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Collection of precipitation in a raingage located in Lake Michigan near Chicago over an 11-yr period has permitted a study of the average monthly, seasonal and annual precipitation received off the southwestern shore of the lake. These values are compared with average precipitation occurring in the Chicago urban area and with amounts from other nearby rural and shore stations. From these comparisons, the effects of lake and urban influences on the precipitation pattern are evaluated.
The results of this study compare favorably with results from similar lake-precipitation studies performed by the Corps of Engineers. The precipitation data from this station in the lake indicate that precipitation over southern Lake Michigan may be considerably less than previously estimated from data of stations along the shore. The effect of precipitation on lake levels may be better evaluated now that additional information on lake precipitation is available.
Collection of precipitation in a raingage located in Lake Michigan near Chicago over an 11-yr period has permitted a study of the average monthly, seasonal and annual precipitation received off the southwestern shore of the lake. These values are compared with average precipitation occurring in the Chicago urban area and with amounts from other nearby rural and shore stations. From these comparisons, the effects of lake and urban influences on the precipitation pattern are evaluated.
The results of this study compare favorably with results from similar lake-precipitation studies performed by the Corps of Engineers. The precipitation data from this station in the lake indicate that precipitation over southern Lake Michigan may be considerably less than previously estimated from data of stations along the shore. The effect of precipitation on lake levels may be better evaluated now that additional information on lake precipitation is available.
Abstract
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.
Abstract
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.
Abstract
Four forms of hail data in Illinois were analyzed to obtain indirect measures of the areal and seasonal variations in hail intensity. These data were also examined to ascertain which hail characteristics correlated best with crop damage.
The frequency of intense hail in the crop season (May–October) was found to increase with time, reaching a maximum in September. Insurance statistics indicated that corn damage from hail was usually greater in July than in the later months because corn was more susceptible to damage in July. Observations from a mesoscale network in central Illinois indicated that hailstone sizes and number (volume of ice) and durations of hailstorms related moderately well with crop-hail damage, but that strong surface winds were more closely related. Significant areal variations of hail intensity were found, with some portions of Illinois experiencing intense hail six times more often than other areas.
Abstract
Four forms of hail data in Illinois were analyzed to obtain indirect measures of the areal and seasonal variations in hail intensity. These data were also examined to ascertain which hail characteristics correlated best with crop damage.
The frequency of intense hail in the crop season (May–October) was found to increase with time, reaching a maximum in September. Insurance statistics indicated that corn damage from hail was usually greater in July than in the later months because corn was more susceptible to damage in July. Observations from a mesoscale network in central Illinois indicated that hailstone sizes and number (volume of ice) and durations of hailstorms related moderately well with crop-hail damage, but that strong surface winds were more closely related. Significant areal variations of hail intensity were found, with some portions of Illinois experiencing intense hail six times more often than other areas.
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.
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.
Abstract
The average temporal and spatial distributions of thunder events (periods of discrete thunder activity heard at a point) in the conterminous United States were found to be generally similar to those of thunder days. Annual averages of thunder events peak along the Gulf Coast (>100) and are also quite high in the central United States (Kansas, Missouri, Illinois with >75 events), and in the southwest (Arizona with 60 events). Thunder events are least along the west coast (<20) and in the northeast (<30). Multiple events per day are greatest in the Midwest (Illinois, Iowa) averaging 1.7 events per summer day, and are also high in the southwest (Arizona) with 1.5 events. This causes these two maxima in thunder event activity to be more pronounced than those found on the pattern of average thunder days.
The average patterns for the thunder event frequencies, multiple events per day, and durations reveal that convective activity is weakest and shortlived along the west coast and in the northeast. The high incidence of events per day in the Midwest reflects multiple storm incidences likely related to MCCs and nocturnal storm activity. The peak in thunder event activity is present in the central United States in all months and rotates from the lower Mississippi Valley to the central Great Plains-Midwest and then back, and its position is always closely related to the major center of cold frontal activity. The thunder peak in the southwest is related to the summer monsoon intrusion of moist tropical Pacific air and related frontal activity. The summer-fall peak in thunder events along the Gulf Coast-Florida is a result of sea breeze induced convergence, localized heating, and occasional tropical disturbances.
