Cooler, wetter weather is heading our way, the National Weather Service said today. A Pacific low-pressure system is moving slowly across the Northwest this weekend, and steady rain is falling along much of the Cascades. The system is expected to weaken as it moves west toward the Spokane area, the agency said, with rain concentrated in the mountains of northeast Washington. Spokane faces a 50 percent chance of showers tonight and a 60 percent chance of showers Sunday, forecasters said. The chance of rain diminishes for the labor Day holiday Monday, and drier, warmer weather is expected by the middle of next week.