PorchWeather watches one saved location and a set of conditions you pick (temperature range, wind, rain, dew point, air quality) and sends you a notification when conditions become nice, and another when they stop. That's the whole product. It's free, web-native (not an app), and notifications are browser push or email.

Some implementation details HN might find interesting:

Stack: SvelteKit SPA, Rust backend, DynamoDB, Cognito for auth, SES for email, Self-hosted Open-Meteo for weather all on ECS Fargate. The weather layer serves ECMWF global plus NOAA HRRR at 3 km resolution for the US.

Notifications are primarily through web push. I'd love to do SMS through twilio, but it seems prohibitively expensive for a free service unfortunately. iOS devices make this a little harder because you have to "install" the app on the home screen to get push notifications. I may end up creating an app at some point to make this easier if there's demand.