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- Author or Editor: STANLEY A. CHANGNON JR. x
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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
Unique detailed hail and rain data from dense networks operated in central Illinois during 1967 and 1968 have been used to define and study in detail hailstreaks and their associated rainfall. A hailstreak is an area of continuous hail with temporal coherence and is considered an entity of hail generated within a thunderstorm. The average hailstreak represents a fast-moving, short-lived, and relatively small phenomenon. Eighty per cent of all hailstreaks had areas <16 mi2 and hail impact energy values <0.1 ft-lb ft−2, but areas extremes were 0.9–788 mi2 and energy extremes sampled were 0.0001–12.6 ft-lb ft−2. A hail-producing system in a 1600 mi2 area normally produced five hailstreaks with an average separation distance of 15 mi. Cold fronts and unstable air mass conditions led in the production of hall systems and hailstreaks, respectively. Hailstreaks produced by different synoptic weather conditions differed considerably. Point durations of hailstreaks averaged 3 min, 43% occurring in the 1500–1900 CDT period. Eighty-eight per cent of all hailstones had diameters ≤¼ inch and only 1% were ≥1 inch. A 1-ft2 area in a hailstreak normally experienced 24 hailstones. Hailstreaks occurred in all locations and stages of age of their associated rain cells, but their preferred location was along the major axis and in the mature stage. Normally, a rain cell produced only one hailstreak, although 20% produced four or more. However, 52% of the rain cells in hail-producing systems did not produce hail. The average rainfall in a hailstreak was 0.19 inch, with an average point rainfall rate of 0.63 inch hr1. Rainfall produced throughout the network areas during hail-producing systems accounted for 38% of the 1967 network warm season total and 57% of the 1968 total.
Abstract
Unique detailed hail and rain data from dense networks operated in central Illinois during 1967 and 1968 have been used to define and study in detail hailstreaks and their associated rainfall. A hailstreak is an area of continuous hail with temporal coherence and is considered an entity of hail generated within a thunderstorm. The average hailstreak represents a fast-moving, short-lived, and relatively small phenomenon. Eighty per cent of all hailstreaks had areas <16 mi2 and hail impact energy values <0.1 ft-lb ft−2, but areas extremes were 0.9–788 mi2 and energy extremes sampled were 0.0001–12.6 ft-lb ft−2. A hail-producing system in a 1600 mi2 area normally produced five hailstreaks with an average separation distance of 15 mi. Cold fronts and unstable air mass conditions led in the production of hall systems and hailstreaks, respectively. Hailstreaks produced by different synoptic weather conditions differed considerably. Point durations of hailstreaks averaged 3 min, 43% occurring in the 1500–1900 CDT period. Eighty-eight per cent of all hailstones had diameters ≤¼ inch and only 1% were ≥1 inch. A 1-ft2 area in a hailstreak normally experienced 24 hailstones. Hailstreaks occurred in all locations and stages of age of their associated rain cells, but their preferred location was along the major axis and in the mature stage. Normally, a rain cell produced only one hailstreak, although 20% produced four or more. However, 52% of the rain cells in hail-producing systems did not produce hail. The average rainfall in a hailstreak was 0.19 inch, with an average point rainfall rate of 0.63 inch hr1. Rainfall produced throughout the network areas during hail-producing systems accounted for 38% of the 1967 network warm season total and 57% of the 1968 total.
Abstract
Convective raincells, as delineated by surface rainfall data from large and dense raingage networks in Illinois, were analyzed to define various characteristics. Raincells are the surface expression of convective entitles, and as such are important in furthering our understanding of convective storms, for designing mesoscale studies, and for evaluating numerical cloud models. The raincells exhibited great variability in most characteristics, but were typically 16 km long, 6 km wide, and had a mean rainfall of 2.5 mm. Their orientations varied widely but the most frequent was WSW–ENE. There was a second but infrequent class of large raincells that often exceed 43 km in length and can be up to 40 km wide.
Abstract
Convective raincells, as delineated by surface rainfall data from large and dense raingage networks in Illinois, were analyzed to define various characteristics. Raincells are the surface expression of convective entitles, and as such are important in furthering our understanding of convective storms, for designing mesoscale studies, and for evaluating numerical cloud models. The raincells exhibited great variability in most characteristics, but were typically 16 km long, 6 km wide, and had a mean rainfall of 2.5 mm. Their orientations varied widely but the most frequent was WSW–ENE. There was a second but infrequent class of large raincells that often exceed 43 km in length and can be up to 40 km wide.
Abstract
Temporal and spatial relationships between thunderstorms (events) and flashes were investigated using data for 1983–85 for 25 first-order stations (10 in the West and 15 along the East Coast). Thunder events were compared with flashes within three ranges: 5 km, 10 km, and 20 km, around each station. Cluster analysis revealed six geographic regions: Florida, Southeast (South Carolina, Georgia), Mid-Atlantic (Virginia, Maryland Pennsylvania), Northeast (New York and New England), Rocky Mountains, and an intermontane area.
Periods of multiple flashes not within thunder events and within 10 km of a point (most realistic for audibility), revealed that 10% to 20% (depending upon region) of all thunderstorms were missed. Also, 13% (Rockies) to 44% (Mid-Atlantic) of all thunderstorms have recorded durations too short (missed flashes before their reported start), and the average underestimated durations were from 55% (Northeast Mid-Atlantic) to 26% (Rockies). Flashes isolated in time and space, due to locational errors, represent 1% of all flashes in the east and 3% to 5% in the west where the data are poorer. Errors in flush data appear minimal but the errors in thunder events are sizable.
