GRAND RAPIDS (WZZM) -- Sunday afternoon, if you were outdoors near the west side of Grand Rapids and happened to look skyward, you would have noticed a rare cloud formation that lasted roughly an hour.
It's called a fallstreak hole or a hole punch cloud. Appropriately named for the apparent hole in a thick layer of clouds.
Conditions need to be just right in the atmosphere for this to occur.
Clouds are either made of water vapor (when the temperature is above freezing) or ice crystals (when the temperature is below freezing). This afternoon's clouds were primarily made of ice crystals but there was a very small patch that remained water vapor in spite of the fact that the temperature in the cloud deck was below freezing. This results in what's known as "super cooled" water droplets - water that's in liquid form simultaneously measuring slightly below freezing (32°F). It's a very delicate phase and the slightest disruption will cause each droplet to convert to a more stable phase. Once this happens, the particle is too heavy to be suspended in thin air with the rest of the cloud so it falls toward the earth. A sort of domino effect is created as the patch of air tries to reach a similar state as the rest of the cloud. The result is a circle of clear sky that spreads out like a ripple from a stone dropped into a calm pond.