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Stanley A. Changnon Jr.

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Stanley A. Changnon Jr.

Abstract

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Stanley A. Changnon Jr.

Abstract

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Stanley A. Changnon Jr.

Abstract

An understanding of applied climatology and its information-generating research requires recognition of the total cause-and-effect spectrum including the issue detection, the research effort pursued, the type of product, the users, and their applications of findings. Twenty climatic information studies done at the Illinois Climate Center in 1977-79 are reviewed to illustrate why they were done, often as a result of general inquiries or specific requests, and a few of their key results. The studies each required from weeks to months to complete. Most users of the results fell in two general classes, government or business-industry. The studies revealed applications in three areas: the design of facilities, the planning and/or operations of facilities and activities, and the climatic assessment of weather extremes.

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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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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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Stanley A. Changnon Jr.

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As part of METROMEX, a five-year study of how St. Louis affects summer weather, studies were made of possible urban effects on severe local storm phenomena. Localized (within 40 km of the city) increases were found in various thunderstorm characteristics (about +10 to +115%), in hailstorm conditions (+3 to +330%), in various heavy rainfall characteristics (+35 to +100%) and strong gusts (+90 to +100%). No indication of effects on tornado activity was found. The more substantial percentage increases were found in the expressions of storm intensity (very frequent thunder, hailfall impact energy and high rainfall rates). Urban-related increases in severe local storm conditions appeared at midday, were greatest in the evening and ended by midnight. Urban-induced increases occurred with all synoptic weather types but were most frequent and intense with squall lines and cold fronts. Results suggest that urban-induced factors alter the microphysical and dynamic properties of clouds and storms.

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Stanley A. Changnon Jr.

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The first climatic investigations of hail in North America were by Lemons and Flora during the 1940's. These were followed by more intensive, state-scale climatic investigations in the 1960's to meet insurance concerns. Subsequent concerns with hail by the aviation industry and the weather modification community led to the first collection of mesoscale hail data from dense networks and radar studies during the 1960's and 1970's.

This paper is a review of available hail information presented in a series of time and space scales. Although the North American hail data and information are less than adequate, there is much more hail information than exists elsewhere in the world. Very extensive findings on hail are available for Alberta, Illinois and Colorado. Phenomenologically oriented studies have focused on hailstones, point hailfalls, hailstreaks, hailstorm, hailswaths and hail days over various sized areas. Results for each of these classifications are presented according to studies that focused on national, regional and small-scale areas.

The principal hail area of the continent is in and to the lee of the Rocky, Mountains where hail is both frequent and intense; hence the Great Plains suffers great damages. Another high-frequency area related to spring storms extends from Texas to Michigan, but causes less crop damage since it largely precedes the crop season. Certain inexpensive data collection efforts and analyses which would greatly improve our knowledge of hail are recommended.

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Stanley A. Changnon Jr.

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Crop-hail insurance companies, both private and governmental, insure about 15% of the national crop value, and their data represent a better source of information to evaluate economic aspects of hail loss than exist for any other form of severe weather. Past results and these insurance data were used 1) to illustrate variations in hall losses on various time and space scales, and 2) to reveal through these Illustrations the limitations in the available information and the need to make estimates to derive total hail loss for any period or place. The nation's greatest hail loss area is the Great Plains ($86 million annually) with the Corn Belt area ranking second ($67 million). Illinois rank first in the amount of liability; North Carolina ranks first in total insurance premiums and in number of paid losses; Idaho first in the average amount paid for an individual loss; and North Dakota first in total crop loss. Little information exists about property losses from hail, but limited Illinois studies suggest it represents about 10% of the crop losses. Catastrophic hailstorm lost days that create $1 to $5 million in losses and thus 15–75% of the total annual loss in a state are a major problem for farmers, hail insurance companies, and hail modification groups. The total estimated average annual crop-hail loss in the United States is $284 million, which represents about 1% of the national crop production, and the total national loss (crops and property) due to hail is estimated to be $315 million.

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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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