You guys definitely created an amazing value here. Pretty much the only app I use for weather forecasting these days. I am sure I'm not the only one.
Creating so much value which doesn't sustain itself - is not healthy. IMO - you should experiment with various models until you find the right one! I come from startup world - in it we know that you definitely can find a way, you just need to put some effort into finding it.
I understand your dedication to keep app free, but that doesn't mean for example that people can't willingly pay you :)
Few initial ideas :
A donation button somewhere in the app could be a way for you to monetize. It could also be tied to crypto too, not just regular currencies. Crypto might be easier to test if this is a viable idea.
Lots of artists are using Patreon these days to monetize their otherwise free content. Maybe it could work for you as well?
Package data conveniently and sell it to someone? Paid API's?
Ads... Hate them, so would resort to it as final option :) maybe ads in some smart way, not as intrusive, like something visible on the map, but transparent? Just ideating here...
Really love this app, and would hate to see it go down just because you didn't seek for monetization. My 2 cents :)