A few blurbs on Rings around the Moon tell the following findings.
Moon Ring Weather Folklore
Folklore has it that a ring around the moon signifies bad weather is coming, and in many cases this may be true. So how can rings around the moon be a predictor of weather to come?
The ice crystals that cover the halo signify high altitude, thin cirrus clouds that normally precede a warm front by one or two days. Typically, a warm front will be associated with a low pressure system which is commonly referred to as a storm.
It is believed that the number of stars within a moon halo indicate the number days before bad weather will arrive. Give it a try the next time you observe a moon halo.