A little rain isn't going to kill a horse... Hurricanes are another story... And what are the honest chances of a horse getting struck by lightning? If there are trees around the horse will be fine =) I guess I'm going by Canadian weather, there isn't hurricanes XP rain storms and blizzards are no big deal here. The horse has a thick enough coat to deal with rain and blizzards, but if you're really concerned put a blanket on the horse =)
Yup...the odds of a horse developing COPD, hoof, or behavioral issues from being stalled are far greater than the odds of getting struck by lightning. That's not to say I condemn those who stall their horses, I just don't believe in it myself, although mine have access to the barn any time they want to get away from the flies or weather.
On a side note, I got hit by a tornado 4 years ago - demolished my hay barn and coral area. When the horses heard the tornado (people can hear them a mile or so away - horses obviously farther) they went to the center of the pasture away from structures and trees, and stood as a group facing the tornado...all of them emerged untouched. The barn they have access to wasn't damaged, but coral panels and steel sheeting from the hay barn were flying everywhere. Horses obviously do get injured or worse in storms, but it's funny how they instinctively do what gives them the best possible chance of survival. The coral panels that are up in the picture I put up after the tornado passed to keep the horses as much away from the dangerous debris as possible...then had to borrow someones metal detector to get as many of the nails and metal fragments as I could out of the pasture - a pain in the hiney.
Didn't mean to hijack the thread - just a sidebar on weather and horse safety.
This was taken by a passing motorist and posted on the net - it just happened to be taken when the tornado was on my ranch, which is just over that ridge. When it hit my place it was an F-4...one of those big wedge tornados...