This Google Map based application will send you a warning when rain is approaching.
Rain Alarm displays an animation of current precipitation and can warn you against approaching rain or snow. The app checks a perimeter of 75 km around your selected location every 30 minutes. If rain is approaching your location the map will then sound the alarm.
The app is currently available for the USA, Canada, Australia, the UK, Ireland, Norway, Germany, the Netherlands and Spain including the Balearic and the Canary Islands.