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If you stepped outside this morning, you likely saw a ring or “halo” around the moon. I noticed it on my way into work this morning. What causes this and what does it mean?

The ring is caused by ice crystals that are very high up in our atmosphere.  These ice crystals "bend" the moon's light (which is, of course, sunlight that is being reflected by the moon's surface).  Most of these ice crystals have the same shape, so the refracted light can often make a perfect circle.

Here's a simple explanation (courtesy: www.hiwaay.net):

Years ago, people used to use moon rings as a way of forecasting.  The ice crystals are related to thin cirrus clouds (those are very high, soft, wavy clouds) that normally precede a warm front by one or two days.  Usually when we see warm fronts, we see active weather.  Sure enough, if you are paying attention to my forecast, we are expected to see storms as we head into tonight and a warm front move through the area as we head through Friday.

-Brian