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The four seasons are distinct in all parts of Idaho, but not simultaneous. Spring comes earlier and winter later to Boise and Lewiston, which are protected from severe weather by nearby mountains and call themselves "banana belts." Eastern Idaho has a more continental climate, with more extreme temperatures; climatic conditions there and elsewhere vary with the elevation. Mean temperatures in Boise range from 29°F (–2°C) in January to 74°F (23°C) in July. The record low, –60°F (–51°C), was set at Island Park Dam on 16 January 1943; the record high, 118°F

(48°C), at Orofino on 28 July 1934. The corresponding extremes for Boise are –23°F (–31°C) and 111°F (44°C).

Humidity is low throughout the state. Precipitation in southern Idaho averages 13 in (33 cm) per year; in the north, over 30 in (76 cm). Average annual precipitation (1971–2000) at Boise was 12.2 in (31 cm), with more than 21 in (53 cm) of snow. Much greater accumulations of snow are experienced in the mountains.