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- Author or Editor: Robert A. Maddox x
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Abstract
Objective analyses of composited meteorological conditions attending ten Mesoscale Couvective Complexes (MCC) reveal a number of distinctive characteristics and important interactions with the large-scale environment. The systems appear to be linked to eastward progression of a weak, middle-tropospheric, short-wave trough. Initial thunderstorms develop within a region of mesoscale convergence and lifting that is apparently forced primarily by low-level warm advection. The MCC system acquires mesoscale organization while it moves eastward ahead of the short-wave trough. Diabatic heating eventually produces a system that is warm core in the middle troposphere and cold core in upper levels. The mature MCC exhibits many similarities to tropical convective systems, although it occurs within a considerably different large-scale setting. Inflow within the lower half of the troposphere feeds convection within a region characterized by significant net upward mass flux and widespread precipitation. Thickness increases within this region produce anomalously high heights in the upper-troposphere above the MCC and intense outflow develops in the region where the height gradient has increased. Decay typically occurs as the system moves east of the region of conditionally unstable air and low-level warm advection. However, as the system decays, atmospheric response to residual temperature perturbations results in intensification of the precursor short-wave trough within the upper half of the troposphere.
Abstract
Objective analyses of composited meteorological conditions attending ten Mesoscale Couvective Complexes (MCC) reveal a number of distinctive characteristics and important interactions with the large-scale environment. The systems appear to be linked to eastward progression of a weak, middle-tropospheric, short-wave trough. Initial thunderstorms develop within a region of mesoscale convergence and lifting that is apparently forced primarily by low-level warm advection. The MCC system acquires mesoscale organization while it moves eastward ahead of the short-wave trough. Diabatic heating eventually produces a system that is warm core in the middle troposphere and cold core in upper levels. The mature MCC exhibits many similarities to tropical convective systems, although it occurs within a considerably different large-scale setting. Inflow within the lower half of the troposphere feeds convection within a region characterized by significant net upward mass flux and widespread precipitation. Thickness increases within this region produce anomalously high heights in the upper-troposphere above the MCC and intense outflow develops in the region where the height gradient has increased. Decay typically occurs as the system moves east of the region of conditionally unstable air and low-level warm advection. However, as the system decays, atmospheric response to residual temperature perturbations results in intensification of the precursor short-wave trough within the upper half of the troposphere.
Abstract
No abstract available.
Abstract
No abstract available.
Abstract
An objective technique for quantitative scale separation has been developed to study atmospheric circulations associated with large complexes of thunderstorms. The scheme utilizes two separate low-pass filter analyses of the same data set to extract mesoscale and macroscale signals. An objective analysis of the total meteorological field (with microscale variations suppressed) is recovered as the sum of the mesoscale and macroscale components. Case study examples demonstrate that the technique is indeed useful for studying mesoscale convective systems. It is shown that convectively forced mesoscale circulations may significantly perturb the environmental flow on scales large enough to be detected in synoptic upper air data. The case studies also suggest that the analysis routines could be utilized in operational forecasting applications.
Abstract
An objective technique for quantitative scale separation has been developed to study atmospheric circulations associated with large complexes of thunderstorms. The scheme utilizes two separate low-pass filter analyses of the same data set to extract mesoscale and macroscale signals. An objective analysis of the total meteorological field (with microscale variations suppressed) is recovered as the sum of the mesoscale and macroscale components. Case study examples demonstrate that the technique is indeed useful for studying mesoscale convective systems. It is shown that convectively forced mesoscale circulations may significantly perturb the environmental flow on scales large enough to be detected in synoptic upper air data. The case studies also suggest that the analysis routines could be utilized in operational forecasting applications.
Abstract
Examination of National Hail Research Experiment (NHRE) mesoscale data taken on 31 July 1976 revealed significant fluctuations with time in the temperature, dewpoint temperature and wind speed. These variations displayed characteristics typical of summertime frontal passages. However, GOES-1 imagery revealed meso-β (weather systems having wavelengths of 20–200 km) scale features that were likely responsible for the observed phenomena. It is shown that geosynchronous satellite data can be of significant value in the analysis and interpretation of mesonetwork data.
Abstract
Examination of National Hail Research Experiment (NHRE) mesoscale data taken on 31 July 1976 revealed significant fluctuations with time in the temperature, dewpoint temperature and wind speed. These variations displayed characteristics typical of summertime frontal passages. However, GOES-1 imagery revealed meso-β (weather systems having wavelengths of 20–200 km) scale features that were likely responsible for the observed phenomena. It is shown that geosynchronous satellite data can be of significant value in the analysis and interpretation of mesonetwork data.
