Climate
An arid region of high xeric scrubland and desert steppe, the canyon and wider basin average 8 inches (200 mm) of rainfall annually; the park averages 9.1 inches (230 mm). Chaco Canyon lies on the leeward side of extensive mountain ranges to the south and west, resulting in a rainshadow effect that fosters the prevailing lack of moisture in the region. The region sees four distinct seasons. Rainfall is most likely between July and September; May and June are the driest months. Orographic precipitation, which results from moisture wrung out of storm systems ascending the mountain ranges around Chaco Canyon, is responsible for most of the summer and winter precipitation; rainfall increases with higher elevation. Occasional aberrant northward excursions of the intertropical convergence zone may boost precipitation in some years.
Chaco endures remarkable climatic extremes: temperatures range between -38 to 102 °F (-39 to 39 °C), and may swing 60 °F (33 °C) in one day. The region averages less than 150 frost-free days per year, and the local climate swings wildly from years of plentiful rainfall to prolonged drought. The heavy influence of the El Niño-Southern Oscillation contributes to the canyon's fickle climate.
Read more about this topic: Chaco Culture National Historical Park
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