Since 1960, the average high temperature on July 4 in Chicago has increased about eight degrees Fahrenheit. Similarly, residents of East Tennessee's Knoxville have seen an increase of about seven degrees during that 40-year period, according to statistics provided by researchers at the Department of Energy's Oak Ridge National Laboratory. Meanwhile, residents of Seattle have actually seen the high temperature for the Fourth of July drop by nearly nine degrees.
For most of the 21 cities included in this survey, using the standard 95 percent confidence level test -- the criteria of whether results are statistically significant -- there hasn't been a big difference in high temperatures for the Fourth of July.
In Chicago, however, high temperatures below 80 degrees have occurred just three times since 1980 (79 in 1996, 68 in 1997 and 77 in 1998), and the average temperature on July 4 has increased to 83 degrees. During the same 20-year-period, Knoxville has hit the 90-degree mark six times in the 1990s after reaching 90 or above just twice in the 1980s. The high for the last 40 years in Knoxville was 96 degrees in 1993, and the average temperature on Independence Day has increased to 86 degrees.
Looking at Middle Tennessee, in Nashville the Fourth of July temperature has been 90 or better 11 times since 1980 with the high for that period being 95 in 1980. The lowest temperature for the holiday in Nashville in the last 40 years is 79 degrees in 1976. The average temperature for July 4 in Nashville is 89. Meanwhile, Memphis has an average Fourth of July temperature of 91 and has recorded temperatures above 90 a dozen times since 1980.
Of the 21 cities included in this survey, Tahoe City, Calif., has the lowest average temperature since 1960 with 75 degrees. Phoenix took honors for the highest average temperature with 110 degrees on the Fourth of July. Dallas was next at 95 degrees followed by Memphis at 91.
If you're looking for the perfect place for a holiday picnic, Boston might be a good choice, where the average July 4 temperature is a comfortable 79 degrees. Looking toward the South, Atlanta's average Fourth of July temperature since 1960 is 89 degrees. The high for Atlanta since 1960 is 98 degrees (1996) and the low 74 (1994). From 1960 to 1999, Atlanta had Fourth of July highs in the 90s nine times.
While the results are interesting, Bob Cushman, director of ORNL's Carbon Dioxide Information Analysis Center, advised against reading too much into the analysis. "After all, we're only looking at the high temperature on one specific day for each of those 40 years. Whatever that temperature might be may or may not relate to the larger issue of whether the U.S., or any region in the country, is experiencing an overall warming trend."
Although many people associate July 4 with being one of the hottest days of the year, the highest temperatures in most parts of the country usually occur in late July and early August, according to Dale Kaiser, a meteorologist with the Carbon Dioxide Information Analysis Center. Kaiser and Daria Scott, a student from St. Cloud State University in St. Cloud, Minn., compiled the data for this survey.
Other cities - with average temperatures for the Fourth of July in parentheses -- included in the survey were: Bismarck, N.D. (82); Cincinnati (82); Detroit (82); Denver (85); Kansas City, Mo. (88); Los Angeles (88); Miami (90); Minneapolis (82); New York (84); Salt Lake City (87); and Washington, D.C (87).
For many cities, the temperatures used in this survey were actually recorded at a suburban station several miles away. For example, the temperatures used for Chicago were from Aurora, Ill., and for Washington, D.C., they were from Glen Dale, Md. The survey covered the years 1960 through 1999.
The Carbon Dioxide Information Analysis Center (http://cdiac.
ORNL is a DOE multiprogram research facility managed by UT-Battelle.
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