Search Results
Abstract
Cooperative substation records of hail and thunder incidences have been used as a source of data to develop more accurate and detailed average patterns of these phenomena. Since the accuracy and completeness of records by volunteer observers are generally considered questionable, a method of determining accurate substation records of thunder and hail was devised. The evaluation method relies strongly on comparisons of substation data with those from nearby first-order stations. The number of stations with accurate hail records was found to be greater than the number with accurate thunder records. Reliable records of both events in Illinois and surrounding States have provided very useful information.
Abstract
Cooperative substation records of hail and thunder incidences have been used as a source of data to develop more accurate and detailed average patterns of these phenomena. Since the accuracy and completeness of records by volunteer observers are generally considered questionable, a method of determining accurate substation records of thunder and hail was devised. The evaluation method relies strongly on comparisons of substation data with those from nearby first-order stations. The number of stations with accurate hail records was found to be greater than the number with accurate thunder records. Reliable records of both events in Illinois and surrounding States have provided very useful information.
Abstract
Research concerning long-term temperature changes in the United States has shown the need to adjust measured increases in the 1901–1950 period to remove the effects of environmental changes. Unique long-term 3-ft. soil temperature data at Urbana, III., provide a measure of the natural increase in temperature in the 1903–1947 period and also permit an evaluation of the increase shown by the air temperature at Urbana. The increase in mean annual soil temperatures between 1903 and 1947 amounted to 1.2° F. The mean annual air temperatures during this period inercased 2.3° F., but when adjusted statistically to remove environmental effects, the natural increase in the air temperature was 1.1° F. Thus, at Urbana, the adjusted increase in air temperatures appears to be substantiated by the increase shown by the 3-ft. soil temperature data.
Abstract
Research concerning long-term temperature changes in the United States has shown the need to adjust measured increases in the 1901–1950 period to remove the effects of environmental changes. Unique long-term 3-ft. soil temperature data at Urbana, III., provide a measure of the natural increase in temperature in the 1903–1947 period and also permit an evaluation of the increase shown by the air temperature at Urbana. The increase in mean annual soil temperatures between 1903 and 1947 amounted to 1.2° F. The mean annual air temperatures during this period inercased 2.3° F., but when adjusted statistically to remove environmental effects, the natural increase in the air temperature was 1.1° F. Thus, at Urbana, the adjusted increase in air temperatures appears to be substantiated by the increase shown by the 3-ft. soil temperature data.
Abstract
Statistics on thc incidence of damaging lighting in Illinois during the 1914–47 period were gleaned largely from published and unpublished records of the U.S. Weather Bureau to perform a climatological investigation. On the average, damaging lightning was most frequent during July and August. Normally, 14 days per year had damaging lightning, and during the 1926–47 period lightning was responsible for more deaths than any other form of severe weather. Other forms of severe weather occurred on less than 50 percent of the days of damaging lightning. On an areal basis, damaging lightning occurred most frequently in west-southwestern Illinois which is the same area that has been found to have a high incidence of thunderstorms, tornadoes, hailstorms, and excessive rainstorms. Lightning caused deaths and injuries to a greater percentage of the rural population than of the urban population of the State. In rural areas the structures most frequently damaged by lighnting were farm barns, whereas in urban areas residences were the structures most frequently damaged.
Abstract
Statistics on thc incidence of damaging lighting in Illinois during the 1914–47 period were gleaned largely from published and unpublished records of the U.S. Weather Bureau to perform a climatological investigation. On the average, damaging lightning was most frequent during July and August. Normally, 14 days per year had damaging lightning, and during the 1926–47 period lightning was responsible for more deaths than any other form of severe weather. Other forms of severe weather occurred on less than 50 percent of the days of damaging lightning. On an areal basis, damaging lightning occurred most frequently in west-southwestern Illinois which is the same area that has been found to have a high incidence of thunderstorms, tornadoes, hailstorms, and excessive rainstorms. Lightning caused deaths and injuries to a greater percentage of the rural population than of the urban population of the State. In rural areas the structures most frequently damaged by lighnting were farm barns, whereas in urban areas residences were the structures most frequently damaged.
