A humid continental climate with warm summers is classified as Dfb. In this code, “D” denotes a continental climate, “f” means there is no distinct dry season, and “b” indicates a warm rather than hot summer.
The “b” criterion generally means the warmest month averages below 22°C, while at least four months average above 10°C. This distinguishes Dfb from Dfa, the hot-summer humid continental subtype, whose warmest month reaches at least 22°C.
Dfb climates are widespread across northern and eastern North America and large parts of Europe and Asia. They commonly have substantial seasonal contrasts: cold winters, moderately warm summers, and precipitation in every season. Southern Ontario, parts of the northern United States, Poland, Finland, and southern Siberia contain examples.
The code is often confused with Cfb, the oceanic climate code. Both end in “fb,” but the first letter matters: “C” indicates a temperate climate, whereas “D” indicates a colder continental regime with a colder winter threshold.