If you’ve spotted lunar halo in the night sky, you can have some forecasting fun.
If you look closely, you might see a few stars inside the ring. Grandma believed that the number of stars inside the circle was the same as the number of days before the rain or snow would move in.
Why? Well, you have a much better chance of seeing lots of stars inside the ring if the sky is very clear. In order for the rings to form in the first place, there must be a thin veil of cirro-stratus clouds. Those clouds are made up of wispy sheets of ice crystals, as high as five kilometres above the ground. They’re also forerunner clouds: they reach out ahead of an advancing weather system. The density of those ice crystals increases as the weather system approaches. That increased density will make the sky look quite hazy or milky and block out some of the starlight.
The more stars you see, the more time you have before the rain arrives. Fewer stars indicate that the system is not far off. Count the stars inside the ring and wait. Grandma wasn’t wrong very often.
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Cindy Day is the chief meteorologist for SaltWire Network.