Chapter 10 Thunderstorms

Mid-latitude cyclone: counter-clockwise circulation around a low-pressure center

Where are thunderstorms located?Along the warm front or the cold front?

Tornado over Kansas - May 2004

Thunderstorms…

• Form in conjunction with MLC, but can also form on their own.

• Generate lightning and thunder, wind gusts and hail• Can cover a small area (single cloud) or a large area;

cluster of clouds• Have strong up and down (not spiraling counter clockwise)

movement of gusty, variable winds• Forms in unstable air.

Thunderstorm Scavenger Hunt

1. What are some other names/types of thunderstorms?2. Where are thunderstorms most common on Earth?3. During what time of day/season are thunderstorms most active?4. What three ‘ingredients’ are needed to form a thunderstorm?5. What is the size and duration of a thunderstorm?6. What are the warning signs that a thunderstorm is approaching?7. What is the #1 thunderstorm killer?8. What are “super-cells”, how big are they?9. What is a microburst?10. What are three stages of thunderstorm development?11. What is a mesocyclone?12. According to the National Weather Service (NWS), when is a severe

thunderstorm watch or warning issued?

Compare…

Pg. 287-Formation Size

Air Mass thunderstorm

Frontal thunderstorm

Air Mass Thunderstorms

• Air near surface is warmed during the day.• Warm air rises and condenses to form

cumulous clouds in the afternoon.• Scattered, isolated.• Most moisture evaporates

but eventually it accumulates into

taller clouds.

Forms along a Cold Front

8

Or…along a Warm Front

Unstable air mass

9

Orographic lifting over mountains

11

Forms when air converges, is forced up, cools adiabatically, form clouds

These tend to be brief, short-lived storms with moderately heavy downpours.

3 Stages of Development of a ThunderstormPg. 288

Cloud continues to grow as long as there is a supply of warm, moist air.Updraft occurs.

13

http://www.youtube.com/watch?v=DualOU_gBn0

Stage 1

Bergeron Process

Ice crystals collect water molecules and grow larger

while cloud droplets evaporate and get smaller.

Stage 2

• Mature stage

15

Stage 3

16

Fair-Weather Cumulus

DevelopingCumulonimbus

Well-Developed Cumulonimbus

Severe Thunderstorm Development along a Cold Front

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Roll Cloud

http://www.youtube.com/watch?v=QHHUfb7olQ0

???????????

• Where in the U.S. do thunderstorms occur most frequently?

• How many are occurring at any given time world-wide?

Average Number of Thunderstorm Days

Flash Floods - Number One Thunderstorm Killer

AtmosphericHazard

Bell work

1. T or F? A mature stage thunderstorm cloud can be as high as the mesosphere.2. Severe thunderstorms form along (cold, warm) fronts.3. Which can have the higher wind speeds – hurricanes or tornadoes?4. T or F? Thunderstorms have vertical air movement while tornadoes have spiral air movement.5. Does an updraft cause a “up-dog” ?

Supercell Thunderstorm

Supercell:

A single, very large (65,000 ft. high) massive cloud 12-30- miles in diameter,Lasts for many hours

Cluster of Supercell Thunderstorms

Temperature Inversion enhances formation of severe thunderstorms: dense, cold layer above prevents warm, moist air from rising.Surface air heats up, and finally erupts upward, producing an unusually large cumulus cloud

Mammatus Sky

Text book Questions pg. 315

1.

2.

4.

5.

6.

Microburst

Strong DOWNDRAFTSBeneath the thunderstorm

Small 2.5 miles across

Cold dense, sinking air

Last 2-5 minutes

Also called wind shears

http://www.youtube.com/watch?v=fjFTH3s6BlM