Influences on Weather

What is weather?Weather is the state of the atmosphere at a

certain time and place.

The state of the atmosphere includes: the amount of water in the air, the temperature of the air and precipitation.

These aspects of weather have an effect on air pressure and winds.

Water in the Air

Humidity-is the amount of water vapor in the air.

If there is enough water vapor in the air, clouds may form. Too much water vapor in the air at a certain location, the water will condense and fall to Earth’s surface as precipitation.

Relative HumidityIf the air is at 100-percent

relative humidity, sweat will not evaporate into the air. As a result, we feel much hotter than the actual temperature when the relative humidity is high.

We measure humidity with a hygrometer.

TemperatureTemperature determines how much water

vapor air can hold.Warm air can hold more water vapor than

colder air can.If air that is warm and humid begins to cool,

the water vapor may condense and fall as rain because the cooler air cannot hold as much water vapor as the warmer air can.

Clouds

Cloud Cover- the amount of clouds in the sky

Temperature and humidity of the air affects the formation of clouds.

Clouds are made up of millions of tiny water droplets or ice crystals.

If there is enough water vapor in the air and the air cools clouds will form.

AIR PRESSUREAir Pressure -the weight of the air

in an area

Low Air PressureAir pressure is determined partly by the Sun.Because Earth is titled on its axis, it is heated

unevenly by the Sun.

As the Sun heats the air in SOME places, the temperature of the air rises.Warmer air becomes

less dense. This lighter, less dense air rises, creating an area of low air pressure.

Warmer air rises!!!!!!

High Air PressureAreas of high

pressure are caused by air that has cooled and become heavy.

As the air cools and becomes heavier, it sinks.

Air in high pressure areas tends to flow into area of low air pressure.

Barometer-a tool for measuring air pressure

Air Pressure is also referred to as Barometric Pressure.

LOW-Warm temps, storms, and rain

HIGH-Cooler temps and clear skies

Why does air move from areas of high pressure to low pressure?

Answer-Air in low-pressure areas rises as its temperature increases. As the air rises, the heavier dense air in a high-pressure area has room to move into the space created by the rising, low-pressure air.

LOW-Warm temps, storms, and rain

HIGH-Cooler temps and clear skies

WINDHave you ever wondered what causes

wind?

Wind is caused by differences in air pressure.

Air pressure combined with temperature determines the speed of the wind.

How do we get winds of high speed?1. When high-pressure areas are near the low-

pressure areas.

2. When there is a LARGE difference in temperature between the high- and low-pressure areas

Winds are named for the direction they flow and their speed.Prevailing Westerlies- this wind pattern

affects our state (NC). The Prevailing Westerlies move weather from west to east.

Jet StreamThe jet stream is a river of wind that blows horizontally

through the upper layers of the troposphere, generally from west to east, at an altitude of 20,000 - 50,000 feet, or about 7 miles up.

A jet stream develops where air masses of differing temperatures meet. For this reason, surface temperatures determine where the jet stream will form. The greater the difference in temperature, the faster the wind velocity inside the jet stream. Jet streams can flow up to 200 mph , are 1000's of miles long, 100's of miles wide, and a few miles thick.

There is a polar and subtropical jet stream.