipitation by the middle of next week.
Santorelli
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:
- Much below normal temperatures across portions of mainland
Alaska, Fri-Sun, Jan 10-Jan 12.
- Much below normal temperatures across portions of the Alaska
Panhandle, Fri-Mon, Jan 10-Jan 13.
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