IND has had 5 days in a row with a sub 80º maximum temperature. The last time that occurred was on July 4-8, 1979. Since 1943, when the airport became the official site for Indianapolis, the longest streak in July is 6 days on July 26-31, 1971. The forecast for the last 3 days of July is for temps to max out in the 70's...so this current one could be the longest streak since 1943.
July 26-31, 1971: 6 days* (78, 76, 75, 77, 75, 75)
July 24-28, 2013: 5 days (77, 79, 79, 78, 73)
July 4-8, 1979: 5 days (75, 76, 76, 79, 77)
July 10-14, 1975: 5 days (78, 74, 76, 67, 78)
July 19-23, 1947: 5 days (73, 75, 73, 72, 77)
July 17-20, 2009: 4 days (75, 71, 75, 79)
July 24-27, 2004: 4 days (75, 67, 68, 73)
July 19-22, 2000: 4 days (75, 77, 79, 78)
July 12-15, 1990: 4 days (67, 64, 78, 75)
July 4-7, 1972: 4 days (73, 71, 73, 77)
July 4-7, 1960: 4 days (73, 77, 76, 77)
July 13-16, 1960: 4 days (76, 75, 77, 78)
July 19-22, 1958: 4 days (77, 66, 75, 79)
July 16-19, 1956: 4 days (79, 76, 78, 77)
*lasted 7 days, including a 79º on August 1, 1971
July 2013 so far, has had 9 days with maximum temperatures not reaching 80º. Since the airport era began (1943), July 2009 has the most with 14 days.
July 2009: 14 days
July 1947: 11 days
July 1960: 10 days
July 1945: 10 days
July 2013: 9 days
July 1971: 9 days
July 1958: 9 days
July 1956: 9 days
July 2004: 8 days
July 2001: 8 days
July 1984: 8 days
July 1981: 8 days
July 1964: 8 days
July 1962: 8 days