As the eclipse begins, some view-blocking clouds could actually disappear. A recent study found that after 15 percent of the sun becomes obscured, cumulus clouds, the small cotton ball-like ones typical for a sunny day, can dissipate. Even if you are outside the path of totality, watch what happens to the clouds.
If the sky is full of these little clouds at the start of Monday’s eclipse, it would be fun to count them and watch as they slowly disappear, said Victor Trees, an author of the study and a Ph.D. candidate at the Delft University of Technology and Royal Netherlands Meteorological Institute. But if the skies are overcast, he said, “we do not expect the eclipse to let this cloud deck disappear, and it indeed could ruin the view of the eclipse for a local observer.”
The type of clouds in Dr. Trees’s study, cumulus, tends to bubble up because the sun’s warmth on the Earth’s surface forces low-level air to rise, similar to the way water bubbles up as it boils in a pot. As the warm air rises, it cools to a point where condensation can occur. During the eclipse, the temperature near the ground will cool, limiting the rising air, almost like someone reducing the heat on a pot of boiling water to a simmer.
While some cumulus clouds may be present on Monday, the dominant cloud cover in portions of the South and Northeast is likely to come from a few storm systems that create types of clouds less affected by the temperature change created by the eclipse.
For those lucky enough to be in a place where clouds disappear, wait and watch them begin to pop back into view after totality.