Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
639 PM EST Thu Dec 19 2019
Valid 12Z Mon Dec 23 2019 - 12Z Fri Dec 27 2019
...Below average temperatures expected across parts of mainland
Alaska into next week...
...A couple of potentially strong storms may track near the
Aleutians, bringing precipitation and strong winds...
...Wet pattern along the southeastern coast/Panhandle...
The guidance for today continue to show relatively good agreement
to begin the medium range period on the larger scale flow, but
significant differences remain on the smaller scale/less
predictable details especially towards the end of next week. Upper
troughing over the mainland should persist through much of the
period, which would promote an extended period of below normal
temperatures which the core of should shift slowly westward with
time next week.
To the south, the guidance continues to show a very active North
Pacific/Aleutians stream that should include a series of
shortwaves traversing near or south of the Aleutians. To begin the
period on Monday, one low pressure system looks to cross the
Panhandle into the Gulf with low pressure lingering through next
week over the Gulf of Alaska. Models show fairly good agreement on
this, though the ECMWF remains a bit south of the consensus on low
placement. This would support a persistent focus for precipitation
along the southeastern coast/Panhandle, with heavy precipitation
potentially more likely early in the week.
Behind this another system looks to pass south of the Aleutians on
Tuesday with greater uncertainty on timing as it enters the
Gulf/Northeast Pacific Wednesday and beyond. The GFS/ECMWF are
better clustered than the CMC, but are still displaced south of
the ensemble means with the low center. On Thursday, yet another
potentially deep low pressure system approaches the
western/central Aleutians, but the deterministic models show large
uncertainties on placement and strength of this low for days 7 and
8. Depending on the exact track and intensities of varies lows,
some precipitation and strong winds are possible for parts of the
Aleutians next week.
This cycle of the WPC guidance favors a mostly deterministic model
blend for days 4-5 between the 12z GFS and the 12z ECMWF, with
smaller contributions from the 00z ECENS mean and the 12z GEFS
mean. For days 6-8, weighting of the ensemble means was increased
significantly to account for continued uncertainty in the
deterministic runs.
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:
- Heavy precipitation across portions of the Alaska Panhandle and
mainland Alaska, Mon, Dec 23.
- High winds across portions of the Aleutians, Sun-Mon, Dec 22-Dec
23and Tue-Wed, Dec 24-Dec 25.
- Much below normal temperatures across portions of mainland
Alaska, Sun-Mon, Dec 22-Dec 23.
- High significant wave heights for coastal portions of mainland
Alaska and the Aleutians, Sun-Mon, Dec 22-Dec 23.
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