Abstract
Over 250 tornado proximity soundings have been closely studied. Emphasis was given to a detailed examination of the wind profiles and stabilities of the soundings. The uncertainties inherent in severe storm reports, and in the positioning of proximity data relative to moving storms, were examined. It was found that the small-scale storm environment cannot be resolved with mean proximity data. On the synoptic scale a very large range of winds and stabilities was found to be associated with confirmed tornadoes. Only slight differences were found between mean tornado proximity soundings, mean soundings associated with destructive tornado outbreaks, and mean soundings associated with outbreaks of non-tornadic severe thunderstorms. Storm relative wind fields were found to be similar for all types of tornado soundings studied. The storm relative flow fields vary dramatically as thunderstorm velocity changes within a given environment.
Abstract
Over 250 tornado proximity soundings have been closely studied. Emphasis was given to a detailed examination of the wind profiles and stabilities of the soundings. The uncertainties inherent in severe storm reports, and in the positioning of proximity data relative to moving storms, were examined. It was found that the small-scale storm environment cannot be resolved with mean proximity data. On the synoptic scale a very large range of winds and stabilities was found to be associated with confirmed tornadoes. Only slight differences were found between mean tornado proximity soundings, mean soundings associated with destructive tornado outbreaks, and mean soundings associated with outbreaks of non-tornadic severe thunderstorms. Storm relative wind fields were found to be similar for all types of tornado soundings studied. The storm relative flow fields vary dramatically as thunderstorm velocity changes within a given environment.
Abstract
During March of 1948 Tinker Air Force Base was hit directly by two tornadoes during a period of only five days. The first tornado was the most destructive, to that point, ever to occur in Oklahoma. The second storm caused considerable additional damage and was remarkable in another, more significant, way. The first operational tornado forecast had been issued by Air Force Officers E. J. Fawbush and R. C. Miller a few hours before the tornado moved across the base. This extremely unusual meteorological situation, two tornadoes hitting the same location within five days, coupled with the fortuitous forecast of the event, had a profound impact on the evolution of operational severe weather forecasting in the United States. These events eventually stimulated the initiation of public severe thunderstorm forecasting by the Weather Bureau.
Miller often presented anecdotal accounts of the events leading up to the landmark forecast, for example, in seminars and interviews during a visit to the National Severe Storms Laboratory during March 1994. He often stressed that the remarkable similarity of the synoptic settings on 21 and 25 March 1948 helped give him and Fawbush the courage to issue the now famous forecast. In this paper the synoptic environments that led to the two tornado occurrences at Tinker are analyzed and discussed. There were indeed similarities; however, it is surprising how different many aspects of the storm settings actually were. Similarities and important differences are illustrated with a series of synoptic surface and upper-air charts. It is likely that development of a base severe weather plan following the tornado disaster of 20 March, in addition to the presence and exhortations of General F. S. Borum at the base weather station on 25 March, provided as great a motivation for the first tornado forecast as did the similarity of the synoptic settings.
Abstract
During March of 1948 Tinker Air Force Base was hit directly by two tornadoes during a period of only five days. The first tornado was the most destructive, to that point, ever to occur in Oklahoma. The second storm caused considerable additional damage and was remarkable in another, more significant, way. The first operational tornado forecast had been issued by Air Force Officers E. J. Fawbush and R. C. Miller a few hours before the tornado moved across the base. This extremely unusual meteorological situation, two tornadoes hitting the same location within five days, coupled with the fortuitous forecast of the event, had a profound impact on the evolution of operational severe weather forecasting in the United States. These events eventually stimulated the initiation of public severe thunderstorm forecasting by the Weather Bureau.
Miller often presented anecdotal accounts of the events leading up to the landmark forecast, for example, in seminars and interviews during a visit to the National Severe Storms Laboratory during March 1994. He often stressed that the remarkable similarity of the synoptic settings on 21 and 25 March 1948 helped give him and Fawbush the courage to issue the now famous forecast. In this paper the synoptic environments that led to the two tornado occurrences at Tinker are analyzed and discussed. There were indeed similarities; however, it is surprising how different many aspects of the storm settings actually were. Similarities and important differences are illustrated with a series of synoptic surface and upper-air charts. It is likely that development of a base severe weather plan following the tornado disaster of 20 March, in addition to the presence and exhortations of General F. S. Borum at the base weather station on 25 March, provided as great a motivation for the first tornado forecast as did the similarity of the synoptic settings.
Abstract
A case study is presented involving an unusually intense mesoscale convective system (MCS) which produced extensive hail and wind damage in northeast Kansas and northern Missouri, including the Kansas City metropolitan area, during the predawn hours of 7 June 1982. The study emphasizes the preconvective period and examines interactions between mesoscale processes and the synoptic scale environment that led to thunderstorm development. The initial storms formed after dark over the western High Plains, in an area characterized by relatively weak convective potential making the thunderstorm difficult to forecast. Near midnight the convection rapidly intensified into an MCS as it progressed eastward into a much more convectively unstable environment. Several meteorological scenarios that might have led to the initiation and intensification of convection are proposed and examined. These scenarios consider lower tropospheric convergence within an air mass which initially had weak convective potential, and the evolution of this air mass into one that could support moderate thunderstorms after sunset. This work, along with similar studies, illustrates the wide range of complex factors which must be considered in thunderstorm forecast decision making.
