major weather events 2011:

US:

April tornado outbreak

http://yearinreview.yahoo.com/2011/us_extreme_weather#3spring-tornado-outbreak

According to the National Oceanic and Atmospheric Administration (NOAA), April set the record as the most active tornado month in history with 753 tornadoes causing 364 fatalities. 

The second outbreak of tornadoes hit the Southeast from April 24 to April 29. This five-day outbreak is now the greatest in recorded world history. It had double the number of tornadoes (353 in 21 states) than the previous record, which was set just two weeks earlier, and killed 321 people. On April 27 alone, there were 188 confirmed tornadoes, including the devastating EF-4 that hit Tuscaloosa -- one of the most damaging of all time.

On May 22, an F-5-rated tornado tore through southwest Missouri, destroying one-third of the town of Joplin. With winds over 200 mph and a path spanning nearly a mile wide and six miles long, if left behind utter destruction. It claimed the lives of 157 people, making it the deadliest tornado since official records started being kept in the 1950s. 

Midwest flooding

http://www.nytimes.com/2011/05/03/us/03levee.html?pagewanted=all
http://www.reuters.com/article/2011/05/11/us-flooding-idUSTRE74462I20110511

The cost of the Mississippi floods totaled over $4 billion.

Midwest heatwave

http://www.wunderground.com/blog/weatherhistorian/comment.html?entrynum=33

Hurricane Irene (New England flooding)

http://www.businessweek.com/news/2011-08-29/covered-bridges-lost-as-irene-brings-major-flood-to-vermont.html

Global: