What you pay for isn’t generally updates to the app, but the service of sourcing, processing and consolidating the weather data for the way it is presented by the app. I use three different weather apps (only one of them with a subscription, $1 per year) because each has unique aspects of its data and presentation that are useful depending on the use case. One of them has diagrams combining forecasts from 20 different data sources for the next week (which gives a nice overview of the spread of forecasts for each day), sources which I don’t think are all free.