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.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
What are some other names/types of thunderstorms?
Where are thunderstorms most common on Earth?
During what time of day/season are thunderstorms most active?
What three ‘ingredients’ are needed to form a thunderstorm?
What is the size and duration of a thunderstorm?
What are the warning signs that a thunderstorm is approaching?
What is the #1 thunderstorm killer?
What are “super-cells”, how big are they?
What is a microburst?
What are three stages of thunderstorm development?
What is a mesocyclone?
According to the National Weather Service (NWS), when is a severe
thunderstorm watch or warning issued?
Compare…
Pg. 287-
Air Mass
thunderstorm
Frontal
thunderstorm
Formation
Size
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
Forms when air converges, is forced up, cools
adiabatically, form clouds
These tend to be brief, short-lived
storms with moderately heavy
downpours.
11
3 Stages of Development of a Thunderstorm
Pg. 288
Stage 1
Cloud continues to grow
as long as there is a
supply of warm, moist air.
Updraft occurs.
http://www.youtube.com/watc
h?v=DualOU_gBn0
13
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
Developing
Cumulonimbus
FairWeather
Cumulus
Well-Developed Cumulonimbus
Severe Thunderstorm Development along a Cold Front
19
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
Atmospheric
Hazard
Flash Floods - Number One Thunderstorm Killer
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 DOWNDRAFTS
Beneath 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