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A brief but intense heat wave developed in the central and eastern United States in mid-July 1995, causing hundreds of fatalities. The most notable feature of this event was the development of very high dewpoint temperature ([T.sub.d]) over the southern Great Lakes region and the Upper Mississippi River Basin. At many locations, hourly values of [T.sub.d] set new records. The combination of high air and dewpoint temperatures resulted in daily average apparent temperatures exceeding 36 [degrees] C over a large area on some days. A comparison with past heat waves shows that this was the most intense short-duration heat wave in at least the last 48 years at some locations in the southern Great Lakes region and Upper Mississippi River Basin. An analysis of historical data for Chicago, where the majority of fatalities occurred, indicates the intensity of this heat wave was exceeded only by a few periods in the 1910s and 1930s. Impacts in the Chicago urban center were exacerbated by an urban heat island that raised nocturnal temperatures by more than 2 [degrees] C. An analysis of radiosonde data indicates that maximum daytime boundary layer mixing depths were only a few hundred meters in the core region of the heat wave. Simulations using a single-column version of a three-dimensional mesoscale model strongly suggest that this contributed to the very high values of [T.sub.d] since soil moisture in the central United States was near to above average and evapotransporation was likely high, causing a rapid moistening of the shallow boundary layer.

The short but intense heat wave in mid-July 1995 caused 830 deaths nationally, with 525 of these deaths in Chicago. Many of the dead were elderly, and the event raised great concern over why it happened. Assessment of causes for the heat wave-related deaths in Chicago revealed many factors were at fault, including an inadequate local heat wave warning system, power failures, questionable death assessments, inadequate ambulance service and hospital facilities, the heat island, an aging population, and the inability of many persons to properly ventilate their residences due to fear of crime or a lack of resources for fans or air conditioning. Heat-related deaths appear to be on the increase in the United States. Heat-related deaths greatly exceed those caused by other life-threatening weather conditions. Analysis of the impacts and responses to this heat wave reveals a need to 1) define the heat island conditions during heat waves for all major cities as a means to improve forecasts of threatening conditions, 2) develop a nationally uniform means for classifying heat-related deaths, 3) improve warning systems that are designed around local conditions of large cities, and 4) increase research on the meteorological and climatological aspects of heat stress and heat waves.

Effective responses by government agencies, businesses, and private industry to climate disasters such as the disastrous Mississippi River flood of 1993 hinge on the regional availability of diverse up-to-date weather, climate, and water information. In addition to the obvious need for accurate forecasts and warnings of severe weather and floods, other types of meteorologically based information can contribute to effective responses. Some examples of information requested during and after the 1993 flood include 1) hydroclimatic assessments of the magnitude of the event, 2) agricultural assessments of the impacts of heavy rains and flooding on corn and soybean production, and 3) probabilistic outlooks of the recurrence of flooding based on soil moisture conditions. Quick responses to these climate information needs necessitate 1) a real-time climate monitoring system, 2) physical models to assess effects and impacts, and 3) scientific expertise to address complex issues.