If you're planning to go in Uruguay, their summer is the best season to go to their beaches.In the months of April and November, winds, rain, and cool temperature combines. The month of July's average temperature is around 11°C and January's is within 21°C and 26°C.
Although the weather in the country is relatively cool, snow is not common, just in 1962 and 1991.
More about Uruguay's weather and more, on the lonely planet.
Link: Weather in Uruguay - Lonely Planet Travel Information