Thunderstorms

GPH 111

Purpose of Lecture

This lecture focuses on how changes in lapse rates (temperature change with elevation) influence rainshadows, air pollution, and thunderstorm development. Then, the lecture turns entirely to thunderstorms.

Outline

1. Atmospheric stability (or instability)

2. How stability influences air pollution

3. How stability influences rainshadows

4. How stability influences thunderstorms

5. Thunderstorm processes and hazards

Is the atmosphere stable or unstable?

Is the atmosphere stable or unstable?

Details on Instability/Stability

Details on Instability/Stability

Details on Instability/Stability

Details on Instability/Stability

Details on Instability/Stability

So let’s compare …

Temperature

of the atmosphere

vs.

Temperature

of future

thunderstorm

(parcel of air)

Red (dry) & Blue (condensing): how air parcel changes

As parcel goes up, cools & reaches the dew point

At the Lifting Condensation Level

Temperature decrease in lapse rate lessens because latent heat is

released with condensation

Graph it out

Is parcel or the surrounding air warmer?

At 1500 m? 2500m?

Mountains in summer often have very unstable air

LAPSE RATES:WALR – condensing (wet)DALR – not yet

condensing (dry)ELR - surrounding air

(environment)

Opposite: air parcel colder so colder air wants to stay

Extreme state of stability: inversion where bottom of atmosphere is

colder than air above

Stable is Warm on ColdNormally, its warmer closer

to Earth. But if its colder, the condition is called

an inversion layer (inverse is opposite of normal) that is very stable

Temperature InversionsWhen warmer air overlies cooler air, pollutants and fog are trapped beneath the inversion.

Common Winter Radiation Inversion in Valleys

Temperature Inversions

Common Summer Inversion in Los Angeles

Inversions trap air pollution

Central Valley

California from space

Salt Lake City

Inversions trap air pollution

China

Lapse Rate Changes Explain Rainshadows

Can see evaporation of clouds as air descends and warms

Grand Canyon Anza Borrego

Warming Winds have Regional Names

Not from raining out moisture,but descending & warming air

Sierra Nevada, California Olympic Mountains

Atacama in Rainshadow

Tibetan Plateau in the “lee” of Himalaya Mountains

Back to Thunderstorms & Instability

Can also generate lift other ways

Life Cycle of a Typical Cumulonimbus Cell

Instability leads to quick change(full life cycle usually about 30 minutes)

Cumulus Mature Stage

Instability leads to quick change(full life cycle usually about 30 minutes)

Cumulonimbus: Mature Stage

End of Thunderstorm

Geography of Thunderstorms (as seen through lightning): most common around intertropical

convergence zone

Geography of Thunderstorms(as mapped by lightning)

Most common in Florida

Summer moisture key to this geography

Arizona (Mexican) Monsoon is Thunderstorm Season

• Storms are spotty

• Often start at the Mogollon rim

Five recent severe monsoon events

Urban effects?

Hazard: Dust Storms (haboob)

Texas Australia

Middle EastTempe

Hazard: Microbursts

Classroom Resource

Not tornadoes – straight line winds

Tornado winds are

upward spiral

Damage is in a line

Microburst hazard: Flying

Doppler Radar

detects the hazard

Hazard: Flash Flooding

Hazard: Hail

Sizes Differ

Damage ($1B/yr) from size and speed (> 100 mph)

Sydney, AustraliaBlue tarps

Corn in Illinois

Ouch!

Hazard: Tornadoes

Tornado comes from severe Tstorms

Rotating Thunderstorms

Where?

Focus: East of Rocky Mtns

Greensburg Kansas, Spring 07

Why East of Rocky Mtns?

Where cold/dry and warm/moist air masses collide

Why Spring (and Fall)?

When biggest contrast in cold/warm air masses occur

Rotation important in damage

Flying objects big danger (record)

1) Pay attention to watches and warnings

2) Don’t risk outrunning them3) If caught in the open, find a

low place away from streams

4) If in a car, get out. Most deaths occur in cars and mobile homes.

5) If in a building, head to the lowest floor, center of the building and smallest room

Avoid Overpasses

Other locations

Hazard: Lightning

Distribution

As soon as the positive and negative parts of the stepped leader and traveling spark connect, there is a conductive path to the ground and negative rush causes visible stroke

Look at case story

of 1 hit

Lots of travelling sparks trying to connect

The chosen

path

Even a failed

stepped leader

You tube video shows traveling spark (luckily, not ‘chosen’ to connect with return stroke)

Normal Lightning Types

Cloud to Ground Cloud to Cloud and

Intracloud

Other Types of Lightning

Online Resource

http://news.nationalgeographic.com/news/2006/05/0504_060504_lightning_video.html

Why more men hit?

Thunder

• Caused by extreme heat of lightning, causing air to expand.

• Sound travels 1 mile in 5 seconds, so 30 seconds means lightning is 6 miles away

• Close thunder will crack or snap. Far thunder will rumble as the sound arrives at different times from different parts of the lightning flash

Lightning Myths

Other Myths

Other Myths#5: People struck DO NOT carry and

electrical charge. Call 911 and do CPR, if necessary.

#6: If it is not raining, lightning can still strike you, as faras 10 milesfrom rain

Lightning SafetyTeach the “30-30” rule: Go in when you

count 30 seconds between lightning & thunder (6 miles). Go back out after 30 minutes

Lightning Fatalities

Get inside (but where?)

• Not picnic shelters, beach shacks, golf shelters, camping tents, baseball dugouts

• A safe building means fully enclosed with roof, walls like home, school, or shoping centers

• A safe vehicle is a hard-topped car (not a convertible) and making sure all doors closed, windows rolled up, and not touching metal surfaces

Boating: No!!

• But if you are stuck,get in the cabin away from metal

• If you are scuba diving, stay deep for duration of the storm

If you are outside

Avoid tall isolated trees

If you are outside• Avoid wet ropes or metal fences. They

both make good conductors of electricity

If you are outside

• Stay 15 feet apart from other members of your group, so lightning won’t travel between you if hit. Keep your feet together and sit on the ground out in the open.

Some Last Resort Choices

• Wait below an overpass (avoiding steel girders and your bike)

• Seek shelter directly underneath high voltage electrical tension wires, but stay 50 feet or more away from the towers

• Find a low spot or ditch (but not a stream, to avoid flash flooding)

Inside your home

#1: Avoid contact with corded phones#2: Avoid contact with electrical equipment or

cords. Unplug your equipment well before the storm arrives

#3: Avoid contact with plumbing. Don’t wash your hands. Don’t take a shower. Don’t do the dishes or laundry

#4: Stay away from windows, doors and porches#5: Don’t like on concrete floors or lean against

concrete walls

Stay safe