Abstract
The average temporal and spatial distributions of thunder events (periods of discrete thunder activity heard at a point) in the conterminous United States were found to be generally similar to those of thunder days. Annual averages of thunder events peak along the Gulf Coast (>100) and are also quite high in the central United States (Kansas, Missouri, Illinois with >75 events), and in the southwest (Arizona with 60 events). Thunder events are least along the west coast (<20) and in the northeast (<30). Multiple events per day are greatest in the Midwest (Illinois, Iowa) averaging 1.7 events per summer day, and are also high in the southwest (Arizona) with 1.5 events. This causes these two maxima in thunder event activity to be more pronounced than those found on the pattern of average thunder days.
The average patterns for the thunder event frequencies, multiple events per day, and durations reveal that convective activity is weakest and shortlived along the west coast and in the northeast. The high incidence of events per day in the Midwest reflects multiple storm incidences likely related to MCCs and nocturnal storm activity. The peak in thunder event activity is present in the central United States in all months and rotates from the lower Mississippi Valley to the central Great Plains-Midwest and then back, and its position is always closely related to the major center of cold frontal activity. The thunder peak in the southwest is related to the summer monsoon intrusion of moist tropical Pacific air and related frontal activity. The summer-fall peak in thunder events along the Gulf Coast-Florida is a result of sea breeze induced convergence, localized heating, and occasional tropical disturbances.
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
Two datasets were used to investigate the potential presence of urban-related precipitation anomalies in the fall, winter and spring seasons St. Louis, Missouri, and to ascertain under what conditions anomalies occurred- if indeed they did occur. The 1971–75 METROMEX dense raingage network data were used along with 1941–80 data from NWS stations in the area. Spatial and temporal analyses of seasonal precipitation showed the reality of urban-related influences northeast of St. Louis in all seasons, plus urban-related increases to the east and southeast in winter and fall. The maximum alterations in precipitation were northeast of St. Louis with increases of 14% in spring, 5% in winter, and 7% in fall when averaged over the 40-yr sampling period. Topographic effects that increased rainfall, particularly in the winter and fall, were quite evident in the hill and bluff areas southwest and southeast of St. Louis. Studies of snowstorms during 1971–75 revealed 5% to 10% less snowfall over the city than over adjacent rural areas.
Only 10% to 15% of the rain events related to areas of urban increases were altered in each season, and in most cases, they occurred with well-organized precipitation systems having convection. This agrees with the METROMEX summer findings. Good agreement between the precipitation patterns of METROMEX and climate network stations suggest that future studies of urban influences on winter and transition season precipitation can be based on the less dense climatic network of NWS.
Abstract
Two datasets were used to investigate the potential presence of urban-related precipitation anomalies in the fall, winter and spring seasons St. Louis, Missouri, and to ascertain under what conditions anomalies occurred- if indeed they did occur. The 1971–75 METROMEX dense raingage network data were used along with 1941–80 data from NWS stations in the area. Spatial and temporal analyses of seasonal precipitation showed the reality of urban-related influences northeast of St. Louis in all seasons, plus urban-related increases to the east and southeast in winter and fall. The maximum alterations in precipitation were northeast of St. Louis with increases of 14% in spring, 5% in winter, and 7% in fall when averaged over the 40-yr sampling period. Topographic effects that increased rainfall, particularly in the winter and fall, were quite evident in the hill and bluff areas southwest and southeast of St. Louis. Studies of snowstorms during 1971–75 revealed 5% to 10% less snowfall over the city than over adjacent rural areas.
Only 10% to 15% of the rain events related to areas of urban increases were altered in each season, and in most cases, they occurred with well-organized precipitation systems having convection. This agrees with the METROMEX summer findings. Good agreement between the precipitation patterns of METROMEX and climate network stations suggest that future studies of urban influences on winter and transition season precipitation can be based on the less dense climatic network of NWS.
