The National Weather Service in Phoenix has issued a dust-storm warning until 7 p.m. for the greater Phoenix metropolitan area.
SRP is reporting about 1,400 customers who've lost power as of 6 p.m., mostly in the south of the Valley.
By just before 5:30 p.m., 12 News' helicopter was capturing video of a wall of dust beginning to cover parts of Casa Grande. Live video from a news team just west of Casa Grande on Highway 84 showed dark skies and light rain beginning to fall.
Radar showed rain moving north behind the dust, said 12 News meteorologist Caribe Devine, as the dust storm continues to move north into the Valley. By 5:45, storms were forming north and west of Casa Grande, with scattered rain storms and lightning south of the Valley, but no rainfall for the Phoenix area so far.
Visibility on the roads in the affected area is very low. Reports have ranged from no visibility to 1/2 mile just south of the Valley.
Officials advise anyone encountering blowing dust or blowing sand on the roadway to pull off the road as far as possible and put the vehicle in park. Turn the lights all the way off and keep your foot off the brake pedal.