With the strong easterly winds the balloon ascended directly into the thunderstorms, and as a result, was terminated prematurely. Enough of a profile was obtained though to give evidence as to the cause of the extreme thunderstorm development and the resulting flood. The atmosphere had become very unstable with a precipitable water of 1.44 inches. Two ingredients necessary for thunderstorms with torrential downpours. What follows is a pictorial recreation of the thunderstorms based on radar observations, surface observations, eye-witness accounts, and fundamental atmospheric processes.
Precipitable water is an indication of the amount of water that is available to produce rain.
This is a concept termed upslope flow. While mid level winds blew out of the east and southeast, high level winds at the thunderstorm tops were out of the west. This caused the anvil and ice portion of the thunderstorm to blow over the top of newly developing thunderstorms. Ice crystals and snow falling out of the anvil fed into the newly developing cells, creating an effect of natural cloud seeding. Usual precipitation efficiency for thunderstorms is 30 to 40 percent, that is 30 to 40 percent of the moisture for storm development is released as precipitation.