Your outdoor plans only become more important if there is the possibility for rain, wind, cold or other adversities from Mother Nature. You have BBQ's, family get-togethers, pool parties for the kids, birthday parties. You want to make sure that when you go and see the foliage at its peak, it really IS at its peak, and if the weather is going to be wet and chilly, then perhaps the tenting plans should be changed.
Organizations hold parades, fairs and the like.
The Indy500 Race comes and goes. There's even weather insurance you can buy for any event. If your investment is substantial, it would be sensible to get the insurance from a broker, and the forecast from right here. OR, you can order an advanced forecast which will let you know accurately whether the sun will shine or the rain will pour. Moreover, perhaps it is just being prudent to make a good return on investment.