Distinguish weather, short-term, day-to-day atmospheric conditions, from climate, the typical long-term pattern of weather in a region over many years.
Weather and climate are easy to mix up, but they describe different time scales. Weather is what is happening in the sky right now or today, and it can change hour to hour or day to day. Climate is the TYPICAL pattern of weather in a place over MANY years, such as "this area usually has hot, dry summers and mild, wet winters."
A single unusual day, like an unexpected snowy day somewhere that is normally warm, is weather, not a sign that the climate itself has changed.
Mastery looks like: They correctly label new statements as weather or climate and explain the time-scale difference between the two.
Common stumbles: Assuming one unusual weather day proves a change in climate, or using the words "weather" and "climate" as if they mean the same thing.