Weather is what the air is doing at one place and time: today's temperature, wind, clouds and rain, shaped by the air masses and fronts passing by. Climate is the pattern of weather over a long time, usually 30 years or more. Weather is your mood today; climate is your personality.
Key idea
Weather changes from hour to hour and day to day. Climate is the long-term average and range of weather, usually figured over 30 years. One hot or cold day, week or even year is weather, not climate.
Why it works
Any single day is a mix of a long-term pattern and a lot of short-term ups and downs. Taking the mean over many years makes the ups and downs cancel out, leaving the pattern. That is why NOAA describes each place's climate with 30-year averages, called climate normals (the current ones cover 1991 to 2020).
Worked example: Weather or climate?
Sort these: (1) "It's snowing in Denver right now." (2) "Phoenix gets about 20 cm of rain a year."
- (1) describes one moment in one place: weather.
- (2) describes a long-term average: climate.
Answer: (1) weather; (2) climate
Worked example: Finding a mean
A town's July average temperatures for five years were 24, 26, 23, 25 and 27 °C. What is the mean?
- Add: $24 + 26 + 23 + 25 + 27 = 125$.
- Divide by 5: $125 \div 5 = 25$ °C.
- A real climate normal would use 30 years, not 5.
Answer: 25 °C
Common mistake
Treating one cold week as evidence against a warming climate. A cold week is weather. Climate change shows up in long-term averages over decades. Check: ask what time span the evidence covers; if it is days or weeks, it is weather.