Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
555 PM EST Thu Jan 09 2020
Valid 12Z Mon Jan 13 2020 - 12Z Fri Jan 17 2020
...Guidance/Predictability Assessment...
The latest runs of the 12z deterministic guidance show fairly good
agreement on a weakening surface low crossing the Bering Straights
Monday up into the Arctic Ocean early next week.
Farther south, a frontal wave with weak low pressure embedded
within the frontal circulation persists over the southern Gulf of
Alaska by Tuesday and into Wednesday, and merges with low pressure
moving further south in the northern Pacific by Wed 15 Jan.
By next Tue, a large cyclone and frontal system move slowly east
into the western Bering Sea. The trailing front crosses the
Aleutians, with waves of low pressure possible developing along
the front and moving north across the Aleutians.
The big changes on the 12z ECMWF make the forecast challenging,
with low confidence on the magnitude of the run to run change in
the operational ECMWF forecast from the 00-12z runs.
The 12z ECMWF has better continuity with the low developing and
located just south of the lower Aleutians next Fri 17 Jan., as the
12z Canadian cyclone position is close by, resulting in good
overlap among the 2 ECMWF operational runs/ECMWF ensemble Mean,
and Canadian global cyclone positions.
To mitigate the various model solutions, for the 500 mb and sfc
forecast mass field forecasts, a blend of the 12z Canadian, GFS,
UKMET. and 00z ECMWF/ECMWF Ensemble Mean solutions was used for
days 4-8.
...Weather/Hazards Highlights...
Much of AK south of the north slope will have lingering much below
normal temperatures expected days 4-5 over the eastern
Interior/Southeast and Panhandle region as arctic high pressure
continues in place. Temperatures across some of the more
sheltered valleys in the eastern Interior may approach 50 below
Monday morning. On next Thu-Fri, marine modified air starts moving
onshore in most solutions from the Bering Sea and north Pacific
into western Alaska, so the air mass starts to moderate.
No major heavy precipitation events are expected through the
middle of next week. The next surface cyclone crossing the
Aleutians/nearby waters may bring a period of gusty winds and
precipitation during the middle of next week.
Petersen
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, Sun, Jan 12.
- Much below normal temperatures across portions of the Alaska
Panhandle, Sun-Tue, Jan 12-Jan 14.
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