Guided Notes on Guided Notes on ThunderstormsThunderstorms

Chapter 13, Section 1Chapter 13, Section 1

Describe the 3 conditions that must Describe the 3 conditions that must exist for a thunderstorm to form:exist for a thunderstorm to form:

1.1. Abundant moisture in the lower levels of Abundant moisture in the lower levels of the atmospherethe atmosphere

2.2. A mechanism must lift the air so that A mechanism must lift the air so that moisture will condense and release latent moisture will condense and release latent heatheat

3.3. The portion of the atmosphere through The portion of the atmosphere through which the cloud grows must be unstablewhich the cloud grows must be unstable

2. Typical thunderstorms last only 2. Typical thunderstorms last only about about 3030 minutes, and individual minutes, and individual storms are only about storms are only about 24 24 kilometerskilometers in diameter. in diameter.

3. Thunderstorms are classified according to 3. Thunderstorms are classified according to the mechanism that caused the air to risethe mechanism that caused the air to rise. . An air mass thunderstorm forms if An air mass thunderstorm forms if the air the air rose because of unequal heating of Earth’s rose because of unequal heating of Earth’s surface within one air masssurface within one air mass. This reaches . This reaches its maximum during its maximum during mid-afternoonmid-afternoon, so air-, so air-mass thunderstorms are most common mass thunderstorms are most common then.then.

4. Mountain thunderstorms occur 4. Mountain thunderstorms occur when an air mass rises because when an air mass rises because of of orographic liftingorographic lifting..

5. Sea-breeze thunderstorms are local air-5. Sea-breeze thunderstorms are local air-mass thunderstorms caused by mass thunderstorms caused by temperature differences between the air temperature differences between the air over land and the air over waterover land and the air over water. They are . They are most common in coastal areas during the most common in coastal areas during the summersummer, especially in the , especially in the tropicstropics and and subtropicssubtropics..

6. Frontal thunderstorms are produced 6. Frontal thunderstorms are produced by by advancing cold frontsadvancing cold fronts and rarely, and rarely, warm fronts. Because they are not warm fronts. Because they are not dependent on daytime heating, these dependent on daytime heating, these thunderstorms can persist thunderstorms can persist long into long into the nightthe night..

Describe the 3 stages of Describe the 3 stages of thunderstorm development:thunderstorm development:

Cumulus Stage: air rises vertically, creating Cumulus Stage: air rises vertically, creating updrafts which transport moisture to the updrafts which transport moisture to the upper reaches of the cloudupper reaches of the cloud

Mature Stage: as precipitation falls, it cools Mature Stage: as precipitation falls, it cools the air around it, creating downdrafts that the air around it, creating downdrafts that produce gusty surface windsproduce gusty surface winds

Dissipation Stage: the supply of warm, moist Dissipation Stage: the supply of warm, moist air runs out because downdrafts spread in air runs out because downdrafts spread in all directions as they reach the surfaceall directions as they reach the surface