Even on clear, cloudless days you may not be safe!
When Lightning Strikes Out of a Blue Sky
https://www.nbcnews.com/id/wbna43941393
I heard of a case of a high school student in Albuquerque who was playing in a soccer meet when he got struck by lightning from a clear blue sky.
What nobody knew what that on the backside of the mountains there was a thunderstorm nobody knew about. The lightning traveled that far ahead of the storm.