Rain Alarm is a smart app which can warn you about imminent snow or rain. That doesn't sound too special - there are a host of tools promising to do the same thing - but this one has what it takes to stand out from the crowd.
It's about as cross-platform as you can get, for instance: there are apps for Android, iOS, Windows Phone and Windows 8; add-ons for Firefox and Chrome, or you can just visit the Rain Alarm website from almost anything with a browser.
It doesn't trust a single website for its forecasts, either, instead using data from 25+ government weather services (USA, Canada, Mexico, El Salvador, Argentina, Australia, Taiwan, Japan, Republic of Korea, Malaysia, Singapore, Brunei, the UK, Ireland, Germany, Austria, Finland, Norway, Iceland, the Netherlands, Spain, Slovenia, Croatia, Belarus, Ukraine, Russia).
Rain Alarm normally uses Google Maps, which for most people will be just fine. If your device doesn't have Google Maps, though, or you have problems getting it to work, the flexibility continues: Rain Alarm OSM uses OpenStreetMap as an alternative. (The developer also says the OSM version "loads faster", which might also be a plus for older or slower devices.)
Whatever version you're using, Rain Alarm displays a repeated animation showing the weather in your area (and can share an animated image, if you want to warn others). Every 30 minutes it checks for rain within a 35KM radius of your location. But you don't have to worry about the details; just close the app and you'll get a warning whenever rain is on the way.
If this isn't enough then you can upgrade to a Pro version, which drops the ads, has customisable settings (update interval, search radius, animation rate) and alarms (time frame, distance, sound, vibration, more). It's yours for around $5.
The free version is short on configuration options, but it looks good, is easy to use, and delivers reliable results across most platforms.