Seasonality Core is an excellent weather application for OS X. It has lots of detailed information that's presented in a unique and customizable format. We took a look at an earlier version of the program about a year ago and had good things to say about it.
The app supports more than 34,000 locations in more than 200 countries. It shows radar images and provides a seven-day forecast. With its new Particle Mode, you can see wind flow in a helpful graphical presentation.
The app is fast and includes things its competitors don't bother with, such as sunrise and sunset times, and special graphs that let you look back at weather history for things like winds and precipitation totals.
The only missing features for me are any weather warnings or alerts. The developer says they are coming, but it is an essential part of any weather app.
Now about that price. At US$24.99, as good as Seasonality Core is, that price is too high. Searching the Mac App Store, there are dozens of weather apps that range from free to $6.99. Some, such as the $0.99 WeatherMan and the $1.99 Plus for the Weather Channel have plenty of features and details. Seasonality Core is a really good app, but I think it should be in the $5-$6.99 range.