I missed that it's a "personal" blog, but they prominently describe their position as the emoji subcommittee chair, so it's more or less an official outlet.

Northern bias, yes. What about emoji or Unicode is tied to the weather? Why not use more universal time markers? If dates or months are truly too precise for this timeline, quarters are good enough. They could also just have a month range or "approx".

Being near the equator (whether northern side or southern), I don't have an innate sense of seasons at all, so have to remember what people are referring to when they use these terms.