Weather within 24 hours of the shoot: you’re going to pay something no matter what, because the crew and gear are already committed. If you try to shoot and then get stopped by lightning, that’s not the crew’s fault, and they should get full pay for the hours, at least a half day’s pay if you send them packing. If you can cancel inside of 24 hours, but before they have to travel, that could reduce your outlay by some amount, maybe fifty percent or more.
I don’t know that there is a universal standard for these things, wish there was. Should look at what a union camer operator’s contract says. I would put it in writing when booking the crew, something like: Cancel/re-schedule within 48 hours or more of contracted time for shoot, no charge. Cancel within 24 or fewer hours, pay one-half day rate plus any travel used before the cancellation. This might take the form of an additionl charge tacked onto the actual rescheduled shoot day’s numbers instead of a payment up front, if it adds up the same way but makes the paperwork more streamlined, I’d go for that, figuring most weather-related delays are rescheduled within the same week. Some other arrangement might be to add on extra meal break hours to even up the score.
When you get along with your crews, deals can be very flexible. I had a producer once that went out of his way to really REALLY feed us very well, real restaurants, food and drinks on him, order whatever you want, no special limits, real plates and silverware, etc. …This all with the understanding that when we get back to the job, if we have to go an extra hour or two past the normal break time to nail something important, nobody is gonna complain or stop work and leave the set for anything but the briefest bathroom break. We were all onboard for that.
My bottom line is always, what’s fair to both sides: if my gig means you had to pass up another job, and you didn’t have time to score another job to replace the rain-out, you need to get at least a partial payment out of that rain-out, since you committed to the work and gave up time to be there, particularly if you traveled. If there is enough cushion that you didn;t have to be put-out, then no charge, we’ll get the money when it’s rescheduled.