Which one is harder to predict accurately, and why?

Weather is harder to predict accurately.

This is because weather is governed by chaotic atmospheric dynamics, where small errors in initial data—such as a slight miscalculation in temperature or wind speed—can grow exponentially over time. This sensitivity, often called the "butterfly effect," limits the reliable predictability of specific weather events to about 10 to 14 days.

Climate is easier to predict because it deals with long-term averages rather than individual events. While we cannot predict the weather on a specific date a year from now, we can accurately predict the climatic range for that month based on historical trends, energy balance, and solar radiation, which are much more stable and predictable over long periods.