- 11/27/12

If you looked up in the sky tonight (Tuesday), you not only saw the beautiful, nearly-full moon in the sky (the moon is full tomorrow night), you also probably saw a large ring around the moon.  The effect is the result of increasing moisture in the upper atmosphere, a thin layer of cirrus clouds that in tonight's case, are moving in ahead of a thicker band of cloudiness which will be here overnight.  The moisture is made up of ice crystals which refract the moon's light, creating the circle of light.

Weather folklore says when you see a ring around the moon (or the sun), you can expect rain within 24 hours; often, that's true, but not always.  The scientific explanation for the folklore often being correct is that ahead of precipitation-bearing systems, the moisture typically builds from the highest levels of the atmosphere downward.  Cirrus clouds, made of ice crystals, develop first, then clouds thicken as the moisture builds in the atmosphere.  In tonight's case, there won't likely be enough moisture to produce precipitation.  However, the ring around the moon is an accurate predictor of more clouds to come.  Forecast models show the cloudiness quickly clearing around daybreak tomorrow (Wednesday), leaving us with partly to mostly sunny skies.

So, the next time you see a ring around the moon (or sun), remember that thicker clouds are likely on the way, and maybe some precipitation too.