Some are caused by thaw in April. Most avalanches occur in the backcountry, outside of developed ski areas. Large avalanches are most likely to happen in obvious paths, such as bowls, gullys and above timberline. Look for signs of avalanches in the past, like bent or damaged trees. When the snow cover is very unstable, nature often broadcasts clear danger signals.
Fresh avalanches are the best clue.
Snow that cracks, collapses, or makes hollow sounds is also unstable. Weak layers that are found by digging snow pits are signs of unstable snow. Snow that has become wet from thaw or rain can be dangerous. You should practice frequently to be proficient in using your beacon. Remember that only 1 of 3 victims buried without a beacon survives.