US Extreme Weather and Climate Change Dashboard

NCEI Storm Events annual tornado count, by F/EF-scale rating. Unit: tornadoes per year.

Hail, tracked on the same source page, has no reliable trend window at any point in the record and this site deliberately excludes it from trend assessment entirely — see /severe-storms. Each tornado's F/EF rating here is the peak intensity across the reconstructed track (Storm Events records one row per county a tornado crosses rather than one row per tornado; the pipeline merges county-segment rows into a single physical-tornado track before counting — see the Methodology page).

Source: NCEI Storm Events Database (reconstructed tornado tracks)

Computing trend…

Annual count of distinct calendar days with at least one tornado -- less sensitive than the raw annual count to the NEXRAD-era weak-tornado detection artifact, since a busy outbreak day still counts as one tornado-day regardless of how many weak tornadoes within it modern radar newly detects. Unit: days per year.

Distinct calendar days (local time, as Storm Events records it) with at least one reconstructed tornado track -- a standard alternative to raw annual counts in the severe-weather literature, far less sensitive to the NEXRAD-era weak-tornado detection artifact than the raw total: a busy outbreak day still counts as one tornado-day no matter how many additional weak tornadoes modern radar/spotter coverage would newly detect within it. This series uses an earlier reliable-trend window (1954+) than the raw total's 1997+: tornado days settle into a sustained ~150-210/year band decades before the raw total's NEXRAD-era jump. See the Methodology page.

Source: NCEI Storm Events Database (reconstructed tornado tracks)

Computing trend…

Mean tornado count on 'outbreak days' (calendar days with 6+ tornadoes, per Galway 1977 / Tippett, Lepore & Cohen 2016) each year -- some literature finds outbreak clustering trending upward even where raw annual counts don't. Unit: tornadoes per outbreak day.

An "outbreak day" is a calendar day with 6 or more reconstructed tornado tracks. The threshold and day-based (not rolling-window) bucketing remain disclosed judgment calls -- 6 sits at the low end of the published range of tornado-outbreak definitions and matches Tippett, Lepore & Cohen (2016, Science), though that paper uses a 6-hour rolling start-time-gap cluster restricted to (E)F1+ tornadoes rather than calendar-day, all-tracks bucketing, so these numbers don't claim to reproduce that paper's published counts. Unlike tornado days, outbreak size reuses the raw total's 1997+ reliable-trend window: it inherits essentially the same NEXRAD-era weak-tornado artifact. See the Methodology page.

Source: NCEI Storm Events Database (reconstructed tornado tracks)

Computing trend…

CONUS convective available potential energy (CAPE) from ERA5 reanalysis at 21Z daily, independent of any human tornado/hail/wind report -- an environment-based instability proxy rather than a report count. This panel measures CAPE only: it deliberately omits wind shear (the ingredient that specifically differentiates tornadic from ordinary severe environments), so read it as 'was the atmosphere unstable enough for organized severe thunderstorms,' not a tornado-probability index. Unit: J/kg.

This panel measures CAPE (instability) only -- it deliberately excludes wind shear, the ingredient that specifically differentiates tornadic storms from ordinary severe thunderstorms/hail in the literature (e.g. the Significant Tornado Parameter). Read this series as "was the atmosphere unstable enough for organized severe thunderstorms," not as a tornado-probability index: a real, major tornado outbreak on Dec 15, 2021 had unremarkable CAPE, because it formed as a high-shear/low-CAPE event. See the Methodology page.

Source: ARCO-ERA5 (Google Research)

Computing trend…

Mean daily share of the CONUS reanalysis grid at or above a moderate (1,000 J/kg) or extreme (2,500 J/kg) CAPE threshold -- a spatial-coverage view, since severe weather is regional rather than continent-wide, and a plain national average dilutes any real signal. Unit: % of CONUS grid.

Unlike every other severe-weather series here (which counts human reports/observations of tornadoes or hail), this series draws purely on reanalysis-assimilated atmospheric fields -- it doesn't depend on anyone observing or reporting anything, so it isn't subject to the population-density/spotter-network/radar-deployment reporting-practice issues that affect tornado and hail counts. It has different limitations instead (reanalysis quality by era, spatial/temporal sampling choices) -- see the Methodology page.

Source: ARCO-ERA5 (Google Research)

Computing trend…

Annual count of days meeting a disclosed instability threshold -- 'widespread' days (≥10% of the CONUS grid at moderate CAPE) and 'high-CAPE' days (any grid cell at extreme CAPE) -- structurally parallel to this site's tornado-outbreak-day metric, but built from reanalysis fields rather than human reports. Unit: days per year.

The reliable-trend window reflects ERA5's documented reanalysis-quality break rather than a reporting-practice artifact like the tornado record's window: ECMWF's back-extension documentation states reanalysis skill "improves dramatically following the first assimilation of satellite data from the TOVS satellites at the end of 1978." This independently matches the severe-weather-environment reanalysis literature's practical start year (NARR, and the Tippett/Gensini-Brooks STP climatologies built on it, also begin in 1979). See the Methodology page.

Source: ARCO-ERA5 (Google Research)

Computing trend…