13.1 Thunderstorms

Pages 328 - 333

Goal 1

Describe the 3 conditions required for thunderstorms to

form

Requirement # 1

Abundant moisture in the lower atmosphere

Image credit: steamy window by lyle58 on Flickr

Requirement # 2

Mechanism to lift moist air up for condensation to occur

Image credit: Arrow up the tree by net_efekt on Flickr

Requirement # 3

Unstable atmosphere

Image credit: May be Unstable by Ann Douglas on Flickr

Goal 2

Relate types of thunderstorms to their uplift mechanism

• Mountain thunderstorm– Uplift mechanism air mass convection

• May be assisted by orographic lift– Sunlit mountain surface warms air– Warm air rises to create thunderstorm– Usually occur in afternoon, after sufficient

warming

Image credit: “Storm clouds a’ Brewin” by Abu on Flickr

Mountain Thunderstorm

• Sea-Breeze thunderstorm– Uplift mechanism air mass convection– Sun warms land faster than water– Warm land air rises– Cool sea-breeze replaces warm air causing a

convection current– Rising air produces thunderstorms– Often occur in summer afternoons

Sea Breeze Thunderstorms

Image credit: NOAA, image is public domain (government)

• Frontal thunderstorm– Uplift mechanism air mass collision– Cold front advancement– Line of storm formation at frontal boundary– More common in summer months– Can occur at any time of day

Frontal Thunderstorms

Image credit: Beau Dodson, educational use permission can be seen at: http://www.weatherphotography.net/index.html

• Rare warm-front thunderstorm– These can occur if the warm air mass has a

high moisture content

Goal 3

Relate the 3 stages in the life cycle of thunderstorm to the

direction of air flow

• 1. Cumulus Stage– Updrafts of warm air rising– Moisture transported up– Condensation occurs– Latent heat relseased = more rising– Coalescence of raindrops

• 2. Maturation Stage– Updrafts and downdrafts occur equally– Cold air sinking– Rain falling– Warm air still rising– Windy

• 3. Dissipation Stage– Downdrafts of cool air falling– Storm loses energy, no more air rising– No new precipitation forming– Remaining rain falls from storm

Image credit: NOAA, image is public domain (government)