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SEVERE WEATHER

SEVERE WEATHER. Thunderstorms and Lightning. Thunderstorms. Form in warm, moist, unstable air when a “trigger” such as a mountain or cold front forces the air to rise quickly. Storm clouds may be up to 20 km high in the atmosphere. Life Cycle of a Thunderstorm.

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SEVERE WEATHER

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  1. SEVERE WEATHER Thunderstorms and Lightning

  2. Thunderstorms • Form in warm, moist, unstable air when a “trigger” such as a mountain or cold front forces the air to rise quickly. • Storm clouds may be up to 20 km high in the atmosphere.

  3. Life Cycle of a Thunderstorm • Cumulus Stage – Air rises and a cumulonimbus cloud forms. The rising air is an updraft. The updraft prevents precipitation from reaching the ground. • Mature Stage – the precipitation becomes heavy enough to fall through the updraft and reach the ground. The falling precipitation creates a downdraft.

  4. Life Cycle of a Thunderstorm • Dissipating Stage – the downdraft weakens the updraft, cutting off the supply of moist air rising in the cloud. The cloud begins to evaporate.

  5. Lightning • Lightning is a discharge of electricity • Typically occurs during thunderstorms • In the atmospheric electrical discharge, a bolt of lightning can travel at speeds of 60,000 m/s (220,000 km/h), and can reach temperatures of 30,000 °C (54,000 °F). This is hot enough to fuse sand into glass • There are some 16 million lightning storms in the world every year

  6. Lightning • The top of the cloud becomes (+) charged and the bottom (–) charged from friction and other processes. • This charge is then discharged as lightning

  7. Lightning • Discharge of electricity. • The temperature may reach 50,000oF. (5X hotter than the sun’s surface) • Thunder is produced by the shock wave sent out due to the heated air expanding so violently.

  8. Hail Formation • Hail is produced during some thunderstorms under these conditions: • Condensation nuclei is available (dust) • Super cooled (<0oC) water droplets are carried through the updrafts and downdrafts of a cumulonimbus cloud.

  9. Types of Thunderstorms • Single Cell: A single thunderstorm with one main updraft • Rarely severe • Result from local unstable atmosphere • Typical summer thunderstorm

  10. Types of Thunderstorms • Multicell cluster: • Formed from a cluster of storms • Each cell is it’s own separate updraft • Can develop into squall lines • Squall Line (Multicell line): • Form when multicell clusters from a line • Can be hundreds of miles long

  11. Largest and most severe thunderstorm that can last for hours • Have a mesocyclone, a rotating updraft • Produce large amount of rain, hail, and strong winds • About 30% produce tornadoes Supercells

  12. Most supercells and tornadoes rotate counter-colockwise in the Northern Hemisphere

  13. Supercell Video

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