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Stanley A. Changnon Jr.

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Stanley A. Changnon Jr.

Abstract

Average durations of thunder events are greatest (>120 min) in the Oklahoma–Kansas area and least (<60 min) along the west coast and northeast. The average point duration of thunder activity ranges from 10 000 to 12 000 min along the Gulf Coast, 8000 to 10 000 min in the Midwest, exceed 6000 min in Arizona, but is only 1000 to 2000 min in the northeast, and 500 to 1000 min along the west coast. Nocturnal thunder events typically last 10 to 30 min longer than those in the daytime in all areas except for the western mountains and extreme southeast where daytime events exceed those at night by 5 to 15 min, on the average.

The trends in thunder event activity during the 1948–77 period indicate four distinctly different characteristics. The stations in the southwestern and northwestern United States exhibit flat, unchanging trends in events during the 30 years, but events in the northern Great Plains-Midwest gradually decreased with time; those in the Great Lakes increased since 1950; and those in the southeastern United States decreased to minimums in the 1960s and then increased to 1977. The temporal distribution of extratropical cyclonic activity in July explains 25% to 50% of the temporal variations in July thunder events over most of the central and eastern United States. However, increases in thunder events since the late 1960s in the Upper Midwest and along the East Coast were not associated with increased cyclonic activity.

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Stanley A. Changnon Jr.

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Stanley A. Changnon Jr.

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The temporal histories of 702 convective echoes measured in the St. Louis area during the 1973 summer were studied to discern potential effects on echo behavior of the urban influences and those effects resulting from the merger of two or more echoes. The 190 echoes that merged grew faster (50%), became taller (52%), and lasted longer (122%) than non-merger echoes. The average echo top growth 10 min after a merger was 1500 m, and on any given day 80% of the heights of merger echoes at a given stage of echo life were higher than those of non-merger echoes. The 137 echoes that crossed the urban area were longer lasting (119%), faster growing (61%), taller (30%), and more merged (44% vs 23%) than the non-urban echoes. The 61 urban echoes that subsequently merged over or beyond St. Louis were demonstrably longer lasting (110 vs 44 min) and taller (4800 m at 10 min after entry into the urban area and 5900 m at urban exit) than 76 urban echoes that did not merge. The urban echo that merged was also measurably different than the rural merged echo. The average urban merged echo lasted 51% longer, grew 100% faster, and achieved a height 20 min after merger that was 133% higher. The urban area apparently affected nearly half (44%) of the echoes over it leading to larger, more vigorous, and longer lasting storms that always merged with one or more other storms. This dynamic process leads to more rain, short-duration rainstorms and hailstorms in and east of St. Louis.

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Stanley A. Changnon Jr.

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Collection of crop loss assessment values adjacent to halipads has allowed a comparative investigation to determine which hailfall characteristics were related to the degree of loss to wheat, corn and soybean crops in Illinois. Establishment of such relationships is important information because it indicates which characteristics must be measured, either with hailpads or other hail-sensing devices, to provide meaningful evaluations of hail suppression project results and useful data for crop-hail studies. Because of factors related to the thickness of wheat stands, wheat losses were found to be closely related to the frequency of hailstones with diameters >0.25 inch. Corn and soybean losses exhibited varying seasonal relationships with either hailstone frequency and/or hailfall energy values. Corn losses in May related only to stone frequency, whereas corn losses in later growth stages (July-August) related well to both stone frequency and energy. A given number of hailstones falling in May produced considerably less corn damage than the same number in the June-August period. Soybean losses also related to both energy and stone frequency, although marked seasonal variations existed with each characteristic. An energy value of 1.0 ft-lb ft−2 produced, on the average, soybean loss of 12% in May, 15% in July-August, and 61% in June. Derived relationships indicated that 100 hailstones ft−2 (each >0.25 inch diameter) produced a 42% soybean loss in June, but only a 13% loss in July-August. The high correlations between crop losses and hailstone frequency and/or energy values indicate that potential crop losses in uncropped areas can be estimated from hail-sensing devices that measure both hail characteristics.

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Stanley A. Changnon Jr.

