Climate change is suspected to be behind the roller coaster weather. Sounds like non-sense? Let's assume that you agree on that the average temperature of atmosphere is going up, then here are some brief explanations which I summarized from various sources:
- Higher surface temperature increases total amount of vapor in atmosphere. More vapor ends up with higher precipitation.
- Higher surface temperature increases the power of low pressure system. Surface air rises more easily. Stronger low pressure system in the middle altitude pulls down arctic cold air or up equatorial hot air.