A strong Pacific storm will begin to uncoil across Oregon, Washington and Northern California through the weekend, promising heavy rain and snow that will replenish water supplies but could also unleash destruction.

A low-pressure system moving across the state through Wednesday was expected to bring scattered showers to the Valley and snow in the north. Rainfall hit the north and northwest edges of the Valley before noon on Monday, but no measurable showers hit Phoenix Sky Harbor International Airport, where the office records weather, Worley said.