Abstract
Hail and thunderstorm statistics for the 1951–60 period obtained from 119 U.S. Weather Bureau stations in Illinois were combined with crop-hail insurance data for this same period for performing a detailed climatological investigation of the frequencies of hail days and thunderstorm days in Illinois. In the crop-growing season thunderstorms occur on 1 out of every 2 days on the average and hail occurs somewhere in Illinois on 4 out of every 10 days. The hail-thunderstorm areal ratio for Illinois is 68 percent as compared with point ratios varying from 3 to 7 percent. It appears that some thunderstorms may not contain hail since 32 percent of all the thunderstorm days had no hail reported at the surface anywhere in Illinois. Thunderstorms on days without hail most frequently occurred in southern Illinois and were associated more frequently with air mass and warm frontal conditions than were the hail-thunderstorms. This research also has shown how “Days With” data from cooperative substations of the Weather Bureau can be used to enlarge our knowledge of regional climatology.
Abstract
Hail and thunderstorm statistics for the 1951–60 period obtained from 119 U.S. Weather Bureau stations in Illinois were combined with crop-hail insurance data for this same period for performing a detailed climatological investigation of the frequencies of hail days and thunderstorm days in Illinois. In the crop-growing season thunderstorms occur on 1 out of every 2 days on the average and hail occurs somewhere in Illinois on 4 out of every 10 days. The hail-thunderstorm areal ratio for Illinois is 68 percent as compared with point ratios varying from 3 to 7 percent. It appears that some thunderstorms may not contain hail since 32 percent of all the thunderstorm days had no hail reported at the surface anywhere in Illinois. Thunderstorms on days without hail most frequently occurred in southern Illinois and were associated more frequently with air mass and warm frontal conditions than were the hail-thunderstorms. This research also has shown how “Days With” data from cooperative substations of the Weather Bureau can be used to enlarge our knowledge of regional climatology.
Abstract
Historical hail-day records of U.S. Weather Bureau first-order stations and cooperative substations are the only long, objective records of hail occurrence available throughout the United States. Although hail-day data are limited in areal density and are not necessarily the most desired measure of seeding effects, they are the only data available to obtain a measure of the areal-temporal variability of hail for most areas of the United States. Consequently, hail-day data from Illinois have been employed in a pilot project to determine the time required to obtain statistically significant changes in hail-day frequencies over various sized areas. Four statistical designs were investigated using the historical hail-day data for five areas in Illinois. The results show that the optimum design for hail-day data is the continuous seeding (seeding on all days likely to have hail) over an area. The optimum test is the sequential test involving the Poisson and Negative Binomial distributions. Detection of a 20-percent reduction in summer hail days would require, on the average, a continuous seeding program ranging from 13 to 37 yr, depending on the level of precision desired, and the size and location of the seeded area. Major reductions, those in excess of 60 percent, would require experiments of only 1- to 3-yr length.
Abstract
Historical hail-day records of U.S. Weather Bureau first-order stations and cooperative substations are the only long, objective records of hail occurrence available throughout the United States. Although hail-day data are limited in areal density and are not necessarily the most desired measure of seeding effects, they are the only data available to obtain a measure of the areal-temporal variability of hail for most areas of the United States. Consequently, hail-day data from Illinois have been employed in a pilot project to determine the time required to obtain statistically significant changes in hail-day frequencies over various sized areas. Four statistical designs were investigated using the historical hail-day data for five areas in Illinois. The results show that the optimum design for hail-day data is the continuous seeding (seeding on all days likely to have hail) over an area. The optimum test is the sequential test involving the Poisson and Negative Binomial distributions. Detection of a 20-percent reduction in summer hail days would require, on the average, a continuous seeding program ranging from 13 to 37 yr, depending on the level of precision desired, and the size and location of the seeded area. Major reductions, those in excess of 60 percent, would require experiments of only 1- to 3-yr length.
