I wouldn't mind building a weather station at some point as well. It's not something I really
need but it would be neat. In conjunction with that, I could also use an RTL-SDR dongle to make a receiver for satellite weather data from various publicly available weather satellites.
The other idea I've toyed with is an automatic plant watering system, in service of my aspiration to start growing my own hot peppers (ghost peppers, habaneros, carolina reapers, etc.)
so I have a lot to learn and figure out in processing the raw data.
If you're interested in weather / environmental "stuff" in a broader sense, you might also be interested in a lot of the other data the USG (and others) make available. NOAA, the USGS, etc. put out all sorts of neat datasets. You can get all the obvious stuff (temp, barometric pressure, etc.) as well as water levels in various creeks and lakes and rivers, discharge volume for same, ground conductivity, stuff about lightning, severe storms (tornados, hurricanes, etc.), wildfires, etc., etc., etc. I'm pretty sure somebody creative could find some really interesting applications for all of that stuff.