Mac: Weather is a fickle thing, but if you like to stay on top of it from your Mac, you don't have a ton of options beyond refreshing a web site. Forecast Bar is an app that will help you do just that, with a forecast in your menu bar, weather alerts, and more.
Forecast Bar uses Forecast.io, so the interface should be pretty familiar to anyone who's used that or an app like Dark Sky. It's simple, but still packed with a ton of information. The app has a bunch of customisable settings, so you can set it up show the weather in the menu bar or dock, show different amounts of days, dig into specifics like visibility or UV, and more. In short, it's a pretty powerful little weather app that's customisable enough that just about anyone can find a use for it. It's pretty similar to Carrot Weather, minus all the snark.
The rub is the pricing. The base version is $7.49, but there are in-app purchases to unlock how often the app updates. By default, it updates the weather once an hour. If you want faster updates, you'll have to pay for them. That's a bit absurd, but the good news is that most of us should be fine with hourly updates anyway.
Forecast Bar ($US5.99) [Mac App Store]