Obvious clues to look for that a thunderstorm is on the way include a static noise on an AM radio station, the smell of rain and a sudden drop in temperature along with a strong breeze. Other signs are a change in wind direction, billowing and darkening clouds, flashes of lightning in the distance or the faint sound of thunder.
Certain types of cloud formations are also warnings of a pending storm. Cumulus clouds are giant pillows of heaped up clouds that are a common sign of severe thunderstorms with lightning. These clouds grow fast due to an increase in temperature and progress into large cumulonimbus clouds, which bring on a thunderstorm.
Cirrus clouds are wispy high clouds that form at 20,000 feet or higher and portend changes in weather patterns that can be an indication of incoming bad weather. Lenticular clouds are smooth, long and wavelike. They are an indication of approaching winds high up in the atmosphere. These clouds may appear to be stationary, but are often an indication of a large, incoming storm.
When barometric or atmospheric pressure suddenly decreases, this is often a sign that either snow, rain or thunderstorms are possible within the next 24 hours.