Water in the Atmosphere, Precipitation, and Air Masses

Evaporation makes the “feels like” temperature cooler because it removes heat from your body. Winds increase evaporation.

Warm air can hold more water than cold air.

A hygrometer is also an instrument used to measure relative humidity.

Only the highest clouds such as cirrus have ice crystals.

Cirro- “curl” High clouds use the prefix cirro- Cumulo- “ heap” or “pile” Strato- “layer” or “sheet” Alto- “middle” Nimbus- or Nimbo- “rain”

When the water evaporates it is called evapotranspiration.

The water cycle is driven by the Sun. The Sun causes unequal heating on Earth.

They are seen during fair weather.

When they are at Earth’s surface we call it fog. They can bring light rain or drizzle.

Frosty

To form a cloud the tiny water droplets need particles like dust to cling to. These are called condensation nuclei.

In the morning the atmosphere at ground level is the coolest. If the air is saturated with water vapor, it will condense on surfaces at the dew point. Example: dew on grass

Cirrocumulus are cumulus clouds with a high altitude.

“Nimbo-” means rain.

These are referred to as “thunderheads.” They are towering cumulus clouds with flat tops and dark gray or black bottoms. They may weigh several tons.

They differ in that they can be solid (frozen) or liquid, and they have different sizes.

The ice pellets are greater than 5 mm in diameter and can grow to the size of baseballs.

If the air is dry, powdery snow falls. If it is humid, the snowflakes join together in clumps. It can melt before it hits the ground if it passes through warmer air.

All five factors interact to bring us our daily weather.

Cold air is dense (the molecules are closer together) and exerts greater pressure. Cold, dense, dry, drops!

The molecules in warm air have more energy (kinetic) and move around faster. It is less dense (less mass per volume) and rises. It can hold more water than cold air. Warm, less dense, moist, rises!

Air masses are classified according to humidity and temperature.

There’s an easy way to remember! Pay close attention.

The Prevailing Westerlies affect the U.S. and they flow west to east.

The jet stream moves west to east.

When air masses meet at a front, the collision often causes storms & changeable weather.

When two fronts meet, there is usually a change in weather conditions. All can bring clouds & precipitation.

The cold air mass is denser and plows under the warm (moist) air mass lifting it up. Clouds & precipitation. As it passes it leaves cold, dry air.

The warm air rises above the cold mass. Warm fronts bring clouds and rain. This is much slower than when a cold front moves in.

Stationary means “still.” Stationary fronts may bring days of clouds and precipitation.

It may cause clouds and precipitation.

1.Winds spiral inward in a cyclone. 2. Cyclones cause clouds, winds, and precipitation. 3. Cyclones are called “lows ” & are shown by a circled “L” on a weather map. 4. They spin counterclockwise due to the Coriolis effect.

1. An anticyclone spins clockwise in the Northern Hemisphere. 2. They are called “highs” & are shown as a circled “H” on a weather map.

Wind is measured in miles per hour or kilometers per hour.

There are two types: 1. Mercury barometer (contains liquid mercury) that measures in inches of mercury. 2. Aneroid barometer (filled with air) that measures in millibars. About 30” of mercury = 1016 millibars