My guess is that it will come down to "what data can be pulled in automatically by ZIP", and Dave can auto-populate those if he decides to. Everything else will have to be editable by the member. Probably the auto fields also need to be user-editable, since some ZIP codes contain varied micro-climates.
Not many members will want to go into the statistical detail that has been discussed recently (like, % cloud cover per month, or cloudy days per month).
My image was that there would be optional fields like those in the Plant Database. Some radio buttons or check-boxes, and then an "other" field for free form text. You might be able to check "frequently overcast winters" and "clear dry summers", but would have to type by hand something like "many gray, cool foggy mornings but sunny and hot by noon.
Some balance would have to be struck between ease of entry for new members, and the kin d of detail loved by nerds. Whenever I write or design something, wiser people tell me that I like too much detail! Yes, I do!
Or, asking for the Sun, the Moon and the Stars, perhaps one "short form" that most people would enjoy checking off and entering comments/complaints into (what gardener can resist complaining about their weather?) ...
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... and then an "Advanced Climate Data Entry Button" that would offer the option of entering different comments for each season or each month. Different regions care about different things, like dates of scorching heat in summer, frequency of late cold snaps, which seasons have the worst winds, etc.
Sometimes, just being confronted with a place to record the data tempts me into paying closer attention. I don't know, like a year-by-year list of "actual, observed SERIOUS" frosts in my exact microclimate and what I consider a "serious" frost.