Since we can't collect data from the future, models have to use estimates and assumptions to predict future weather. The atmosphere is changing all the time, so those estimates are less reliable the further you get into the future.

Why is it difficult to predict the weather?

Weather is the day-to-day condition of the atmosphere at a place with respect to the temperature, humidity, rainfall, etc. It is a process which can change very rapidly, Hence it is difficult to predict. On the other side, it is easier to predict climate as it is the average weather pattern taken for a long time.

Is weather easy or difficult to predict?

constitute the weather of a place. Weather is never constant anywhere. The weather at a place changes even over short periods of time. Therefore, it is difficult to predict weather of a place.