What factors affect our weather? Heat in our atmosphere Winds Water cycle

Who predicts the weather? Meteorologists! –Scientists who study the causes weather & try to predict it –They use a variety of methods to predict weather...

What type of tools do they use? Barometer Anemometer Wind/Weather Vane Thermometer

What other tools do they use in forecasting our weather? Local weather observers Weather balloons Satellites Weather Stations Maps Charts Computers Radar

What is an air mass? Huge body of air that has similar temp, humidity, & air pressure Classified by temperature & humidity

Air Mass Types: Tropical Continental Maritime Polar

Tropical Warm air mass with low pressure that forming in the tropics

Continental Dry air mass over land

Maritime Humid air mass over an ocean

Polar Cold air mass with high pressure 50ºN/S latitude

What are the major types of air masses that affect the weather in North America? Maritime Tropical Maritime Polar Continental Tropical Continental Polar

Maritime Tropical Form over Pacific-affects weather on the west coast Form over Gulf of Mexico or Atlantic- affects weather in the central & eastern US

Maritime Polar Form over North Atlantic-most are pushed out to sea by prevailing westerly winds Form over North Pacific-affects weather on west coast

Continental Tropical Form over Southwest & Mexico-brings dry, hot air to southwest & central US

Continental Polar Forms over central/northern Canada and Alaska Brings cold air to central & eastern US

How do these air masses move across the US? Prevailing westerlies

What is a front? The area where 2 air masses, with different temperatures & densities meet & do not mix A front may be km wide & extend 10km up into the troposphere

4 types of fronts: Cold Warm Stationary Occluded

Cold Front Rapidly moving cold air runs into slower moving warm air Cold air slides under the warm air

Warm Front Warm air runs into cold air Warm air moves over the cold air

Stationary Front Warm and cold air meet Neither has enough force to move the other

Occluded Front Warm air is caught between 2 cold air masses Most complex Warm air rises & the 2 cold air masses mix

What types of severe weather affect the US? Thunderstorms Tornadoes Hurricanes Tropical Storms Flooding

Thunderstorms Heavy rainstorm accompanied by thunder & lightning Form within cumulonimbus clouds or “thunderheads”

Which occurs first…the thunder or lightning?

Lightning A sudden spark or energy discharge between 2 nearby clouds

Thunder The sound of the explosion when lightning occurs

…so which happens first? Lightning! Light travels faster than sound

Tornadoes A rapid, whirling, funnel-shaped cloud that reaches down from a storm cloud & touches Earth’s surface

How do tornadoes form? They form in low, heavy cumulonimbus clouds in spring/early summer in late afternoon when the ground is warm

May only last 15mins or less, but causes serious damage with winds up to 480km per hour

How is the damage measured? Fujita Scale

Where do most tornadoes occur in the US? Tornado Alley Great Plains area including: –Central Texas –Kansas –Central Oklahoma –Nebraska

What’s the difference between a tornado warning & a tornado watch? Tornado Warning:a tornado has been spotted in the sky or on radar Tornado Watch: a tornado is possible in your area

Waterspout Tornado that forms over a body of water

The US has more tornadoes than any other country …over 800 a year!

How do hurricanes affect the US? A hurricane is a tropical storm with winds of 119km per hour & 600km across

Hurricane Facts Longest lasting storm at over a week Hurricane Season: June-November Hurricane in the Pacific is called a typhoon Hurricanes gain strength from warm humid air over the ocean Hurricanes are propelled by winds

How does a hurricane form? They begin over warm water as an area of low pressure or a tropical disturbance Disturbance grows in size & strength called a tropical storm

What is the eye of the hurricane? The calm, clear center of a hurricane

Hurricane Watch vs. a Warning! Hurricane Watch: hurricane conditions are possible Hurricane Warning: hurricane conditions are expected within 24hours

How do floods affect the people in the US? A flood occurs when so much water pours into a stream/river overflowing its banks, covering land on either side

Floods can be the most violent type of storm to affect the US

What is a flash flood? Unexpected, violent flood occurring within hours/minutes of a storm

What causes a flash flood? Snow/Ice melt Heavy Thunderstorms Breaking Dam Hurricanes/tropical storms

What is climate? The Average year-after-year conditions of an area –Conditions: temp, precipitation, winds, clouds

5 climate regions: Classified according to temp & precipitation 1.Tropical rainy 2.Dry 3.Temperate marine 4.Temperate continental 5.Polar