I can't remember where I spotted it, but when researching the climate of a region of Japan I was planning on visiting, I found a city's tourism website that had

I can't remember where I spotted it, but when researching the climate of a region of Japan I was planning on visiting, I found a city's tourism website that had a table of months of the year with pictograms of the appropriate attire (shorts, sweaters, umbrellas, etc.) for a typical day. It stuck with me as a nearly perfect way to convey this information instead of burdening the visitor with the job of translating average temperature and rainfall data into what to pack. And it needs virtually no translation to other languages.