Severe Storms: Thunderstorms, Tornadoes & Hurricanes

Storm Formation Overview

  • Weather driven by interaction of solar heating, oceans, Earth/Moon motion, landscape → uneven heating → air-pressure changes.
  • Warm, moist air + rising motion (convection) = energy source for all three storm types.
  • Fronts form where air masses meet; strong lifting along fronts often triggers storms.

Thunderstorms

  • Definition: localized storm with lightning ⚡ and thunder; becomes “severe” at winds ≥ 57.5 mph & hail ≥ 1 in.
  • Formation steps:
    1. Sun heats surface → warm, moist air rises (convection).
    2. Air cools aloft ⇒ water vapor condenses → cumulonimbus cloud.
    3. Ice/water collisions build electric charge ⇒ lightning + thunder.
  • Hazards: flash flooding (inches of rain in minutes), lightning fires/fatalities, hail (≥ softball size), straight-line winds.
  • U.S. hotspots: Florida & Great Plains; peak in warm afternoons of spring–summer.

Tornadoes

  • Definition: narrow, rotating funnel from storm cloud to ground; diam. < 100 m, lifespan minutes, winds > 300 mph.
  • Key ingredients: warm, moist Gulf air + cool, dry Canadian air + strong wind shear ⇒ supercell thunderstorm ⇒ rotation tightens into funnel.
  • Peak region: “Tornado Alley” (N. Texas → S. Dakota/Minnesota); U.S. sees ≈ 1200 tornadoes yr⁻¹, 60 deaths, 1500 injuries, 4\times10^{8} USD damage.
  • Hazards: extreme winds, debris missiles, pressure drop, paths up to 50 mi.

Hurricanes

  • Definition: tropical cyclone with sustained winds ≥ 74 mph; diameter ≤ 600 mi; lifespan ~1 week+.
  • Requirements: sea-surface temp ≥ 80 °F, moist air, low vertical wind shear, Coriolis force for spin.
  • Structure: spiral rainbands & eyewall around calm eye; winds can reach 200 mph; storm surge water rise up to 25 ft.
  • Tracks: form in Atlantic Basin, move W/NW by trade winds, weaken over land.
  • Example impact: Hurricane Katrina (2005) → 81\times10^{9} USD damage, 80 % of New Orleans flooded.

Safety Measures Summary

  • Thunderstorm: go indoors/car (windows shut); avoid tall objects, water, electronics; no showers.
  • Tornado:
    • Indoors → basement/inner room, away from windows, cover head.
    • Outdoors → ditch/low spot; out of vehicle; never outrun.
  • Hurricane:
    • Pre-storm: disaster plan, board windows, know evacuation route.
    • During: avoid low areas, stay away from windows, shelter on high ground.
    • After: stay indoors until cleared, beware flooding, assist trapped individuals.

Key Comparisons

  • Duration: Thunderstorm < Tornado < Hurricane (hours → minutes → week).
  • Wind speed peak: Thunderstorm ≤ 120 mph; Tornado ≤ 300 mph; Hurricane ≤ 200 mph.
  • Damage focus: Thunderstorm (localized rain/hail/wind); Tornado (narrow, intense inland path); Hurricane (wide-scale coastal flooding & wind).