I have often wondered why many generally use the words climate and weather interchangeably.

Quoting the meaning given in the dictionary.com from The American Heritage Science Dictionary,

Weather – The state of the atmosphere at a particular time and place. Weather is described in terms of variable conditions such as temperature, humidity, wind velocity, precipitation, and barometric pressure. The average weather conditions of a region over time are used to define a region’s climate.

Climate – The general or average weather conditions of a certain region, including temperature, rainfall, and wind.

Why do many say that the climate on a particular day is nice or bad when weather is the word that should be used? Talking about weather, I hate the weather in Chennai today! I wish it would stop raining. Roads are so messy.