Climate change models predict we'll see summer storms of far greater severity than in the past.
There are good reasons for this forecast. First, as the atmosphere warms, it will be able to hold more water vapour. So when conditions are right, more rain will fall.
Second, a warmer arctic zone results in a weaker jet stream. As these west-to-east winds weaken, they will tend to meander, much as a slow prairie river weaves across the landscape. Weather patterns will tend to stall in places as a result. Again, when conditions are right, a storm that might have lasted hours can turn into one lasting for days.
This is what happened last summer in Alberta - and Calgary suffered massive flood damage as a result. A storm system stalled over the eastern Rockies for three days, dumping huge amounts of rain and overwhelming any flood defences that existed downstream.