Last time this happend = scary. Gates of Lodore. Huge microburst storm, hail, wind, lightning. Rafts in the water were fine. I got out and squatted in the lightning position. Damn kayak nearly blew away. Primary hazard was falling rocks and trees from deluge created land slides. Pretty fun in hind sight. Needless to say, the rainbows were really nice after the storm. What ever you do, don't stand at the base of a gully. The chances of getting struck by lightning = slim. The chances of getting pounded by rocks in a gully during a gully-washer = good.
Sorry to hear of loss of a young man. Thoughts and prayers with his family.