What do the letters s, w, and f indicate in Type C and D climate codes?

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Köppen climate classification map — Köppen climate classification The major climatic types are based on patterns of average precipitation, average temperature, and natural vegetation. This map depicts the world distribution of climate types based on the classification originally invented by Wladimir Köppen in 1900.

In the Köppen climate classification system, the second letter in the codes for Type C and D climates describes the seasonality of precipitation. These letters indicate the following:12

f (no dry season): Precipitation is more evenly distributed throughout the year, and the criteria for the other two designations are not met.2
w (winter dry): The precipitation in the driest month of the winter half of the year is less than one-tenth of the amount in the wettest month of the summer half.2
s (summer dry): The precipitation in the driest month of the summer half of the year is less than 30 mm and less than one-third of the wettest month of the winter half.2

These designations help climatologists categorize midlatitude climates based on their specific moisture patterns.12