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Seasonal Variability
How do tornado characteristics and environments differ between Illinois warm- and cool-season tornadoes?
Research / Illinois Tornado Climatology
Research Project / In Development
Climatological Characteristics of Illinois Tornadoes Across Warm and Cool Seasons
2007–2025
A climatological analysis of Illinois tornadoes examining seasonal, regional, storm-scale, and environmental variability across the state.
1,128
Tornadoes Analyzed
2007–2025
Study Period
950
Warm-Season Tornadoes
178
Cool-Season Tornadoes
Research Question
How do Illinois tornadoes change across seasons, environments, and regions?
This study examines how tornado characteristics vary between warm and cool seasons and across northern, central, and southern Illinois. Particular attention is given to tornado intensity, storm organization, environmental conditions, boundary environments, timing, and path characteristics.
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Regional Variability
How do tornado occurrence and intensity vary across northern, central, and southern Illinois?
03
Environmental Characteristics
How are storm organization, boundary environments, and atmospheric parameters associated with tornado characteristics?
Study Motivation
Why study tornadoes across Illinois?
Illinois occupies a geographically important position within the central United States, where different severe-weather regimes influence the state across the year.
Warm-season tornadoes can develop in environments with substantial thermodynamic instability, while cool-season tornadoes more frequently occur within strongly forced, kinematically supportive environments.
Examining these environments together provides an opportunity to investigate whether Illinois tornado climatology is best represented as a single statewide population or as a collection of distinct seasonal and geographic regimes.
The Dataset
A structured climatology built from event-level analysis.
The database combines tornado reports with geographic, observational, radar, surface-analysis, and mesoscale environmental information.
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Tornado Reports
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Geographic Processing
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Storm Classification
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Environmental Reconstruction
Data Sources
The research incorporates tornado reports, geographic information, historical radar and surface-analysis information, observational datasets, and archived mesoscale environmental parameters used to reconstruct the atmospheric context surrounding individual tornado events.
Methodology
Multiple dimensions of the tornado environment.
Each event was classified across storm organization, environmental conditions, boundary environment, and spatial and temporal characteristics.
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Storm Organization
SupercellQLCSSingle / Multicell
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Environmental Conditions
MLCAPEEffective Bulk ShearSTP
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Boundary Environment
Cold FrontWarm FrontStationary FrontOccluded FrontSurface TroughNo Boundary
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Spatial & Temporal
Northern IllinoisCentral IllinoisSouthern IllinoisTime of DayEF2+ ClassificationOutbreak Designation
Seasonal Regimes
Illinois tornado climatology is shaped by distinct seasonal environments.
March–August
Warm Season
- Higher overall tornado frequency
- Broader range of thermodynamic environments
- Afternoon and evening activity maximum
- Greater diversity of storm organizations
November–February
Cool Season
- Lower overall tornado frequency
- Stronger effective bulk shear environments
- Greater proportion of stronger tornadoes
- More organized and synoptically forced environments
Regional Analysis
A geographic signal emerges from northern to southern Illinois.
Regional comparisons reveal differences in tornado intensity and environmental characteristics across the state.
Northern Illinois
15.0%
EF2+ Proportion
The northern region exhibited the lowest EF2+ proportion among the three Illinois regions examined.
Central Illinois
21.3%
EF2+ Proportion
Central Illinois exhibited an intermediate EF2+ proportion within the statewide regional comparison.
Southern Illinois
40.0%
Cool-Season EF2+
Southern Illinois showed the strongest cool-season EF2+ signal in the regional analysis.
The observed regional pattern should not be interpreted as evidence that Illinois physiography or topography directly causes differences in tornado intensity. The present study identifies climatological and environmental relationships; determining the physical mechanisms behind those relationships requires additional targeted research.
Key Findings
What the study found.
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A North-to-South Intensity Gradient
The proportion of EF2+ tornadoes increased from northern toward southern Illinois during both seasons, with the strongest regional signal occurring during the cool season.
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Cool-Season Tornadoes Occurred in Stronger Shear
Cool-season tornado environments exhibited higher median effective bulk shear than warm-season environments, highlighting the importance of stronger kinematic support during the cool season.
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Instability Alone Did Not Explain Intensity
MLCAPE category was not significantly associated with EF2+ occurrence, while effective bulk shear and STP showed stronger relationships with significant tornado occurrence.
