Köppen and Geiger further divided each major division (A, B, C, D, E, F, H) into smaller groups based upon precipitation and temperature patterns. These subcategories are as follows:
Second letter (lower case) adds divisions based on precipitation patterns.
- f - wet year-round
- s - dry summer season
- w - dry winter season
- m - monsoon
Third letter (lower case) adds divisions based on temperature patterns.
- a - hot summer
- b - warm summer
- c - cool summer
- d - very cold winters
| Af | Equatorial rainforest | No dry season. The driest month has at least 2.36" (60 mm) of rain. Rainfall is generally evenly distributed throughout the year. All average monthly temperatures are greater than 64°F (18°C). |
|---|---|---|
| Am | Equatorial monsoon | Pronounced wet season. Short dry season. There are one or more months with less than 2.36" (60 mm). All average monthly temperatures are greater than 64°F (18°C). Highest annual temperature occurs just prior to the rainy season. |
| As | Equatorial savanna | Summer dry season. There are more than two months with less than 2.36" (60 mm) in summer. All average monthly temperatures are greater than 64°F (18°C). |
| Aw | Equatorial savanna | Winter dry season. There are more than two months with less than 2.36" (60 mm) in winter. All average monthly temperatures are greater than 64°F (18°C). |
| BWk | Mid-latitude desert | Mid-latitude desert. Evaporation exceeds precipitation on average but is less than half potential evaporation. Average temperature is less than 64°F (18°C). Winter has below freezing temperatures. |
| BWh | Subtropical desert | Low-latitude desert. Evaporation exceeds precipitation on average but is less than half potential evaporation. Average temperature is more than 64°F (18°C). Frost is absent or infrequent. |
| BSk | Mid-latitude steppe | Mid-latitude dry. Evaporation exceeds precipitation on average but is less than potential evaporation. Average temperature is less than 64°F (18°C). |
| BSh | Subtropical steppe | Low-latitude dry. Evaporation exceeds precipitation on average but is less than potential evaporation. Average temperature is more than 64°F (18°C). |
| Cfa | Humid subtropical | Mild with no dry season, hot summer. Average temperature of warmest months are over 72°F (22°C). Average temperature of coldest month is under 64°F (18°C). Year around rainfall but highly variable. |
| Cfb | Marine west coast | Mild with no dry season, warm summer. Average temperature of all months is lower than 72°F (22°C). At least four months with average temperatures over 50°F (10°C). Year around equally spread rainfall. |
| Cfc | Marine west coast | Mild with no dry season, cool summer. Average temperature of all months is lower than 72°F (22°C). There are one to three months with average temperatures over 50°F (10°C). Year around equally spread rainfall. |
| Csa | Mediterranean | Mild with dry, hot summer. Warmest month has average temperature more than 72°F (22°C). At least four months with average temperatures over 50°F (10°C). Frost danger in winter. At least three times as much precipitation during wettest winter months as in the driest summer month. |
| Csb | Mediterranean | Mild with cool, dry summer. No month with average temperature of warmest months are over 72°F (22°C). At least four months with average temperatures over 50°F (10°C). Frost danger in winter. At least three times as much precipitation during wettest winter months as in the driest summer month. |
| Cwa | Humid subtropical | Mild with dry winter, hot summer |
| Dfa | Humid continental | Humid with hot summer |
| Dfb | Humid continental | Humid with severe winter, no dry season, warm summer |
| Dfc | Subarctic | Severe winter, no dry season, cool summer |
| Dfd | Subarctic | Severe, very cold winter, no dry season, cool summer |
| Dwa | Humid continental | Humid with severe, dry winter, hot summer |
| Dwb | Humid continental | Humid with severe, dry winter, warm summer |
| Dwc | Subarctic | Severe, dry winter, cool summer |
| Dwd | Subarctic | Severe, very cold and dry winter, cool summer |
| ET | Tundra | Polar tundra, no true summer |
| EF | Ice Cap | Perennial ice |
| H | Complex zone | Can encompass any of the above classifications due to the mountainous terrain. |