The American one seems to match this, which has “National Climatic Data Center’s U.S. Stations 1961-1990 Monthly Normals for the Atypical Climate Elements” as its source.
The European one seems to be from this Wikimedia Commons user, but they never specified their source beyond “according to national data”
The American one seems to match this, which has “National Climatic Data Center’s U.S. Stations 1961-1990 Monthly Normals for the Atypical Climate Elements” as its source.
The European one seems to be from this Wikimedia Commons user, but they never specified their source beyond “according to national data”
This is the sauce every map needs. Thank you.