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Collection of hail data that will provide meaningful measures of the results of hail suppression projects varies according to five factors, including the geographical-climatic site, the statistical design, and the goal of the project. Eight possible techniques of collecting hail data are evaluated with respect to their use in different areas, availability of historical data, and with different project designs. Each technique provides data that have distinct limitations. However, the two data collection techniques rated best for projects having a continuous seeding (on all hail days) design are networks of passive hailpads and raingages, and crop-hail damage records. The best technique for use in projects utilizing a single-storm seeding design or a random daily seeding (single area) design is a network of recording hailgages.

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Stanley A. Changnon Jr.

The State of Illinois has just established a climate center addressing a wide variety of climate-related activities. This center has evolved after 25 years of services, research, and data management addressing the climatology of Illinois and the Midwest. The products of this effort reflect state-related interests in climate information and data. The Illinois program may also help serve as a model for some states who will evolve centers as part of the federal-state cooperative effort that is to be an integral part of the National Climate Program.

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Stanley A. Changnon Jr.

The winter of 1977–78 was the worst, on the basis of both low temperatures and snow, on record in Illinois and many other areas of the Midwest. Representatives of 70 households in central Illinois participated in a detailed study of how the extreme cold and snow affected individuals. The average added cost was $93 per individual, largely to residences and vehicles, and extrapolation of this to all Illinois citizens results in an estimated statewide cost in excess of $1 billion. This was compounded by a wide variety of personal inconveniences, worries, extra work, and injuries. There were no deaths in the sampled group but 52 Illinoisans were killed by the 18 winter storms. For those living in rural areas beyond the city of their employment, costs and inconveniences were greater. The average individual cost was $120, and rural dwellers experienced more travel problems, more delayed services, and more absences from school and work.

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Stanley A. Changnon Jr.

A paradox has developed involving on one hand sizeable reductions during the last two years in federal support of weather modification, as opposed to major scientific-technical advances in the field plus strong recommendations for increased federal support from the scientific community. The major recent advances include the capability to operationally dissipate cold fogs, to enhance snow from orographic clouds, and to increase rain from tropical clouds, plus the discovery of sizeable urban-related increases in rainfall. Other advances include special weather radars, aircraft with new cloud sensors and the capability to penetrate thunderstorms, new seeding materials and delivery systems, and new techniques for evaluation of projects. These have been coupled with the spread of weather modification around the world and with the initiation of major seeding projects in Colorado (NHRE, HIPLEX, and San Juan Project), Florida, South Dakota, and Illinois-Missouri (METROMEX). Several groups (NACOA, NAS, ICAS, NWC, AMS) all made a series of positive recommendations for advancing the field through more federal support and reorganization. Yet, beginning in FY74, federal support for weather modification dropped 21% when other R&D increased 11%. Many possible causes for the paradox appear, including fear of weather changes, lack of scientific commitment, and a series of public, scientific, political, and military controversies. The three basic issues are that weather modification is still an immature technology; the socio-economic impacts are ill defined; and its management has been uncertain. Proper resolution of the paradox is more apt to occur either because of a dramatic scientific breakthrough or from growing concerns about weather and climate-related environmental changes.

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Stanley A. Changnon Jr.

Abstract

A study of summer precipitation conditions in the Chicago area sought to discern evidence of urban influences on precipitation processes and rainfall magnitude by investigating cloud, radar echo, rainfall and thunderstorm data. The rainfall studies identified an area of 15% greater rainfall in central Chicago, considered largely a result of urban influences. The degree of change is less than found at St. Louis, possibly a result of the inhibiting lake influences at Chicago. With respect to the placement of the rain change, the synoptic weather conditions when rain changes occur (squall lines and zones), and the tendency for rain changes to exist in heavier rainfall conditions, the Chicago findings reveal good agreement with those at St. Louis. Limited causative studies suggest an urban enhancement of convective clouds over Chicago and southern Lake Michigan during late afternoon, and case studies of radar echo behavior showed maximum echo intensification repeatedly occurred over the city and at higher elevations than in non-urban cells. Results suggest urban enhancement of strong convection although more study is needed.

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