Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
535 PM EST Sat Dec 21 2019
Valid 12Z Wed Dec 25 2019 - 12Z Sun Dec 29 2019
...Below Average Temperatures for much of Mainland Alaska...
...Strong storms to track near the Aleutians and the
Southern/Southeast Mainland...
...Guidance/Uncertainty Assessment...
Guidance is well clustered days 4/5 (Christmas/Day After
Christmas), bolstering forecast confidence. A composite blend of
the 12 UTC GFS/ECMWF and GEFS/NAEFS/ECMWF ensemble means seems to
provide a solid starting point for production of the WPC Alaskan
medium range product suite along with input from the 19 UTC
National Blend of Models. Model forecast spread and run to run
continuity variance becomes more robust days 6-8, especially with
offshore systems. However, the preferred 12 UTC GEFS/NAEFS/ECMWF
ensembles remain fairly well clustered and seem to offer
reasonable predictability that coupled with the NBM maintains
decent continuity.
...Weather/Hazards Highlights...
A lingering and unsettling mean upper trough centered over the
interior with have cold lower atmospheric air underneath in a
pattern with below normal temperatures for much of the mainland
next week. A strong storm track underneath will feature two main
systems. A lead low and frontal system is progged to track near
the Aleutians and Alaskan Penisula/Kodiak Island onward over the
far northern Gulf of Alaska near southern/southeast Alaska. This
will offer a maritime risk of high wind/waves along with a focus
for heavy precipitation that will also feed inland, mainly into
coastal areas and favored terrain of southern/southeast Alaska
Christmas into Friday, with lingering activity into next weekend.
Meanwhile, there is also a growing signal supporting another
significant/deep low back upstream than works northward to the
Aleutians next weekend that will also offer a maritime and onshore
threat for the region, with heavy seas/winds also feeding up into
the Bering Sea.
Schichtel
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
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