---
source: https://iinventedlight.com/library/notes/thunderstorm-basics.md
title: "Thunderstorms: what they are and when they turn severe"
license: CC-BY-4.0
license_url: https://creativecommons.org/licenses/by/4.0/
source_license: "US government work, public domain; restated in our own words"
attribution: "Summary by iinventedlight (AI-assisted). Sources: NOAA, Severe Weather 101: Thunderstorm Basics, US government work, public domain; NOAA, Severe Thunderstorm Safety, US government work, public domain."
author: "iinventedlight (synthesis of cited sources); text drafted with AI assistance"
date: 2026-11-04
status: published
checked_on: 2026-11-04
as_of: 2026-11-04
confidence: medium
untested: "No observation or experiment was done; only the fetched government pages were read."
category: coverage-gaps
topic_area: "science-explain: weather and atmosphere"
tags: science, weather, thunderstorms, lightning
sources:
  - id: S1
    title: "Severe Weather 101: Thunderstorm Basics"
    publisher: NOAA
    url: https://www.nssl.noaa.gov/education/svrwx101/thunderstorms/
    accessed: 2026-11-04
    license: "US government work, public domain"
  - id: S2
    title: "Severe Thunderstorm Safety"
    publisher: NOAA
    url: https://www.weather.gov/safety/thunderstorm
    accessed: 2026-11-04
    license: "US government work, public domain"
---
# Thunderstorms: what they are and when they turn severe

## Short answer
A thunderstorm is a rain shower with thunder, and since thunder comes from lightning, every thunderstorm has lightning. It is called severe when it brings hail one inch or larger, wind gusts over about 58 mph (50 knots), or a tornado. [S1][S2]

## How they form
Surface heating drives convection: air rises and carries moisture up with it, building the storm cloud. [S1]

## What severe storms can do
Inch-size hail damages roofs, plants and cars; strong gusts break branches and knock trees over. Some storms bring softball-size hail or winds over 100 mph. [S2]

## Claims
- id: C1
  claim: All thunderstorms have lightning because thunder comes from lightning.
  source: S1
  evidence: "Since thunder comes from lightning, all thunderstorms have lightning."
- id: C2
  claim: Convection is upward atmospheric motion usually created by surface heating.
  source: S1
  evidence: "Usually created by surface heating, convection is upward atmospheric motion"
- id: C3
  claim: A severe storm has hail one inch or larger, strong gusts, or a tornado.
  source: S1
  evidence: "hail one inch or greater, winds gusting in excess of 50 knots"
- id: C4
  claim: Some severe storms produce hail larger than softballs.
  source: S2
  evidence: "Some severe thunderstorms can produce hail larger than softballs"

## Sources
- [S1] Severe Weather 101: Thunderstorm Basics. NOAA. https://www.nssl.noaa.gov/education/svrwx101/thunderstorms/ . License: US government work, public domain. Accessed 2026-11-04.
- [S2] Severe Thunderstorm Safety. NOAA. https://www.weather.gov/safety/thunderstorm . License: US government work, public domain. Accessed 2026-11-04.

License: this note is CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Summary by iinventedlight (AI-assisted).