What causes weather? Humidity, Temperature, Pressure, Fronts, clouds, precipitation, lightning, hurricanes, tornadoes, jet stream, and ocean currents.

Humidity  Humidity: The amount of water vapor in the air.  Water is a greenhouse gas, so much of the warmth on our planet is because we have water in our atmosphere.  There are 3,100 CUBIC MILES of water dispersed in the atmosphere as water vapor.

Humidity  Dangers: Our bodies use sweat to cool down. As the sweat evaporates, it removes heat from your skin.  If there is too much water in the air, your sweat will not evaporate and your body will overheat.  It is important to pay attention to the humidity when working out, and stop if you feel fatigued, a headache, a high pulse rate or shallow breathing.

Air Pressure  Air pressure: Pressure force divided by the area it is applied. Air pressure is pushing against your entire body. At sea level air pressure is about N/cm 2  Hold your hand out in front of you, palm up. You are holding the weight equal to that of a washing machine. This is because air has mass, and is being pulled down by gravity.

Pressure and Elevation  Pressure and Elevation: Air pressure decreases as elevation increases.  If you have ever gone up in an airplane, your ears will "pop". That popping sensation as you go up in the plane is the air inside your ear being released, so less pressure inside your ear.  The popping sensation as you come down is the air coming back into your ear to even out the increased pressure as you come back down.

Fluid Pressure  Why does air pressure decrease as you go above sea level?  Why would water pressure increase going deeper underwater?

Weather Fronts  Weather Fronts: are bodies of air with different pressure, temperature, and/or humidity, which create weather patterns.

 Weather Fronts: as warm front and cold front meet, the water held in the warm air is forced out by the cold, creating precipitation.

Clouds  Clouds: water droplets or ice crystals held in suspension by the air. The droplets are so small air holds them up.  Clouds occur primarily in the troposphere, but some form in the stratosphere or mesosphere.

Cloud Chart Cloud GroupCloud HeightCloud Types High Clouds = CirrusAbove 18,000 feet Cirrus Cirrostratus Cirrocumulus Middle Clouds = Alto6,500 feet to 18,000 feet Altostratus Altocumulus Low Clouds = StratusUp to 6,500 feet Stratus Stratocumulus Nimbostratus Clouds with Vertical Growth Cumulus Cumulonimbus Special Clouds Mammatus Lenticular Fog Contrails

Precipitation  Precipitation: is when condensation in the clouds becomes too heavy and falls to Earth.  Types of precipitation:  Rain- water droplets  Snow- ice crystals deposited directly from vapor  Sleet- frozen rain  Hail- frozen water that is held aloft by strong currents of air long enough to become a large ball of ice.

Lightning  Lightning: particles in clouds brushing against each other can cause the lower particles of a cloud to become negative. This results in a discharge of electrons as it evens out the charges.

LIGHTNING!  Most lightning never leaves the clouds, passing electrons from one to another to even charges.  Can reach 30,000 degrees Celsius (54,000 F)  Lasts 30 millionths of a second.  Up to one billion volts  2,000 people are killed by lightning every year.

Hurricane!  Hurricane(typhoon): A hurricane is a huge storm! It can be up to 600 miles across and have strong winds spiraling inward and upward at speeds of 75 to 200 mph. Each hurricane usually lasts for over a week.  Hurricanes gather heat and energy through contact with warm ocean waters. Evaporation from the seawater increases their power.

Hurricane!  Hurricane: Hurricanes rotate in a counter-clockwise direction around an "eye" in the Northern Hemisphere and clockwise direction in the Southern Hemisphere.  The center of the storm or "eye" is the calmest part.

Hurricane!  The Atlantic hurricane season is from June 1 to November 30, but most hurricanes occur during the fall months. Tropical Wave A low pressure trough moving generally westward with the trade winds. Tropical Disturbance An organized area of thunderstorms that usually forms in the tropics. Typically, they maintain their identity for 24 hours and are accompanied by heavy rains and gusty winds. Tropical Cyclone A generic term for any organized low pressure that develops over tropical and sometimes sub-tropical waters. Tropical depressions, tropical storms, and hurricanes are all example of tropical cyclones. Tropical Depression An organized area of low pressure in which sustained winds are 38 mph or less. Tropical Storm A tropical cyclone with maximum sustained wind speeds that range from 39 to 73 mph. HurricaneA tropical cyclone with sustained winds of at least 74 mph.

CategoryWinds (MPH) Pressure (Millibars) Pressure (Inches) Storm Surge (Feet) Damage <980<28.944'-5'Minimal '-8'Moderate ' -12'Extensive '-18'Extreme 5>155<920<27.17>18'Catastrophic

Tornadoes  Tornadoes: Created when warm, moist air meets eastward moving cold air fronts. (twister, cyclone)  Most tornadoes are about 100 mph  The most damaging tornadoes can be higher than 200 mph.

Tornadoes: Indicators  Dark, often greenish sky  Wall cloud  Large hail  Loud roar; similar to a freight train

Jetstream  Jetstream- very fast, very narrow air currents. Caused by the rotation of Earth.  57 mph-247 mph  Flow west to east

Ocean Currents  Ocean Currents: portions of the Ocean moving through the ocean. Ocean currents are important to life on Earth, they effect global climate, wind, waves, and habitats of sea creatures.