How hot was the month of July in 2011? So hot that just by plotting the location of each daily heat record that was broken, a nearly complete image of the contiguous United States is visible. Almost 9,000 daily records were broken or tied last month, including 2,755 highest maximum temperatures and 6,171 highest minimum temperatures (i.e., nighttime records). It should be noted that the tally of records collected so far is not complete – more are expected to come in as station data from across the U.S. is mailed to the National Climatic Data Center. The statistics reported here only include weather stations with real-time electronic reporting, which accounts for about two-thirds of the locations. Final numbers should be available later in August.
This image plots how many times a heat record was broken or tied in a given location. Some cities reached daily high temperatures 19 out of the 31 days in the month. The largest concentration of these records occur in the southern Plains, Midwest, and Northeast U.S., which were gripped by a series of heat waves pushing heat indices well into the 100’s (Fahrenheit) for many days at a time.
Temperature records are based on historical data from NCDC’s Cooperative Summary of the Day data set and the preliminary reports from the Cooperative Observers and National Weather Service stations around the country. All stations have at least 30 years of data upon which these records are based.