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The weather of the McMurdo Dry Valleys, Antarctica, the largest ice-free region of the Antarctica, has been continuously monitored since 1985 with currently 14 operational meteorological stations distributed throughout the valleys. Because climate is based on a 30-year record of weather, this is the first study to truly define the contemporary climate of the McMurdo Dry Valleys. Mean air temperature and solar radiation based on all stations were -20 degrees C and 102 W m(-2), respectively. Depending on the site location, the mean annual air temperatures on the valleys floors ranged between -15 degrees C and -30 degrees C, and mean annual solar radiation varied between 72 and 122 W m(-2). Surface air temperature decreased by 0.7 degrees C per decade from 1986 to 2006 at Lake Hoare station (longest continuous record), after which the record is highly variable with no trend. All stations with sufficiently long records showed similar trend shifts in 2005 +/- 1 year. Summer is defined as November through February, using a physically based process: up-valley warming from the coast associated with a change in atmospheric stability.