Both weather and climate models currently do a decent job. Weather can be predicted pretty accurately up to about four days ahead and the broad patterns of global climate are well replicated in climate models. That’s because over past decades a multitude of researchers have tested and refined the models, improving how they represent the atmosphere and oceans and their interaction.
When scientists talk about uncertainties, they are not saying they are clueless. They are saying they have a working explanation of the world which gives a range of answers, usually a usefully narrow range.
While it is true that snow is a thing of the past, I am not so sure about the barbecue summer prediction.