Basically, when you see the storm threatening,...
draw Cho-ku-rei in the air
draw Halu and Harth over the area you want to keep the rain away from
repeat over and over as you feel guided to do
draw Tibeten Dia-Ko-Myo and direct at the clouds you want to break up...in essence punching them apart, repeat as needed.
draw anymore symbols you feel guided to do
look away from the clouds for a minute or two, and take another look, you may be amazed to see the sun popping out of of the spots you "punched" and the clouds moving by a bit quicker
keep your reiki energy On for as long as you want to keep the storm away (or least try to have the intent to do so)
I have been to a few art festivals recently and have used this each time and the rain would stay away till I was done wht the festival. The moment I stopped on the first time, it started raining, luckily I was heading back to the car by that time. The next time the rain stayed away the whole time. I have found that I can do this if it has not already started raining, I guess once it starts coming down there is no stopping it then, or maybe I just need more practice or more people to help. But if it was only a drop or two I was able. The limit of our abilities is unknown, the best thing to do is to try it all (safely and smartly) and just be open to the possibilties.