BOSTON (CBS) – Once the snow clears Friday, it’s going to get very cold for Halloween.

Temperatures will plummet into the 20’s on Saturday morning. By the late afternoon it will be sunny and bright in the mid-to upper 40’s. Once the sun sets for trick-or-treating, there will be an eerie and spooky full moon.

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It’s also a rare blue moon, which is the second full moon of the month. This will be the first blue moon in the U.S. since March 2018. The phrase “once in a blue moon” usually means a rare event that can either be something lucky, or unlucky. Therefore, if something weird happens this Halloween, you’ll know why.

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If you’re going outside Saturday evening, be prepared, it will be very chilly. Temperatures will dip into the mid-30’s, so wear an extra layer under that costume and bring a jacket.

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The temperatures will continue to fall into the 20’s overnight into Sunday morning as Daylight Saving Time ends and we turn the clocks back an hour. There will be scattered showers on Sunday.