An early monsoon system crept into the state, swapping the excessive heat wave with high humidity on Monday morning.

Motorists in the Valley were resigned to driving dirty cars to work, and will for a few days, as the early monsoon storm rolls in waves of alternating dust and rain.

Meteorologist James Sawtell with the National Weather Service forecasted the storm will bring with it a 50 percent chance of rain in the valley.

"Very favorable for thunderstorm activity through the end of the week and into next weekend," he predicted, "although the storm chances do decrease slightly on Friday and Saturday."

That, in turn, will help drop high temperatures, even in the valley.

"We're actually looking for a high of only 100 degrees," he said, "so that would be seven degrees below normal, if we got down that low."

The same system should also return Flagstaff highs to the upper 70s.

Sawtell warned that these early monsoon storms produce a lot of dust ahead of each system. Drivers should expect to pull over and turn off lights when visibility is reduced.