Clouds reduce photosynthetically active radiation by about 25% when you can still see your shadow. When you can't see your shadow, that's about 50% of PAR blocked. And when you can't see your shadow and can't find what part of the sky the sun is in, that's about 75% PAR reduction.

Read about this on a cloudy day in Tokyo, and see two apps that allow you to either check the full sun instantaneous PAR, the full sun daily PAR, or the past year of PAR, for pretty much anywhere in the world: https://www.asianturfgrass.com/post/shade-effect-of-clouds/

Read more about all kinds of turfgrass topics at https://www.asianturfgrass.com/
Find turfgrass information and decision-making tools at https://www.paceturf.org/
See the PACE Turf YouTube channel at https://www.youtube.com/user/paceturf
See the ATC newsletters at https://subscribepage.com/atc_newsletters
Listen to the ATC Doublecut with Micah Woods podcast at https://atc-doublecut.transistor.fm/
Listen to the ATC Office Hours podcast at https://atc-office-hours.transistor.fm/

Find Turf Without Borders at https://turfwb.asianturfgrass.com/
More about ATC soil tests at https://www.asianturfgrass.com/project/soil-tests/