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Storm Mode Influenced Intensity
QLCSs produced more tornadoes overall in the dataset, while supercells produced a substantially larger proportion of EF2+ tornadoes.
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Illinois Does Not Have One Homogeneous Tornado Environment
Tornado characteristics varied across both season and geographic region, demonstrating that statewide tornado climatology contains distinct spatial and temporal regimes.
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Environmental Context Matters
The observed tornado characteristics reflect interactions among storm organization, shear, instability, boundaries, and broader environmental structure rather than a single controlling variable.
Statistical Framework
Differences were evaluated using statistical evidence.
Statistical testing was used to evaluate whether observed seasonal, regional, environmental, and categorical differences were supported by the data rather than relying solely on visual differences in distributions.
Mann–Whitney UKruskal–Wallis HChi-squareMonte Carlo permutation testingRank-biserial correlationEpsilon squaredCramér's V
Significance threshold / α = 0.05
Research Visualizations
Research figures and data exploration.
Selected figures from the study will be presented here as the research documentation and visualization system develops.
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Coming Soon
Research Figures
Seasonal Climatology
Figures examining tornado occurrence, path characteristics, timing, and environmental differences between warm and cool seasons.
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Coming Soon
Research Figures
Regional Characteristics
Visualizations examining geographic differences across northern, central, and southern Illinois.
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Coming Soon
Research Figures
Storm Organization
Figures examining relationships among storm mode, tornado intensity, path characteristics, and environmental conditions.
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Coming Soon
Research Figures
Boundary Environment
Visualizations examining tornado characteristics and environmental conditions across different boundary classifications.
Research Limitations
Understanding what the study cannot establish.
Limitations are documented as part of the research process and provide important context for interpreting the study's results.
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Damage-based EF ratings introduce uncertainty into historical intensity classification.
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EFU tornadoes introduce additional uncertainty where damage-based intensity estimates are unavailable.
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Historical tornado reporting practices may introduce temporal or geographic inconsistencies.
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Storm-mode classification involves manual interpretation and therefore contains classification uncertainty.
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Boundary classification also relies on manual analysis of historical atmospheric information.
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Archived mesoscale analysis products have limitations in spatial and temporal resolution.
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Environmental data may not perfectly represent conditions at the exact location and time of tornado occurrence.
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The study is geographically limited to Illinois and temporally limited to 2007–2025.
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September and October were excluded from the primary seasonal comparison as transition months.
What This Study Does Not Establish
The observed geographic patterns should not be interpreted as evidence that Illinois physiography or topography directly causes differences in tornado intensity. This study identifies climatological and environmental relationships; determining the physical mechanisms behind those relationships requires additional targeted research.
Scientific Significance
Illinois tornado climatology is better understood as a set of interacting regimes.
The study demonstrates meaningful differences in tornado characteristics across both season and geography. Warm- and cool-season tornadoes occur within different environmental contexts, while regional comparisons reveal additional variability across Illinois.
These results provide a more detailed view of Illinois tornado climatology than statewide totals alone and provide a foundation for future research examining the physical processes responsible for the observed patterns.
The project also contributes to TARL's broader interest in regional atmospheric behavior and the relationship between environmental structure, geographic variability, and severe weather.
Project Status
Research / In Development
Research documentation is being finalized.
The underlying climatology and analysis have been developed as part of the research project, while manuscript documentation, visualization, and publication materials continue to be refined.
Additional figures, documentation, and research resources will be added to this page as the project progresses toward publication.
Research Documentation
Manuscript, dataset, and research documentation.
Manuscript
Climatological Characteristics of Illinois Tornadoes Across Warm and Cool Seasons (2007–2025)
Author
Jakob Barton
Academic Affiliation
Parkland College
Research Organization
Terrain-Atmosphere Research Laboratory (TARL)
Status
In Development
Dataset
Research dataset and supporting documentation will be made available as the project documentation is finalized.
Coming SoonPublication
Publication and final manuscript information will be added when the research reaches its publication stage.
Coming SoonTARL Research
Research built around measurable questions.
This project represents the foundation of TARL's broader research program examining regional atmospheric behavior, environmental variability, and the interaction between atmospheric processes and geographic structure.