Methodology
Every figure on this site is computed from public agency files listed on the data sources page. This page explains each step. Storm records run through 30 Jun 2026; the site was built 30 Sep 2026.
Storm events
NCEI publishes one details file per year. All 2,044,303 rows since 1950 are streamed; marine events (66,863: marine zones, waterspouts, rip currents, high surf and similar) are dropped, as are events in territories. Each remaining event is assigned to one of 13 groups by its NCEI event type:
| Group | NCEI event types |
|---|---|
| Hail | Hail |
| Tornado | Tornado |
| Flood | Flood, Flash Flood, Coastal Flood, Lakeshore Flood |
| Wind | Thunderstorm Wind, High Wind, Strong Wind |
| Winter | Winter Storm, Winter Weather, Heavy Snow, Blizzard, Ice Storm, Lake-Effect Snow, Sleet |
| Tropical | Hurricane (Typhoon), Hurricane, Tropical Storm, Tropical Depression, Storm Surge/Tide |
| Heat | Heat, Excessive Heat |
| Cold | Cold/Wind Chill, Extreme Cold/Wind Chill, Frost/Freeze |
| Drought | Drought |
| Wildfire | Wildfire |
| Lightning | Lightning |
| Fog | Dense Fog, Freezing Fog |
| Other | every other non-marine type (heavy rain, debris flow, dust storm, funnel cloud, avalanche, volcanic ash, tsunami and others) |
County versus forecast zone
NCEI records some events (mainly hail, tornado, thunderstorm wind, flash flood and flood) against a county and others (mainly winter weather, high wind, heat, cold, drought) against an NWS forecast zone. County-typed events are attached to the county by FIPS code. Zone-typed events are attached to a county only when the zone's name is exactly a county name in the same state (439,973 events); the rest (233,679) count toward state and national totals only. Zone-attached events are marked "Forecast zone" in tables. This means county winter and heat counts are conservative and vary with how each NWS office names its zones.
Dates, magnitudes and damage
Events are dated by their recorded start. Hail size is in inches, wind speed is converted from knots (1 kt = 1.151 mph), and tornado ratings are shown as recorded (Fujita before February 2007, Enhanced Fujita after). Damage is NCEI's estimate, parsed from its K/M/B notation and summed without inflation adjustment. Deaths and injuries add NCEI's direct and indirect counts.
Kept events
County pages keep at most 200 events per major hazard: the 120 most recent plus the 80 with the most deaths, injuries and damage. Counts, decade and month series and magnitude bins use every event. "Largest recorded events" ranks by deaths, then injuries, then damage.
The record changes over time
NCEI recorded only tornadoes (from 1950), and hail and thunderstorm wind (from 1955), until 1996, when all event types began. Reporting density has risen since with spotter networks and automated observations. Decade strips and yearly charts should be read with that in mind; per-area and per-capita comparisons between counties in the same state are the fairest use of the data.
Rates
Events per 100 square miles use Census land area; events per 10,000 residents and NFIP claims per 1,000 residents use the 2021 Census population estimate (the last vintage in which Connecticut's eight counties match the codes NCEI, FEMA and the NFIP still use). Claims per 100 policies in force divide claims by year of loss in the ten years to 2026 by residential policies in force as of 3 Aug 2026.
Disaster declarations
OpenFEMA's Disaster Declarations Summaries carry one row per designated area per declaration. County pages list rows whose FIPS county code matches the county; statewide and tribal rows (county code 000) appear on state pages only. State counts count each disaster number once. Types are DR (major disaster), EM (emergency) and FM (fire management assistance).
NFIP claims, repetitive losses and policies
OpenFEMA's redacted NFIP claims file (v3) is pulled in full and aggregated by reported ZIP code, county code and year of loss; amounts sum the building, contents and increased-cost-of-compliance payments. A ZIP is assigned to the county carried by most of its claims. Repetitive-loss and severe repetitive-loss counts come from the NFIP Multiple Loss Properties file; only counts are kept. Policies in force are FEMA's residential penetration-rate figures by county; ZIP-level policy counts are not published in a form this site can use.
National Risk Index
The county table of FEMA's National Risk Index (December 2025 release) is read from FEMA's public feature service. Ratings and expected annual loss are FEMA's own; this site does not recompute them. Connecticut rows in that release use planning regions and therefore do not attach to the counties shown here.
Hurricane passes
HURDAT2 best-track positions (Atlantic and Northeast Pacific) with winds of 34 kt or more are compared with each county's Census centre point. A storm counts once per county if any such position lies within 100 miles; "within 50 miles at hurricane strength" requires a position within 50 miles with winds of 64 kt or more. Distance from the track centre says nothing about the width of the wind field, rainfall or surge.
Thresholds and indexing
Every county has a page. County hazard pages need ten recorded events of that group. ZIP pages are built for every ZIP with a claim but are indexed only with five or more claims. State-year pages with fewer than three records (events, declarations and claims combined) are marked noindex.
Territories and Connecticut
Puerto Rico and the other territories are not covered because the Census county population file used here does not include them. Connecticut is shown by its eight counties; the planning regions the Census Bureau adopted in 2022 are not used.