A Flood Watch is in effect for all of northern and central Arizona from late Tuesday night through Thursday evening, the National Weather Service in Flagstaff said in an alert issued at 12:37 a.m. MST on Tuesday, October 20, running until 11:00 p.m. MST on Thursday, October 22. The weather service said an upper-level trough will bring a deep surge of subtropical and tropical moisture into the region, with showers and thunderstorms developing early Wednesday and continuing through Thursday evening. Flash flooding is possible in creeks, normally dry washes, swimming holes and recently burned areas, and low-water crossings may be flooded.

A second Flood Watch covers south-central Arizona, including central Phoenix and the East and West Valley, from Wednesday evening through Thursday afternoon, according to the National Weather Service in Phoenix. Forecasters there expect widespread showers and thunderstorms with localized rainfall rates of 1 to 2 inches per hour at times, and warned that excessive runoff may flood rivers, creeks, streams and other low-lying areas.

Fox Weather reported that the same storm system will push heavy rain and storms across the Southwest on Wednesday and Thursday, with a rare Level 3 severe weather risk for northern Arizona on Wednesday for damaging winds and possible tornadoes, and a Level 2 out of 4 flash flood risk across parts of Arizona, Utah, Colorado and New Mexico. Rain totals of 1 to 2 inches are possible across parts of the region through Friday, Fox Weather said.

Drivers — including truckers on Arizona's desert highways — should never cross flooded washes or low-water crossings, should monitor National Weather Service updates, and should be ready to act if Flash Flood Warnings are issued. Sources: National Weather Service Flagstaff and Phoenix alerts; Fox Weather.