Thunderstorms

Section 13-1 p 329-333

Thunderstorms

Section 13-1 p 329-333

HOW DO THUNDERSTORMS FORM ?

• Three Conditions that are Responsible

– lots of moisture in lower levels of the atmosphere

– air has to rise so water vapor can condense to release latent heat

– Portion of atmosphere where clouds mature must be unstable

Two types of Thunderstorms

1. AIR-MASS THUNDERSTORMSWhen air rises because unequal heating within one air mass of the Earth’s surface

2. FRONTAL THUNDERSTORMS Formed by advancing cold fronts or in some cases advancing warm fronts(rare)

Two Common Types of Air-Mass Thunderstorms

• 1. Mountain Thunderstorms

- result of orographic lifting

- air travels up the side of a Mt.

2. Sea-Breeze Thunderstorms

- result of extreme temperature changes in the air over land and air over water

Two Common Types of Air-Mass Thunderstorms

1. Cold Front: cold air pushing warm air quickly up cold-front boundary

– this motion produces a line of storms along leading edge of cold front, can be 100’s of km long

– Initial lift from push of cold air– Can continue long into night

Two Common Types of Frontal Thunderstorms

Frontal Thunderstorm – COLD FRONT

• Warm Front: warm air slides up and cold air mass , very mild t-storms can occur.

• Last for short period of time (less than an hour)

Two Common Types of Frontal Thunderstorms

Frontal Thunderstorm – WARM FRONT

CUMULUS STAGE

• Air rises vertically upward creating updrafts

• Moisture transported to upper portions of clouds

• Moisture condensed into droplets, releasing latent heat

MATURE STAGE

• Precipitation Falls cooling surrounding air

• Creation of cool more dense air sinks to ground with precipitation

• Up & down drafts exist side by side in cumulonimbus clouds

• Convection cells form developing gusty winds

DISSIPATION STAGE

• Characterized by the lingering of downdrafts

• Lack of warm air stops updrafts and the development of precipitation

• Cloud runs out of previously formed raindrops