Lots of concern about the milky-white rain that fell in southwestern New Mexico on January 7th.
Pure water in equilibrium with CO2 should have a pH about 5.6. Most rain in remote areas, containing organic acids, would be a bit more acid - pH ~ 5. This stuff apparently had a pH of 7.9: very alkaline!
So far, speculation on a cause centers on white dust kicked up from Willcox Playa in southeastern Arizona, and that seems quite likely as an explanation to me.