* WHAT...Flash flooding caused by excessive rainfall is possible. * WHERE...Tucson Metro Area, Southeast Pinal County, Tohono O'odham Nation, Upper San Pedro River Valley Upper Santa Cruz River Valley/Altar Valley, Baboquivari Mountains, Catalina and Rincon Mountains, Dragoon and Mule and Huachuca and Santa Rita Mountains. * WHEN...From Saturday morning through late Sunday night. * IMPACTS...Excessive runoff may result in flooding of rivers, creeks, streams, and other low-lying and flood-prone locations. Low-water crossings may be flooded. Flooding may occur in poor drainage and urban areas. * ADDITIONAL DETAILS... - An increase in moisture will bring scattered thunderstorms Saturday and Sunday. Rainfall rates in excess of 1 inch per hour are expected with the stronger storms with isolated areas having the potential of 1-3 inches. Additional rainfall from the previous day and overnight activity will result in faster responses in normally dry washes, creeks and roadway dips. - Http://www.weather.gov/safety/flood