Sometimes you need to know whether there was rain or hail on a specific day in the past in order to investigate a leak or to identify problems with a roof installation. Or you may need to know if there's a 30% chance of rain tomorrow at 5 am in order to be able to schedule things properly.
Webcam Images at Weather Underground can be found here. You have to zoom in on the map at the location you want in order to find your picture. After you see a picture at the location, click on it for a bigger view.
If you have to travel to look at a roof, it helps to know what the weather conditions are in real time, at the actual location. Webcams can tell you more about this than weather reports. There may be snow on the roof that's been there for weeks, even though the weather report calls for a bright sunny day.
If you can't find a useful webcam image at those sites, you can try here. Our experience with this site is that some of the images won't be available or might not be outdoor pictures at all.
National Weather Service (US) - Provides historical weather data.
Irish Meteorological Service - Provides historical weather data.
Radar.com - National Weather Service enhanced radar site (US).
Weather (Canada) - Provides historical weather data.