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I have gotten a number of requests for statistics regarding the
decade mark in temperature.  Reaching 100 degrees has been somewhat
an anomaly since the drought of 1988.  The speculated reason for this
is the intensive cropping (more plants per acre, better genetics) that
increases transpiration and thus moisture in the lower atmosphere.
This makes it difficult for the air to heat up rapidly due to the
sun's energy going into heating extra water vapor.

Anyway, here is a listing of the number of days per year that the high
temperature was 100 degrees or higher.  You can see how 1988 stands
out and relative lack of 100+ temperatures in the 90s

 Year  #   Year  #  Year  #  Year   #  Year  #  Year  #
 1950  0   1960  0  1970  0  1980  27  1990  8  2000  8
 1951  0   1961  3  1971  5  1981   4  1991  3  2001  6
 1952  8   1962  0  1972  1  1982   2  1992  0  2002  6
 1953 15   1963  7  1973  2  1983  31  1993  0  2003 13
 1954 22   1964  9  1974 19  1984   7  1994  0  2004  0
 1955 30   1965  5  1975 10  1985   4  1995  5
 1956 17   1966  8  1976 14  1986   1  1996  0
 1957 13   1967  5  1977 18  1987  13  1997  3
 1958  0   1968  2  1978  1  1988  34  1998  1
 1959  3   1969  1  1979  2  1989   8  1999  9
Total by decade
 50s 108   60s  40  70s  72  80s  131  90s  29  00s  33

I don't have a total for 2005 using official data, but it would appear
that the total to date (20 Jul) is 0.

Note: These numbers are for any location in Iowa hitting 100+

Iowa Environmental Mesonet

Iowa State University Department of Agronomy

Days over 100 degrees