Made especially for you… MORE Air Pressure Info Made especially for you…

BAROMETER High pressure- High mercury level Low pressure- low mercury level When a barometer a falling that means low pressure. A rising barometer indicates high pressure.

What is “air pressure”… -Think of air pressure as little molecules of air… Picture an inflated balloon, the molecules of air inside are in a high pressure zone inside of that balloon because they are tightly compacted together; when you release that balloon the air comes out into a low pressure zone, where there is more space for the air molecules.

High Pressure Zones Cold, dense (heavy/tightly compacted), air sinks Cold air cannot hold much water, so this leads to clear skies and calm weather conditions A barometer will read higher than 30 inches when there is a high pressure zone

Low Pressure Zones Warm air, less dense (lighter/more spread out) rises Warm air rises into the atmosphere, cools as it gets higher and attaches onto dust particles- forming clouds Once the water vapor becomes too heavy- precipitation occurs A barometer will read lower than 30 inches if it is a low pressure zone

Density How tightly packed molecules are. Low Pressure- More spread out, room to move, room for moisture Warm air is less dense than cold air. High Pressure- Tightly compacted/close together air particles Cold air is more dense than warm air.

When Air Pressures Meet High and low air pressures do not MIX- they push against each other. A cold front occurs when a faster-moving cold air mass forms a wedge that drives under a warm air mass. It can cause weather changes like thunderstorms and even tornadoes. A warm front happens when a warm air mass moves up at a gradual slope over a cold air mass, usually resulting in less drastic weather change.

Air Pressure & Wind The wind blows because air has weight. Cold air weighs more than warm air, so the pressure of cold air is greater. When the sun warms the air, the air expands, gets lighter, and rises. Cooler, heavier air blows to where the warmer and lighter air was, or in other words, wind usually blows from areas of high air pressure to areas of low pressure. If the high pressure area is very close to the low pressure area, or if the pressure difference (or temperature difference) is very great, the wind can blow very fast.

How Air Pressure Effects Weather U.S. winters- High pressure from NW Canada moves to SE U.S., bring cool and dry weather U.S. summers- Low pressure from Gulf of Mexico comes to NE U.S. brining warm, wet conditions

Fronts When two air masses meet, the air within them does not easily mix. That is to say that the air in one air mass will not easily mix with the air from another air mass. Instead the air stays within its own air mass. Because of this, a border forms between two clashing air masses, as they rub together. This border is called a front.

Mountain and Valley Breezes During the day the surface of a mountain heats the air up faster than a valley floor can, creating an area of low pressure at the mountain top. The cool air in the valley is attracted to this low pressure zone, creating a breeze that blows from the valley to the mountain. *Birds often fly with these breezes in order to preserve their energy.*