You can unlock professional Foreca, Open-Meteo, and Dark Sky forecast sources, weather alerts, nowcast, and all styles and options via a reasonably priced subscription, which covers the cost of data and allows me to further improve Weathergraph.
Weathergraph is a beautiful visual hourly weather widget and forecast for Watch, iPhone, iPad, and Mac, with the Apple Watch app and complications.
Hourly forecast is updated every hour and cached offline — the chart always shows the current temperature according to the last obtained forecast, even when you go off for a long trek without a data connection.
If rain or snow is expected during the next 3 hours, you will get a notice on a widget (iPhone, iPad & Mac), a large complication (Watch), and a detailed 3-hour precipitation chart in the app.
Nowcast and alerts are powered by Foreca and depend on the precision of rain radars in your area.