Abstract
Data from 103 hail echoes on 24 days in 1967 and 50 no-hail echoes from the same days were analyzed to describe hailstorm characteristics and to provide information useful in operational detection and forecasting of hail-producing echoes. Echo characteristics investigated included locations of echo formation and dissipation, echo reflectivities, echo-top heights, echo duration, direction of motion, speed, time of occurrence, and associated synoptic weather conditions. A single hail-echo model could not be derived because of the extreme variability found in all characteristics. However, distinctive echo models could be developed for the three predominant hail-producing synoptic weather conditions, cold fronts, stationary fronts, and low-pressure centers. The frontal hailstorms were faster moving, longer lived, and had taller echoes than those with low-pressure systems. Hail production after echo inception varied from an average of 32 min for low conditions to 59 min for cold frontal echoes. The average hail-echo top exhibited a 5,000-ft growth in the 15-min period prior to the average time of hail, suggesting that a major updraft surge was the prime producer of hail. The no-hail echoes occurring on hail days had characteristics of speed, direction of motion, reflectivity, and location that were very similar to the hail-producing echoes. The only distinct consistent difference between the hail and no-hail echoes in all synoptic situations was that the hail-echo tops averaged between 2,000 and 4,000 ft higher throughout their entire durations.
Abstract
Data from 103 hail echoes on 24 days in 1967 and 50 no-hail echoes from the same days were analyzed to describe hailstorm characteristics and to provide information useful in operational detection and forecasting of hail-producing echoes. Echo characteristics investigated included locations of echo formation and dissipation, echo reflectivities, echo-top heights, echo duration, direction of motion, speed, time of occurrence, and associated synoptic weather conditions. A single hail-echo model could not be derived because of the extreme variability found in all characteristics. However, distinctive echo models could be developed for the three predominant hail-producing synoptic weather conditions, cold fronts, stationary fronts, and low-pressure centers. The frontal hailstorms were faster moving, longer lived, and had taller echoes than those with low-pressure systems. Hail production after echo inception varied from an average of 32 min for low conditions to 59 min for cold frontal echoes. The average hail-echo top exhibited a 5,000-ft growth in the 15-min period prior to the average time of hail, suggesting that a major updraft surge was the prime producer of hail. The no-hail echoes occurring on hail days had characteristics of speed, direction of motion, reflectivity, and location that were very similar to the hail-producing echoes. The only distinct consistent difference between the hail and no-hail echoes in all synoptic situations was that the hail-echo tops averaged between 2,000 and 4,000 ft higher throughout their entire durations.
Abstract
A statistical methodology involving the analysis of three basic types of historical hail data on an areal approach is presented for the planning and evaluation of hail suppression experiments in Illinois. The methodology was used to generate nomograms relating the number of years required to detect significant results to 1) type I error, 2) type II error, and 3) power of the test for various statistical tests and experimental designs. These nomograms were constructed for various area sizes and geographical locations within the State.
Results indicate that, for an Illinois experiment, insurance crop-loss data are the optimum hail measurement if the study area has more than 60 percent insurance coverage. The optimum experimental design is the random-historical design in which all potential storms are seeded on a particular day, and 80 percent of the forecasted hail days are chosen at random to be “seeded days.” The recommended statistical analysis is the sequential analytical approach. If, however, conditions for the sequential analytical approach are not fulfilled by the data sample, the nonsequential approach utilizing a one-sample test with the historical record as the control (random-historical design) should be employed.
For a significance level of 0.05 and a beta error of 0.3, the average detection time in an area of approximately 1,500 sq mi would be 11 yr for a 20 percent reduction in the number of acres damaged, 2 yr for a 40 percent reduction, and 1 yr for a 60 and 80 percent reduction. If the nonsequential analyses were required, the number of years would be 25, 5, and 1, respectively.
