Tornadoes and Extreme Weather Notes

Tornadoes and Extreme Weather

Air Masses

• Definition: Large bodies of air, over 1600 kilometers (1000 miles) across and several kilometers thick,

  • Characteristics:

  • Similar temperature and moisture at given altitudes

  • Move and affect large continental areas

Frigid Air Mass Invasion

• Examples of temperatures (°C):

  • -46°C in Winnipeg

  • -33°C in Sioux Falls

  • -9°C in Dallas

  • 10°C in Tampico

Source Regions of Air Masses

• Area where an air mass acquires its properties

• Classification of air mass:

  • By source region

  • By surface nature in the source region

Types of Air Masses

• Polar (P): High latitudes; cold

• Tropical (T): Low latitudes; warm

• Continental (c): Over land; likely dry

• Maritime (m): Over water; humid

Air Masses Affecting North America

• Continental Polar (cP):

  • Origin: Northern Canada, Alaska

  • Effects: Cold, dry air leading to lake-effect snow

• Maritime Tropical (mT):

  • Origin: Gulf of Mexico, Atlantic Ocean

  • Effects: Warm, moist air; precipitation in the eastern US

• Continental Tropical (cT):

  • Origin: Southwest United States, Mexico

  • Effects: Hot, dry air

Lake Effect Snow

• Snowfall patterns affected by nearby bodies of water (e.g., Great Lakes)

• Areas near lakes like Michigan and Superior experience significantly higher snowfall.

Maritime Polar (mP)

• Originates from the ocean, reaches western mountains, and influences Nor'easters in New England.

Fronts

• Definition: Boundaries separating differing air masses with varying densities; retain identities.

• Warm Front:

  • Warmer air replaces cooler air; slope of 1:200; light to moderate precipitation

• Cold Front:

  • Cooler air replaces warm air; steeper slope of 1:100; associated with violent weather.

Midlatitude Cyclones

• Move eastward across the U.S., requiring 2-4 days to pass.

• Weather contrasts most pronounced in spring.

Thunderstorms

• Features: Cumulonimbus clouds, heavy rainfall, lightning, potential for hail.

• Occurrence: Up to 2000 active thunderstorms at once in the U.S.; peak in Florida.

• Require warm, moist air and instability, generally occurring in afternoon/evening.

Tornadoes

• Characteristics: Localized violent windstorm; rotating column of air from cumulonimbus cloud; winds can reach 480 km/h (300 mph).

• Occurrence peaks from April to June, often following severe thunderstorms.

Enhanced Fujita Scale

• Wind Speed and Damage Assessment (EF Scale):

  • EF-0: 105-137 km/h - Light damage

  • EF-1: 138-177 km/h - Moderate damage

  • EF-2: 178-217 km/h - Considerable damage

  • EF-3: 218-265 km/h - Severe damage

  • EF-4: 266-322 km/h - Devastating damage

  • EF-5: >322 km/h - Incredible damage

Tornado Forecasting

• Nature of Watches/Warnings:

  • Tornado Watch: Conditions auspicious for tornadoes.

  • Tornado Warning: Tornado sighted or indicated by radar.

El Niño/La Niña – Southern Oscillation (ENSO)

• Normal Conditions: Define low/high-pressure areas across the Pacific.

• El Niño: High pressure near Indonesia; trade winds weaken, creating warmer waters near South America.

• La Niña: Opposite conditions of El Niño, lasting 3-5 years, affecting global weather patterns.

Drought and Desertification

• Drought: Extended periods of lower water availability; impacts agriculture and ecosystems.

• Desertification: Degradation in drylands caused by climatic changes and human activities.

The Dust Bowl Lessons

• Transformation of farming practices; restoration of prairie grasses to prevent soil erosion due to past mistakes during extreme drought periods.

• Importance of sustainable practices to mitigate drought effects.

Global and Regional Patterns in Weather

• Global Distribution: Related to land and water distribution; regions can have varying precipitation amounts.

• Drought Effects: Especially severe in developing regions due to factors like agricultural vulnerability and climatic variability.