Powerful Doppler radar help to see into clouds and satellites provide surveillance. We certainly need all of this to forecast the weather, but sometimes a look outside can really tell the story. An old forecaster once said to me, only a fool doesn't look outside. Always keep your eye on the sky if you really want to understand the weather. Remember it's never rained out of a clear sky.
Clouds are the signposts of the weather.
Clouds reflect the moisture in the air and the signature of the wind. Watching for changes in the clouds can tell you a lot about the weather. Watch cloud cover, if it's increasing, that usually means the weather is deteriorating. In the mountains, keep an eye on the base of the clouds. If the ceiling or cloud bases are coming down the weather and visibility will be getting worse.