 Big Z weather is a service of Alton Auto Butler. Become a member today. Wash every day at one low price. Alton Auto Butler, where every vehicle gets the royal treatment. Mostly cloudy tonight, a few showers possible during the evening. Better chance overnight, a low in the mid-70s. Partly sunny Saturday, a slight chance of showers and thunderstorms. High around 90. Saturday night, mostly clear, a low in the mid-60s and sunny on Sunday with a high in the low 80s.