Photographs by NSSL
Lecture #1: Clouds and
Airmass Thunderstorms
Friday, 19 January 2001
Photographs by NSSL
Purpose
We begin the course by examining the basics of clouds and thunderstorms, including
general air motion, the physics of condensation and latent heating, and precipitation
mechanisms. We also will examine how and why such storms produce wind shear that can
be dangerous to aviation. Hail and lightning will be deferred to the section on
severe thunderstorms.
Text Reading for Lecture #1
Airmass (single-cell) thunderstorms: pages 381-384; 395-396
Web Resources
Single-Cell
(Airmass) Thunderstorms
Thunderstorms
Thunderstorms
Definition: By definition, a thunderstorm is a local storm, invariably produced by a cumulonimbus cloud, that always is accompanied by lightning and thunder. It usually contains strong gusts of wind, heavy rain, and sometimes hail. Meteorologists often use the word "convection" to describe such storms in a general manner, though the term convection specifically refers to the motion of a fluid resulting in the transport and mixing of properties of the fluid. To be more precise, a convective cloud is one which owes its vertical development, and possibly its origin, to convection (upward air currents).
Climatology:
At any given time there are an estimated 2000 thunderstorms in progress, mostly in tropical and subtropical latitudes. About 45,000 thunderstorms take place each day. Annually, The U.S. experiences about 100,000 thunderstorms. About 16 million thunderstorms occur annually around the world!
The Weather Channel 
Harold Brooks, NSSL 
Harold Brooks, NSSL
Types: Although a continuous spectrum of storms exists, meteorologists find it convenient to classify storms into specific categories according to their structure, intensity, environments in which they form, and weather produced. The most basic classification includes single-cell or air-mass storms, multicells, squall lines, supercells, and mesoscale convective systems.
General Requirements: a) Abundant low-level moisture; b) Instability over a large depth of the atmosphere (dense air at upper levels and less-dense air below); c) A mechanism to trigger the instability (front, dryline, terrain)
