Weather lesson 3: What Causes Severe Weather? Some severe weather we’ll look at includes: Thunderstorms Tornadoes Hurricanes Monsoons

Thunderstorms One way it forms: Strong, quickly rising moist air (clouds grow) Precipitation starts & pulls some air downward All air currents go downwards & cloud gets smaller as precipitation leaves it

Thunderstorms: Lightning A thunderstorm cloud has positive and negative electrical charges. The ground has positive charges. Lightning is a large electrical spark moving between areas of o__________ charges. When we see lighting, it is actually many flashes of both positive and negative charges going up and down.

Thunderstorms: Thunder Is thunder really God bowling? Actually, lightning warms the air to 30,000 degrees Celsius for a fraction of a second. This causes the air to expand so quickly that it makes vibrations in the air. These vibrations are thunder.

Thunderstorm Watches and Warnings A “severe thunderstorm watch” means that thunderstorms with high winds and hail might form. A “severe thunderstorm warning” means that thunderstorms have already formed and you should prepare for them.

Lightning Safety Lightning seeks out: Metal objects Water High places To be safe: Stay inside away from windows Stay out of the shower/bathtub, pool Stay off the phone, unplug the TV, computer If outside, stay away from trees, stay low

Tornadoes How does a tornado form? Thunderstorms bring thunder, lightning, strong winds, rain and sometimes tornadoes. How does a tornado form? Layers of wind blow at different speeds in different directions. A column of air spins like a log and then wind lifts it upright. This column is called a f_______ cloud. When this touches the ground it is called a tornado.

Tornadoes If a tornado is over water, it is called a w_____ s_____.

Tornadoes How long do tornadoes usually last? Minutes? Hours? Days? Weeks? Tornadoes can cause extreme damage to buildings and cars and can cause fatalities.

Where do Most United States Tornadoes Occur? Tornadoes usually occur during March – May, in “Tornado Alley” which is in the central part of the United States.

Tornado Safety What’s the difference between a tornado watch and a tornado warning? How to prepare for a tornado? Outside? Inside? Would you go to the highest or lowest place in your home? Why?

Hurricanes How does a hurricane start? Warm air rises rapidly over the ocean, near the equator. Winds of 39 mph or less spin around a center of low pressure are called a tropical depression. When the winds reach 40 mph or greater, the storm changes into a tropical storm, and it's given a name. If winds reach 74 mph or greater, the storm becomes a hurricane.

Hurricanes The middle of a hurricane is called the e___. It has calm winds and low pressure and is surrounded by an eyewall of intense thunderstorms with high winds and heavy rain.

Hurricane Rating Scale Hurricanes are rated on a scale similar to a tornado: according to their strength. Saffir-Simpson Hurricane Wind Scale: Wind Speed Range (MPH) Category 1 Hurricane Rita 74 – 95 Category 2 96 – 110 Category 3 111 – 130 Category 4 131 – 155 Category 5 > 155

Hurricanes When do most hurricanes occur? Why?

Hurricanes Hurricanes are always near the equator. Why? Hurricanes have different names around the world.

Hurricanes Which is more destructive, a hurricane or a tornado? Why? Duration Size/width Flooding

Preparing for a Hurricane Evacuate? Outside the home Inside the home If you stayed during a hurricane, would you go to the highest or lowest place in your home? Why?

Monsoons Monsoons are common in southern and southeast Asia. Monsoons happen when winds change directions with the summer season. Monsoons brings strong winds and very heavy rains/flooding.