This chart is a measure of atmospheric mositure from the surface up to about 30,000 feet and is similar to Satellite Precipitable Water Imagery. However rather than a direct measurement from a satellite, a computer numerical model generates these values. While not as accurate as upper air soundings or satellitle imagery, this tracking method does provide continous data across the Southwest when the other methods may be missing data.

Thunderstorms are more likely to occur when precipitable water values rise above an inch and a half (1.50") along the Colorado River, above one inch (1.00") over southeast and central Arizona, and above a half an inch (0.50") along the Mogollon Rim. On the wettest days, the precipitable water can rise over 2.00 inches along the Colorado River, over 1.50 inches in southeast Arizona, and up to 1.00 inch along the Rim. During periods of high precipitable water, the risk of a flash flood occuring with a thunderstorm is significantly enhanced.