Thunder events and flash frequencies related well based on major features in their average areal patterns and their between-year changes at stations. Correlations of fishes with events varied; their annual point frequencies had coefficients of +0.83 (east) and +0.67 (west). Durations of events and Bash frequencies were poorly correlated with skewed distributions (often large flash frequencies in a few storms). The percent of all recorded flashes (within 10 km) in thunder events varied from 28% to 44% at western stations and from 13% to 20% at eastern stations. Thunder events with ≥ 1 flash varied widely, from 71 % of all events at Washington, D.C. to 30% at Boston.
Major east-west differences existed in the frequency of thunder events with flashes, reflecting poorer audibility of thunder in the west. Part of the difference is due to flash recording problems in the west, leaving flash frequencies that are underestimates of the true values. latitudinal distributions were marked with north-to-south increases in thunder events and their durations, frequency of flashes, and number of flashes not in events. More missed flashes in the south suggested that atmospheric conditions in northerly U.S. latitudes enhance audibility. With a 20-km sampling radius, between 6 (Northeast) and 23 (Southeast) thunder events are not recorded yearly, but these averages drop to 1 (Northeast) and 4 (Southeast) based on flashes within 5 km. The data on thunderstorms is generally poor from two perspectives: 1) the recorded data miss sizable numbers of storm events, and 2) when recorded, 30% to 50% often underestimate durations based on nearby lightning activity.
Abstract
Temporal and spatial relationships between thunderstorms (events) and flashes were investigated using data for 1983–85 for 25 first-order stations (10 in the West and 15 along the East Coast). Thunder events were compared with flashes within three ranges: 5 km, 10 km, and 20 km, around each station. Cluster analysis revealed six geographic regions: Florida, Southeast (South Carolina, Georgia), Mid-Atlantic (Virginia, Maryland Pennsylvania), Northeast (New York and New England), Rocky Mountains, and an intermontane area.
Periods of multiple flashes not within thunder events and within 10 km of a point (most realistic for audibility), revealed that 10% to 20% (depending upon region) of all thunderstorms were missed. Also, 13% (Rockies) to 44% (Mid-Atlantic) of all thunderstorms have recorded durations too short (missed flashes before their reported start), and the average underestimated durations were from 55% (Northeast Mid-Atlantic) to 26% (Rockies). Flashes isolated in time and space, due to locational errors, represent 1% of all flashes in the east and 3% to 5% in the west where the data are poorer. Errors in flush data appear minimal but the errors in thunder events are sizable.
Thunder events and flash frequencies related well based on major features in their average areal patterns and their between-year changes at stations. Correlations of fishes with events varied; their annual point frequencies had coefficients of +0.83 (east) and +0.67 (west). Durations of events and Bash frequencies were poorly correlated with skewed distributions (often large flash frequencies in a few storms). The percent of all recorded flashes (within 10 km) in thunder events varied from 28% to 44% at western stations and from 13% to 20% at eastern stations. Thunder events with ≥ 1 flash varied widely, from 71 % of all events at Washington, D.C. to 30% at Boston.
Major east-west differences existed in the frequency of thunder events with flashes, reflecting poorer audibility of thunder in the west. Part of the difference is due to flash recording problems in the west, leaving flash frequencies that are underestimates of the true values. latitudinal distributions were marked with north-to-south increases in thunder events and their durations, frequency of flashes, and number of flashes not in events. More missed flashes in the south suggested that atmospheric conditions in northerly U.S. latitudes enhance audibility. With a 20-km sampling radius, between 6 (Northeast) and 23 (Southeast) thunder events are not recorded yearly, but these averages drop to 1 (Northeast) and 4 (Southeast) based on flashes within 5 km. The data on thunderstorms is generally poor from two perspectives: 1) the recorded data miss sizable numbers of storm events, and 2) when recorded, 30% to 50% often underestimate durations based on nearby lightning activity.
Abstract
The distribution of hail days during 1961–80 in the northern Great Plains-Midwest was evaluated on a temporal and spatial basis to help interpret crop-hail losses. Comparisons with earlier (1901–60) hail day data revealed the seven-state study area contained eight permanent areas of high and low incidences found in any 5-year or longer period. The high hail incidence areas were related either to major topographic features or to areas of frequent frontal occurrences. Certain other areas of high or low hail incidence appeared at random locales, lasted 5 to 20 years, and disappeared. The annual and July incidences of hail increased sporadically but steadily from 1901 to 1980 in the Dakotas, Nebraska and Minnesota, reaching a peak during 1961–80. This has led to relatively more crop damage in recent years. In Montana, eastern Iowa, and Illinois, hail has decreased to a low in 1961–80. During the 1961–80 period, hail maximized in 1961–65, being 30% more frequent than in any subsequent 5-year period.
Abstract
The distribution of hail days during 1961–80 in the northern Great Plains-Midwest was evaluated on a temporal and spatial basis to help interpret crop-hail losses. Comparisons with earlier (1901–60) hail day data revealed the seven-state study area contained eight permanent areas of high and low incidences found in any 5-year or longer period. The high hail incidence areas were related either to major topographic features or to areas of frequent frontal occurrences. Certain other areas of high or low hail incidence appeared at random locales, lasted 5 to 20 years, and disappeared. The annual and July incidences of hail increased sporadically but steadily from 1901 to 1980 in the Dakotas, Nebraska and Minnesota, reaching a peak during 1961–80. This has led to relatively more crop damage in recent years. In Montana, eastern Iowa, and Illinois, hail has decreased to a low in 1961–80. During the 1961–80 period, hail maximized in 1961–65, being 30% more frequent than in any subsequent 5-year period.
Abstract
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.
Abstract
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.
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.
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.