Abstract
A statistical methodology involving the analysis of three basic types of historical hail data on an areal approach is presented for the planning and evaluation of hail suppression experiments in Illinois. The methodology was used to generate nomograms relating the number of years required to detect significant results to 1) type I error, 2) type II error, and 3) power of the test for various statistical tests and experimental designs. These nomograms were constructed for various area sizes and geographical locations within the State.
Results indicate that, for an Illinois experiment, insurance crop-loss data are the optimum hail measurement if the study area has more than 60 percent insurance coverage. The optimum experimental design is the random-historical design in which all potential storms are seeded on a particular day, and 80 percent of the forecasted hail days are chosen at random to be “seeded days.” The recommended statistical analysis is the sequential analytical approach. If, however, conditions for the sequential analytical approach are not fulfilled by the data sample, the nonsequential approach utilizing a one-sample test with the historical record as the control (random-historical design) should be employed.
For a significance level of 0.05 and a beta error of 0.3, the average detection time in an area of approximately 1,500 sq mi would be 11 yr for a 20 percent reduction in the number of acres damaged, 2 yr for a 40 percent reduction, and 1 yr for a 60 and 80 percent reduction. If the nonsequential analyses were required, the number of years would be 25, 5, and 1, respectively.
Abstract
Long-term precipitation records indicated that, on the average, 15% more warm season precipitation falls on the forested western Shawnee Hills of southern Illinois than falls on the rural farm flatlands at 120 m lower elevations both north and south of the hills. This precipitation difference with relatively little elevation change offered an interesting opportunity to study the effect of orographic and land-use differences upon convective precipitation. Initially, two methods differing in scale and time were used to delineate the bill anomaly and to investigate its causes. Extensive climatic studies of all available precipitation data revealed that the effect of the hills was most pronounced during the warm season when showers and thunderstorms are the major source of precipitation. A subsequent 5-yr study involving a dense recording raingage and wind recording network showed that the hill-related increases apparently came through enhancement of heavy showers, particularly those associated with squall-line and cold-frontal conditions. This led to an intensive field study in July 1970 described in the companion paper (Part 2).
Abstract
Long-term precipitation records indicated that, on the average, 15% more warm season precipitation falls on the forested western Shawnee Hills of southern Illinois than falls on the rural farm flatlands at 120 m lower elevations both north and south of the hills. This precipitation difference with relatively little elevation change offered an interesting opportunity to study the effect of orographic and land-use differences upon convective precipitation. Initially, two methods differing in scale and time were used to delineate the bill anomaly and to investigate its causes. Extensive climatic studies of all available precipitation data revealed that the effect of the hills was most pronounced during the warm season when showers and thunderstorms are the major source of precipitation. A subsequent 5-yr study involving a dense recording raingage and wind recording network showed that the hill-related increases apparently came through enhancement of heavy showers, particularly those associated with squall-line and cold-frontal conditions. This led to an intensive field study in July 1970 described in the companion paper (Part 2).
Abstract
The studies described in the companion paper (Part 1) led to an intensive field study in July 1970. The field study employed networks of recording raingages, wind recorders, and hygrothermographs, along with a meteorological radar, cloud cameras, and a meteorologically-instrumented aircraft. The study occurred in an abnormally dry period with mostly air mass showers (non-frontal storm). These air mass showers were found to be enhanced partially by the moisture derived from the forested hills under low wind speed conditions. In addition, the low speed winds from the south were found to be directed by the valleys within the hills, so as to develop a convergent pattern above the hills where the atmosphere was convectively unstable.
Abstract
The studies described in the companion paper (Part 1) led to an intensive field study in July 1970. The field study employed networks of recording raingages, wind recorders, and hygrothermographs, along with a meteorological radar, cloud cameras, and a meteorologically-instrumented aircraft. The study occurred in an abnormally dry period with mostly air mass showers (non-frontal storm). These air mass showers were found to be enhanced partially by the moisture derived from the forested hills under low wind speed conditions. In addition, the low speed winds from the south were found to be directed by the valleys within the hills, so as to develop a convergent pattern above the hills where the atmosphere was convectively unstable.
