Tornadoes most commonly develop from wall clouds attached to the rain free base. However, tornadoes can form from the rain free base itself. While these signatures do not show a tornado on the ground, they are ominous signs that a tornado may be present or forming. Spotter reports from these areas are crucial to determine if a tornado is present. Some floods occur seasonally when winter or spring rains, coupled with melting snow, fill river basins with too much water, too quickly.
River floods develop and reach their peak more slowly than flash floods.
In many cases, river floods reach their peak after the rain has ended. SCUD Scud clouds are small, ragged, low cloud fragments that are not attached to a larger cloud base. These clouds are often seen behind thunderstorm gust fronts. Generally associated with cool moist air, like thunderstorm outflow. Scud may be mistaken for a funnel cloud.