2. Moisture - Preferably in the lower or mid levels of the atmosphere Source of lift – Agent which lifts the warm, moist air starting the thunderstorm – Fronts colliding – Terrain Instability – Ability for air to accelerate upward/downward

3. Thunderstorm Life Cycle Cumulus Stage Mature Stage Dissipating Stage 1.Cumulus stage: Regular cumulus cloud with an updraft (rising warm, humid air). Will grow into a cumulonimbus cloud (20,000 ft high) 2.Mature stage: Updraft + Downdraft (sinking rain-cooled air). Will grow into 40,000 to 60,000 ft high. Strongest stage. 3.Dissipating stage: Downdraft is stronger than updraft, cooling the warm air below and cutting off storm’s fuel supply.

4. Some storms are single cell and last about 30 minutes before dissipating Others form from a cluster of cells and last several hours – Produce large hail, damaging winds, flash floods, tornadoes

5. “Soft hail” collides with water droplets and hail which shears electrons off of rising particles. Electrons collect on sinking particles

6. A moving thunderstorm gathers a pool of positively charged particles along the ground that travel with the storm (1). Positively charged particles rise up taller objects such as trees, houses, and telephone poles. A channel of negative charge, called a "stepped leader" will descend from the bottom of the storm toward the ground (2). It is invisible to the human eye. The positive charge "reaches" out to the approaching negative charge with its own channel, called a "streamer" (3). The resulting electrical transfer is what we see as lightning.

7. Thunder is the sound of lightning, but lightning is seen before thunder is heard Lightning can be as hot as 54,000 ° F, causing air molecules to expand very quickly and form shockwaves Nearby strikes sound like a loud bang, or crack and are short in duration Farther strikes result in long, rumbling sounds because the shock waves have spread to be many miles across

8. In supercell thunderstorms, the updrafts are particularly strong. If they are strong enough that the horizontal vortex of air can be pulled upright. This called a mesocyclone, and is typically 2 to 6 miles wide. There's a 50% chance that the storm will escalate into a tornado in 30 minutes.

9. What is a Tornado? A rapidly whirling, funnel-shaped cloud that reaches down from a storm cloud to touch Earth’s surface

10. How the column of air begins to rotate is not completely understood by scientists The rotation appears to happen when winds at two different altitudes blow at two different speeds creating wind shear. For example, a wind at 1000 ft above the surface might blow at 5mph and a wind at 5000 ft might blow at 25mph. This causes a horizontal rotating column of air.

11. Tornadoes were originally rated on the Fujita Scale, named for its inventor, University of Chicago meteorologist T. Theodore Fujita. – Based on the wind speed and type of damage caused by a tornado – Updated to the Enhanced Fujita Scale in 2007 – The average tornado has maximum wind speeds of about 112 mph or less, measures around 250 feet in width and travels approximately one mile before falling apart.

13. A storm with strong winds and rain that forms over tropical waters (80° F) Can be 600 miles in diameter, 9 miles high Hole in the middle = Eye – Up to 20 miles wide – Calm Other names: – Typhoons: near Philippines/Northwest Pacific Ocean – Tropical cyclones: near Australia/Indian Ocean

14. Northern hemisphere: spiral counter-clockwise Southern hemisphere: spiral clockwise Due to the earth’s rotation Known as the Coriolis effectCoriolis effect – This force is greatest at the poles and weakest at the equator because of earth’s spherical shape – Hurricanes form at 15° to 20° N or S of equator – not at equator (Coriolis too weak)

15. Tropical depressions are tropical storms in the making Tropical storms are Hurricanes in the making Tropical depression Tropical Storm 38 mph or less 39-73mph Hurricane 74 mph or above

17. Sudden, heavy rainfall over a short time period Also caused by dam bursts or overflows. Water rises above its natural banks Caused by snowmelts and prolonged, heavy precipitation. Take days, weeks, or months to rise to its max and return to normal FlashRiverine

18. All of the following criteria must be met Blowing snow Winds >39 mph for at least 3 hours Air temperature less than 0ºC (< 32ºF) Visibility less than 1/4 mile There is no total snowfall criteria, but most blizzards have large snowfall totals Heavy snowfall limits travel, and paralyzes large regions for several days

19. Basics: Localized heavy snowfalls along the coasts of large lakes (e.g. the Great Lakes) Occurs when lake temperatures are higher than land temperatures Average yearly snowfalls can be >200 inches in some zones

20. The atmosphere contains greenhouse gases in tiny amounts The sun gives off rays of heat (infrared radiation) The rays warm the Earth and the heat travels back into the atmosphere. Gases in the atmosphere stop some of the heat from escaping into space.

22. Some human activities can also produce greenhouse gases. Carbon dioxide – Burning fossil fuels (coal, oil, natural gas) – Cutting down and burning trees This extra heat trapping gas upsets the balance of the atmosphere and causes global warming Known as Global Climate Change. Climate = the average weather conditions in an area