Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
646 PM EST Tue Jan 14 2020
Valid 12Z Sat Jan 18 2020 - 12Z Wed Jan 22 2020
...Overview...
Most guidance shows an evolution toward a period of upper
troughing from Siberia into the northeastern Pacific/Gulf of
Alaska as an upper ridge initially over the North Slope and
northwest Canada rapidly rotates to the north and east. There
will also be a fairly progressive North Pacific/Aleutians/Bering
stream that will feed into the mean trough. This pattern will
promote a moderating trend from the well below normal temperatures
across the Panhandle and southern half of the mainland at the
start of the period. Expect the primary precipitation focus to be
over the Panhandle and westward to around the eastern part of the
Kenai Peninsula with one or more northeastern Pacific/Gulf waves.
The Aleutians should see some light precipitation through the
weekend, followed by the possible arrival of an organized area of
moisture associated with a North Pacific system by Tue-Wed.
...Guidance/Predictability Assessment...
In spite of the agreement for the overall pattern evolution, there
are multiple uncertainties with forecast specifics--especially for
features across the North Pacific and into the Gulf of Alaska.
Early in the period a blend of the 00Z/12Z ECMWF runs and 06Z/12Z
GFS provides better definition than the ensemble means while still
accounting for detail spread that already exists at this time
frame. This consensus depicts energy initially near the Alaska
Peninsula organizing into a compact upper low that tracks
north-northwest along the western coast of the mainland and/or the
western tip of Siberia, possibly interacting with separate upper
low/trough energy that approaches from the west. As this occurs
expect surface low pressure to evolve over the eastern/northern
Bering, eventually lifting northward along with the upper
dynamics. Meanwhile low pressure should track northward into the
Gulf during the first half of the period, with the best cluster
suggesting it may reach somewhat north of the 12Z GFS. Confidence
decreases for specifics of one or more trailing waves over the
northeastern Pacific/Gulf.
There is a decent cluster of guidance signaling a fairly strong
North Pacific system that could have some influence on the
Aleutians by Tue-Wed. Over the past day GFS/ECMWF/ECMWF mean/CMC
runs have been consistent in depicting this system albeit with
considerable latitude and timing spread. Latest ECMWF runs have
been in the northern part of the spread as was the 00Z CMC. The
12Z CMC adjusted somewhat south/east, while GFS runs and the ECMWF
mean are more suppressed due to keeping southern Bering flow
flatter (versus the upper ridge that develops in the operational
ECMWF). An intermediate solution currently appears best given the
CMC trend and ECMWF mean runs that are closer in principle to the
GFS.
...Weather/Hazards Highlights...
Southern portions of the mainland as well as the Panhandle will
see a warming trend from below normal temperatures this weekend.
Some pockets of above normal readings may be possible over the
southeastern corner of the mainland by next week. The North Slope
and vicinity should see above normal temperatures, with greatest
anomalies on Sat. Expect the best focus for precipitation to
extend between the eastern Kenai Peninsula and the Panhandle from
Sun into next week with one or more waves reaching the Gulf.
Activity could be locally moderate to heavy at times. The
Aleutians will see light to isolated moderate precipitation
through the weekend into early next week, followed by uncertain
coverage/intensity of organized precipitation depending on the
track of the system to the south.
Rausch
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
- Much below normal temperatures across portions of the Alaska
Panhandle and mainland Alaska, Fri-Sun, Jan 17-Jan 19.
- Much below normal temperatures across portions of the Alaska
Panhandle, Fri-Sat, Jan 17-Jan 18.
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