This means that in addition to the direct moonlight, you will also see diffracted moonlight in a circle 22 degrees away from the moon. This is about the distance of your fist, held at arm's length.
Like a rainbow, this halo can even be slightly colored; red on the inside, and blue on the outside.
Yes, it can mean that rain or snow is coming soon. Those high, wispy clouds could be the forerunners of storm clouds right behind them

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