Abstract
A case study is presented involving an unusually intense mesoscale convective system (MCS) which produced extensive hail and wind damage in northeast Kansas and northern Missouri, including the Kansas City metropolitan area, during the predawn hours of 7 June 1982. The study emphasizes the preconvective period and examines interactions between mesoscale processes and the synoptic scale environment that led to thunderstorm development. The initial storms formed after dark over the western High Plains, in an area characterized by relatively weak convective potential making the thunderstorm difficult to forecast. Near midnight the convection rapidly intensified into an MCS as it progressed eastward into a much more convectively unstable environment. Several meteorological scenarios that might have led to the initiation and intensification of convection are proposed and examined. These scenarios consider lower tropospheric convergence within an air mass which initially had weak convective potential, and the evolution of this air mass into one that could support moderate thunderstorms after sunset. This work, along with similar studies, illustrates the wide range of complex factors which must be considered in thunderstorm forecast decision making.
Abstract
An extended series of surface observations is used to compare observed surface winds with winds computed using the geostrophic relationship. These computations are done for both steady and unsteady wind regimes. Large differences are found in the comparisons of observed to computed winds. The differences exhibit pronounced seasonal and diurnal variability that appear to reflect both boundary layer stability and small-scale wind and pressure fields-for example, those attending land-sea breezes and thunderstorms.
The results of this study may be useful to those engaged in studying global datasets and to modelers, who are continually challenged to improve the treatment of parameterization of turbulent processes. However, it is not obvious that any simple parameterization can be applied to obtain an accurate estimate of the surface wind in central Florida, given only the large-scale pressure gradient or a model-predicted wind above the surface as input. The use of the pressure field to estimate surface winds is an uncertain exercise at best.
Abstract
An extended series of surface observations is used to compare observed surface winds with winds computed using the geostrophic relationship. These computations are done for both steady and unsteady wind regimes. Large differences are found in the comparisons of observed to computed winds. The differences exhibit pronounced seasonal and diurnal variability that appear to reflect both boundary layer stability and small-scale wind and pressure fields-for example, those attending land-sea breezes and thunderstorms.
The results of this study may be useful to those engaged in studying global datasets and to modelers, who are continually challenged to improve the treatment of parameterization of turbulent processes. However, it is not obvious that any simple parameterization can be applied to obtain an accurate estimate of the surface wind in central Florida, given only the large-scale pressure gradient or a model-predicted wind above the surface as input. The use of the pressure field to estimate surface winds is an uncertain exercise at best.
Abstract
No abstract available.
Abstract
No abstract available.
Abstract
On 25 April 1975, as part of the National Aeronautics and Space Administration's Atmospheric Variability Experiment IV, frequent upper-air soundings were taken at eastern United States synoptic sounding sites. An intense, long-lived mesoscale convective weather system developed late in the AVE IV period and moved eastward during the remainder of the experiment. With the use of dry and moist numerical simulations, performed with Drexel University's Limited Area and Mesoscale Prediction System (LAMPS), interaction between the widespread, long-lived convective complex and its large-scale environment are examined.
Dissecting the differences between moist and dry simulations reveals that, within the moist numerical simulation, significant up-scale feedbacks occur between the convective system and its large-scale meteorological setting. Pronounced differences in temperature, divergence, vorticity, and height develop between the two simulations. Physical reasons for these differences are discussed. Comparison of the model forecast with analyses of the actual evolution of large-scale features indicates that this type of weather event cannot be properly simulated without inclusion of the effects of the latent-heat driven, mesoscale convective system.
Abstract
On 25 April 1975, as part of the National Aeronautics and Space Administration's Atmospheric Variability Experiment IV, frequent upper-air soundings were taken at eastern United States synoptic sounding sites. An intense, long-lived mesoscale convective weather system developed late in the AVE IV period and moved eastward during the remainder of the experiment. With the use of dry and moist numerical simulations, performed with Drexel University's Limited Area and Mesoscale Prediction System (LAMPS), interaction between the widespread, long-lived convective complex and its large-scale environment are examined.
Dissecting the differences between moist and dry simulations reveals that, within the moist numerical simulation, significant up-scale feedbacks occur between the convective system and its large-scale meteorological setting. Pronounced differences in temperature, divergence, vorticity, and height develop between the two simulations. Physical reasons for these differences are discussed. Comparison of the model forecast with analyses of the actual evolution of large-scale features indicates that this type of weather event cannot be properly simulated without inclusion of the effects of the latent-heat driven, mesoscale convective system.
