The presence of a ring around the sun or, more commonly, the moon in the night sky, indicates very high ice crystals composing cirrostratus clouds. The brighter the ring, the greater the odds of precipitation and the sooner it may be expected. Rain or snow will not always fall, but two times out of three, precipitation will start to fall within 12 to 18 hours. These cirroform clouds are a forerunner of an approaching warm front and an associated low pressure system.