As I mentioned earlier, I am no expert, but having examined various possibilities, I’d like to propose a possible explanation for the origins of the Fairweather name.
Given my own DNA results and the research outlined on this website, while there may be a Viking connection through the Norsemen and the Normans, the DNA markers are minimal. Most Western Europeans will carry a low percentage of Norse DNA markers. We can’t be too sure about what the name in its earlier spellings may have meant, but there are strong indications that its origins are in the Low Countries. Any explanation using the modern name “fairweather” as the starting point is likely to arrive at the wrong conclusion. The word has its roots in older spellings such as fairvedder, fawvedder, Farewethir, Farewedder, and Fairwodder. Simplistically explaining it as someone with a “sunny disposition” or from the Bible, “fair weather cometh out of the north”, or as I did, using the standard spelling to describe a supposed past activity, all, in fact, miss the point.
The ChatGPT conversation recorded on the “Flemish Connection?” page provides a strong link to the Flemish. There is also further evidence of a strong Flemish connection outlined on this page – Further Flemish Evidence.
Setting aside the word “faer”, perhaps the Norse connection is a red herring. The Flemish connection fits three pieces of evidence: the historical migrations of the Flemish people, my DNA that clearly links me to the Low Countries, and in 1792, my ancestor John Fairweather, at the time of his marriage, was a weaver of sailcloth with close connections to Dundee merchants and their clippers, which regularly sailed to the continent. Sunny disposition or not, it explains why we do not have a tartan and credibly explains who we are and where we came from. We were skilled artisans, masons, weavers, and farmers who, at the invitation of Scottish and English kings, came to share our skills and make our adopted country a more successful and vibrant place to live. The Fairweathers were undoubtedly one of the families who helped to make Scotland. This, to me, is a satisfactory and credible explanation.

YES! I totally agree with your reasoning for the origins of “Fairweather”. I am very interested in reading more from you and others on this subject. “Our” Fairweather line has been traced back to England with the arrival of Thomas Fayerweather in Boston in 1630 with the Winthrop Fleet.