Tres Arroyos has an oceanic climate (Köppen climate classification Cfb) bordering on humid subtropical. Summers are warm while winters are mild with snowfall happening sometimes, but accumulation is rare. Rain is rather evenly distributed (836mm per year), with winter being a bit drier. Sunshine is moderate, with summer being sunnier, and averages to about 200 hours a month and 2374 hours a year.
Climate data for Tres Arroyos (1991–2020, extremes 1961–present)
Roughly 5 km from the city of Tres Arroyos lies the "Arroyo Seco" archaeological site, which is considered to be one of the oldest yet found in Argentina. Over 40 skeletons, presumably in burial positions, were found at the site, dated to estimated age of 9000 years B.P. The site includes tools, hunting implements and fossils of extinct mammals. Much of the extensive materials are on display at the José A. Mulazzi Municipal Museum, which includes reconstructions of how the people of the time lived..