Köppen climate classification
The Köppen climate classification divides climates into five main climate groups, with each group being divided based on seasonal precipitation and temperature patterns. The five main groups are "A" (tropical), "B" (dry), "C" (temperate), "D" (continental), and "E" (polar). Each group and subgroup is represented by a letter. All climates are assigned a main group (the first letter). All climates except for those in the "E" group are assigned a seasonal precipitation subgroup (the second letter). For example, "Af" indicates a tropical rainforest climate. The system assigns a temperature subgroup for all groups other than those in the "A" group, indicated by the third letter for climates in "B", "C", and "D", and the second letter for climates in "E". For example, "Cfb" indicates an oceanic climate with warm summers as indicated by the ending "b". Climates are classified based on specific criteria unique to each climate type.
Climate of Minneapolis–Saint Paul
The Twin Cities experiences a wide range of precipitation types. Rain is the most common form during the summer months, while snow, sleet, freezing rain, and occasionally rain occur during the winter. The summer months of June, July and August account for nearly half of the annual precipitation total across the Twin Cities. Most of this rain falls from thunderstorms, a frequent summer occurrence. Even though summer is the primary season for the Twin Cities to experience thunderstorms, they can occur from March to November. On rare occasions thundersnow can occur, where thunder and lightning accompanies winter or (more usually) spring snowstorms. During spring and summer, some thunderstorms are severe. These storms produce damaging straight line winds, large hail and, occasionally, a tornado. The Twin Cities has experienced several major derecho events, most recently during the Late-May 1998 Tornado Outbreak and Derecho which traveled from South Dakota to New York on May 30 – May 31, 1998. Summertime thunderstorms are fueled by dew points that often reach into the 70s °F (21 °C) and sometimes even .