The temporal distribution of surface atmospheric water vapor levels during shortduration extreme heat events at Chicago was assessed. Heat events were characterized by at least 3 consecutive days with a minimum temperature greater than 24°C (75°F) and a maximum temperature greater than 35°C (95°F). Thirteen such heat events were identified during the 75 yr record at Chicago Midway Airport located inside the city. Average dew points in events fluctuated considerably over time, but generally increased. Event average hourly dew-point values before the mid 1980s were generally below 21°C, rising to an average of 24°C during the mid 1990s. The temporal changes in dew-point values were related to 2 factors: (1) the existence of average to aboveaverage regional precipitation anomalies occurring in May and during the 20 d period prior to the heat event, and (2) changes in agricultural practices that have led to enhanced evapotranspiration rates in the Midwest.KEY WORDS: Short-duration heat waves · Surface dew-point temperature · Chicago · Climate variability · Evapotranspiration Resale or republication not permitted without written consent of the publisherClim Res 24: [243][244][245][246][247][248][249][250][251][252][253][254] 2003 western heat-related fatalities were nearly one-fourth of those in 1995, a reduction partially due to improved municipal response efforts for heat waves.Record high dew points experienced during these 2 events of the 1990s raised questions about dew point levels experienced during earlier Chicago heat waves. A recent study (Sparks et al. 2002) identified that the frequency of hours with extreme dew points (> 24°C) at 2 northeastern Illinois first-order NWS stations, Rockford and Chicago O'Hare, had increased significantly during a 42 yr period .The primary goal of this study was to determine whether and why dew point levels had changed over time during short-duration Chicago heat waves. The Chicago Midway Airport weather records were examined for a 75 yr period . Any changes would have a significant impact on human health, the design and operation of air conditioning systems, as well as electrical demand in the Midwest (Cohen & Kosar 2000, Changnon 2002, Sparks et al. 2002.Both Kunkel et al. (1996) and Palecki et al. (2001) concluded that the extreme high dew points experienced during the 1995 and 1999 heat events occurred as a result of widespread regional rainfalls that preceded the heat waves. These rains were believed to have increased evapotranspiration rates from actively growing Midwestern corn (Zea mays L.) and soybean (Glycine max L.) crops. Studies that examined conditions prior to the development of Midwest mesoscale convective systems (MCSs) postulated that the primary source for low-level moisture during weak-flow (anticyclonic) situations was evapotranspiration from crops, not moisture advection from the Gulf of Mexico (Chang & Wetzel 1991, Bentley & Mote 1998, Changnon & Kunkel 1999. The possibility exists that changes in agricultural practices relating to corn a...

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Corn earworm (Helicoverpa zea) (CEW) generally are not able to overwinter annually in the Upper Midwest, thus they must migrate northward to affect the primary vegetable-growing locations in this area. Migration of CEW is highly dependent on the weather. Provided a source region in the southern United States, migration of CEW from south to north appeared to occur when a high-pressure system was located in the eastern United States and a low-pressure system and attendant frontal boundary was observed to the east of the Rocky Mountains and/or northern plains states. Southerly wind flow located west of the high and east of the low forms an “insect pump.” Convection cells allowed CEW to lift and advance from their source region northward in the low-level insect pump. When CEW encountered an area of downward motion during their northward flight, such as a frontal boundary or a light precipitation area, they had a tendency to “drop out” of the sky into fields below, an area referred to as the “Drop Zone.” Favorable weather patterns for CEW migration and subsequent infestation of fields in north-central Illinois were confirmed by high CEW trap counts at Rochelle over the last four decades. Accepted for publication 5 September 2006. Published 19 July 2007.

Grazing ability is difficult to record in animals under free-ranging conditions without sophisticated methods. Alternatively, grazing ability may be indirectly inferred from changes in BW and production characteristics during the grazing period. The present study investigated the effect of grazing on resource-limited rangelands on BW, wool characteristics, and offspring weaning weights in nine hundred five 5/8, 7/8, and fullblood Merino ewes of 2 to 7 yr of age during a grazing period of approximately 2.5 mo (between January and March). A total of 469 ewes gave birth to a single lamb, 248 to twin lambs, and 188 did not give birth. Body weights were measured and wool samples taken before and after the ewes were allowed to graze freely on the rangelands; absolute change in BW and change in BW as a percentage of initial BW were estimated. On average, grazing on resource-poor rangelands resulted in BW loss, a reduction in fiber diameter and its CV, and increased staple length. Animals with finer wool at the start of the grazing period lost phenotypically (r = -0.07, P < 0.05) and genetically (r = -0.23, P < 0.05) less BW during the grazing period and had a greater probability to carry 1 lamb (or 2) to term (P < 0.05). Animals that lost less BW produced more greasy fleece (r = 0.09, P < 0.01). Body weight change did not significantly influence offspring weaning weights. Change in BW was moderately heritable at h(2) = 0.29; fiber diameter was strongly heritable at h(2) = 0.51. Animals with the least inclusion of Merino genetics lost more BW (P < 0.01) during the grazing period and had a more uniform fiber diameter (P < 0.05) but shorter staples (P < 0.05) and less fleece (P < 0.0001) than animals with a greater level of Merino genetics. Our results indicate that animals with finer wool appeared to be better adapted to the cold Nevada desert. Thus, selection for finer wool may positively influence adaptability to resource-limited cold climate conditions; alternatively, BW change may be selected for directly. Because nutritional deficiencies during pregnancy can have adverse consequences for the offspring, indirect selection for grazing ability would foremost result in healthier ewes that can produce lambs and wool without compromising their welfare.

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