Gray areas in meteogram

[luigiparisi]

I apologize if this has already been explained, but I could not find the answer.
What do the gray areas in the image I attached correspond to?

Thank you to those who will help me

[idefix37]

@luigiparisi
These grey areas are clouds as forecasted in the Meteogram at different levels. The level scale is shown at left side of the Meteogram.

[luigiparisi]

Thank you @idefix37 !