Tornado Data Sources & Methodology

The source archive

We use SPC’s “actual tornadoes” single-track CSV, which summarizes U.S. tornado records from National Weather Service Storm Data. The downloaded release ends on 2025-12-28. It is a historical release, not a live feed.

• SPC maps, graphics, and data index
• Download the original 1950–2025 single-track CSV
• SPC database field specification (PDF)
• Download this site’s provenance and yearly counts
• U.S. map boundaries: us-atlas / U.S. Census Bureau

How we prepare it

Records with an entire-track flag (sg=1) are retained, including tracks that cross states. We split them into yearly JSON files so the browser loads only the selected year. Exactly identical rows would be removed; none were found in this release. Three reused year/number identifiers describe different source rows, which are retained with distinct suffixes.

Crossed-state names come from state segments in the matching SPC all-tornadoes release, linked to the single-track record. These segments add names without adding events or changing track totals. The start state is the recorded touchdown state. For interstate tracks, the end state is shown only when a state segment has the same recorded endpoint. Incomplete or ambiguous state information stays unavailable; states are never inferred from the straight line on the map.

Ratings outside 0–5 remain unknown. Zero or invalid coordinates are treated as missing, never plotted at the origin. Negative unavailable measurements are kept as null. Path length is in miles and path width in yards. The width field’s reporting conventions have changed historically; it should not be treated as a uniform measure over the entire period.

The map retains the original archive date and time. Time-zone code 3 is interpreted as CST and code 9 as UTC. Other codes remain unknown. F and EF labels follow the February 1, 2007 U.S. transition. We do not estimate measured winds, intermediate positions, or storm duration.

Property and crop loss fields

The source CSV includes loss and closs. We retain the original download but omit these fields from the explorer's derived records. Historical property entries include loss categories; later monetary encodings require period-specific verification. Zero is not proof of no loss.

The April 2010 SPC specification preserved by NOAA CPC (PDF) describes older encodings and anticipates a unit change. It does not verify all later values in our release. The SPC index also cautions about monetary-loss reliability. We do not publish loss totals or cost rankings from unverified values.

Whole-track records can cover multiple states. Their losses and casualties cannot be assigned entirely to the touchdown state. The source specification directs state-impact totals to state-segment records, which are a different product from this site's single-track archive. Read about financial loss and damage ratings.

How archive summaries are calculated

State pages select retained tracks by touchdown state; year pages select their source calendar year. Monthly counts include records without ratings or coordinates. F and EF counts stay separate, and unknown ratings have their own count. Selected records are sorted by rating number, then descending date and ascending archive ID. The chart and tables are generated from the same yearly files as the map.

These are unadjusted archive counts, not tornado probabilities or climate trends. No state casualty totals or monetary totals are calculated. See state and year summaries and tornado geography and seasonality.

Reproducibility and updates

Downloaded on 2026-09-11. The manifest stores the exact source URL, SHA-256 checksum, access date, missing-coordinate counts, and counts by year and month. Refreshing downloads the latest single-track CSV linked from SPC’s index; a rebuild and deployment make it available to visitors.

Coverage and limits

This is a U.S. archive, not a global one. The explorer keeps records that cannot be located on the map. Early reporting is incomplete and recent records can be revised. Paths connect endpoints and do not represent detailed damage footprints. This independent site is not affiliated with NOAA and provides no forecasts or warnings.