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The 1993 record-breaking summerflood in the Upper Mississippi River Basin resulted from an unprecedentedly persistent heavy rain pattern. Rainfall totals for the Upper Mississippi River Basin were, by a large margin, the largest of this century for the 2-, 3-, 4-, and 12month periods encompassing the 1993 summer. The totals for these periods are estimated to have a probability of occurrence of less than 0.005 yr\ In addition, the number of reporting stations receiving weekly totals in excess of 100 mm (events identified in a previous study as being closely correlated with floods) was the largest in at least the last 45 yr. Other conditions contributing to the flood include above-normal soil moisture levels at the beginning of June 1993; large-sized areas of moderate to heavy rains; occurrence of rain areas oriented along the main stems of major rivers; a large number of localized extreme daily rainfall totals (greater than 150 mm); and below-normal evaporation. The large-scale atmospheric circulation patterns during the summer of 1993 were similar to the patterns associated with past heavy rain events, although much more persistent than past events.

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The use of temperature data from poorly sited stations can lead to a false sense of confidence in the robustness of multidecadal surface air temperature trend assessments.

Mexico was above normal during E1 Nifio events and below normal during La Nifia events. In this paper, we examine the relationship of ENSO to snowfall for the entire United States, expanding on these earlier regional studies. Data and Methods of Analysis

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Daily observations of precipitation and maximum and minimum temperature from the National Weather Service's cooperative observer network collected prior to 1948 were keyed into a digital database. This database includes stations in the nine midwestern states of Illinois, Indiana, Iowa, Kentucky, Michigan, Minnesota, Missouri, Ohio, and Wisconsin. The primary source used in this project was the publication Climatological Data, which began in 1896. This database provides a substantial enhancement to the National Climatic Data Center's TD-3200 Summary of the Day database, which includes little data prior to 1948. Approximately 2 x 10 7 data values were keyed, increasing the amount of pre-1948 digital data by about a factor of 3 and substantially improving its spatial uniformity. The data were subjected to an extensive set of quality control procedures. It is expected that these data will find their greatest value in applications requiring very long historical records, such as assessments of the risks of extreme events.