2011 (MMXI) was a common year that started on a Saturday in the Gregorian calendar. It was the 2011th year of the Common Era (CE) and Anno Domini (AD) designations; the 11th year of the 3rd millennium and of the 21st century; and the 2nd of the 2010s.

The United Nations designated 2011 as the International Year of Forests and the International Year of Chemistry. It was marked by a wave of revolutions in the Arab World known as the Arab Spring, including the beginnings of several unresolved protest movements and armed conflicts.

A humid continental climate (Köppen prefix D and a third letter of a or b) is a climatic region typified by large seasonal temperature differences, with warm to hot (and often humid) summers and cold (sometimes severely cold) winters.

Precipitation is relatively well-distributed year-round in many areas with this climate, while others may see a marked reduction in wintry precipitation and even a wintertime drought. Snowfall, regardless of average seasonal totals, occurs in all areas with a humid continental climate and in many such places is more common than rain during the height of winter. In places with sufficient wintertime precipitation, the snow cover is often deep. Most summer rainfall occurs during thunderstorms and a very occasional tropical system. Though humidity levels are often high in locations with humid continental climates, it is important to note that the "humid" designation does not mean that the humidity levels are necessarily high, but that the climate is not dry enough to be classified as semi-arid or arid. Very few areas with a humid continental climate fall in the Dsa or Dsb categories; generally these are adjacent to Mediterranean climates where the elevation precludes such classification due to colder winters.