Difference between Weather and Climate. Key Difference: Weather is the state or conditions of the atmosphere over a short period of time, usually a day or so. Climate is the average conditions that are expected at a certain place over a number of years. Weather and climate are words that are often heard in meteorology, while weather is also used in day to day in order to refer to the conditions outside. Weather and climate are similar, but different. The main difference between the two is weather changes day to day, while climate does not change for longer periods of day. Weather is the state or conditions of the atmosphere over a short period of time, usually a day or so.