TornadoScore

Methodology

How TornadoScore risk scores are computed: data sources, modeling approach, and limitations.

TornadoScore publishes tornado risk scores at neighborhood resolution across Tornado Alley, Dixie Alley, and the wider US tornado belt. Every score on this site is computed by PerilScore using the same data layer used by insurance and risk management professionals.

Data sources

We start from public scientific records. Every input is auditable, and we don’t use proprietary or paywalled data.

NOAA Storm Events Database: full tornado record including EF-rating, path length, path width, and casualties.
NOAA Storm Prediction Center (SPC) climatology: tornado climatology and high-risk outlook frequency.
ERA5 reanalysis: long-run atmospheric parameters including Convective Available Potential Energy (CAPE), 0–6 km wind shear, and Significant Tornado Parameter (STP).

Modeling approach

We combine the historical track record with atmospheric favorability indices to estimate long-run tornado frequency by EF rating. The result is a single 0 to 10 probability score at each neighborhood-scale sample point (about 5 km²).

Output metrics include long-run tornado frequency, EF2+ and EF4+ counts per decade, total path-length exposure, EF2+ return period, and atmospheric favorability indices.

Resolution

Scores are computed at neighborhood resolution: approximately 5 km² sample points across the contiguous US. This is much finer than the county-level averages most public tornado data provides.

Update cadence

The model is refreshed annually following the end of severe-weather season, incorporating the prior year’s tornado tracks. Major model updates are versioned and disclosed.

Validation

Models are evaluated against held-out historical seasons and benchmarked against the SPC tornado climatology where available. The exact validation protocol is documented in the PerilScore technical papers.

Limitations

Forecast boundary. TornadoScore reflects long-run probability from the historical record. For real-time warnings, refer to the National Weather Service.
Property-specific detail. Scores reflect a neighborhood-scale sample point. For a property-specific score that incorporates construction, safe-room presence, and protection class, use the free PerilScore app.
Pre-1995 detection is incomplete. Doppler radar coverage was uneven before NEXRAD deployment finished; weak tornadoes are under-counted in older records.

Attribution

Risk scores powered by PerilScore. Visit perilscore.com for the full platform, API access, and commercial-use licensing.

Methodology

Public data. Real science. No black boxes.

Every score is computed from decades of public weather records using physics-based probability modeling. It's the same approach used by insurance and risk management professionals.

Decades of public weather data: Hurricane tracks, storm intensities, fire perimeters, hail reports, all drawn from public scientific archives. We don't use proprietary data. You can audit every input.
Physics-based probability modeling: Scores reflect how the actual peril behaves: wind fields, fire spread, ground shaking, and storm tracks. The model keeps the physics visible instead of flattening every place into a broad average.
Used by professionals: The same PerilScore data layer is used by insurance and risk management professionals. We publish it here so anyone can find authoritative risk numbers for their location.

Frequently asked questions

Where does the tornado risk score come from?

Every score is computed from decades of public weather data (NOAA Storm Events tornado records, including EF-rating, path length, and width) using physics-based probability modeling.

Does this match the SPC tornado climatology?

Our model uses the same underlying NOAA records as the Storm Prediction Center’s climatology, but produces a single comparable 0–10 risk score per location designed for risk modeling and insurance use.

How is Dixie Alley risk different from Tornado Alley?

Dixie Alley (AL, MS, TN, AR) has a higher proportion of long-track and nocturnal tornadoes, which raises the risk score even where overall tornado counts are similar.

Want the full picture for a specific property?

The scores on this site show the representative tornado layer for a local area. Enter a street address to add building age, construction type, roof details, occupancy, surroundings, and property-level context.