CfaCfb

CfaCfb is an informal designation used in discussions of the Köppen climate classification to describe a transitional zone that exhibits characteristics of both humid subtropical (Cfa) and temperate oceanic (Cfb) climates. It is not an official category; rather, it signals local variability where the thresholds that separate Cfa from Cfb are near, producing a mixed climate signal.

In Köppen terms, Cfa is a temperate climate with no dry season and hot summers (the warmest month above 22°C), while Cfb is a temperate climate with no dry season and warm summers (the warmest month below 22°C). The coldest month in both groups is typically between -3°C and 18°C. Regions designated CfaCfb often feature strong maritime or elevational influences that allow some locations to cross one threshold while adjacent areas remain below it, creating a gradient rather than a sharp boundary. Precipitation tends to be distributed year-round in both types, though Cfa areas may experience more pronounced summer rainfall in some regions.

Geographically, CfaCfb occurs in coastal or highland zones where oceanic air moderates heat yet seasonal temperatures swing enough to push summers above or below 22°C, yielding a mosaic climate. Climate change and land-use changes can shift local conditions, expanding or contracting the mixed zone.

Uses and limitations: The CfaCfb label helps researchers describe spatial climate variability relevant to ecology, agriculture, and urban planning. As an informal descriptor, it depends on data resolution and threshold definitions.